Three-dimensional maximum probability atlas of the human brain, with particular reference to the temporal lobe

GAN-based synthetic FDG PET images from T1 brain MRI can serve to improve performance of deep unsupervised anomaly detection models

BACKGROUND AND OBJECTIVE

Research in the cross-modal medical image translation domain has been very productive over the past few years in tackling the scarce availability of large curated multi-modality datasets with the promising performance of GAN-based architectures. However, only a few of these studies assessed task-based related performance of these synthetic data, especially for the training of deep models.

METHODS

We design and compare different GAN-based frameworks for generating synthetic brain[18F]fluorodeoxyglucose (FDG) PET images from T1 weighted MRI data. We first perform standard qualitative and quantitative visual quality evaluation. Then, we explore further impact of using these fake PET data in the training of a deep unsupervised anomaly detection (UAD) model designed to detect subtle epilepsy lesions in T1 MRI and FDG PET images. We introduce novel diagnostic task-oriented quality metrics of the synthetic FDG PET data tailored to our unsupervised detection task, then use these fake data to train a use case UAD model combining a deep representation learning based on siamese autoencoders with a OC-SVM density support estimation model. This model is trained on normal subjects only and allows the detection of any variation from the pattern of the normal population. We compare the detection performance of models trained on 35 paired real MR T1 of normal subjects paired either on 35 true PET images or on 35 synthetic PET images generated from the best performing generative models. Performance analysis is conducted on 17 exams of epilepsy patients undergoing surgery.

RESULTS

The best performing GAN-based models allow generating realistic fake PET images of control subject with SSIM and PSNR values around 0.9 and 23.8, respectively and in distribution (ID) with regard to the true control dataset. The best UAD model trained on these synthetic normative PET data allows reaching 74% sensitivity.

CONCLUSION

Our results confirm that GAN-based models are the best suited for MR T1 to FDG PET translation, outperforming transformer or diffusion models. We also demonstrate the diagnostic value of these synthetic data for the training of UAD models and evaluation on clinical exams of epilepsy patients. Our code and the normative image dataset are available.

A road map to manual segmentation of cerebral structures

Manual segmentation is an essential tool in the researcher's technical arsenal. It is a frequent practice necessary for image analysis in many protocols, especially in neuroimaging and comparative brain anatomy. In the framework of emergence of studies focusing on alternative animal models, manual segmentation procedures play a critical role. Nevertheless, this critical task is often assigned to students, a process that, unfortunately, tends to be time-consuming and repetitive. Well-conducted and well-described segmentation procedures can potentially guide novice and even expert operators and enhance research works' internal and external validity, making it possible to harmonize studies and facilitate data sharing. Furthermore, recent advances in neuroimaging, such as ex vivo imaging or ultra-high-field MRI, enable new acquisition modalities and the identification of minute structures that are barely visible with typical approaches. In this context of increasingly detailed and multimodal brain studies, reflecting on methodology is relevant and necessary. Because it is crucial to implement good practices in manual segmentation per se but also in the description of the segmentation procedures in research papers, we propose a general roadmap for optimizing the technique, its process and the reporting of manual segmentation. For each of them, the relevant elements of the literature have been collected and cited. The article is accompanied by a checklist that the reader can use to verify that the critical steps are being followed.

Peripheral-central immune crosstalk in Parkinson's disease and its association with clinical severity

BACKGROUND

Increasingly, the immune system is implicated in the aetiology and progression of Parkinson's disease (PD). Immune activation is seen both peripherally in the blood, with a tendency towards a pro-inflammatory profile, and centrally in the cerebrospinal fluid and brain parenchyma, with microglial activation and increased numbers of immune cells in the central nervous system. However, the relationship between this peripheral and central immune profile, as well as the association with clinical measures of disease severity is not clear.

METHODS

61 people with PD, within three years of diagnosis and no immune comorbidities, and 51 matched controls underwent detailed blood immunophenotyping using a flow cytometry panel with markers to characterise adaptive and innate immune populations. In the PD cohort, 35 also had cerebrospinal fluid (CSF) immune cell analysis and 31 underwent positron emission tomography (PET) brain imaging with the radioligand [11C]-PK11195 to assess microglial activation. PD participants were assessed with the Movement Disorder Society-Unified Parkinson's disease rating Scale (MDS-UPDRS) and the Addenbrooke's Cognitive Examination (ACE-III). The immune profiles of PD and control participants were compared. In the PD group, relationships between peripheral and CSF immune cell populations, [11C]-PK11195 binding, and clinical measures were investigated in exploratory analyses using multiple linear regression.

RESULTS

Compared to controls, PD participants had a pro-inflammatory profile in the blood with an elevated Systemic Inflammatory Index (SII) (p = 0.049), a higher percentage of classical monocytes (p = 0.046), and decreased expression of functional markers of T regulatory cells (FoxP3 (p = 0.030) and Helios (p = 0.015)) and B regulatory cells (CD1d (p = 0.031)). Immune cell subset numbers in blood and CSF were correlated for CD8+ cells (rho = 0.42, p = 0.011), CD16+ NK cells (rho = 0.49, p = 0.004) and classical monocytes (rho = -0.38, p = 0.028). CSF immune populations were also correlated with [11C]-PK11195 binding in disease-relevant regions of interest. Several blood and CSF immune cell subsets and regional [11C]-PK11195 binding showed relationships with motor and cognitive scores, with a consistent trend of pro-inflammatory markers being related to a more severe disease phenotype. Increased Toll-like receptor 2 expression on classical monocytes in the CSF and [11C]-PK11195 binding in the substantia nigra independently predicted motor score (MDS-UPDRS-III).

CONCLUSION

This exploratory study suggests that peripheral and central immune changes are closely linked in PD, and relevant to clinical disease severity. These findings warrant further validation and exploration to identify immune biomarkers linked to disease state, as well as candidate therapeutic targets.

Dynamic PET imaging in patients with unilateral carotid occlusion shows lateralized cerebral hypoperfusion, but no amyloid binding

BackgroundCarotid occlusive disease is a risk factor for cognitive decline. A possible underlying etiology is that hemodynamic impairment results in decreased cerebral perfusion, exacerbated amyloid-β accumulation (Aβ) and poorer cognitive performance.ObjectiveWe aimed to determine whether patients with unilateral internal carotid artery (ICA) occlusion have less cerebral perfusion and more Aβ in the ipsilateral than in the contralateral hemisphere, and whether perfusion and Aβ are associated with cognitive functioning.MethodsWe included 20 patients (age 67.2 ± 7.0 years, 8 females, MMSE 29 [27-29]) with unilateral ICA occlusion, which underwent neuropsychological assessment and dynamic 18F-Florbetaben positron emission tomography (PET). Global and regional relative perfusion (R1) and binding potential (BPND) were obtained from the PET-images using a simplified reference tissue model. We performed Wilcoxon signed-rank tests to examine differences between hemispheres within subjects and linear regression to investigate associations with cognitive functioning.ResultsMedian global R1 was 0.911 (0.883-0.950) and global BPND was 0.172 (0.129-0.187). R1 was lower in the hemisphere ipsilateral to the ICA occlusion than in the contralateral hemisphere (0.899 [0.876-0.921] versus 0.935 [0.889-0.970]). BPND did not differ significantly between hemispheres (ipsilateral 0.172 [0.124-0.181] versus contralateral 0.168 [0.137-0.191]). Neither cerebral perfusion nor Aβ burden were associated with cognitive functioning.ConclusionsPatients with unilateral ICA occlusion did not have more Aβ in the ipsilateral hemisphere than in the contralateral hemisphere despite ipsilateral hypoperfusion. Perfusion and Aβ were unrelated to cognitive functioning. This indicates that cognitive impairment in patients with ICA occlusion is not due to exacerbated Aβ accumulation.

PET imaging of functional 5-HT1A receptors with [18F]F13640: From PET kinetics modeling to static Standardized Uptake Values Ratio

PURPOSE

F13640 is a highly selective serotonin 5-HT1A receptor ligand with agonist properties identified as a PET radiopharmaceutical candidate. In previous work, we showed the possibility to use long dynamic PET acquisition (225 min) combined with simplified kinetic modelling for [18F]F13640 quantification. In this work, we assessed the feasibility of static acquisition and quantification using standardized uptake value ratio (SUVR) as an alternative.

METHODS

Test-retest PET-MRI scans of 225 min were conducted in eight healthy male volunteers. For 17 brain regions, distribution volume ratios (DVR) were calculated from the whole kinetics using Logan plot modelling method with the cerebellum white matter as reference region. For the same regions, SUVR were also calculated from static images, for four 20-minute and four 10-minute time-intervals at various time of uptake. Reliability between SUVR and DVR measures were studied, and test-retest parameters were assessed between PET sessions for each time-interval.

RESULTS

Reproducibility of measures of SUVR compared to DVR were excellent, whatever the time interval (p < 0.001). For the 20-min. time-intervals, SUVR150-170 showed the best reproducibility and correlation parameters (R2 = 0.95 ± 0.03, intercept = 0.06 ± 0.02, slope = 0.95 ± 0.01). As well, for the 10-min. time-intervals, SUVR150-160 showed the best correlation (R2 = 0.94 ± 0.03, intercept = 0.07 ± 0.02, slope = 0.94 ± 0.01). SUVR reproducibility between test-retest sessions was also excellent for each time-interval. These results were valid for pooled regions as well as at regional level.

CONCLUSION

This study confirms the feasibility of static acquisitions to facilitate clinical use of the [18F]F13640 radiopharmaceutical to image functional 5-HT1A receptors. This involves off-camera injection, 10 to 20 mins static acquisition duration, and quantification using SUVR, while improving patient comfort.

Exploratory structural neuroimaging examination of impulsivity in severe alcohol use disorder: Persistent implication of the ventral striatum

BACKGROUND

While Alcohol Use Disorder (AUD) is frequently associated with impulsivity, its structural brain substrates are still poorly defined. The triadic model of addiction postulates that impulsive behavior is regulated by an amygdalo-striatal impulsive subcomponent, a prefrontal and cerebellar reflective subcomponent, and an insular regulatory subcomponent. The objective of this study was thus to examine the relationships between self-evaluated impulsivity and structural brain abnormalities in patients with severe AUD (sAUD) using the triadic model as a theoretical framework.

METHODS

Twenty-two inpatients with sAUD and 17 Healthy Controls (HC) completed two impulsivity scales: the Barratt Impulsiveness Scale-11 (BIS-11), and the Urgency, Premeditation, Perseverance, Sensation Seeking, Positive Urgency Impulsive Behavior Scale (UPPS). They also underwent an anatomical MRI. The brain volumes of the regions described as involved in the three subcomponents of the triadic model were extracted.

RESULTS

The two groups did not significantly differ on self-reported impulsivity measures. However, the volumes of the caudate nuclei, executive cerebellum and insula were smaller in sAUD than in HC. In the sAUD group there were significant positive correlations between certain impulsivity measures and gray matter volume of the nucleus accumbens.

CONCLUSIONS

In sAUD, self-evaluated impulsivity specifically relates to the integrity of the ventral striatum that belongs to the impulsive subcomponent of the triadic neurocognitive model of addiction. It is not related to the integrity or deterioration of the brain regions that underlie the reflexive or regulatory sub-component. Although these results have methodological limitations, they are consistent with the impulsive/compulsive model of addiction and confirms the persistence of the relationship between impulsivity and ventral striatum in sAUD.

A Case for Automated Segmentation of MRI Data in Neurodegenerative Diseases: Type II GM1 Gangliosidosis

BACKGROUND

Volumetric analysis and segmentation of magnetic resonance imaging (MRI) data is an important tool for evaluating neurological disease progression and neurodevelopment. Fully automated segmentation pipelines offer faster and more reproducible results. However, since these analysis pipelines were trained on or run based on atlases consisting of neurotypical controls, it is important to evaluate how accurate these methods are for neurodegenerative diseases. In this study, we compared five fully automated segmentation pipelines, including FSL, Freesurfer, volBrain, SPM12, and SimNIBS, with a manual segmentation process in GM1 gangliosidosis patients and neurotypical controls.

METHODS

We analyzed 45 MRI scans from 16 juvenile GM1 gangliosidosis patients, 11 MRI scans from 8 late-infantile GM1 gangliosidosis patients, and 19 MRI scans from 11 neurotypical controls. We compared the results for seven brain structures, including volumes of the total brain, bilateral thalamus, ventricles, bilateral caudate nucleus, bilateral lentiform nucleus, corpus callosum, and cerebellum.

RESULTS

We found volBrain's vol2Brain pipeline to have the strongest correlations with the manual segmentation process for the whole brain, ventricles, and thalamus. We also found Freesurfer's recon-all pipeline to have the strongest correlations with the manual segmentation process for the caudate nucleus. For the cerebellum, we found a combination of volBrain's vol2Brain and SimNIBS' headreco to have the strongest correlations, depending on the cohort. For the lentiform nucleus, we found a combination of recon-all and FSL's FIRST to give the strongest correlations, depending on the cohort. Lastly, we found segmentation of the corpus callosum to be highly variable.

CONCLUSIONS

Previous studies have considered automated segmentation techniques to be unreliable, particularly in neurodegenerative diseases. However, in our study, we produced results comparable to those obtained with a manual segmentation process. While manual segmentation processes conducted by neuroradiologists remain the gold standard, we present evidence to the capabilities and advantages of using an automated process that includes the ability to segment white matter throughout the brain or analyze large datasets, which pose feasibility issues to fully manual processes. Future investigations should consider the use of artificial intelligence-based segmentation pipelines to determine their accuracy in GM1 gangliosidosis, lysosomal storage disorders, and other neurodegenerative diseases.

Exploratory Study of Sex Differences in P-Glycoprotein Function at the Blood-Brain Barrier

Permeability-glycoprotein (P-gp), a crucial efflux pump transporter encoded by the ABCB1 gene, plays a pivotal role in drug disposition at the blood-brain barrier (BBB) and is involved in the pharmacokinetics of numerous therapeutic agents. This study investigates differences in P-gp function at the BBB between males and females in a cohort of older (55+) healthy volunteers (HV) using [18F]MC225 and PET. Twenty HV (11 males and 9 females), free from medications that affect P-gp function and without a history of neurological or psychiatric disorders, underwent [18F]MC225 PET scans with manual arterial blood sampling. Tissue time-activity curves (TAC) were extracted using the Hammers maximum-probability atlas. Whole-blood TAC was derived from the internal carotid arteries, calibrated using manual arterial samples, and adjusted for the plasma-to-whole blood ratio and plasma parent fraction to obtain the image-derived input function. The volume of distribution (VT) was estimated using a reversible two-tissue compartment model, yielding the parameter of interest. Statistical analysis revealed no significant differences in P-gp function between sexes, based on VT values across various brain regions (Cohen's d < 0.2). Furthermore, the arterial blood concentration, plasma parent fraction, and microparameters demonstrated no statistical differences between male and female participants. These findings suggest that P-gp function at the BBB does not exhibit substantial sex-related variability in healthy older adults (55+). For future [18F]MC225 PET studies, a mixed-sex population can serve as an appropriate age-matched control group for neurodegenerative studies. Further research is needed to explore sex-related differences in younger populations, particularly with respect to hormonal cycles.

Multi-angle acquisition and 3D composite reconstruction for organ-targeted PET using planar detectors

BACKGROUND

This study investigates a multi-angle acquisition method aimed at improving image quality in organ-targeted PET detectors with planar detector heads. Organ-targeted PET technologies have emerged to address limitations of conventional whole-body PET/CT systems, such as restricted axial field-of-view (AFOV), limited spatial resolution, and high radiation exposure associated with PET procedures. The AFOV in organ-targeted PET can be adjusted to the organ of interest, minimizing unwanted signals from other parts of the body, thus improving signal collection efficiency and reducing the dose of administered radiotracer. However, while planar detector PET technology allows for quasi-3D image reconstruction due to the separation between detector heads, it suffers from degraded axial spatial resolution and, consequently, reduced recovery coefficients (RCs) along the axial direction perpendicular to the detectors.

PURPOSE

The purpose of this study was to evaluate the concept of multi-angle image acquisition with two planar PET detectors and composite full 3D image reconstruction. This leverages data collection from multiple polar angles to improve the axial spatial resolution in the direction perpendicular to the detector heads. In such, the concept allows to overcome the intrinsic limitations of planar detectors in axial resolution.

METHODS

This study evaluates the improvement in the quality of images acquired with the Radialis organ-targeted PET camera through multi-angle image acquisition, in both experimental and simulated imaging scenarios. This includes the use of custom-made phantom with fillable spherical hot inserts, the NEMA NU4-2008 image quality (IQ) phantom, and simulations with a digital brain phantom. The analysis involves the comparison of line profiles drawn through the spherical hot inserts, image uniformity, RCs, and the reduction of smearing observed in the axial planes with and without the multi-angle acquisition strategy.

RESULTS

Significant improvements were observed in reducing smearing, enhancing image uniformity, and increasing RCs using the evaluated multi-angle acquisition method. In the composite images, the hot spheres appear more symmetrical in all planes. The image uniformity, calculated from the IQ phantom, improves from 7.79% and 10.98%, as measured in the images from the individual acquisitions, to 2.72% in the composite image. There is also an overall improvement in the RCs as measured from the hot rods of the IQ phantom. Furthermore, the simulation study using the digital human brain phantom demonstrates minimal smearing in the four-angle scan, as opposed to a two-angle scan.

CONCLUSION

The multi-angle acquisition method offers a promising approach to transform planar PET detector technology into a true tomographic organ-targeted PET system and to enable improvement in image quality while preserving a versatility inherent to planar detector technology. Future research will focus on optimizing the multi-angle imaging protocol, including adjustments to detector separations, number of acquisition angles, and reconstruction iterations, alongside incorporating TOF, and reconstruction with point spread function modeling to further improve image quality.

Characterizing visual read tau-PET-negative participants with Alzheimer's disease dementia

INTRODUCTION

A subset of amyloid beta (Aβ)-positive Alzheimer's disease (AD) patients is tau-positron emission tomography (PET) negative. We aimed to characterize this subgroup using [18F]flortaucipir PET visual read (VR), as this is important for prognosis and selection for therapies.

METHODS

Aβ-positive VR tau-PET-negative AD dementia patients (AD A+T-) were compared to tau-PET-positive AD patients (AD A+T+) and control groups (CU A-T-; CU A+T-) included from the Amsterdam-based cohort and Alzheimer's Disease Neuroimaging Initiative (ADNI). We compared [18F]flortaucipir binding in an early- and late-stage tau ROI, atrophy, cognition, and co-pathologies.

RESULTS

AD A+T- were older, showed less hippocampal atrophy and slower cognitive decline compared to AD A+T+. In ADNI, AD A+T- showed higher early-stage tau binding compared to both control groups and more late-stage tau compared to CU A-T-, but no tau accumulation over time.

DISCUSSION

VR tau-PET-negative AD patients show neurodegenerative and cognitive processes consistent with the AD trajectory, but milder progression compared to tau-PET-positive AD patients.

HIGHLIGHTS

We used the novel Food and Drug Administration (FDA)-approved VR method for defining tau-PET positivity. AD A+T- patients were older and showed less atrophy and cognitive decline than AD A+T+. We did not find convincing evidence of tau accumulation in AD A+T- or copathologies. The group of AD A+T- patients is likely very heterogeneous.

TCDE-Net: An unsupervised dual-encoder network for 3D brain medical image registration

Medical image registration is a critical task in aligning medical images from different time points, modalities, or individuals, essential for accurate diagnosis and treatment planning. Despite significant progress in deep learning-based registration methods, current approaches still face considerable challenges, such as insufficient capture of local details, difficulty in effectively modeling global contextual information, and limited robustness in handling complex deformations. These limitations hinder the precision of high-resolution registration, particularly when dealing with medical images with intricate structures. To address these issues, this paper presents a novel registration network (TCDE-Net), an unsupervised medical image registration method based on a dual-encoder architecture. The dual encoders complement each other in feature extraction, enabling the model to effectively handle large-scale nonlinear deformations and capture intricate local details, thereby enhancing registration accuracy. Additionally, the detail-enhancement attention module aids in restoring fine-grained features, improving the network's capability to address complex deformations such as those at gray-white matter boundaries. Experimental results on the OASIS, IXI, and Hammers-n30r95 3D brain MR dataset demonstrate that this method outperforms commonly used registration techniques across multiple evaluation metrics, achieving superior performance and robustness. Our code is available at https://github.com/muzidongxue/TCDE-Net.

Cholinergic neurotransmission in the anterior cingulate cortex is associated with cognitive performance in healthy older adults: Baseline characteristics of the Improving Neurological Health in Aging via Neuroplasticity-based Computerized Exercise (INHANCE) trial

Aging is associated with dysfunction in the cholinergic system, including degeneration of basal forebrain cholinergic terminals that innervate the cortex, which directly contributes to age- and disease-related cognitive decline. In this study, we used [18F]fluoroethoxybenzovesamicol ([18F]FEOBV) positron emission tomography (PET) imaging to assess the effect of age on cholinergic terminal integrity in predefined regions of interest and its relationship to cognitive performance in healthy older adults who underwent neuropsychological assessment and FEOBV PET brain imaging. Our results showed age-related reductions in FEOBV binding, particularly in the anterior cingulate cortex-the primary region of interest-as well as in the striatum, posterior cingulate cortex, and primary auditory cortex. Notably, FEOBV binding in the anterior cingulate cortex was positively correlated with cognitive performance on the NIH EXAMINER Executive Composite Score. These findings suggest that [18F] FEOBV PET imaging can be used as a reliable biomarker to assess cholinergic changes in the human brain and indicate that preserving the cholinergic integrity of the basal forebrain may help maintain cognitive function and protect against age-related cognitive decline.

Investigating dopaminergic abnormalities in schizophrenia and first-episode psychosis with normative modelling and multisite molecular neuroimaging

Molecular neuroimaging techniques, like PET and SPECT, offer invaluable insights into the brain's in-vivo biology and its dysfunction in neuropsychiatric patients. However, the transition of molecular neuroimaging into diagnostics and precision medicine has been limited to a few clinical applications, hindered by issues like practical feasibility, high costs, and high between-subject heterogeneity of neuroimaging measures. In this study, we explore the use of normative modelling (NM) to identify individual patient alterations by describing the physiological variability of molecular functions. NM potentially addresses challenges such as small sample sizes and diverse acquisition protocols typical of molecular neuroimaging studies. We applied NM to two PET radiotracers targeting the dopaminergic system ([11C]-(+)-PHNO and [18F]FDOPA) to create a reference-cohort model of healthy controls. The models were subsequently utilized on different independent cohorts of patients with psychosis in different disease stages and treatment outcomes. Our results showed that patients with psychosis exhibited a higher degree of extreme deviations (~3-fold increase) than controls, although this pattern was heterogeneous, with minimal overlap of extreme deviations topology (max 20%). We also confirmed that striatal [18F]FDOPA signal, when referenced to a normative distribution, can predict treatment response (striatal AUC ROC: 0.77-0.83). In conclusion, our results indicate that normative modelling can be effectively applied to molecular neuroimaging after proper harmonization, enabling insights into disease mechanisms and advancing precision medicine. In addition, the method is valuable in understanding the heterogeneity of patient populations and can contribute to maximising cost efficiency in studies aimed at comparing cases and controls.

Hypometabolism and atrophy patterns associated with Niemann-Pick type C

BACKGROUND

Niemann-Pick disease type C (NP-C) is a rare genetic lysosomal lipid storage disorder characterized by progressive neurological impairment. Early diagnosis is critical for initiating treatment with miglustat, which can decelerate disease progression. In this study, we evaluated a cohort of 22 NP-C patients who underwent MRI, [18F]FDG PET, and clinical assessment at baseline. We performed a cross-sectional and longitudinal imaging study evaluating the role of [18F]FDG PET as an adjunct diagnostic tool for NP-C alongside MRI, the current neuroimaging standard.

RESULTS

Group-level MRI analysis identified significant cerebellar and thalamic atrophy (d = 1.56, p < 0.0001 and d = 1.09, p < 0.001, respectively), with less pronounced involvement of the frontal lobe and hippocampus, which aligned with existing neuropathological understanding and guidelines. Conversely, [18F]FDG PET imaging revealed extensive hypometabolism in the cerebellum, thalamus, and cingulate cortex (d = 1.42, p < 0.0001), and moderate hypometabolism in broad frontotemporal areas. [18F]FDG PET provided higher effect sizes across all brain regions, including regions without apparent atrophy, which suggests that it may be more sensitive than MRI for detecting NP-C neurodegenerative changes. Single-subject visual assessment of individual PET images further validated the clinical utility of [18F]FDG PET, with significant hypometabolism observed in the cerebellum, thalamus and anterior and posterior cingulate reported by physicians in 17/22 patients. Both hypometabolism and atrophy in the cerebellum were associated with ataxia, (more strongly indicated by [18F]FDG PET, p < 0.0001 vs. MRI, p = 0.07). Medial temporal lobe atrophy was associated with cognitive impairment (p < 0.05), and frontal hypometabolism was slightly related to behavioural impairment (p < 0.07). Longitudinal [18F]FDG PET analysis revealed progressive subcortical, cortical and cerebellar hypometabolism, which was most pronounced in the cerebellum (-12% per year, p < 0.001). Patients treated with miglustat showed a trend towards attenuated cerebellar hypometabolism progression compared to untreated patients (p = 0.10).

CONCLUSIONS

Our findings delineate a discernible hypometabolism pattern specific to NP-C that distinguishes it from other neurodegenerative conditions, thus suggesting that [18F]FDG PET might be a promising tool for NP-C diagnosis and to study disease progression.

TRIAL REGISTRATION

XUNTA 2015/140. Registered 21 April 2015.

A Case for Automated Segmentation of MRI Data in Milder Neurodegenerative Diseases

Background

Volumetric analysis and segmentation of magnetic resonance imaging (MRI) data is an important tool for evaluating neurological disease progression and neurodevelopment. Fully automated segmentation pipelines offer faster and more reproducible results. However, since these analysis pipelines were trained on or run based on atlases consisting of neurotypical controls, it is important to evaluate how accurate these methods are for neurodegenerative diseases. In this study, we compared 5 fully automated segmentation pipelines including FSL, Freesurfer, volBrain, SPM12, and SimNIBS with a manual segmentation process in GM1 gangliosidosis patients and neurotypical controls.

Methods

We analyzed 45 MRI scans from 16 juvenile GM1 gangliosidosis patients, 11 MRI scans from 8 late-infantile GM1 gangliosidosis patients, and 19 MRI scans from 11 neurotypical controls. We compared results for 7 brain structures including volumes of the total brain, bilateral thalamus, ventricles, bilateral caudate nucleus, bilateral lentiform nucleus, corpus callosum, and cerebellum.

Results

We found volBrain's vol2Brain pipeline to have the strongest correlations with the manual segmentation process for the whole brain, ventricles, and thalamus. We also found Freesurfer's recon-all pipeline to have the strongest correlations with the manual segmentation process for the caudate nucleus. For the cerebellum, we found a combination of volBrain's vol2Brain and SimNIBS' headreco to have the strongest correlations depending on the cohort. For the lentiform nucleus, we found a combination of recon-all and FSL's FIRST to give the strongest correlations depending on the cohort. Lastly, we found segmentation of the corpus callosum to be highly variable.

Conclusion

Previous studies have considered automated segmentation techniques to be unreliable, particularly in neurodegenerative diseases. However, in our study we produced results comparable to those obtained with a manual segmentation process. While manual segmentation processes conducted by neuroradiologists remain the gold standard, we present evidence to the capabilities and advantages of using an automated process including the ability to segment white matter throughout the brain or analyze large datasets, which pose feasibility issues to fully manual processes. Future investigations should consider the use of artificial intelligence-based segmentation pipelines to determine their accuracy in GM1 gangliosidosis, lysosomal storage disorders, and other neurodegenerative diseases.

Locus coeruleus neuromelanin, cognitive dysfunction, and brain metabolism in multiple system atrophy

BACKGROUND

Cognitive dysfunction is increasingly recognized in multiple system atrophy (MSA). Locus coeruleus (LC) integrity is associated with cognitive performance both in healthy controls (HC) and neurodegenerative conditions such as Parkinson's disease (PD). Furthermore, cortical glucose hypometabolism is associated with impaired cognitive performance in MSA. However, knowledge about LC sub-regional degeneration and its association with cognitive dysfunction and cortical glucose metabolism is lacking.

OBJECTIVE

To investigate LC sub-regional involvement and its association with cognitive impairment and brain metabolism in MSA.

METHODS

Eleven MSA, eighteen PD, and eighteen HC participants were included in the study. Neuromelanin-sensitive MRI was used to determine rostral, middle and caudal LC neuromelanin signals. Brain glucose metabolism was investigated with [18F]Fluorodeoxyglucose PET (FDG-PET). The Montreal Cognitive Assessment (MoCA) was used as a measure of global cognition.

RESULTS

Middle LC neuromelanin signal was significantly reduced in MSA [t(43) = 3.70, corrected-p = 0.004] and PD [t(43) = 2.63, corrected-p = 0.041] compared to HC, while caudal LC was only reduced in MSA [t(43) = 2.82, corrected-p = 0.030]. In MSA, decreased rostral LC neuromelanin was associated with lower MoCA scores (ρ = 0.760, p = 0.006) which, in turn, were associated with lower frontal cortex glucose metabolism. An association between rostral LC neuromelanin signal and frontal cortex glucose metabolism was found in exploratory analyses.

CONCLUSION

Loss of LC neuromelanin signal was found in MSA, the middle and caudal parts being targeted. Rostral LC neuromelanin signal loss was associated with both frontal cortex hypometabolism and lower MoCA scores. This pathophysiological link should be further investigated as the noradrenergic system transmission is amenable to pharmacological manipulation.

Plasma pTau217 ratio predicts continuous regional brain tau accumulation in amyloid-positive early Alzheimer's disease

BACKGROUND

This study examines whether phosphorylated plasma Tau217 ratio (pTau217R) can predict tau accumulation in different brain regions, as measured by positron emission tomography (PET) standardized uptake value ratio (SUVR), for staging Alzheimer's disease (AD).

METHODS

Plasma pTau217R was measured using immunoprecipitation-mass spectrometry. Models for predicting tau PET SUVR, developed with 144 early AD individuals using [18F]MK6240, were validated in two validation sets, VS1 (98 early AD) and VS2 (47 preclinical/early AD with a different tracer, flortaucipir (Tauvid)), all amyloid-beta positive (Aβ+).

RESULTS

The pTau217R-based model predicted tau levels up to an SUVR of 2 in multiple brain regions, effectively assessing tau status at different tau levels with receiver operating characteristic (ROC) curve areas of 0.84-0.95 in VS1 and 0.71-0.88 in VS2 (using a different tracer). It reduced PET scan needs by 65% while maintaining 95% sensitivity.

DISCUSSION

PTau217R reliably predicts regional tau accumulation in early AD, reducing reliance on tau PET scans and broadening its clinical application.

CLINICAL TRIAL REGISTRATION NUMBER

NCT03887455 (ClarityAD) HIGHLIGHTS: Developed a model using plasma pTau217R to predict tau levels across brain regions. pTau217R model outperformed models based on clinical, MRI, and other blood biomarkers. The model reliably predicted tau levels exceeding tau positivity and higher thresholds. Screening with pTau217R could reduce tau PET scans by 65% at 95% sensitivity. pTau217R model aids in disease staging and monitoring in early AD.

Individual-level metabolic connectivity from dynamic [18F]FDG PET reveals glioma-induced impairments in brain architecture and offers novel insights beyond the SUVR clinical standard

PURPOSE

This study evaluates the potential of within-individual Metabolic Connectivity (wi-MC), from dynamic [18F]FDG PET data, based on the Euclidean Similarity method. This approach leverages the biological information of the tracer's full temporal dynamics, enabling the direct extraction of individual metabolic connectomes. Specifically, the proposed framework, applied to glioma pathology, seeks to assess sensitivity to metabolic dysfunctions in the whole brain, while simultaneously providing further insights into the pathophysiological mechanisms regulating glioma progression.

METHODS

We designed an index (Distance from Healthy Group, DfHG) based on the alteration of wi-MC in each patient (n = 44) compared to a healthy reference (from 57 healthy controls), to individually quantify metabolic connectivity abnormalities, resulting in an Impairment Map highlighting significantly compromised areas. We then assessed whether our measure of metabolic network alteration is associated with well-established markers of disease severity (tumor grade and volume, with and without edema). Subsequently, we investigated disruptions in wi-MC homotopic connectivity, assessing both affected and seemingly healthy tissue to deepen the pathology's impact on neural communication. Finally, we compared network impairments with local metabolic alterations determined from SUVR, a validated diagnostic tool in clinical practice.

RESULTS

Our framework revealed how gliomas cause extensive alterations in the topography of brain networks, even in structurally unaffected regions outside the lesion area, with a significant reduction in connectivity between contralateral homologous regions. High-grade gliomas have a stronger impact on brain networks, and edema plays a mediating role in global metabolic alterations. As compared to the conventional SUVR-based analysis, our approach offers a more holistic view of the disease burden in individual patients, providing interesting additional insights into glioma-related alterations.

CONCLUSION

Considering our results, individual PET connectivity estimates could hold significant clinical value, potentially allowing the identification of new prognostic factors and personalized treatment in gliomas or other focal pathologies.

Mapping punishment avoidance learning deficits in non-suicidal self-injury in young adults with and without borderline personality disorder: An fMRI study

INTRODUCTION

Non-suicidal self-injury (NSSI) is a growing public health concern among young adults in both clinical and non-clinical settings. Despite evidence linking NSSI to alterations in learning from reward and punishment, this area remains understudied, especially in non-clinical populations without borderline personality disorder (BPD).

METHODS

We employed a modified version of the Probabilistic Stimulus Selection (PSS) task in two groups of young adults with recurrent NSSI, with (NSSI+BPD) and without BPD (NSSI), and an additional group of healthy controls (HC). While undergoing functional magnetic resonance imaging (fMRI), participants were asked to choose between pairs of stimuli with different reward probabilities. In the training phase, they received probabilistic feedback and learned to identify the most rewarding option within fixed pairs. In the test phase, these learned stimuli were recombined into novel pairs, where participants' accuracy in selecting the most rewarding and avoiding the most punishing options reflected their ability to learn from reward and punishment, respectively.

RESULTS

Compared to HC, participants in the NSSI and NSSI+BPD groups were less accurate at avoiding the most punishing options than at choosing the most rewarding options, and showed reduced activity in the nucleus accumbens (NAcc) during punishment avoidance relative to reward selection.

LIMITATIONS

The modest sample size, descriptive rather than modeling approach, and absence of ecological momentary assessments may limit the results.

CONCLUSION

Findings suggest that reduced activation of the NAcc when avoiding loss may underlie difficulties in learning to avoid punishment in young adults with NSSI, regardless of the presence of BPD.

Cortical Diffusivity, a Biomarker for Early Neuronal Damage, Is Associated with Amyloid-β Deposition: A Pilot Study

Pathological alterations in Alzheimer's disease (AD) begin several years prior to symptom onset. Cortical mean diffusivity (cMD) may be used as a measure of early grey matter damage in AD as it reflects the breakdown of microstructural barriers preceding volumetric changes and affecting cognitive function. We investigated cMD changes early in the disease trajectory and evaluated the influence of amyloid-β (Aβ) and tau deposition. In this cross-sectional study, we analysed multimodal PET, DTI, and MRI data of 87 participants, and stratified them into Aβ-negative and -positive, cognitively normal, mildly cognitively impaired, and AD patients. cMD was significantly increased in Aβ-positive MCI and AD compared with CN in the frontal, parietal, temporal cortex, hippocampus, and medial temporal lobe. cMD was significantly correlated with cortical thickness only in patients without Aβ deposition but not in Aβ-positive patients. Our results suggest that cMD is an early marker of neuronal damage since it is observed simultaneously with Aβ deposition and is correlated with cortical thickness only in subjects without Aβ deposition. cMD changes may be driven by Aβ but not tau, suggesting that direct Aβ toxicity or associated inflammation causes damage to neurons. cMD may provide information about early microstructural changes before macrostructural changes.

Amyloid-β deposition predicts oscillatory slowing of magnetoencephalography signals and a reduction of functional connectivity over time in cognitively unimpaired adults

With the ongoing developments in the field of anti-amyloid therapy for Alzheimer's disease, it is crucial to better understand the longitudinal associations between amyloid-β deposition and altered network activity in the living human brain. We included 110 cognitively unimpaired individuals (67.9 ± 5.7 years), who underwent [18F]flutemetamol (amyloid-β)-PET imaging and resting-state magnetoencephalography (MEG) recording at baseline and 4-year follow-up. We tested associations between baseline amyloid-β deposition and MEG measures (oscillatory power and functional connectivity). Next, we examined the relationship between baseline amyloid-β deposition and longitudinal MEG measures, as well as between baseline MEG measures and longitudinal amyloid-β deposition. Finally, we assessed associations between longitudinal changes in both amyloid-β deposition and MEG measures. Analyses were performed using linear mixed models corrected for age, sex and family. At baseline, amyloid-β deposition in orbitofrontal-posterior cingulate regions (i.e. early Alzheimer's disease regions) was associated with higher theta (4-8 Hz) power (β = 0.17, P < 0.01) in- and lower functional connectivity [inverted Joint Permutation Entropy (JPEinv) theta, β = -0.24, P < 0.001] of these regions, lower whole-brain beta (13-30 Hz) power (β = -0.13, P < 0.05) and lower whole-brain functional connectivity (JPEinv theta, β = -0.18, P < 0.001). Whole-brain amyloid-β deposition was associated with higher whole-brain theta power (β = 0.17, P < 0.05), lower whole-brain beta power (β = -0.13, P < 0.05) and lower whole-brain functional connectivity (JPEinv theta, β = -0.21, P < 0.001). Baseline amyloid-β deposition in early Alzheimer's disease regions also predicted future oscillatory slowing, reflected by increased theta power over time in early Alzheimer's disease regions and across the whole brain (β = 0.11, β = 0.08, P < 0.001), as well as decreased whole-brain beta power over time (β = -0.04, P < 0.05). Baseline amyloid-β deposition in early Alzheimer's disease regions also predicted a reduction in functional connectivity between these regions and the rest of the brain over time (JPEinv theta, β = -0.07, P < 0.05). Baseline whole-brain amyloid-β deposition was associated with increased whole-brain theta power over time (β = 0.08, P < 0.01). Baseline MEG measures were not associated with longitudinal amyloid-β deposition. Longitudinal changes in amyloid-β deposition in early Alzheimer's disease regions were associated with longitudinal changes in functional connectivity of early Alzheimer's disease regions (JPEinv theta, β = -0.19, P < 0.05) and the whole brain [corrected amplitude envelope correlations alpha (8-13 Hz), β = -0.22, P < 0.05]. Finally, longitudinal changes in whole-brain amyloid-β deposition were associated with longitudinal changes in whole-brain relative theta power (β = 0.21, P < 0.05). Disruptions of oscillatory power and functional connectivity appear to represent early functional consequences of emerging amyloid-β deposition in cognitively unimpaired individuals. These findings suggest a role for neurophysiology in monitoring disease progression and potential treatment effects in pre-clinical Alzheimer's disease.

Neuroanatomical heterogeneity drives divergent cognitive and motor trajectories in Parkinson's disease subtypes

INTRODUCTION

Cognitive symptoms of Parkinson's disease (PD) may initially present subtly, often overshadowed by more noticeable motor symptoms. However, as PD progresses, predicting which individuals will experience significant cognitive decline becomes challenging due to variability, suggesting distinct PD subtypes with varying cognitive trajectories. This study aimed to identify early PD subtypes based on patterns of gray matter atrophy in brain regions associated with cognition and assess their distinct patterns of cognitive change over time. Recognizing PD primarily as a movement disorder, we also evaluated their motor symptoms.

METHODS

We analyzed T1-weighted MRI data, cognitive, and motor scores from 114 de novo PD patients and 120 healthy controls. Multivariate gray matter volumetric distances (MGMV) across frontal, subcortical, parietal, temporal, and occipital regions were computed, and K-means clustering was used to identify PD subtypes. Subsequently, cognitive assessments were compared between subtypes at baseline and 48 months using linear mixed-effects models and reliable change indices. Motor-symptom changes were assessed using linear mixed-effects models.

RESULTS

Two PD subtypes were identified from baseline MRI. Subtype 1 showed significantly higher MGMV in frontal (p < 0.001) and subcortical (p < 0.001) regions, indicating atrophy. At 48 months, subtype 1 had poorer global cognitive performance than subtype 2 (p = 0.005) and faster progression of postural instability and gait disturbance (p = 0.04).

CONCLUSIONS

PD subtypes identified early by distinct frontal and subcortical atrophy patterns exhibited divergent trajectories of cognitive decline and worsening motor symptoms over time, underscoring the neuroanatomical heterogeneity that drives clinical variability in PD.

Brain inflammation co-localizes highly with tau in mild cognitive impairment due to early-onset Alzheimer's disease

Brain inflammation, with an increased density of microglia and macrophages, is an important component of Alzheimer's disease and a potential therapeutic target. However, it is incompletely characterized, particularly in patients whose disease begins before the age of 65 years and, thus, have few co-pathologies. Inflammation has been usefully imaged with translocator protein (TSPO) PET, but most inflammation PET tracers cannot image subjects with a low-binder TSPO rs6971 genotype. In an important development, participants with any TSPO genotype can be imaged with a novel tracer, 11C-ER176, that has a high binding potential and a more favourable metabolite profile than other TSPO tracers currently available. We applied 11C-ER176 to detect brain inflammation in mild cognitive impairment (MCI) caused by early-onset Alzheimer's disease. Furthermore, we sought to correlate the brain localization of inflammation, volume loss, elevated amyloid-β (Aβ)and tau. We studied brain inflammation in 25 patients with early-onset amnestic MCI (average age 59 ± 4.5 years, 10 female) and 23 healthy controls (average age 65 ± 6.0 years, 12 female), both groups with a similar proportion of all three TSPO-binding affinities. 11C-ER176 total distribution volume (VT), obtained with an arterial input function, was compared across patients and controls using voxel-wise and region-wise analyses. In addition to inflammation PET, most MCI patients had Aβ (n = 23) and tau PET (n = 21). For Aβ and tau tracers, standard uptake value ratios were calculated using cerebellar grey matter as region of reference. Regional correlations among the three tracers were determined. Data were corrected for partial volume effect. Cognitive performance was studied with standard neuropsychological tools. In MCI caused by early-onset Alzheimer's disease, there was inflammation in the default network, reaching statistical significance in precuneus and lateral temporal and parietal association cortex bilaterally, and in the right amygdala. Topographically, inflammation co-localized most strongly with tau (r = 0.63 ± 0.24). This correlation was higher than the co-localization of Aβ with tau (r = 0.55 ± 0.25) and of inflammation with Aβ (0.43 ± 0.22). Inflammation co-localized least with atrophy (-0.29 ± 0.26). These regional correlations could be detected in participants with any of the three rs6971 TSPO polymorphisms. Inflammation in Alzheimer's disease-related regions correlated with impaired cognitive scores. Our data highlight the importance of inflammation, a potential therapeutic target, in the Alzheimer's disease process. Furthermore, they support the notion that, as shown in experimental tissue and animal models, the propagation of tau in humans is associated with brain inflammation.

Modulating effects of fitness and physical activity on Alzheimer's disease: Implications from a six-month randomized controlled sports intervention

BACKGROUND

Physical activity and fitness are major targets in Alzheimer's disease (AD) preventive research. However, current research is heterogeneous and often disregards the relationship between these parameters and disease outcomes.

OBJECTIVE

To assess the effects of physical activity and fitness on AD within the context of a multicomponent sports intervention.

METHODS

46 participants with early-stage AD (mean age 70 ± 7 years, 18 women, mean Montreal Cognitive Assessment (MoCA) score 19±5) were included in a six-month randomized controlled trial (Dementia-MOVE), participating in either a multicomponent sports intervention or a control condition with a psychoeducational program. The modulating effect of fitness and physical activity changes on AD outcome parameters such as cognition, function and cerebral brain structure from 3T-MRI were examined using multiple linear regression analyses.

RESULTS

An increase in VO2max was associated with assignment to the intervention group (p = 0.016), lower baseline fitness (p = 0.001), and an increased rate of physical activity (p = 0.046). Only in the intervention group, ΔVO2max had a beneficial modulating effect on the MoCA score (p = 0.039), the executive functions (p = 0.017) and regional brain volumes of the temporal lobe, e.g., the hippocampus (p = 0.044). High daily step count was associated with preserved executive functions (p = 0.001), and caregivers' quality of life (p ≤ 0.001) in the overall sample.

CONCLUSIONS

Our results confirm that multicomponent exercise improves cardiorespiratory fitness in AD, which is associated with advantageous developments in cognitive performance and preservation of brain structure. These findings suggest that especially patients with comparably worse cognition and fitness benefit and should be encouraged for activity engagement.

Cortical Tau Aggregation Patterns Associated With Apraxia in Patients With Alzheimer Disease

BACKGROUND AND OBJECTIVES

Apraxia is a frequently observed symptom in Alzheimer disease (AD), but the causal pathomechanism underlying this dysfunction is not well understood. Previous studies have demonstrated associations between various cognitive dysfunctions in AD and cortical tau deposition in specific brain areas, suggesting a causal relationship. Thus, we hypothesized that specific regional patterns of tau pathology in praxis-related brain regions may be associated with apraxic deficits in AD. For this purpose, we performed PET imaging with the second-generation tau-PET tracer [18F]PI-2620 in a well-defined group of patients with AD (N = 33) who had been systematically assessed for apraxia.

METHODS

Patients with a biomarker-confirmed diagnosis of AD were recruited in addition to a sample of cognitively unimpaired (CU1) control participants. Both groups underwent apraxia assessments with the Dementia Apraxia Screening Test. In addition, PET imaging with [18F]PI-2620 was performed to assess tau pathology in the patients with AD. To specifically investigate the association of apraxia severity with regional tau pathology, we compared the PET data from this group with an independent sample of amyloid-negative cognitively intact participants (CU2) by generation of z-score deviation maps and submitted these maps to a voxel-based multiple regression analysis.

RESULTS

A total of 120 participants (39% female) with a mean age of 67.9 (9.2) years were included in the study (AD = 33; CU1; N = 33; CU2; N = 54). We identified a significant correlation between circumscribed clusters of tau aggregation in praxis-related brain regions (including parietal (angular gyrus), temporal, and occipital regions) and severity of apraxia in patients with AD. By contrast, no significant correlations between tau tracer uptake in primary motor cortex or subcortical brain regions and apraxia were observed.

DISCUSSION

These results suggest that tau deposition in specific cortical praxis-related brain regions may induce local neuronal dysfunction leading to a dose-dependent functional decline in praxis performance in AD. The awareness of this relationship could further refine a differentiated individual diagnostic characterization and classification of patients with AD.

EMATA: a toolbox for the automatic extraction and modeling of arterial inputs for tracer kinetic analysis in [18F]FDG brain studies

PURPOSE

PET imaging is a pivotal tool for biomarker research aimed at personalized medicine. Leveraging the quantitative nature of PET requires knowledge of plasma radiotracer concentration. Typically, the arterial input function (AIF) is obtained through arterial cannulation, an invasive and technically demanding procedure. A less invasive alternative, especially for [18F]FDG, is the image-derived input function (IDIF), which, however, often requires correction for partial volume effect (PVE), usually performed via venous blood samples. The aim of this paper is to present EMATA: Extraction and Modeling of Arterial inputs for Tracer kinetic Analysis, an open-source MATLAB toolbox. EMATA automates IDIF extraction from [18F]FDG brain PET images and additionally includes a PVE correction procedure that does not require any blood sampling.

METHODS

To assess the toolbox generalizability and present example outputs, EMATA was applied to brain [18F]FDG dynamic data of 80 subjects, extracted from two distinct datasets (40 healthy controls, 40 glioma patients). Additionally, to compare with the reference standard, quantification using both IDIF and AIF was carried out on a third open-access dataset of 18 healthy individuals.

RESULTS

EMATA consistently performs IDIF extraction across all datasets, despite differences in scanners and acquisition protocols. Remarkably high agreement is observed when comparing Patlak's Ki between IDIF and AIF (R2: 0.98 ± 0.02).

CONCLUSION

EMATA proved adaptability to different datasets characteristics and the ability to provide arterial input functions that can be used for reliable PET quantitative analysis.

Multimodal feature fusion-based graph convolutional networks for Alzheimer's disease stage classification using F-18 florbetaben brain PET images and clinical indicators

Alzheimer's disease (AD), the most prevalent degenerative brain disease associated with dementia, requires early diagnosis to alleviate worsening of symptoms through appropriate management and treatment. Recent studies on AD stage classification are increasingly using multimodal data. However, few studies have applied graph neural networks to multimodal data comprising F-18 florbetaben (FBB) amyloid brain positron emission tomography (PET) images and clinical indicators. The objective of this study was to demonstrate the effectiveness of graph convolutional network (GCN) for AD stage classification using multimodal data, specifically FBB PET images and clinical indicators, collected from Dong-A University Hospital (DAUH) and Alzheimer's Disease Neuroimaging Initiative (ADNI). The effectiveness of GCN was demonstrated through comparisons with the support vector machine, random forest, and multilayer perceptron across four classification tasks (normal control (NC) vs. AD, NC vs. mild cognitive impairment (MCI), MCI vs. AD, and NC vs. MCI vs. AD). As input, all models received the same combined feature vectors, created by concatenating the PET imaging feature vectors extracted by the 3D dense convolutional network and non-imaging feature vectors consisting of clinical indicators using multimodal feature fusion method. An adjacency matrix for the population graph was constructed using cosine similarity or the Euclidean distance between subjects' PET imaging feature vectors and/or non-imaging feature vectors. The usage ratio of these different modal data and edge assignment threshold were tuned by setting them as hyperparameters. In this study, GCN-CS-com and GCN-ED-com were the GCN models that received the adjacency matrix constructed using cosine similarity (CS) and the Euclidean distance (ED) between the subjects' PET imaging feature vectors and non-imaging feature vectors, respectively. In modified nested cross validation, GCN-CS-com and GCN-ED-com respectively achieved average test accuracies of 98.40%, 94.58%, 94.01%, 82.63% and 99.68%, 93.82%, 93.88%, 90.43% for the four aforementioned classification tasks using DAUH dataset, outperforming the other models. Furthermore, GCN-CS-com and GCN-ED-com respectively achieved average test accuracies of 76.16% and 90.11% for NC vs. MCI vs. AD classification using ADNI dataset, outperforming the other models. These results demonstrate that GCN could be an effective model for AD stage classification using multimodal data.

Brain age in genetic and idiopathic Parkinson's disease

The brain-age gap, i.e. the difference between the brain age estimated from structural MRI data and the chronological age of an individual, has been proposed as a summary measure of brain integrity in neurodegenerative diseases. Here, we aimed to determine the brain-age gap in genetic and idiopathic Parkinson's disease and its association with surrogate markers of Alzheimer's disease and Parkinson's disease pathology and with rates of cognitive and motor function decline. We studied 1200 cases from the Parkinson's Progression Markers Initiative cohort, including idiopathic Parkinson's disease, asymptomatic and clinical mutation carriers in the leucine-rich repeat kinase 2 gene (LRRK2) and the glucocerebrosidase gene (GBA), and normal controls using a cohort study design. For comparison, we studied 187 Alzheimer's disease dementia cases and 254 controls from the Alzheimer's Disease Neuroimaging Initiative cohort. We used Bayesian ANOVA to determine associations of the brain-age gap with diagnosis, and baseline measures of motor and cognitive function, dopamine transporter activity and CSF markers of Alzheimer's disease type amyloid-β42 and phosphotau pathology. Associations of brain-age gap with rates of cognitive and motor function decline were determined using Bayesian generalized mixed effect models. The brain-age gap in idiopathic Parkinson's disease patients was 0.7 years compared to controls, but 5.9 years in Alzheimer's disease dementia cases. In contrast, asymptomatic LRRK2 individuals had a 1.1. year younger brain age than controls. Across all cases, the brain-age gap was associated with motor impairment and (in the clinically manifest PD cases) reduced dopamine transporter activity, but less with CSF amyloid-β42 and phosphotau. In idiopathic Parkinson's disease cases, however, the brain-age gap was associated with lower CSF amyloid-β42 levels. In sporadic and genetic Parkinson's disease cases, a higher brain-age gap was associated with faster decline in episodic memory, and executive and motor function, whereas in asymptomatic LRRK2 cases, a smaller brain-age gap was associated with faster cognitive decline. In conclusion, brain age was sensitive to Alzheimer's disease like rather than Parkinson's disease like brain atrophy. Once an individual had idiopathic Parkinson's disease, their brain age was associated with markers of Alzheimer's disease rather than Parkinson's disease. Asymptomatic LRRK2 cases had seemingly younger brains than controls, and in these cases, younger brain age was associated with poorer cognitive outcome. This suggests that the term brain age is misleading when applied to disease stages where reactive brain changes with apparent volume increases rather than atrophy may drive the calculation of the brain age.

Multiclass classification of Alzheimer's disease prodromal stages using sequential feature embeddings and regularized multikernel support vector machine

The detection of patients in the cognitive normal (CN), mild cognitive impairment (MCI), and Alzheimer's disease (AD) stages of neurodegeneration is crucial for early treatment interventions. However, the heterogeneity of MCI data samples poses a challenge for CN vs. MCI vs. AD multiclass classification, as some samples are closer to AD while others are closer to CN in the feature space. Previous attempts to address this challenge produced inaccurate results, leading most frameworks to break the assessment into binary classification tasks such as AD vs. CN, AD vs. MCI, and CN vs. MCI. Other methods proposed sequential binary classifications such as CN vs. others and dividing others into AD vs. MCI. While those approaches may have yielded encouraging results, the sequential binary classification method makes interpretation and comparison with other frameworks challenging and subjective. Those frameworks exhibited varying accuracy scores for different binary tasks, making it unclear how to compare the model performance with other direct multiclass methods. Therefore, we introduce a classification framework comprising unsupervised ensemble manifold regularized sparse low-rank approximation and regularized multikernel support vector machine (SVM). This framework first extracts a joint feature embedding from MRI and PET neuroimaging features, which were then combined with the Apoe4, Adas11, MPACC digits, and Intracranial volume features using a regularized multikernel SVM. Using that framework, we achieved a state-of-the-art (SOTA) result in a CN vs. MCI vs. AD multiclass classification (mean accuracy: 84.87±6.09, F1 score: 84.83±6.12 vs 67.69). The methods generalize well to binary classification tasks, achieving SOTA results in all but the CN vs. MCI category, which was slightly lower than the best score by just 0.2%.

PET clinical study of novel antipsychotic LB-102 demonstrates unexpectedly prolonged dopamine receptor target engagement

Regulation of dopamine activity has important clinical consequences, most notably in schizophrenia. LB-102, N-methyl amisulpride, is a novel dopamine D2/3/5-HT7 inhibitor being developed as a treatment for schizophrenia and other psychiatric disorders. The characteristic that is common to all current antipsychotics is their engagement of D2 dopamine receptors. The goal of this study was to measure the dopamine receptor occupancy of orally administered LB-102 at three different doses (50, 75, and 100 mg as single doses and 50 and 100 mg as multiple doses) and at different timepoints in healthy volunteers using positron emission tomography (PET) with 11C raclopride as a radiotracer. Results of this study (NCT04588129) showed that steady-state once daily oral dosing of 50 mg LB-102 afforded striatal dopamine occupancy (RO) in the desired 60-80% range consistently over the course of 24 h. Contrary to the often observed relationship between RO vs plasma concentrations, maximum dopamine RO significantly lagged maximum plasma concentration and showed little variability under steady state conditions. A similar phenomenon has recently been reported with a non-racemic version of amisulpride [1]. LB-102 was generally safe and well-tolerated at all doses. Results of this study were used to inform dosing in a subsequent Phase 2 clinical study in schizophrenia patients.

Quantitative Imaging of Regional Cerebral Protein Synthesis in Clinical Alzheimer's Disease by [11C]Leucine PET

PURPOSE

Protein synthesis is essential to maintain integrity and function of the human brain, and protein synthesis is associated specifically with the formation of long-term memory. Experimental and clinical observations indicate that this process is disturbed in Alzheimer's dementia and other neurodegenerative diseases. In-vivo investigation with positron emission tomography (PET) using [11C]leucine provides a unique possibility to measure regional cerebral protein synthesis (rCPS) rates in human brain and to determine whether it is altered in Alzheimer's disease (AD), and thus may provide a target for future therapeutic interventions.

PROCEDURES

In this first human study, we measured rCPS by [11C]leucine PET in four patients with AD (age 57-73 years) and compared the results with six healthy controls (three of whom were age matched and the other three were young controls). Quantification of rCPS also required measurement of amino acid (AA) levels and of free and protein-bound [11C]leucine in plasma during the 90 min PET scans conducted following at least six hours of fasting.

RESULTS

Rates of rCPS measured in absolute units of nmol/g/min ranged between 1.81 and 2.53 in AD patients, 2.10 and 2.54 in matched controls, and 2.21 to 2.35 in the young controls. Mean and median values did not show significant differences between the groups. Rates of rCPS also depended upon whether corrections for plasma AA levels were included in the calculations. When considering regional values relative to the corpus callosum as a reference region, there was a tendency towards impairment of rCPS in patients, which was most prominent in the parietal cortex, but did not reach significance. Similar findings were observed with normalisation of rCPS to global cortical mean.

CONCLUSIONS

In summary, this first human study assessing regional protein synthesis with [11C]leucine in AD has demonstrated where the sources of variance in measurements of cerebral protein synthesis may arise, along with the potential magnitude of this variance. This study also indicates that there is a tendency towards impairment of rCPS in patients with Alzheimer's disease, which requires further investigation including possible partial volume effects due to atrophy.

Social Buffering of Posttraumatic Stress Disorder: Longitudinal Effects and Neural Mediators

BACKGROUND

Posttraumatic stress disorder (PTSD) is a well-characterized psychiatric disorder that features changes in mood and arousal following traumatic events. Previous animal and human studies of social support during the peritraumatic window have demonstrated a buffering effect with regard to acute biological and psychological stress symptoms. Fewer studies have explored the magnitude of and mechanism through which early posttrauma social support can reduce longitudinal PTSD severity.

METHODS

In this study, we investigated the beneficial impact of social support on longitudinal PTSD symptoms and probed brain regions sensitive to this buffering phenomenon, such as the amygdala and ventromedial prefrontal cortex. In the multisite AURORA study, 315 participants reported PTSD symptoms (PTSD Checklist for DSM-5) and perceived emotional support (Patient-Reported Outcomes Measurement Information System) at 2 weeks, 8 weeks, 3 months, and 6 months post emergency department visit. Additionally, neuroimaging data were collected at 2 weeks posttrauma.

RESULTS

We hypothesized that early posttrauma social support would be linked with greater fractional anisotropic values in white matter tracts that have known connectivity between the amygdala and prefrontal cortex and would predict reduced neural reactivity to social threat cues in the amygdala. Interestingly, while we observed greater fractional anisotropy in the bilateral cingulum and bilateral uncinate fasciculus as a function of early posttrauma emotional support, we also identified greater threat reactivity in the precuneus/posterior cingulate, a component of the default mode network.

CONCLUSIONS

Our findings suggest that the neurocircuitry underlying the response to social threat cues is facilitated through broader pathways that involve the posterior hub of the default mode network.

Neuronal and oligodendroglial, but not astroglial, tau translates to in vivo tau PET signals in individuals with primary tauopathies

Tau PET has attracted increasing interest as an imaging biomarker for 4-repeat (4R)-tauopathy progressive supranuclear palsy (PSP). However, the translation of in vitro 4R-tau binding to in vivo tau PET signals is still unclear. Therefore, we performed a translational study using a broad spectrum of advanced methodologies to investigate the sources of [18F]PI-2620 tau PET signals in individuals with 4R-tauopathies, including a pilot PET autopsy study in patients. First, we conducted a longitudinal [18F]PI-2620 PET/MRI study in a 4-repeat-tau mouse model (PS19) and detected elevated [18F]PI-2620 PET signals in the presence of high levels of neuronal tau. An innovative approach involving cell sorting after radiotracer injection in vivo revealed higher tracer uptake in single neurons than in the astrocytes of PS19 mice. Regional [18F]PI-2620 tau PET signals during the lifetime correlated with the abundance of fibrillary tau and with autoradiography signal intensity in PSP patients and disease controls who underwent autopsy 2-63 months after tau PET. In autoradiography, tau-positive neurons and oligodendrocytes with a high AT8 density, but not tau-positive astrocytes, were the drivers of [18F]PI-2620 autoradiography signals in individuals with PSP. The high tau abundance in oligodendrocytes at the boundary of gray and white matter facilitated the identification of an optimized frontal lobe target region to detect the tau burden in patients with PSP. In summary, neuronal and oligodendroglial tau constitutes the dominant source of tau PET radiotracer binding in 4-repeat-tauopathies, translating to an in vivo signal.

Specific structural changes in Parkinson's disease-related olfactory dysfunction compared to others forms of olfactory dysfunction

Context

Olfactory dysfunction (OD) is a common early symptom of Parkinson’s disease (PD). However, OD is not specific to PD, as approximatively 20% of the general population exhibit different forms of OD. To use olfactory measures for early Parkinson screening, it is crucial to distinguish PD-related OD from Non-Parkinsonian OD (NPOD).

Objectives and hypothesis

This study aimed to compare the structural changes associated with PD-related OD (n = 15) with NPOD (n = 15), focusing on gray matter volumes and white matter fiber integrity in chemosensory regions. We hypothesized that PD-related OD presents specific structural alterations in these regions.

Methods

Participants underwent a 3 T MRI scan, which included anatomical T1 and diffusion-weighted imaging. Gray and white matter integrity were assessed using both whole-brain analyses (voxel-based morphometry—VBM and tract-based spatial statistics—TBSS, respectively) and localized approaches, including regions of interest and tractography.

Results

PD patients exhibited significantly higher gray matter volume in the left insula using restricted regions-of-interest analyses, while no other significant gray or white matter differences were found between groups.

Conclusion

Structural imaging of the gray matter, particularly the insula, but not of white matter, differentiates PD-related OD from NPOD.

α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor density underlies intraregional and interregional functional centrality

Local and global functional connectivity densities (lFCD and gFCD, respectively), derived from functional magnetic resonance imaging (fMRI) data, represent the degree of functional centrality within local and global brain networks. While these methods are well-established for mapping brain connectivity, the molecular and synaptic foundations of these connectivity patterns remain unclear. Glutamate, the principal excitatory neurotransmitter in the brain, plays a key role in these processes. Among its receptors, the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) is crucial for neurotransmission, particularly in cognitive functions such as learning and memory. This study aimed to examine the association of the AMPAR density and FCD metrics of intraregional and interregional functional centrality. Using [11C]K-2, a positron emission tomography (PET) tracer specific for AMPARs, we measured AMPAR density in the brains of 35 healthy participants. Our findings revealed a strong positive correlation between AMPAR density and both lFCD and gFCD-lFCD across the entire brain. This correlation was especially notable in key regions such as the anterior cingulate cortex, posterior cingulate cortex, pre-subgenual frontal cortex, Default Mode Network, and Visual Network. These results highlight that postsynaptic AMPARs significantly contribute to both local and global functional connectivity in the brain, particularly in network hub regions. This study provides valuable insights into the molecular and synaptic underpinnings of brain functional connectomes.

Improving MR axon radius estimation in human white matter using spiral acquisition and field monitoring

PURPOSE

To compare MR axon radius estimation in human white matter using a multiband spiral sequence combined with field monitoring to the current state-of-the-art echo-planar imaging (EPI)-based approach.

METHODS

A custom multiband spiral sequence was used for diffusion-weighted imaging at ultra-highb $$ b $$ -values. Field monitoring and higher order image reconstruction were employed to greatly reduce artifacts in spiral images. Diffusion weighting parameters were chosen to match a state-of-the art EPI-based axon radius mapping protocol. The spiral approach was compared to the EPI approach by comparing the image signal-to-noise ratio (SNR) and performing a test-retest study to assess the respective variability and repeatability of axon radius mapping. Effective axon radius estimates were compared over white matter voxels and along the left corticospinal tract.

RESULTS

Increased SNR and reduced artifacts in spiral images led to reduced variability in resulting axon radius maps, especially in low-SNR regions. Test-retest variability was reduced by a factor of approximately 1.5 using the spiral approach. Reduced repeatability due to significant bias was found for some subjects in both spiral and EPI approaches, and attributed to scanner instability, pointing to a previously unknown limitation of the state-of-the-art approach.

CONCLUSION

Combining spiral readouts with field monitoring improved mapping of the effective axon radius compared to the conventional EPI approach.

Multimodal and quantitative analysis of the epileptogenic zone network in the pre-surgical evaluation of drug-resistant focal epilepsy

Surgical resection for epilepsy often fails due to incomplete Epileptogenic Zone Network (EZN) localization from scalp electroencephalography (EEG), stereo-EEG (SEEG), and Magnetic Resonance Imaging (MRI). Subjective interpretation based on interictal, or ictal recordings limits conventional EZN localization. This study employs multimodal analysis using high-density-EEG (HDEEG), Magnetoencephalography (MEG), functional-MRI (fMRI), and SEEG to overcome these limitations in a patient with drug-resistant MRI-negative focal epilepsy. A 17-year-old with drug-resistant epilepsy underwent evaluation. HDEEG, MEG, fMRI, and SEEG were used, with a novel HDEEG-cap facilitating simultaneous EEG-MEG and EEG-fMRI recordings. Electrical and magnetic source imaging were performed, and fMRI data were analysed for homogenous regions. SEEG analysis involved spike detection, spike timing analysis, ictal fast activity quantification, and Granger-based connectivity analysis. Non-invasive sessions revealed consistent interictal source imaging results identifying the EZN in the right anterior cingulate cortex. EEG-fMRI highlighted broader activation in the right cingulate cortex. SEEG analysis localized spikes and fast activity in the right anterior and posterior cingulate gyri. Multi-modal analysis suggested the EZN in the right frontal lobe, primarily involving the anterior and mid-cingulate cortices. Multi-modal non-invasive analyses can optimise SEEG implantation and surgical decision-making. Invasive analyses corroborated non-invasive findings, emphasising the importance of individual-case quantitative analysis across modalities in complex epilepsy cases.

Cholinergic neurotransmission in the anterior cingulate cortex is associated with cognitive performance in healthy older adults: Baseline characteristics of the Improving Neurological Health in Aging via Neuroplasticity-based Computerized Exercise (INHANCE) trial

Aging is associated with dysfunction in the cholinergic system, including degeneration of basal forebrain cholinergic terminals that innervate the cortex, which directly contributes to age- and disease-related cognitive decline. In this study, we used [18F]fluoroethoxybenzovesamicol ([18F]FEOBV) positron emission tomography (PET) imaging to assess the effect of age on cholinergic terminal integrity in predefined regions of interest and its relationship to cognitive performance in healthy older adults who underwent neuropsychological assessment and FEOBV PET brain imaging. Our results showed age-related reductions in FEOBV binding, particularly in the anterior cingulate cortex-our primary region of interest-as well as in the striatum, posterior cingulate cortex, and primary auditory cortex. Notably, FEOBV binding in the anterior cingulate cortex was positively correlated with cognitive performance on the NIH EXAMINER Executive Composite Score. These findings suggest that [18F]FEOBV PET imaging can be used as a reliable biomarker to assess cholinergic changes in the human brain and indicate that preserving the cholinergic integrity of the basal forebrain may help maintain cognitive function and protect against age-related cognitive decline.

[11C]Metoclopramide PET can detect a seizure-induced up-regulation of cerebral P-glycoprotein in epilepsy patients

BACKGROUND

P-glycoprotein (P-gp) is an efflux transporter which is abundantly expressed at the blood-brain barrier (BBB) and which has been implicated in the pathophysiology of various brain diseases. The radiolabelled antiemetic drug [11C]metoclopramide is a P-gp substrate for positron emission tomography (PET) imaging of P-gp function at the BBB. To assess whether [11C]metoclopramide can detect increased P-gp function in the human brain, we employed drug-resistant temporal lobe epilepsy (TLE) as a model disease with a well characterised, regional P-gp up-regulation at the BBB.

METHODS

Eight patients with drug-resistant (DRE) TLE, 5 seizure-free patients with drug-sensitive (DSE) focal epilepsy, and 15 healthy subjects underwent brain PET imaging with [11C]metoclopramide on a fully-integrated PET/MRI system. Concurrent with PET, arterial blood sampling was performed to generate a metabolite-corrected arterial plasma input function for kinetic modelling. The choroid plexus was outmasked on the PET images to remove signal contamination from the neighbouring hippocampus. Using a brain atlas, 10 temporal lobe sub-regions were defined and analysed with a 1-tissue-2-rate constant compartmental model to estimate the rate constants for radiotracer transfer from plasma to brain (K1) and from brain to plasma (k2), and the total volume of distribution (VT = K1/k2).

RESULTS

DRE patients but not DSE patients showed significantly higher k2 values and a trend towards lower VT values in several temporal lobe sub-regions located ipsilateral to the epileptic focus as compared to healthy subjects (k2: hippocampus: +34%, anterior temporal lobe, medial part: +28%, superior temporal gyrus, posterior part: +21%).

CONCLUSIONS

[11C]Metoclopramide PET can detect a seizure-induced P-gp up-regulation in the epileptic brain. The efflux rate constant k2 seems to be the most sensitive parameter to measure increased P-gp function with [11C]metoclopramide. Our study provides evidence that disease-induced alterations in P-gp expression at the BBB can lead to changes in the distribution of a central nervous system-active drug to the human brain, which could affect the efficacy and/or safety of drugs. [11C]Metoclopramide PET may be used to assess or predict the contribution of increased P-gp function to drug resistance and disease pathophysiology in various brain diseases.

TRIAL REGISTRATION

EudraCT 2019-003137-42. Registered 28 February 2020.

The brain's "dark energy" puzzle upgraded: [18F]FDG uptake, delivery and phosphorylation, and their coupling with resting-state brain activity

The brain's resting-state energy consumption is expected to be mainly driven by spontaneous activity. In our previous work, we extracted a wide range of features from resting-state fMRI (rs-fMRI), and used them to predict [18F]FDG PET SUVR as a proxy of glucose metabolism. Here, we expanded upon our previous effort by estimating [18F]FDG kinetic parameters according to Sokoloff's model, i.e.,K i (irreversible uptake rate),K 1 (delivery),k 3 (phosphorylation), in a large healthy control group. The parameters' spatial distribution was described at a high spatial resolution. We showed that whileK 1 is the least redundant, there are relevant differences betweenK i andk 3 (occipital cortices, cerebellum and thalamus). Using multilevel modeling, we investigated how much of the regional variability of [18F]FDG parameters could be explained by a combination of rs-fMRI variables only, or with the addition of cerebral blood flow (CBF) and metabolic rate of oxygen (CMRO2), estimated from 15O PET data. We found that combining rs-fMRI and CMRO2 led to satisfactory prediction of individualK i variance (45%). Although more difficult to describe,K i andk 3 were both most sensitive to local rs-fMRI variables, whileK 1 was sensitive to CMRO2. This work represents the most comprehensive assessment to date of the complex functional and metabolic underpinnings of brain glucose consumption.

The Contribution of Cognitive Control Networks in Word Selection Processing in Parkinson's Disease: Novel Insights from a Functional Connectivity Study

Parkinson's disease (PD) patients are impaired in word production when the word has to be selected among competing alternatives requiring higher attentional resources. In PD, word selection processes are correlated with the structural integrity of the inferior frontal gyrus, which is critical for response selection, and the uncinate fasciculus, which is necessary for processing lexical information. In early PD, we investigated the role of the main cognitive large-scale networks, namely the salience network (SN), the central executive networks (CENs), and the default mode network (DMN), in word selection. Eighteen PD patients and sixteen healthy controls were required to derive nouns from verbs or generate verbs from nouns. Participants also underwent a resting-state functional MRI. Functional connectivity (FC) was examined using independent component analysis. Functional seeds for the SN, CENs, and DMN were defined as spheres, centered at the local activation maximum. Correlations were calculated between the FC of each functional seed and word production. A significant association between SN connectivity and task performance and, with less evidence, between CEN connectivity and the task requiring selection among a larger number of competitors, emerged in the PD group. These findings suggest the involvement of the SN and CEN in word selection in early PD, supporting the hypothesis of impaired executive control.

Assessment of [18F]PI-2620 Tau-PET Quantification via Non-Invasive Automatized Image Derived Input Function

PURPOSE

[18F]PI-2620 positron emission tomography (PET) detects misfolded tau in progressive supranuclear palsy (PSP) and Alzheimer's disease (AD). We questioned the feasibility and value of absolute [18F]PI-2620 PET quantification for assessing tau by regional distribution volumes (VT). Here, arterial input functions (AIF) represent the gold standard, but cannot be applied in routine clinical practice, whereas image-derived input functions (IDIF) represent a non-invasive alternative. We aimed to validate IDIF against AIF and we evaluated the potential to discriminate patients with PSP and AD from healthy controls by non-invasive quantification of [18F] PET.

METHODS

In the first part of the study, we validated AIF derived from radial artery whole blood against IDIF by investigating 20 subjects (ten controls and ten patients). IDIF were generated by manual extraction of the carotid artery using the average and the five highest (max5) voxel intensity values and by automated extraction of the carotid artery using the average and the maximum voxel intensity value. In the second part of the study, IDIF quantification using the IDIF with the closest match to the AIF was transferred to group comparison of a large independent cohort of 40 subjects (15 healthy controls, 15 PSP patients and 10 AD patients). We compared VT and VT ratios, both calculated by Logan plots, with distribution volume (DV) ratios using simplified reference tissue modelling and standardized uptake value (SUV) ratios.

RESULTS

AIF and IDIF showed highly correlated input curves for all applied IDIF extraction methods (0.78 < r < 0.83, all p < 0.0001; area under the curves (AUC): 0.73 < r ≤ 0.82, all p ≤ 0.0003). Regarding the VT values, correlations were mainly found between those generated by the AIF and by the IDIF methods using the maximum voxel intensity values. Lowest relative differences (RD) were observed by applying the manual method using the five highest voxel intensity values (max5) (AIF vs. IDIF manual, avg: RD = -82%; AIF vs. IDIF automated, avg: RD = -86%; AIF vs. IDIF manual, max5: RD = -6%; AIF vs. IDIF automated, max: RD = -26%). Regional VT values revealed considerable variance at group level, which was strongly reduced upon scaling by the inferior cerebellum. The resulting VT ratio values were adequate to detect group differences between patients with PSP or AD and healthy controls (HC) (PSP target region (globus pallidus): HC vs. PSP vs. AD: 1.18 vs. 1.32 vs. 1.16; AD target region (Braak region I): HC vs. PSP vs. AD: 1.00 vs. 1.00 vs. 1.22). VT ratios and DV ratios outperformed SUV ratios and VT in detecting differences between PSP and healthy controls, whereas all quantification approaches performed similarly in comparing AD and healthy controls.

CONCLUSION

Blood-free IDIF is a promising approach for quantification of [18F]PI-2620 PET, serving as correlating surrogate for invasive continuous arterial blood sampling. Regional [18F]PI-2620 VT show large variance, in contrast to regional [18F]PI-2620 VT ratios scaled with the inferior cerebellum, which are appropriate for discriminating PSP, AD and healthy controls. DV ratios obtained by simplified reference tissue modeling are similarly suitable for this purpose.

Beyond Hypertension: Examining Variable Blood Pressure's Role in Cognition and Brain Structure

OBJECTIVES

Hypertension or high blood pressure (BP) is one of the 12 modifiable risk factors that contribute to 40% of dementia cases that could be delayed or prevented. Although hypertension is associated with cognitive decline and structural brain changes, less is known about the long-term association between variable BP and cognitive/brain changes. This study examined the relationship between variable BP and longitudinal cognitive, white matter hyperintensity (WMH), gray matter (GM), and white matter (WM) volume change over time and postmortem neuropathology.

METHODS

A total of 4,606 participants (32,776 follow-ups) from RADC Research Resource Sharing Hub (RUSH) and 2,114 participants (9,827 follow-ups) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) were included. Participants were divided into 1 of 3 groups: normal, high, or variable BP. Linear-mixed models investigated the relationship between BP and cognition, brain structure, and neuropathology.

RESULTS

Older adults with variable BP exhibited the highest rate of cognitive decline followed by high and then normal BP. Increased GM volume loss and WMH burden were also observed in variable compared to high and normal BP. In postmortem neuropathology, both variable and high BP had increased rates compared to normal BP. Results were consistent across the RUSH and ADNI participants, supporting the generalizability of the findings.

DISCUSSION

Damages potentially associated with variable BP may reduce resilience to future dementia-related pathology and increased the risk of dementia more than that caused by high BP. Improved treatment and management of variable BP may help reduce cognitive decline in the older adult population.

Quantitative Total-Body Imaging of Blood Flow with High Temporal Resolution Early Dynamic 18F-Fluorodeoxyglucose PET Kinetic Modeling

Quantitative total-body PET imaging of blood flow can be performed with freely diffusible flow radiotracers such as 15O-water and 11C-butanol, but their short half-lives necessitate close access to a cyclotron. Past efforts to measure blood flow with the widely available radiotracer 18F-fluorodeoxyglucose (FDG) were limited to tissues with high 18F-FDG extraction fraction. In this study, we developed an early-dynamic 18F-FDG PET method with high temporal resolution kinetic modeling to assess total-body blood flow based on deriving the vascular transit time of 18F-FDG and conducted a pilot comparison study against a 11C-butanol reference.

Methods

The first two minutes of dynamic PET scans were reconstructed at high temporal resolution (60×1 s, 30×2 s) to resolve the rapid passage of the radiotracer through blood vessels. In contrast to existing methods that use blood-to-tissue transport rate (K 1 ) as a surrogate of blood flow, our method directly estimates blood flow using a distributed kinetic model (adiabatic approximation to the tissue homogeneity model; AATH). To validate our 18F-FDG measurements of blood flow against a flow radiotracer, we analyzed total-body dynamic PET images of six human participants scanned with both 18F-FDG and 11C-butanol. An additional thirty-four total-body dynamic 18F-FDG PET scans of healthy participants were analyzed for comparison against literature blood flow ranges. Regional blood flow was estimated across the body and total-body parametric imaging of blood flow was conducted for visual assessment. AATH and standard compartment model fitting was compared by the Akaike Information Criterion at different temporal resolutions.

Results

18F-FDG blood flow was in quantitative agreement with flow measured from 11C-butanol across same-subject regional measurements (Pearson R=0.955, p<0.001; linear regression y=0.973x-0.012), which was visually corroborated by total-body blood flow parametric imaging. Our method resolved a wide range of blood flow values across the body in broad agreement with literature ranges (e.g., healthy cohort average: 0.51±0.12 ml/min/cm3 in the cerebral cortex and 2.03±0.64 ml/min/cm3 in the lungs, respectively). High temporal resolution (1 to 2 s) was critical to enabling AATH modeling over standard compartment modeling.

Conclusions

Total-body blood flow imaging was feasible using early-dynamic 18F-FDG PET with high-temporal resolution kinetic modeling. Combined with standard 18F-FDG PET methods, this method may enable efficient single-tracer flow-metabolism imaging, with numerous research and clinical applications in oncology, cardiovascular disease, pain medicine, and neuroscience.

Associations of Microbleeds and Their Topography With Imaging and CSF Biomarkers of Alzheimer Pathology in Individuals With Down Syndrome

BACKGROUND AND OBJECTIVES

Cerebral hemorrhages are an exclusion criterion and potential adverse effect of antiamyloid agents. It is, therefore, critical to characterize the natural history of cerebral microbleeds in populations genetically predisposed to Alzheimer disease (AD), such as Down syndrome (DS). We aimed to assess microbleed emergence in adults with DS across the AD spectrum, defining their topography and associations with clinical variables, cognitive outcomes, and fluid and neuroimaging biomarkers.

METHODS

This cross-sectional study included participants aged 18 years or older from the Down-Alzheimer Barcelona Neuroimaging Initiative and Sant Pau Initiative on Neurodegeneration with T1-weighted and susceptibility-weighted images. Participants underwent comprehensive assessments, including apolipoprotein E (APOE) genotyping; fluid and plasma determinations of beta-amyloid, tau, and neurofilament light; cognitive outcomes (Cambridge Cognitive Examination and modified Cued Recall Test); and vascular risk factors (hypertension, diabetes mellitus, and dyslipidemia). We manually segmented microbleeds and characterized their topography. Associations between microbleed severity and AD biomarkers were explored using between-group comparisons (none vs 1 vs 2+) and multivariate linear models.

RESULTS

We included 276 individuals with DS and 158 healthy euploid controls (mean age = 47.8 years, 50.92% female). Individuals with DS were more likely to have microbleeds than controls (20% vs 8.9%, p < 0.001), with more severe presentation (12% with 2+ vs 1.9%). Microbleeds increased with age (12% 20-30 years vs 60% > 60 years) and AD clinical stage (12.42% asymptomatic, 27.9% prodromal, 35.09% dementia) were more common in APOEε4 carriers (26% vs 18.3% noncarriers, p = 0.008), but not associated with vascular risk factors (p > 0.05). Microbleeds were predominantly posterior (cerebellum 33.66%; occipital 14.85%; temporal 21.29%) in participants with DS. Associations with microbleed severity were found for neuroimaging and fluid AD biomarkers, but only hippocampal volumes (standardized β = -0.18 [-0.31, -0.06], p < 0.005) and CSF p-tau-181 concentrations (β = 0.26 [0.12, 0.41], p < 0.005) survived regression controlling for age and disease stage, respectively. Microbleeds had limited effect on cognitive outcomes.

DISCUSSION

In participants with DS, microbleeds present with a posterior, lobar predominance, are associated with disease severity, but do not affect cognitive performance. These results suggest an interplay between AD pathology and vascular lesions, implicating microbleeds as a risk factor limiting the use of antiamyloid agents in this population.

Brain growth until adolescence after a neonatal focal injury: sex related differences beyond lesion effect

Introduction

Early focal brain injuries lead to long-term disabilities with frequent cognitive impairments, suggesting global dysfunction beyond the lesion. While plasticity of the immature brain promotes better learning, outcome variability across individuals is multifactorial. Males are more vulnerable to early injuries and neurodevelopmental disorders than females, but long-term sex differences in brain growth after an early focal lesion have not been described yet. With this MRI longitudinal morphometry study of brain development after a Neonatal Arterial Ischemic Stroke (NAIS), we searched for differences between males and females in the trajectories of ipsi- and contralesional gray matter growth in childhood and adolescence, while accounting for lesion characteristics.

Methods

We relied on a longitudinal cohort (AVCnn) of patients with unilateral NAIS who underwent clinical and MRI assessments at ages 7 and 16 were compared to age-matched controls. Non-lesioned volumes of gray matter (hemispheres, lobes, regions, deep structures, cerebellum) were extracted from segmented T1 MRI images at 7 (Patients: 23 M, 16 F; Controls: 17 M, 18 F) and 16 (Patients: 18 M, 11 F; Controls: 16 M, 15 F). These volumes were analyzed using a Linear Mixed Model accounting for age, sex, and lesion characteristics.

Results

Whole hemisphere volumes were reduced at both ages in patients compared to controls (gray matter volume: -16% in males, -10% in females). In ipsilesional hemisphere, cortical gray matter and thalamic volume losses (average -13%) mostly depended on lesion severity, suggesting diaschisis, with minimal effect of patient sex. In the contralesional hemisphere however, we consistently found sex differences in gray matter volumes, as only male volumes were smaller than in male controls (average -7.5%), mostly in territories mirroring the contralateral lesion. Females did not significantly deviate from the typical trajectories of female controls. Similar sex differences were found in both cerebellar hemispheres.

Discussion

These results suggest sex-dependent growth trajectories after an early brain lesion with a contralesional growth deficit in males only. The similarity of patterns at ages 7 and 16 suggests that puberty has little effect on these trajectories, and that most of the deviation in males occurs in early childhood, in line with the well-described perinatal vulnerability of the male brain, and with no compensation thereafter.

Improving Neurological Health in Aging Via Neuroplasticity-Based Computerized Exercise: Protocol for a Randomized Controlled Trial

BACKGROUND

Our current understanding of how computerized brain training drives cognitive and functional benefits remains incomplete. This paper describes the protocol for Improving Neurological Health in Aging via Neuroplasticity-based Computerized Exercise (INHANCE), a randomized controlled trial in healthy older adults designed to evaluate whether brain training improves cholinergic signaling.

OBJECTIVE

INHANCE evaluates whether 2 computerized training programs alter acetylcholine binding using the vesicular acetylcholine transporter ligand [18F] fluoroethoxybenzovesamicol ([18F] FEOBV) and positron emission tomography (PET).

METHODS

In this phase IIb, prospective, double-blind, parallel-arm, active-controlled randomized trial, a minimum of 92 community-dwelling healthy adults aged 65 years and older are randomly assigned to a brain training program designed using the principles of neuroplasticity (BrainHQ by Posit Science) or to an active control program of computer games designed for entertainment (eg, Solitaire). Both programs consist of 30-minute sessions, 7 times per week for 10 weeks (35 total hours), completed remotely at home using either loaned or personal devices. The primary outcome is the change in FEOBV binding in the anterior cingulate cortex, assessed at baseline and posttest. Exploratory cognitive and behavioral outcomes sensitive to acetylcholine are evaluated before, immediately after, and 3 months following the intervention to assess the maintenance of observed effects.

RESULTS

The trial was funded in September 2019. The study received approval from the Western Institutional Review Board in October 2020 with Research Ethics Board of McGill University Health Centre and Health Canada approvals in June 2021. The trial is currently ongoing. The first participant was enrolled in July 2021, enrollment closed when 93 participants were randomized in December 2023, and the trial will conclude in June 2024. The study team will be unblinded to conduct analyses after the final participant exits the study. We expect to publish the results in the fourth quarter of 2024.

CONCLUSIONS

There remains a critical need to identify effective and scalable nonpharmaceutical interventions to enhance cognition in older adults. This trial contributes to our understanding of brain training by providing a potential neurochemical explanation of cognitive benefit.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04149457; https://clinicaltrials.gov/ct2/show/NCT04149457.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/59705.

The relation between stress-induced dopamine release in the ventromedial prefrontal cortex, fronto-striatal functional connectivity, and negative urgency: A multimodal investigation using [18F]Fallypride PET, MRI and experience sampling

Negative urgency (NU), or the tendency to act rashly when stress of negative affect is high, could be the result of an insufficient control of the ventromedial prefrontal cortex (vmPFC) over the striatum, through an impaired dopamine (DA) transmission. Therefore, we investigated in vivo human stress-induced DA release in the vmPFC, its relation with fronto-striatal functional connectivity (FC), and NU in daily life. In total, 12 female healthy participants performed a simultaneous [18 F]fallypride PET and fMRI scan during which stress was induced. Regions displaying stress-induced DA release were identified and used to investigate stress-induced changes in fronto-striatal FC. Additionally, participants enrolled in an experience sampling study, reporting on daily life stress and rash actions over a 12-month-long period. Mixed models explored whether stress-induced DA release and FC moderated NU in daily life. Stress led to a lower FC between the vmPFC and dorsal striatum, but a higher FC between the vmPFC and contralateral ventral striatum. Participants with a higher FC between the vmPFC and dorsal striatum displayed more NU in daily life. A higher stress-induced DA release in the vmPFC was related to a higher stress-induced change in FC between the vmPFC and striatum. Participants with a higher DA release in the vmPFC displayed more NU in daily life. In conclusion, stress could differentially impact fronto-striatal FC whereby the connectivity with the dorsal striatum is especially important for NU in daily life. This could be mediated by a higher, but not a lower, stress-induced DA release in the vmPFC.

Targeting TGFβ-activated kinase-1 activation in microglia reduces CAR T immune effector cell-associated neurotoxicity syndrome

Cancer immunotherapy with chimeric antigen receptor (CAR) T cells can cause immune effector cell-associated neurotoxicity syndrome (ICANS). However, the molecular mechanisms leading to ICANS are not well understood. Here we examined the role of microglia using mouse models and cohorts of individuals with ICANS. CD19-directed CAR (CAR19) T cell transfer in B cell lymphoma-bearing mice caused microglia activation and neurocognitive deficits. The TGFβ-activated kinase-1 (TAK1)-NF-κB-p38 MAPK pathway was activated in microglia after CAR19 T cell transfer. Pharmacological TAK1 inhibition or genetic Tak1 deletion in microglia using Cx3cr1CreER:Tak1fl/fl mice resulted in reduced microglia activation and improved neurocognitive activity. TAK1 inhibition allowed for potent CAR19-induced antilymphoma effects. Individuals with ICANS exhibited microglia activation in vivo when studied by translocator protein positron emission tomography, and imaging mass cytometry revealed a shift from resting to activated microglia. In summary, we prove a role for microglia in ICANS pathophysiology, identify the TAK1-NF-κB-p38 MAPK axis as a pathogenic signaling pathway and provide a rationale to test TAK1 inhibition in a clinical trial for ICANS prevention after CAR19 T cell-based cancer immunotherapy.

Identification of group differences in predictive anticipatory biasing of pain during uncertainty: preparing for the worst but hoping for the best

ABSTRACT

Pain anticipation during conditions of uncertainty can unveil intrinsic biases, and understanding these biases can guide pain treatment interventions. This study used machine learning and functional magnetic resonance imaging to predict anticipatory responses in a pain anticipation experiment. One hundred forty-seven participants that included healthy controls (n = 57) and individuals with current and/or past mental health diagnosis (n = 90) received cues indicating upcoming pain stimuli: 2 cues predicted high and low temperatures, while a third cue introduced uncertainty. Accurate differentiation of neural patterns associated with specific anticipatory conditions was observed, involving activation in the anterior short gyrus of the insula and the nucleus accumbens. Three distinct response profiles emerged: subjects with a negative bias towards high pain anticipation, those with a positive bias towards low pain anticipation, and individuals whose predictions during uncertainty were unbiased. These profiles remained stable over one year, were consistent across diagnosed psychopathologies, and correlated with cognitive coping styles and underlying insula anatomy. The findings suggest that individualized and stable pain anticipation occurs in uncertain conditions.