(18)F-fluorodeoxyglucose and (18)F-flumazenil positron emission tomography in patients with refractory epilepsy

Hypometabolic patterns of focal cortical dysplasia in PET-MRI co-registration imaging: a retrospective evaluation in a series of 83 patients

Objective

To characterize the PET-MRI co-registration of hypometabolic patterns in focal cortical dysplasia (FCD) types I and II and provide some suggestions in presurgical evaluation of epilepsy surgery.

Methods

We retrospectively analyzed PET-MRI co-registration imaging data from a cohort of 83 epilepsy patients with histologically confirmed FCD types I and II. Hypometabolic patterns were classified into 4 types: bottom of sulcus hypometabolism (BOSH), single island of sulcus hypometabolism (SIOS), single gyrus or sulcus hypometabolism (SGOS), and multiple gyri and sulci hypometabolism (MGOS).

Results

Most of cases that were overlooked by conventional MRI and PET evaluation but positive in PET-MRI co-registration were focalized lesions in dorsolateral frontal lobe (9/15) and FCD type IIa was the most prevalent pathological type (11/15). The FCD histological types (p = 0.027) and locations (p < 0.001) were independent predictors of PET-MRI co-registration hypometabolic patterns. Focalized hypometabolic patterns (BOSH, SIOS, SGOS) were primarily observed in the frontal lobe (33/39) and FCD type II (43/62) and extensive pattern (MGOS) in temporal lobe (18/20) and FCD type I (16/21; p < 0.005).

Conclusion

PET-MRI co-registration enhanced the detection of FCD type IIa compared with conventional MRI and PET reading. The hypometabolic patterns of FCD type I and temporal lobe FCD were more extensive than those of FCD type II and frontal lobe FCD, respectively. The predilection of focalized hypometabolic patterns in frontal lobe FCD suggested that subtle lesions should be checked carefully in patients with suspected frontal lobe epilepsy.

A Molecular Toolbox of Positron Emission Tomography Tracers for General Anesthesia Mechanism Research

With appropriate radiotracers, positron emission tomography (PET) allows direct or indirect monitoring of the spatial and temporal distribution of anesthetics, neurotransmitters, and biomarkers, making it an indispensable tool for studying the general anesthesia mechanism. In this Perspective, PET tracers that have been recruited in general anesthesia research are introduced in the following order: 1) ¹¹C/¹⁸F-labeled anesthetics, i.e., PET tracers made from inhaled and intravenous anesthetics; 2) PET tracers targeting anesthesia-related receptors, e.g., neurotransmitters and voltage-gated ion channels; and 3) PET tracers for studying anesthesia-related neurophysiological effects and neurotoxicity. The radiosynthesis, pharmacodynamics, and pharmacokinetics of the above PET tracers are mainly discussed to provide a practical molecular toolbox for radiochemists, anesthesiologists, and those who are interested in general anesthesia.

Characterization of the anticonvulsant effect of dapsone on metabolic activity assessed by [18F]FDG -PET after kainic acid-induced status epilepticus in rats

BACKGROUND

Development of effective drugs for epilepsy are needed, as nearly 30 % of epileptic patients, are resistant to current treatments. This study is aimed to characterize the anticonvulsant effect of dapsone (DDS), in the kainic acid (KA)-induced Status Epilepticus (SE) by recording the brain metabolic activity with an [¹⁸F]FDG-PET analysis.

METHODS

Wistar rats received KA (10 mg/kg, i.p., single dose) to produce sustained seizures. [¹⁸F]FDG-PET and electroencephalographic (EEG) studies were then performed. DDS or vehicle were administered 30 min before KA. [¹⁸F]FDG uptake and EEG were evaluated at baseline, 2 and 25 h after KA injection. Likewise, caspase-8, 3 hippocampal activities and Fluoro-Jade B neuronal degeneration and Hematoxylin-eosin staining were measured 25 h after KA.

RESULTS

PET data evaluated at 2 h showed hyper-uptake of [¹⁸F]FDG in the control group, which was decreased by DDS. At 25 h, hypo-uptake was observed in the control group and higher values due to DDS effect. EEG spectral power was increased 2 h after KA administration in the control group during the generalized tonic-clonic seizures, which was reversed by DDS, correlated with [¹⁸F]FDG-PET uptake changes. The values of caspases-8 activity decreased 48 and 43 % vs control group in the groups treated with DDS (12.5 y 25 mg/kg respectively), likewise; caspase-3 activity diminished by 57 and 53 %. Fewer degenerated neurons were observed due to DDS treatments.

CONCLUSIONS

This study pinpoints the anticonvulsant therapeutic potential of DDS. Given its safety and effectiveness, DDS may be a viable alternative for patients with drug-resistant epilepsy.

Lack of association between cortical amyloid deposition and glucose metabolism in early stage Alzheimer´s disease patients

Background

Beta amyloid (Aβ) causes synaptic dysfunction leading to neuronal death. It is still controversial if the magnitude of Aβ deposition correlates with the degree of cognitive impairment. Diagnostic imaging may lead to a better understanding the role of Aβ in development of cognitive deficits. The aim of the present study was to investigate if Aβ deposition in the corresponding brain region of early stage Alzheimer´s disease (AD) patients, directly correlates to neuronal dysfunction and cognitive impairment indicated by reduced glucose metabolism.

Patients and methods

In 30 patients with a clinical phenotype of AD and amyloid positive brain imaging, 2-[18F] fluoro-2-deoxy-d-glucose (FDG) PET/CT was performed. We extracted the average [18F] flutemetamol (Vizamyl) uptake for each of the 16 regions of interest in both hemispheres and computed the standardized uptake value ratio (SUVR) by dividing the Vimazyl intensities by the mean signal of positive and negative control regions. Data were analysed using the R environment for statistical computing and graphics.

Results

Any negative correlation between Aβ deposition and glucose metabolism in 32 dementia related and corresponding brain regions in AD patients was not found. None of the correlation coefficient values were statistically significant different from zero based on two-sided p- value.

Conclusions

Regional Aβ deposition did not correlate negatively with local glucose metabolism in early stage AD patients. Our findings support the role of Aβ as a valid biomarker, but does not permit to conclude that Aβ is a direct cause for an aberrant brain glucose metabolism and neuronal dysfunction.

Characterization of metabolic activity induced by kainic acid in adult rat whole brain at the early stage: A 18FDG-PET study

OBJECTIVE

Brain metabolic processes are not fully characterized in the kainic acid (KA)-induced Status Epilepticus (KASE). Thus, we evaluated the usefulness of ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) as an experimental strategy to evaluate in vivo, in a non-invasive way, the glucose consumption in several brain regions, in a semi-quantitative study to compare and to correlate with data from electroencephalography and histology studies.

METHODS

Sixteen male Wistar rats underwent FDG-PET scans at basal state and after KA injection. FDG-PET images were normalized to an MRI-based atlas and segmented to locate regions. Standardized uptake values (SUV) were obtained at several time points. EEGs and cell viability by histological analysis, were also evaluated.

RESULTS

FDG-PET data showed changes in regions such as: amygdala, hippocampus, accumbens, entorhinal cortex, motor cortex and hypothalamus. Remarkably, hippocampal hypermetabolism was found (mean SUV = 2.66 ± 0.057) 2 h after KA administration, while hypometabolism at 24 h (mean SUV = 1.83 ± 0.056) vs basal values (mean SUV = 2.19 ± 0.057). EEG showed increased spectral power values 2 h post-KA administration. Hippocampal viable-cell counting 24 h after KA was decreased, while Fluoro-Jade B-positive cells were increased, as compared to control rats, coinciding with the hypometabolism detected in the same region by semi-quantitative FDG-PET at 24 h after KASE.

CONCLUSIONS

PET is suitable to measure metabolic brain changes in the rat model of status epilepticus induced by KA (KASE) at the first 24 h, compared to that of EEG; PET data may also be sensitive to cell viability.

Application value of molecular imaging technology in epilepsy

Epilepsy is a common neurological disease with various seizure types, complicated etiologies, and unclear mechanisms. Its diagnosis mainly relies on clinical history, but an electroencephalogram is also a crucial auxiliary examination. Recently, brain imaging technology has gained increasing attention in the diagnosis of epilepsy, and conventional magnetic resonance imaging can detect epileptic foci in some patients with epilepsy. However, the results of brain magnetic resonance imaging are normal in some patients. New molecular imaging has gradually developed in recent years and has been applied in the diagnosis of epilepsy, leading to enhanced lesion detection rates. However, the application of these technologies in epilepsy patients with negative brain magnetic resonance must be clarified. Thus, we reviewed the relevant literature and summarized the information to improve the understanding of the molecular imaging application value of epilepsy.

Brain concentrations of glutamate and GABA in human epilepsy: A review

An imbalance between excitation and inhibition has been a longstanding proposed mechanism regarding ictogenesis and epileptogenesis. This imbalance is related to increased extracellular glutamate in the brain and/or reduction in GABA concentrations, leading to excitotoxicity, seizures, and cell death. This review aims to summarize the microdialysis and magnetic resonance spectroscopy (MRS) literature investigating glutamate and GABA concentrations in epilepsy patients, present limitations, and suggest future directions to help direct the search for novel epilepsy treatments. The majority of microdialysis studies demonstrated increased glutamate in epileptic regions either compared to control regions or to baseline levels; however, sample sizes were small, with some statistical comparisons missing. For the MRS research, two of six studies reported significant changes in glutamate levels compared to controls, though the results were mixed, with one reporting increased and the other reporting decreased glutamate levels. Eleven of 20 studies reported significant changes in Glx (glutamate + glutamine) or Glx ratios, with most reporting increased levels, except for a few epilepsy syndromes where reduced levels were reported. Few studies investigated GABA concentrations, with one microdialysis and four spectroscopy studies reporting increased GABA levels, and one study reporting decreased GABA in a different brain region. Based on this review, future research should account for medication use; include measurements of GABA, glutamate, and glutamine; use high-tesla strength MRI; and further evaluate the timing of microdialysis. Understanding the importance of brain glutamate and GABA levels in epilepsy may provide direction for future therapies and treatments.

Performance of PET imaging for the localization of epileptogenic zone in patients with epilepsy: a meta-analysis

OBJECTIVES

The aim of this meta-analysis was to estimate the clinical use value of ¹¹C-FMZ and ¹⁸F-FDG in PET for the localization of epileptogenic zone and to provide evidence for practitioners' clinical decision-making.

METHODS

We searched PubMed and Embase in a time frame from inception to May 31, 2020. Studies utilizing FMZ or FDG-PET or FDG-PET/MRI used in patients with epilepsy, with EEG or surgical outcomes as the gold standard and corresponding outcomes such as concordance rates of PET or PET/MRI scan compared with reference standard, absolute numbers of participants with true-positive (TP), false-positive (FP), true-negative (TN), and false-negative (FN) results in FDG or FMZ PET. Pooled concordance rates, overall sensitivity, and specificity of ¹¹C-FMZ-PET and ¹⁸F-FDG-PET were calculated.

RESULTS

In total, 44 studies met the inclusion criteria. The pooled concordance rates of FDG-PET, FMZ-PET, and FDG-PET/MRI coregistration compared with reference standard were 0.67 (95% CI: 0.60-0.73), 0.75 (95% CI: 0.57-0.93), and 0.93 (95% CI: 0.89-0.97), respectively. The concordance rate of ¹⁸F-FDG-PET in patients with temporal lobe epilepsy (TLE) was 0.79 (0.63; 0.92). The overall sensitivity and specificity of ¹⁸F-FDG-PET were 0.66 (95% CI: 0.58-0.73) and 0.71 (95% CI: 0.63-0.78), respectively. ¹¹C-FMZ-PET displayed an overall sensitivity of 0.62 (95% CI: 0.49-0.73) and specificity of 0.73 (95% CI: 0.59-0.84).

CONCLUSIONS

Both ¹¹C-FMZ PET and ¹⁸F-FDG PET are the choice of modalities for the localization of epileptogenic zone, especially when coregistered with MRI.

KEY POINTS

• ¹¹C-FMZ-PET may be more helpful than ¹⁸F-FDG-PET in the localization of epilepsy foci. • Coregistration of FDG-PET and MRI is recommended in the localization of epileptogenic zone.

Molecular Imaging of Brain Tumor-Associated Epilepsy

Epilepsy is a common clinical manifestation and a source of significant morbidity in patients with brain tumors. Neuroimaging has a pivotal role in neuro-oncology practice, including tumor detection, differentiation, grading, treatment guidance, and posttreatment monitoring. In this review, we highlight studies demonstrating that imaging can also provide information about brain tumor-associated epileptogenicity and assist delineation of the peritumoral epileptic cortex to optimize postsurgical seizure outcome. Most studies focused on gliomas and glioneuronal tumors where positron emission tomography (PET) and advanced magnetic resonance imaging (MRI) techniques can detect metabolic and biochemical changes associated with altered amino acid transport and metabolism, neuroinflammation, and neurotransmitter abnormalities in and around epileptogenic tumors. PET imaging of amino acid uptake and metabolism as well as activated microglia can detect interictal or peri-ictal cortical increased uptake (as compared to non-epileptic cortex) associated with tumor-associated epilepsy. Metabolic tumor volumes may predict seizure outcome based on objective treatment response during glioma chemotherapy. Advanced MRI, especially glutamate imaging, can detect neurotransmitter changes around epileptogenic brain tumors. Recently, developed PET radiotracers targeting specific glutamate receptor types may also identify therapeutic targets for pharmacologic seizure control. Further studies with advanced multimodal imaging approaches may facilitate development of precision treatment strategies to control brain tumor-associated epilepsy.

Innovative Molecular Imaging for Clinical Research, Therapeutic Stratification, and Nosography in Neuroscience

Over the past few decades, several radiotracers have been developed for neuroimaging applications, especially in PET. Because of their low steric hindrance, PET radionuclides can be used to label molecules that are small enough to cross the blood brain barrier, without modifying their biological properties. As the use of 11C is limited by its short physical half-life (20 min), there has been an increasing focus on developing tracers labeled with 18F for clinical use. The first such tracers allowed cerebral blood flow and glucose metabolism to be measured, and the development of molecular imaging has since enabled to focus more closely on specific targets such as receptors, neurotransmitter transporters, and other proteins. Hence, PET and SPECT biomarkers have become indispensable for innovative clinical research. Currently, the treatment options for a number of pathologies, notably neurodegenerative diseases, remain only supportive and symptomatic. Treatments that slow down or reverse disease progression are therefore the subject of numerous studies, in which molecular imaging is proving to be a powerful tool. PET and SPECT biomarkers already make it possible to diagnose several neurological diseases in vivo and at preclinical stages, yielding topographic, and quantitative data about the target. As a result, they can be used for assessing patients' eligibility for new treatments, or for treatment follow-up. The aim of the present review was to map major innovative radiotracers used in neuroscience, and explain their contribution to clinical research. We categorized them according to their target: dopaminergic, cholinergic or serotoninergic systems, β-amyloid plaques, tau protein, neuroinflammation, glutamate or GABA receptors, or α-synuclein. Most neurological disorders, and indeed mental disorders, involve the dysfunction of one or more of these targets. Combinations of molecular imaging biomarkers can afford us a better understanding of the mechanisms underlying disease development over time, and contribute to early detection/screening, diagnosis, therapy delivery/monitoring, and treatment follow-up in both research and clinical settings.

Quantitative Analysis of [18F]FFMZ and [18F]FDG PET Studies in the Localization of Seizure Onset Zone in Drug-Resistant Temporal Lobe Epilepsy

BACKGROUND

Positron emission tomography (PET) imaging in epilepsy is an in vivo technique that allows the localization of a possible seizure onset zone (SOZ) during the interictal period. Stereo-electro-encephalography (SEEG) is the gold standard to define the SOZ. The objective of this research was to evaluate the accuracy of PET imaging in localizing the site of SOZ compared with SEEG.

METHODS

Seven patients with refractory temporal lobe epilepsy (Ep) and 2 healthy controls (HC) underwent 2 PET scans, one with 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) and another with 2'-[18F]fluoroflumazenil (FFMZ), acquired 1 day apart. FDG was acquired for 10 min (static scan) 1 h after administration. An FFMZ scan was acquired for 60 min from radiopharmaceutical administration in a dynamic mode. Each brain PET image was segmented using a standard template implemented in PMOD 3.8. The pons was used as the reference region for modeling of the nondisplaceable binding potential (BPND)for FFMZ, and to obtain uptake ratios for FDG. SEEG studies of patients were performed as a part of their surgical evaluation to define the SOZ.

RESULTS

Well-defined differences between HC and Ep were found with both radiopharmaceuticals, showing the utility to identify abnormal brain regions using quantitative PET imaging. Lateralization of the SOZ findings by PET (lower uptake/binding in a specific brain hemisphere) matched in 86% for FFMZ and 71% for FDG with SEEG data.

CONCLUSION

Quantitative PET imaging is an excellent complementary tool that matches reasonably well with SEEG to define SOZ in presurgical evaluation.

Utility of MRI, PET, and ictal SPECT in presurgical evaluation of non-lesional pediatric epilepsy

Children with epilepsy and normal structural MRI pose a particular challenge in localization of epileptic foci for surgical resection. Many of these patients have subtle structural lesions such as mild cortical dysplasia that can be missed by conventional MRI but may become detectable by optimized and advanced MRI acquisitions and post-processing. Specificity of objective analytic techniques such as voxel-based morphometry remains an issue. Combination of MRI with functional imaging approaches can improve the accuracy of detecting epileptogenic brain regions. Analysis of glucose positron emission tomography (PET) combined with high-resolution MRI can optimize detection of hypometabolic cortex associated with subtle cortical malformations and can also enhance presurgical evaluation in children with epileptic spasms. Additional PET tracers may detect subtle epileptogenic lesions and cortex with enhanced specificity in carefully selected subgroups with various etiologies; e.g., increased tryptophan uptake can identify epileptogenic cortical dysplasia in the interictal state. Subtraction ictal SPECT can be also useful to delineate ictal foci in those with non-localizing PET or after failed surgical resection. Presurgical delineation of language and motor cortex and the corresponding white matter tracts is increasingly reliable by functional MRI and DTI techniques; with careful preparation, these can be useful even in young and sedated children. While evidence-based pediatric guidelines are still lacking, the data accumulated in the last decade strongly indicate that multimodal imaging with combined analysis of MRI, PET, and/or ictal SPECT data can optimize the detection of subtle epileptogenic lesions and facilitate seizure-free outcome while minimizing the postsurgical functional deficit in children with normal conventional MRI.

Construction of a novel Chinese normal brain database using 18F-FDG PET images and MIMneuro software, the initial application in epilepsy

PURPOSE

To create a standard Western Chinese normal functional brain database for quantitative analysis using 2-deoxy-2-[18F] fluoro-d-glucose (¹⁸F-FDG) positron emission tomography (PET) images and MIMneuro software.

METHODS

78 healthy right-handed Chinese volunteers from Tangdu Hospital were scanned using ¹⁸F-FDG PET to evaluate brain metabolism between March and October 2016. All PET images were processed using MIMneuro software to create a normal database platform. The platform included anatomical optimization to facilitate spatial localization of abnormalities and a statistical comparison with normal cases utilizing the Z-scores, which represent the number of standard deviations from the mean of the normal controls in the database.

RESULTS

The novel Chinese brain metabolism database platform including 78 healthy volunteers (male: female 40:38; age 3-78 years, mean age, 45 years) was constructed based on the MIMneuro software, which increased the diagnostic confidence in the test patient by quantifying and emphasizing the abnormality. The BrainAlign^TM deformation algorithm of MIMneuro matched the size, shape, and orientation of the patient's brain scan to a template brain for comparison against a database of normal controls. The quantitative analysis performed on a voxel and regional level was useful in assessing the areas of abnormalities.

CONCLUSIONS

A novel Chinese ¹⁸F-FDG PET-based normal brain function database was created to highlight the local regions of abnormal metabolic activity through quantitative comparisons against the normal database. The Z-scores obtained by MIMneuro potentially aid in visualizing and quantifying the subtle lesions on ¹⁸FDG-PET scan images as observed in a patient diagnosed with epilepsy.

Added Value of NeuroGam Software Analysis in Single Photon Emission Computed Tomography Localization Diagnosis of Epilepsy in Interictal Stage

Background

This study aimed to investigate the added value of NeuroGam software analysis in the localization diagnosis of epileptogenic zone during interictal phase of seizures.

Material/Methods

The clinical data of 67 patients, clinically diagnosed as epilepsy, were analyzed retrospectively. Visual analysis and NeuroGam software analysis were used for independent analysis. The 2 methods were used to compare the efficacy indicator of the diagnosis of epileptogenic zone, and the receiver operating characteristic (ROC) curve evaluated the diagnostic efficacy.

Results

Through the final clinical diagnostic comprehensive localization, among 67 epilepsy patients, the epileptogenic zone in 51 cases could be located distinctly, and those in 16 cases could not be located. Compared to the visual analysis, the NeuroGam software analysis was more sensitive in the location of epileptogenic zone (χ²=4.876, P=0.027). The area under the ROC curve (AUC) and 95% confidence interval (CI) of the NeuroGam software and visual analyses was 0.760 and 0.689, (0.613, 0.908) and (0.547, 0.832), respectively. However, the consistency of the 2 methods was poor (Kappa=0.367, P=0.001). Compared to visual analysis, the NeuroGam software analysis exerted more advantages in the localization diagnosis of the epileptogenic zone (P<0.001).

Conclusions

In the location diagnosis of brain perfusion, single photon emission computed tomography (SPECT) epileptogenic zone was used in interictal phase of seizures, and NeuroGam software analysis exerted a distinct added value for visual analysis.

Whole brain neuronal abnormalities in focal epilepsy quantified with proton MR spectroscopy

OBJECTIVE

To test the hypothesis that localization-related epilepsy is associated with widespread neuronal dysfunction beyond the ictal focus, reflected by a decrease in patients' global concentration of their proton MR spectroscopy (1H-MRS) observed marker, N-acetyl-aspartate (NAA).

METHODS

Thirteen patients with localization-related epilepsy (7 men, 6 women) 40±13 (mean±standard-deviation)years old, 8.3±13.4years of disease duration; and 14 matched controls, were scanned at 3 T with MRI and whole-brain (WB) 1H MRS. Intracranial fractions of brain volume, gray and white matter (fBV, fGM, fWM) were segmented from the MRI, and global absolute NAA creatine (Cr) and choline (Cho) concentrations were estimated from their WB 1H MRS. These metrics were compared between patients and controls using an unequal variance t test.

RESULTS

Patients' fBV, fGM and fWM: 0.81±0.07, 0.47±0.04, 0.31±0.04 were not different from controls' 0.79±0.05, 0.48±0.04, 0.32±0.02; nor were their Cr and Cho concentrations: 7.1±1.1 and 1.3±0.2 millimolar (mM) versus 7.7±0.7 and 1.4±0.1mM (p>0.05 all). Patients' global NAA concentration: 11.5±1.5 mM, however, was 12% lower than controls' 13.0±0.8mM (p=0.004).

CONCLUSIONS

These findings indicate that neuronal dysfunction in localization-related epilepsy extends globally, beyond the ictal zone, but without atrophy or spectroscopic evidence of other pathology. This suggests a diffuse decline in the neurons' health, rather than their number, early in the disease course. WB 1H-MRS assessment, therefore, may be a useful tool for quantification of global neuronal dysfunction load in epilepsy.