MRI index of glymphatic system mediates the influence of locus coeruleus on cognition in Parkinson's disease

INTRODUCTION

Although locus coeruleus (LC) has been demonstrated to play a critical role in the cognitive function of Parkinson's disease (PD), the underlying mechanism has not been elucidated. The objective was to investigate the relationship among LC degeneration, cognitive performance, and the glymphatic function in PD.

METHODS

In this retrospective study, 71 PD subjects (21 with normal cognition; 29 with cognitive impairment (PD-MCI); 21 with dementia (PDD)) and 26 healthy controls were included. All participants underwent neuromelanin-sensitive magnetic resonance imaging (NM-MRI) and diffusion tensor image scanning on a 3.0 T scanner. The brain glymphatic function was measured using diffusion along the perivascular space (ALPS) index, while LC degeneration was estimated using the NM contrast-to-noise ratio of LC (CNRLC).

RESULTS

The ALPS index was significantly lower in both the whole PD group (P = 0.04) and the PDD subgroup (P = 0.02) when compared to the controls. Similarly, the CNRLC was lower in the whole PD group (P < 0.001) compared to the controls. In the PD group, a positive correlation was found between the ALPS index and both the Montreal Cognitive Assessment (MoCA) score (r = 0.36; P = 0.002) and CNRLC (r = 0.26; P = 0.03). Mediation analysis demonstrated that the ALPS index acted as a significant mediator between CNRLC and the MoCA score in PD subjects.

CONCLUSION

The ALPS index, a neuroimaging marker of glymphatic function, serves as a mediator between LC degeneration and cognitive function in PD.

Deep gray matters iron deposition is positively associated with white matter hyperintensity in hypertension

The association and underlying mechanisms between iron deposition and white matter hyperintensity (WMH) remain unclear. In this study, quantitative susceptibility mapping (QSM) was used to quantify deep gray matters iron deposition and to explore the association from both global and regional perspectives. A total of 84 patients with hypertension and 26 healthy controls underwent a strategically acquired gradient echo (STAGE) protocol, and the multi-echo data were used to reconstruct QSM images. The susceptibilities were used to describe iron content. Global region (RI) susceptibilities were measured in regions of interest, and age-related thresholds were used to determine high-iron content region (RII) susceptibilities. Compared with healthy controls, hypertension had higher total WMH scores and regional scores (all p = .001) and higher susceptibilities using the RI or RII analysis (all p < .05). In healthy controls, there was no significant association between susceptibilities and WMH scores. In hypertension, the susceptibilities of deep gray matters were positively correlated with WMH scores (RI analysis: right putamen; RII analysis: bilateral caudate nucleus head, putamen, red nucleus, substantia nigra, and dentate nucleus; age and education corrected p < .05). These findings suggest that iron deposition in deep gray matters was positively associated with WMH in hypertension, especially using the RII analysis.

An automatic interpretable deep learning pipeline for accurate Parkinson's disease diagnosis using quantitative susceptibility mapping and T1-weighted images

Parkinson's disease (PD) diagnosis based on magnetic resonance imaging (MRI) is still challenging clinically. Quantitative susceptibility maps (QSM) can potentially provide underlying pathophysiological information by detecting the iron distribution in deep gray matter (DGM) nuclei. We hypothesized that deep learning (DL) could be used to automatically segment all DGM nuclei and use relevant features for a better differentiation between PD and healthy controls (HC). In this study, we proposed a DL-based pipeline for automatic PD diagnosis based on QSM and T1-weighted (T1W) images. This consists of (1) a convolutional neural network model integrated with multiple attention mechanisms which simultaneously segments caudate nucleus, globus pallidus, putamen, red nucleus, and substantia nigra from QSM and T1W images, and (2) an SE-ResNeXt50 model with an anatomical attention mechanism, which uses QSM data and the segmented nuclei to distinguish PD from HC. The mean dice values for segmentation of the five DGM nuclei are all >0.83 in the internal testing cohort, suggesting that the model could segment brain nuclei accurately. The proposed PD diagnosis model achieved area under the the receiver operating characteristic curve (AUCs) of 0.901 and 0.845 on independent internal and external testing cohorts, respectively. Gradient-weighted class activation mapping (Grad-CAM) heatmaps were used to identify contributing nuclei for PD diagnosis on patient level. In conclusion, the proposed approach can potentially be used as an automatic, explainable pipeline for PD diagnosis in a clinical setting.

Locus coeruleus and substantia nigra neuromelanin magnetic resonance imaging differentiates Parkinson's disease and essential tremor

BACKGROUND

Differential diagnosis of essential tremor (ET) and Parkinson's disease (PD) can still be a challenge in clinical practice. These two tremor disorders may have different pathogenesis related to the substantia nigra (SN) and locus coeruleus (LC). Characterizing neuromelanin (NM) in these structures may help improve the differential diagnosis.

METHODS

Forty-three subjects with tremor-dominant PD (PDTD), 31 subjects with ET, and 30 age- and sex-matched healthy controls were included. All subjects were scanned with NM magnetic resonance imaging (NM-MRI). NM volume and contrast measures for the SN and contrast for the LC were evaluated. Logistic regression was used to calculate predicted probabilities by using the combination of SN and LC NM measures. The discriminative power of the NM measures in detecting subjects with PDTD from ET was assessed with a receiver operative characteristic curve, and the area under the curve (AUC) was calculated.

RESULTS

The NM contrast-to-noise ratio (CNR) of the LC, the NM volume, and CNR of the SN on the right and left sides were significantly lower in PDTD subjects than in ET subjects or healthy controls (all P < 0.05). Furthermore, when combining the best model constructed from the NM measures, the AUC reached 0.92 in differentiating PDTD from ET.

CONCLUSION

The NM volume and contrast measures of the SN and contrast for the LC provided a new perspective on the differential diagnosis of PDTD and ET, and the investigation of the underlying pathophysiology.

Does Vitamin D Provide Added Benefit to Antihypertensive Therapy in Reducing Left Ventricular Hypertrophy Determined by Cardiac Magnetic Resonance?

BACKGROUND

Left ventricular hypertrophy (LVH) and vitamin D deficiency have been linked to hypertension (HTN) and cardiovascular disease, particularly in African Americans (AAs). Our objective was to determine if the addition of vitamin D to antihypertensive therapy would lead to greater regression of LV mass index (LVMI) as determined by cardiac magnetic resonance (CMR) after 1 year in vitamin D deficient AA patients with uncontrolled HTN and LVH.

METHODS

This study was a randomized, double-blind, placebo-controlled, single-center study. AA patients with HTN (systolic blood pressure [BP] >160 mm Hg), increased LVMI, and vitamin D deficiency (<20 ng/ml) were randomized. All patients received antihypertensive therapy combined with biweekly 50,000 IU vitamin D3 (vitamin D group, n = 55) or placebo (placebo group, n = 58).

RESULTS

At 1 year, there were no statistical differences between the vitamin D and placebo groups in LVMI (-14.1 ± 14.6 vs. -16.9 ± 13.1 g/m2; P = 0.34) or systolic BP (-25.6 ± 32.1 vs. -25.7 ± 25.6 mm Hg; P = 0.99) reduction, respectively. Serum vitamin D levels increased significantly in the vitamin D group compared with placebo (12.7 ± 2.0 vs. 1.8 ± 8.2 ng/ml; P < 0.001).

CONCLUSIONS

In this high-risk cohort of AAs we did not find an association between vitamin D supplementation and differential regression of LVMI or reduction in systolic BP. However, our study suffered from a small sample size with low statistical power precluding a definitive conclusion on the therapeutic benefit of vitamin D in such patients.

CLINICAL TRIALS REGISTRATION

Trial Number NCT01360476. Full trial protocol is available from corresponding author.

Neuroimaging Markers for Determining Former American Football Players at Risk for Alzheimer's Disease

NFL players, by virtue of their exposure to traumatic brain injury (TBI), are at higher risk of developing dementia and Alzheimer's disease (AD) than the general population. Early recognition and intervention before the onset of clinical symptoms could potentially avert/delay the long-term consequences of these diseases. Given that AD is thought to have a long pre-clinical incubation period, the aim of the current research was to determine whether former NFL players show evidence of incipient dementia in their structural imaging before diagnosis of AD. To identify neuroimaging markers of AD, against which former NFL players would be compared, we conducted a whole-brain volumetric analysis using a cohort of AD patients (ADNI clinical database) to produce a set of brain regions demonstrating sensitivity to early AD pathology (i.e., the “AD fingerprint”). A group of 46 former NFL players' brain magnetic resonance images were then interrogated using the AD fingerprint, that is, the former NFL subjects were compared volumetrically to AD patients using a T1-weighted magnetization-prepared rapid gradient echo sequence. The FreeSurfer image analysis suite (version 6.0) was used to obtain volumetric and cortical thickness data. The Automated Neuropsychological Assessment Metric-Version 4 was used to assess current cognitive functioning. A total of 55 brain regions demonstrated significant atrophy or ex vacuo dilatation bilaterally in AD patients versus controls. Of the 46 former NFL players, 41% demonstrated a greater than expected number of atrophied/dilated AD regions compared with age-matched controls, presumably reflecting AD pathology.

Quantifying Brain Iron in Hereditary Hemochromatosis Using R2* and Susceptibility Mapping

BACKGROUND AND PURPOSE

Brain iron dyshomeostasis is increasingly recognized as an important contributor to neurodegeneration. Hereditary hemochromatosis is the most commonly inherited disorder of systemic iron overload. Although there is an increasing interest in excessive brain iron deposition, there is a paucity of evidence showing changes in brain iron exceeding that in healthy controls. Quantitative susceptibility mapping and R2* mapping are established MR imaging techniques that we used to noninvasively quantify brain iron in subjects with hereditary hemochromatosis.

MATERIALS AND METHODS

Fifty-two patients with hereditary hemochromatosis and 47 age- and sex-matched healthy controls were imaged using a multiecho gradient-echo sequence at 3T. Quantitative susceptibility mapping and R2* data were generated, and regions within the deep gray matter were manually segmented. Mean susceptibility and R2* relaxation rates were calculated for each region, and iron content was compared between the groups.

RESULTS

We noted elevated iron levels in patients with hereditary hemochromatosis compared with healthy controls using both R2* and QSM methods in the caudate nucleus, putamen, pulvinar thalamus, red nucleus, and dentate nucleus. Additionally, the substantia nigra showed increased susceptibility while the thalamus showed an increased R2* relaxation rate compared with healthy controls, respectively.

CONCLUSIONS

Both quantitative susceptibility mapping and R2* showed abnormal levels of brain iron in subjects with hereditary hemochromatosis compared with controls. Quantitative susceptibility mapping and R2* can be acquired in a single MR imaging sequence and are complementary in quantifying deep gray matter iron.

Automatic detection of neuromelanin and iron in the midbrain nuclei using a magnetic resonance imaging ‐based brain template

Parkinson disease (PD) is a chronic progressive neurodegenerative disorder characterized pathologically by early loss of neuromelanin (NM) in the substantia nigra pars compacta (SNpc) and increased iron deposition in the substantia nigra (SN). Degeneration of the SN presents as a 50 to 70% loss of pigmented neurons in the ventral lateral tier of the SNpc at the onset of symptoms. Also, using magnetic resonance imaging (MRI), iron deposition and volume changes of the red nucleus (RN), and subthalamic nucleus (STN) have been reported to be associated with disease status and rate of progression. Further, the STN serves as an important target for deep brain stimulation treatment in advanced PD patients. Therefore, an accurate in‐vivo delineation of the SN, its subregions and other midbrain structures such as the RN and STN could be useful to better study iron and NM changes in PD. Our goal was to use an MRI template to create an automatic midbrain deep gray matter nuclei segmentation approach based on iron and NM contrast derived from a single, multiecho magnetization transfer contrast gradient echo (MTC‐GRE) imaging sequence. The short echo TE = 7.5 ms data from a 3D MTC‐GRE sequence was used to find the NM‐rich region, while the second echo TE = 15 ms was used to calculate the quantitative susceptibility map for 87 healthy subjects (mean age ± SD: 63.4 ± 6.2 years old, range: 45–81 years). From these data, we created both NM and iron templates and calculated the boundaries of each midbrain nucleus in template space, mapped these boundaries back to the original space and then fine‐tuned the boundaries in the original space using a dynamic programming algorithm to match the details of each individual's NM and iron features. A dual mapping approach was used to improve the performance of the morphological mapping of the midbrain of any given individual to the template space. A threshold approach was used in the NM‐rich region and susceptibility maps to optimize the DICE similarity coefficients and the volume ratios. The results for the NM of the SN as well as the iron containing SN, STN, and RN all indicate a strong agreement with manually drawn structures. The DICE similarity coefficients and volume ratios for these structures were 0.85, 0.87, 0.75, and 0.92 and 0.93, 0.95, 0.89, 1.05, respectively, before applying any threshold on the data. Using this fully automatic template‐based deep gray matter mapping approach, it is possible to accurately measure the tissue properties such as volumes, iron content, and NM content of the midbrain nuclei.

A Comparison of Magnetic Resonance Imaging Methods to Assess Multiple Sclerosis Lesions: Implications for Patient Characterization and Clinical Trial Design

Magnetic resonance imaging (MRI) is a sensitive imaging modality for identifying inflammatory and/or demyelinating lesions, which is critical for a clinical diagnosis of MS and evaluating drug responses. There are many unique means of probing brain tissue status, including conventional T1 and T2 weighted imaging (T1WI, T2WI), T2 fluid attenuated inversion recovery (FLAIR), magnetization transfer, myelin water fraction, diffusion tensor imaging (DTI), phase-sensitive inversion recovery and susceptibility weighted imaging (SWI), but no study has combined all of these modalities into a single well-controlled investigation. The goals of this study were to: compare different MRI measures for lesion visualization and quantification; evaluate the repeatability of various imaging methods in healthy controls; compare quantitative susceptibility mapping (QSM) with myelin water fraction; measure short-term longitudinal changes in the white matter of MS patients and map out the tissue properties of the white matter hyperintensities using STAGE (strategically acquired gradient echo imaging). Additionally, the outcomes of this study were anticipated to aid in the choice of an efficient imaging protocol reducing redundancy of information and alleviating patient burden. Of all the sequences used, T2 FLAIR and T2WI showed the most lesions. To differentiate the putative demyelinating lesions from inflammatory lesions, the fusion of SWI and T2 FLAIR was used. Our study suggests that a practical and efficient imaging protocol combining T2 FLAIR, T1WI and STAGE (with SWI and QSM) can be used to rapidly image MS patients to both find lesions and study the demyelinating and inflammatory characteristics of the lesions.

Stability of AI-Enabled Diagnosis of Parkinson's Disease: A Study Targeting Substantia Nigra in Quantitative Susceptibility Mapping Imaging

Purpose: Parkinson's disease (PD) diagnosis algorithms based on quantitative susceptibility mapping (QSM) and image algorithms rely on substantia nigra (SN) labeling. However, the difference between SN labels from different experts (or segmentation algorithms) will have a negative impact on downstream diagnostic tasks, such as the decrease of the accuracy of the algorithm or different diagnostic results for the same sample. In this article, we quantify the accuracy of the algorithm on different label sets and then improve the convolutional neural network (CNN) model to obtain a high-precision and highly robust diagnosis algorithm. Methods: The logistic regression model and CNN model were first compared for classification between PD patients and healthy controls (HC), given different sets of SN labeling. Then, based on the CNN model with better performance, we further proposed a novel "gated pooling" operation and integrated it with deep learning to attain a joint framework for image segmentation and classification. Results: The experimental results show that, with different sets of SN labeling that mimic different experts, the CNN model can maintain a stable classification accuracy at around 86.4%, while the conventional logistic regression model yields a large fluctuation ranging from 78.9 to 67.9%. Furthermore, the "gated pooling" operation, after being integrated for joint image segmentation and classification, can improve the diagnosis accuracy to 86.9% consistently, which is statistically better than the baseline. Conclusion: The CNN model, compared with the conventional logistic regression model using radiomics features, has better stability in PD diagnosis. Furthermore, the joint end-to-end CNN model is shown to be suitable for PD diagnosis from the perspectives of accuracy, stability, and convenience in actual use.

Predicting Motor Outcome of Subthalamic Nucleus Deep Brain Stimulation for Parkinson's Disease Using Quantitative Susceptibility Mapping and Radiomics: A Pilot Study

Background

Emerging evidence indicates that iron distribution is heterogeneous within the substantia nigra (SN) and it may reflect patient-specific trait of Parkinson’s Disease (PD). We assume it could account for variability in motor outcome of subthalamic nucleus deep brain stimulation (STN-DBS) in PD.

Objective

To investigate whether SN susceptibility features derived from radiomics with machine learning (RA-ML) can predict motor outcome of STN-DBS in PD.

Methods

Thirty-three PD patients underwent bilateral STN-DBS were recruited. The bilateral SN were segmented based on preoperative quantitative susceptibility mapping to extract susceptibility features using RA-ML. MDS-UPDRS III scores were recorded 1–3 days before and 6 months after STN-DBS surgery. Finally, we constructed three predictive models using logistic regression analyses: (1) the RA-ML model based on radiomics features, (2) the RA-ML+LCT (levodopa challenge test) response model which combined radiomics features with preoperative LCT response, (3) the LCT response model alone.

Results

For the predictive performances of global motor outcome, the RA-ML model had 82% accuracy (AUC = 0.85), while the RA-ML+LCT response model had 74% accuracy (AUC = 0.83), and the LCT response model alone had 58% accuracy (AUC = 0.55). For the predictive performance of rigidity outcome, the accuracy of the RA-ML model was 80% (AUC = 0.85), superior to those of the RA-ML+LCT response model (76% accuracy, AUC = 0.82), and the LCT response model alone (58% accuracy, AUC = 0.42).

Conclusion

Our findings demonstrated that SN susceptibility features from radiomics could predict global motor and rigidity outcomes of STN-DBS in PD. This RA-ML predictive model might provide a novel approach to counsel candidates for STN-DBS.

VC-Net: Deep Volume-Composition Networks for Segmentation and Visualization of Highly Sparse and Noisy Image Data

The fundamental motivation of the proposed work is to present a new visualization-guided computing paradigm to combine direct 3D volume processing and volume rendered clues for effective 3D exploration. For example, extracting and visualizing microstructures in-vivo have been a long-standing challenging problem. However, due to the high sparseness and noisiness in cerebrovasculature data as well as highly complex geometry and topology variations of micro vessels, it is still extremely challenging to extract the complete 3D vessel structure and visualize it in 3D with high fidelity. In this paper, we present an end-to-end deep learning method, VC-Net, for robust extraction of 3D microvascular structure through embedding the image composition, generated by maximum intensity projection (MIP), into the 3D volumetric image learning process to enhance the overall performance. The core novelty is to automatically leverage the volume visualization technique (e.g., MIP - a volume rendering scheme for 3D volume images) to enhance the 3D data exploration at the deep learning level. The MIP embedding features can enhance the local vessel signal (through canceling out the noise) and adapt to the geometric variability and scalability of vessels, which is of great importance in microvascular tracking. A multi-stream convolutional neural network (CNN) framework is proposed to effectively learn the 3D volume and 2D MIP feature vectors, respectively, and then explore their inter-dependencies in a joint volume-composition embedding space by unprojecting the 2D feature vectors into the 3D volume embedding space. It is noted that the proposed framework can better capture the small/micro vessels and improve the vessel connectivity. To our knowledge, this is the first time that a deep learning framework is proposed to construct a joint convolutional embedding space, where the computed vessel probabilities from volume rendering based 2D projection and 3D volume can be explored and integrated synergistically. Experimental results are evaluated and compared with the traditional 3D vessel segmentation methods and the state-of-the-art in deep learning, by using extensive public and real patient (micro- )cerebrovascular image datasets. The application of this accurate segmentation and visualization of sparse and complicated 3D microvascular structure facilitated by our method demonstrates the potential in a powerful MR arteriogram and venogram diagnosis of vascular disease.

Iron Content in Deep Gray Matter as a Function of Age Using Quantitative Susceptibility Mapping: A Multicenter Study

PURPOSE

To evaluate the effect of resolution on iron content using quantitative susceptibility mapping (QSM); to verify the consistency of QSM across field strengths and manufacturers in evaluating the iron content of deep gray matter (DGM) of the human brain using subjects from multiple sites; and to establish a susceptibility baseline as a function of age for each DGM structure using both a global and regional iron analysis.

METHODS

Data from 623 healthy adults, ranging from 20 to 90 years old, were collected across 3 sites using gradient echo imaging on one 1.5 Tesla and two 3.0 Tesla MR scanners. Eight subcortical gray matter nuclei were semi-automatically segmented using a full-width half maximum threshold-based analysis of the QSM data. Mean susceptibility, volume and total iron content with age correlations were evaluated for each measured structure for both the whole-region and RII (high iron content regions) analysis. For the purpose of studying the effect of resolution on QSM, a digitized model of the brain was applied.

RESULTS

The mean susceptibilities of the caudate nucleus (CN), globus pallidus (GP) and putamen (PUT) were not significantly affected by changing the slice thickness from 0.5 to 3 mm. But for small structures, the susceptibility was reduced by 10% for 2 mm thick slices. For global analysis, the mean susceptibility correlated positively with age for the CN, PUT, red nucleus (RN), substantia nigra (SN), and dentate nucleus (DN). There was a negative correlation with age in the thalamus (THA). The volumes of most nuclei were negatively correlated with age. Apart from the GP, THA, and pulvinar thalamus (PT), all the other structures showed an increasing total iron content despite the reductions in volume with age. For the RII regional high iron content analysis, mean susceptibility in most of the structures was moderately to strongly correlated with age. Similar to the global analysis, apart from the GP, THA, and PT, all structures showed an increasing total iron content.

CONCLUSION

A reasonable estimate for age-related iron behavior can be obtained from a large cross site, cross manufacturer set of data when high enough resolutions are used. These estimates can be used for correcting for age related iron changes when studying diseases like Parkinson's disease, Alzheimer's disease, and other iron related neurodegenerative diseases.

Quantifying Tissue Properties of the Optic Radiations Using Strategically Acquired Gradient Echo Imaging and Enhancing the Contrast Using Diamagnetic Susceptibility Weighted Imaging

Visualization of the optic radiations is of clinical importance for diagnosing many diseases and depicting their anatomic structures for neurosurgical interventions. In this study, we quantify proton density, T1, T2*, and susceptibility of the optic radiation fiber bundles in a series of 10 healthy control participants using strategically acquired gradient echo imaging. Furthermore, we introduce a novel means to enhance the contrast of the optic radiations using diamagnetic susceptibility weighted imaging.

Imaging patients pre and post deep brain stimulation: Localization of the electrodes and their targets

PURPOSE

Deep brain stimulation (DBS) has become a widely performed surgical procedure for patients with medically refractory movement disorders and mental disorders. It is clinically important to set up a MRI protocol to map the brain targets and electrodes of the patients before and after DBS and to understand the imaging artifacts caused by the electrodes.

METHODS

Five patients with DBS electrodes implanted in the habenula (Hb), fourteen patients with globus pallidus internus (GPi) targeted DBS, three pre-DBS patients and seven healthy controls were included in the study. The MRI protocol consisted of magnetization prepared rapid acquisition gradient echo T1 (MPRAGE T1W), 3D multi-echo gradient recalled echo (ME-GRE) and 2D fast spin echo T2 (FSE T2W) sequences to map the brain targets and electrodes of the patients. Phantom experiments were also run to determine both the artifacts and the susceptibility of the electrodes. Signal to noise ratio (SNR) on T1W, T2W and GRE datasets were measured. The visibility of the brain structures was scored according to the Rose criterion. A detailed analysis of the characteristics of the electrodes in all three sequence types was performed to confirm the reliability of the postoperative MRI approach. In order to understand the signal behavior, we also simulated the corresponding magnitude data using the same imaging parameters as in the phantom sequences.

RESULTS

The mean ± inter-subject variability of the SNRs, across the subjects for T1W, T2W, and GRE datasets were 20.1 ± 8.1, 14.9 ± 3.2, and 43.0 ± 7.6, respectively. High resolution MPRAGE T1W and FSE T2W data both showed excellent contrast for the habenula and were complementary to each other. The mean visibility of the habenula in the 25 cases for the MPRAGE T1W data was 5.28 ± 1.11; and the mean visibility in the 20 cases for the FSE T2W data was 5.78 ± 1.30. Quantitative susceptibility mapping (QSM), reconstructed from the ME-GRE sequence, provided sufficient contrast to distinguish the substructures of the globus pallidus. The susceptibilities of the GPi and globus pallidus externa (GPe) were 0.087 ± 0.013 ppm and 0.115 ± 0.015 ppm, respectively. FSE T2W sequences provided the best image quality with smallest image blooming of stimulator leads compared to MPRAGE T1W images and GRE sequence images, the measured diameters of electrodes were 1.91 ± 0.22, 2.77 ± 0.22, and 2.72 ± 0.20 mm, respectively. High resolution, high bandwidth and short TE (TE = 2.6 ms) GRE helped constrain the artifacts to the area of the electrodes and the dipole effect seen in the GRE filtered phase data provided an effective mean to locate the end of the DBS lead.

CONCLUSION

The imaging protocol consisting of MPRAGE T1W, FSE T2W and ME-GRE sequences provided excellent pre- and post-operative visualization of the brain targets and electrodes for patients undergoing DBS treatment. Although the artifacts around the electrodes can be severe, sometimes these same artifacts can be useful in identifying their location.

Strategically acquired gradient echo (STAGE)-derived MR angiography might be a superior alternative method to time-of-flight MR angiography in visualization of leptomeningeal collaterals

OBJECTIVES

This study aimed to compare the performance of strategically acquired gradient echo (STAGE)-derived MR angiography and time-of-flight MR angiography (TOF-MRA) in visualization of leptomeningeal collaterals (LMCs).

METHODS

Between May 2018 and January 2020, 75 participants (47 healthy volunteers and 28 intracranial atherosclerotic disease [ICAD] patients) undergoing TOF-MRA and STAGE-MRA were prospectively included. Image quality was scored at the internal carotid artery (ICA) terminus, proximal middle cerebral artery (MCA), and LMCs. Quantitative analysis included calculation of contrast-to-noise ratios (CNRs) in the M1-4 segments and number of LMCs counted in the line signal intensity profiles. Comparisons of image qualitative scores, CNRs, and number of LMCs were calculated using the Wilcoxon rank-sum test.

RESULTS

Image qualitative scores were significantly higher in STAGE-MRA than in TOF-MRA for the ICA terminus, proximal MCA, and LMCs (ps < 0.05) in 75 participants. When referred to digital subtraction angiography (DSA) in 25 ICAD patients, STAGE-MRA showed higher qualitative scores only at LMCs. CNRs in the M1-4 segments were significantly higher in STAGE-MRA than in TOF-MRA (218.7 ± 90.7 vs 176.2 ± 72.6, 195.7 ± 86.0 vs 146.6 ± 71.7, 176.4 ± 71.6 vs 125.8 ± 61.1, 126.2 ± 62.9 vs 78.8 ± 43.6; all ps < 0.001). STAGE-MRA showed more LMCs (11.4 ± 3.4) than TOF-MRA (8.4 ± 3.3) with p < 0.05.

CONCLUSIONS

STAGE-MRA might be superior to TOF-MRA in qualitative and quantitative assessment of LMCs in both healthy volunteers and ICAD patients; thus, it may serve as an alternative method in evaluating LMC.

KEY POINTS

• Strategically acquired gradient echo (STAGE)-derived magnetic resonance angiography is a newly developed sequence with a pair of rephasing/dephasing gradient echoes. • STAGE-MRA enables higher image qualitative score, improves contrast-to-noise ratio, and shows greater number of leptomeningeal collaterals (LMCs) in healthy volunteers and patients with intracranial atherosclerotic disease. • LMC visualization by STAGE-MRA shows good to excellent inter-observer agreement.

Regional High Iron in the Substantia Nigra Differentiates Parkinson's Disease Patients From Healthy Controls

Background: Iron is important in the pathophysiology of Parkinson’s disease (PD) specifically related to degeneration of the substantia nigra (SN). Magnetic resonance imaging (MRI) can be used to measure brain iron in the entire structure but this approach is insensitive to regional changes in iron content.

Objective: The goal of this work was to use quantitative susceptibility mapping (QSM) and R2^∗ to quantify both global and regional brain iron in PD patients and healthy controls (HC) to ascertain if regional changes correlate with clinical conditions and can be used to discriminate patients from controls.

Methods: Susceptibility and R2^∗ maps of 25 PD and 24 HC subjects were reconstructed from data collected on a 3T GE scanner. For the susceptibility maps, three-dimensional regions-of-interest (ROIs) were traced on eight deep gray matter (DGM) structures and an age-based threshold was applied to define regions of high iron content. The same multi-slice ROIs were duplicated on the R2^∗ maps as well. Mean susceptibility values of both global and regional high iron (RII) content along with global R2^∗ values were measured and compared not only between the two cohorts, but also to susceptibility and R2^∗ baselines as a function of age. Finally, clinical features were compared for those PD patients lying above and below the upper 95% regional susceptibility-age prediction intervals.

Results: The SN was the only structure showing significantly higher susceptibility in PD patients compared to controls globally (p < 0.01) and regionally (p < 0.001). The R2^∗ values were also higher only in the SN of PD patients compared to the healthy cohort (p < 0.05). Furthermore, those patients with abnormal susceptibility values lying above the upper 95% prediction intervals had significantly higher united Parkinson’s diagnostic rating scores. R2^∗ values had larger errors and showed larger dispersion as a function of age than QSM data for global analysis while the dispersion was significantly less for QSM using the RII iron content.

Conclusion: Abnormal iron deposition in the SN, especially in RII areas, could serve as a biomarker to distinguish PD patients from HC and to assess disease severity.

Venous and glymphatic drainage of the brain: Brief history of the International Society for Neurovascular Disease

The International Society of Neurovascular Diseases is an International, Interdisciplinary Scientific Organization (ISNVD: www.isnvd.org) devoted to the study of intracranial and extracranial vasculature. Different from other scientific societies, ISNVD is interested also in the investigation of the cerebral drainage, including the venous and glymphatic systems. Moreover, ISNVD promotes studies on: stroke, carotid surgery, neurovascular aspects of neurodegeneration, models of circulation, vasoactive peptides, and basic science. This review summarizes the contribution of the society to the fields above, as well as the history of the annual meetings and the major impact papers promoted by ISNVD.

Quantitative Flow Imaging in Human Umbilical Vessels In Utero Using Nongated 2D Phase Contrast MRI

BACKGROUND

Volumetric assessment of afferent blood flow rate provides a measure of global organ perfusion. Phase-contrast magnetic resonance imaging (PCMRI) is a reliable tool for volumetric flow quantification, but given the challenges with motion and lack of physiologic gating signal, such studies, in vivo on the human placenta, are scant.

PURPOSE

To evaluate and apply a nongated (ng) PCMRI technique for quantifying blood flow rates in utero in umbilical vessels.

STUDY TYPE

Prospective study design.

STUDY POPULATION

Twenty-four pregnant women with median gestational age (GA) 30 4/7 weeks and interquartile range (IQR) 8 1/7 weeks.

FIELD STRENGTH/SEQUENCE

All scans were performed on a 3.0T Siemens Verio system using the ng-PCMRI technique.

ASSESSMENT

The GA-dependent increase in umbilical vein (UV) and arterial (UA) flow was compared to previously published values. Systematic error to be expected from ng-PCMRI, in the context of pulsatile UA flow and partial voluming, was studied through Monte-Carlo simulations, as a function of resolution and number of averages.

STATISTICAL TESTS

Correlation between the UA and UV was evaluated using a generalized linear model.

RESULTS

Simulations showed that ng-PCMRI measurement variance reduced by increasing the number of averages. For vessels on the order of 2 voxels in radius, partial voluming led to 10% underestimation in the flow. In fetuses, the average flow rates in UAs and UV were measured to be 203 ± 80 ml/min and 232 ± 92 ml/min and the normalized average flow rates were 140 ± 59 ml/min/kg and 155 ± 57 ml/min/kg, respectively. Excellent correlation was found between the total arterial flow vs. corresponding venous flow, with a slope of 1.08 (P = 0.036).

DATA CONCLUSION

Ng-PCMRI can provide accurate volumetric flow measurements in utero in the human umbilical vessels. Care needs to be taken to ensure sufficiently high-resolution data are acquired to minimize partial voluming-related errors.

LEVEL OF EVIDENCE

2 Technical Efficacy Stage 1 J. Magn. Reson. Imaging 2017.

Jugular Anomalies in Multiple Sclerosis Are Associated with Increased Collateral Venous Flow

BACKGROUND AND PURPOSE

To date, research on extracranial venous collaterals has been focused on structure, with relatively little attention paid to hemodynamics. We addressed this limitation by quantitatively comparing collateral flow in patients with multiple sclerosis and healthy controls by using phase-contrast MR imaging. We hypothesize that patients with MS with structurally anomalous internal jugular veins will have elevated collateral venous flow compared with healthy controls.

MATERIALS AND METHODS

The sample consisted of 276 patients with MS and 106 healthy controls. We used MRV to classify internal jugular veins as stenotic and nonstenotic based on an absolute cross-sectional area threshold in 276 patients with MS and 60 healthy controls; 46 healthy controls lacked this imaging. Individual and total vessel flows were quantified by using phase-contrast MR imaging on all patients. Veins were classified by extracranial drainage type: internal jugular veins (I), paraspinal (II), and superficial (III). Differences among healthy controls, patients with MS, nonstenotic patients, and stenotic subgroups in total venous flow by vessel type were evaluated in a general linear model for statistical analysis.

RESULTS

In the MS group, 153 patients (55%) evidenced stenosis, whereas 12 (20%) healthy controls were classified as stenotic (P < .001). Compared with healthy controls, the MS group showed lower type I flow and increased type II flow. Stenosis was associated with reduced flow in the type I vessels [F(1272) = 68; P < .001]. The stenotic MS group had increased flow in the type II vessels compared with the nonstenotic MS group [F(1272) = 67; P < .001].

CONCLUSIONS

Compared with healthy controls, patients with MS exhibit reduced venous flow in the main extracerebral drainage vein (internal jugular vein). In contrast, flow in the paraspinal venous collaterals is elevated in patients with MS and exacerbated by venous stenosis. Collateral drainage may be a compensatory response to internal jugular vein flow reduction.

T2* mapping combined with conventional T2-weighted image for prostate cancer detection at 3.0T MRI: a multi-observer study

BACKGROUND

T2* relaxation is a primary determinant of image contrast with Gradient echo (GRE) sequences, and it has been widely used across body regions.

PURPOSE

To compare the diagnostic performance of T2* mapping in combination with T2-weighted (T2W) imaging to T2W imaging alone for prostate cancer (PCa) detection.

MATERIAL AND METHODS

The study included 31 patients (mean age, 62 ± 3 years; age range, 45-78 years) who underwent magnetic resonance imaging (MRI) at 3.0T and histological examination. Three observers with varying experience levels reviewed T2W imaging alone, T2* mapping alone, and T2W imaging combined with T2* mapping. A five-point scale was used to assess the probability of PCa in each segment on MR images. Statistical analysis was performed using Z tests after adjusting for data clustering.

RESULTS

The area under the curve (AUC) of T2W imaging and T2* mapping data (observer 1, 0.93; observer 2, 0.90; observer 3, 0.77) was higher than T2W imaging (observer 1, 0.84; observer 2, 0.79; observer 3, 0.69) for all observers (P < 0.01 in all comparisons). The AUC of T2W imaging and T2* mapping data was higher for observers 1 and 2 than for observer 3 (P < 0.01). The sensitivity and specificity of T2W imaging and T2* mapping data (observer 1, 95%, 85%; observer 2, 90%, 83%; and observer 3, 82%, 63%, respectively) was higher than T2W imaging (observer 1, 78%, 79%; observer 2, 76%, 72%; observer 3, 74%, 51%, respectively) for all observers (P < 0.01 for observer 1; P < 0.01 for observers 2 and 3).

CONCLUSION

The addition of T2* mapping to T2W imaging improved the diagnostic performance of MRI in PCa detection.

Validation of a Hemodynamic Model for the Study of the Cerebral Venous Outflow System Using MR Imaging and Echo-Color Doppler Data

BACKGROUND AND PURPOSE

A comprehensive parameter model was developed to investigate correlations between cerebral hemodynamics and alterations in the extracranial venous circulation due to posture changes and/or extracranial venous obstruction (stenosis). The purpose of this work was to validate the simulation results by using MR imaging and echo-color Doppler experimental blood flow data in humans.

MATERIALS AND METHODS

To validate the model outcomes, we used supine average arterial and venous extracerebral blood flow, obtained by using phase-contrast MR imaging from 49 individuals with stenosis in the acquisition plane at the level of the disc between the second and third vertebrae of the left internal jugular vein, 20 with stenosis in the acquisition plane at the level of the disc between the fifth and sixth vertebrae of the right internal jugular vein, and 38 healthy controls without stenosis. Average data from a second group of 10 healthy volunteers screened with an echo-color Doppler technique were used to evaluate flow variations due to posture change.

RESULTS

There was excellent agreement between experimental and simulated supine flows. Every simulated CBF fell inside the standard error from the corresponding average experimental value, as well as most of the simulated extracerebral arterial flow (extracranial blood flow from the head and face, measured at the level of the disc between second and third vertebrae) and venous flows. Simulations of average jugular and vertebral blood flow variations due to a change of posture from supine to upright also matched the experimental data.

CONCLUSIONS

The good agreement between simulated and experimental results means that the model can correctly reproduce the main factors affecting the extracranial circulation and could be used to study other types of stenotic conditions not represented by the experimental data.

Iron and Non-Iron-Related Characteristics of Multiple Sclerosis and Neuromyelitis Optica Lesions at 7T MRI

BACKGROUND AND PURPOSE

Characterization of iron deposition associated with demyelinating lesions of multiple sclerosis and neuromyelitis optica has not been well studied. Our aim was to investigate the potential of ultra-high-field MR imaging to distinguish MS from neuromyelitis optica and to characterize tissue injury associated with iron pathology within lesions.

MATERIALS AND METHODS

Twenty-one patients with MS and 21 patients with neuromyelitis optica underwent 7T high-resolution 2D-gradient-echo-T2* and 3D-susceptibility-weighted imaging. An in-house-developed algorithm was used to reconstruct quantitative susceptibility mapping from SWI. Lesions were classified as "iron-laden" if they demonstrated hypointensity on gradient-echo-T2*-weighted images and/or SWI and hyperintensity on quantitative susceptibility mapping. Lesions were considered "non-iron-laden" if they were hyperintense on gradient-echo-T2* and isointense or hyperintense on quantitative susceptibility mapping.

RESULTS

Of 21 patients with MS, 19 (90.5%) demonstrated at least 1 quantitative susceptibility mapping-hyperintense lesion, and 11/21 (52.4%) had iron-laden lesions. No quantitative susceptibility mapping-hyperintense or iron-laden lesions were observed in any patients with neuromyelitis optica. Iron-laden and non-iron-laden lesions could each be further characterized into 2 distinct patterns based on lesion signal and morphology on gradient-echo-T2*/SWI and quantitative susceptibility mapping. In MS, most lesions (n = 262, 75.9% of all lesions) were hyperintense on gradient-echo T2* and isointense on quantitative susceptibility mapping (pattern A), while a small minority (n = 26, 7.5% of all lesions) were hyperintense on both gradient-echo-T2* and quantitative susceptibility mapping (pattern B). Iron-laden lesions (n = 57, 16.5% of all lesions) were further classified as nodular (n = 22, 6.4%, pattern C) or ringlike (n = 35, 10.1%, pattern D).

CONCLUSIONS

Ultra-high-field MR imaging may be useful in distinguishing MS from neuromyelitis optica. Different patterns related to iron and noniron pathology may provide in vivo insight into the pathophysiology of lesions in MS.

A simulation model to study the role of the extracranial venous drainage pathways in intracranial hemodynamics

Alterations in the extracranial venous circulation due to posture changes, and/or extracranial venous obstructions in patients with vascular diseases, can have important implications on cerebral hemodynamics. A hemodynamic model for the study of cerebral venous outflow was developed to investigate the correlations between extracranial blood redistributions and changes in the intracranial environment. Flow data obtained with both magnetic resonance (MR) and Echo-Color Doppler (ECD) technique are used to validate the model. The very good agreement between simulated supine and upright flows and experimental results means that the model can correctly reproduce the main factors affecting the extracranial venous circulation.

Traumatic Brain Injury by a Closed Head Injury Device Induces Cerebral Blood Flow Changes and Microhemorrhages

OBJECTIVES

Traumatic brain injury is a poly-pathology characterized by changes in the cerebral blood flow, inflammation, diffuse axonal, cellular, and vascular injuries. However, studies related to understanding the temporal changes in the cerebral blood flow following traumatic brain injury extending to sub-acute periods are limited. In addition, knowledge related to microhemorrhages, such as their detection, localization, and temporal progression, is important in the evaluation of traumatic brain injury.

MATERIALS AND METHODS

Cerebral blood flow changes and microhemorrhages in male Sprague Dawley rats at 4 h, 24 h, 3 days, and 7 days were assessed following a closed head injury induced by the Marmarou impact acceleration device (2 m height, 450 g brass weight). Cerebral blood flow was measured by arterial spin labeling. Microhemorrhages were assessed by susceptibility-weighted imaging and Prussian blue histology.

RESULTS

Traumatic brain injury rats showed reduced regional and global cerebral blood flow at 4 h and 7 days post-injury. Injured rats showed hemorrhagic lesions in the cortex, corpus callosum, hippocampus, and brainstem in susceptibility-weighted imaging. Injured rats also showed Prussian blue reaction products in both the white and gray matter regions up to 7 days after the injury. These lesions were observed in various areas of the cortex, corpus callosum, hippocampus, thalamus, and midbrain.

CONCLUSIONS

These results suggest that changes in cerebral blood flow and hemorrhagic lesions can persist for sub-acute periods after the initial traumatic insult in an animal model. In addition, microhemorrhages otherwise not seen by susceptibility-weighted imaging are present in diverse regions of the brain. The combination of altered cerebral blood flow and microhemorrhages can potentially be a source of secondary injury changes following traumatic brain injury and may need to be taken into consideration in the long-term care of these cases.

Longitudinal Changes in Placental Magnetic Resonance Imaging Relaxation Parameter in Murine Pregnancy: Compartmental Analysis

OBJECTIVE

To quantify gestation-dependent longitudinal changes in the magnetic resonance transverse relaxation time (T2) parameter of the major constituent regions of the mouse placenta and to evaluate their relative contributions to changes in overall placental T2.

METHODS

Timed-pregnant CD-1 mice underwent magnetic resonance imaging at 7.0 T field strength, on gestational day 13 (GD13), GD15 and GD17. T2 of the placenta and its constituent high and low blood perfusion regions were quantified. A linear mixed-effects model was used to fit the T2 across gestation, and the significance of coefficients was tested.

RESULTS

A decrease in the T2 values of the placenta and its constituent regions was observed across gestation. The temporal change in T2 was estimated to be -1.85 ms/GD (p < 0.0001) for the placenta, -1.00 ms/GD (p < 0.001) for the high-perfusion zones (HPZs) and -1.66 ms/GD (p < 0.0001) for the low-perfusion zones (LPZs).

CONCLUSION

T2 of the constituent zones of the murine placenta decreases with advancing gestation. While the T2 of the LPZ is smaller than that of the HPZ, there is no difference in their decrease rate relative to that of the whole placenta (p = 0.24). The results suggest an increased role of constituent volume fractions in affecting overall gestation-dependent placental T2 decrease in mice.

Impact of CCSVI on cerebral haemodynamics: a mathematical study using MRI angiographic and flow data

Background

The presence of abnormal anatomy and flow in neck veins has been recently linked to neurological diseases. The precise impact of extra-cranial abnormalities such as stenoses remains unexplored.

Methods

Pressure and velocity fields in the full cardiovascular system are computed by means of a global mathematical model that accounts for the relationship between pulsating cerebral blood flow and intracranial pressure.

Results

Our model predicts that extra-cranial strictures cause increased pressure in the cerebral venous system. Specifically, there is a predicted pressure increase of about 10% in patients with a 90% stenoses. Pressure increases are related to significant flow redistribution with flow reduction of up to 70% in stenosed vessels and consequent flow increase in collateral pathways.

Conclusions

Extra-cranial venous strictures can lead to pressure increases in intra-cranial veins of up to 1.3 mmHg, despite the shielding role of the Starling resistor. The long-term clinical implications of the predicted pressure changes are unclear.

Imaging the effects of oxygen saturation changes in voluntary apnea and hyperventilation on susceptibility-weighted imaging

BACKGROUND AND PURPOSE

Cerebrovascular oxygenation changes during respiratory challenges have clinically important implications for brain function, including cerebral autoregulation and the rate of brain metabolism. SWI is sensitive to venous oxygenation level by exploitation of the magnetic susceptibility of deoxygenated blood. We assessed cerebral venous blood oxygenation changes during simple voluntary breath-holding (apnea) and hyperventilation by use of SWI at 3T.

MATERIALS AND METHODS

We performed SWI scans (3T; acquisition time of 1 minute, 28 seconds; centered on the anterior commissure and the posterior commissure) on 10 healthy male volunteers during baseline breathing as well as during simple voluntary hyperventilation and apnea challenges. The hyperventilation and apnea tasks were separated by a 5-minute resting period. SWI venograms were generated, and the signal changes on SWI before and after the respiratory stress tasks were compared by means of a paired Student t test.

RESULTS

Changes in venous vasculature visibility caused by the respiratory challenges were directly visualized on the SWI venograms. The venogram segmentation results showed that voluntary apnea decreased the mean venous blood voxel number by 1.6% (P < .0001), and hyperventilation increased the mean venous blood voxel number by 2.7% (P < .0001). These results can be explained by blood CO2 changes secondary to the respiratory challenges, which can alter cerebrovascular tone and cerebral blood flow and ultimately affect venous oxygen levels.

CONCLUSIONS

These results highlight the sensitivity of SWI to simple and noninvasive respiratory challenges and its potential utility in assessing cerebral hemodynamics and vasomotor responses.

Improving susceptibility mapping using a threshold-based K-space/image domain iterative reconstruction approach

To improve susceptibility quantification, a threshold-based k-space/image domain iterative approach that uses geometric information from the susceptibility map itself as a constraint to overcome the ill-posed nature of the inverse filter is introduced. Simulations were used to study the accuracy of the method and its robustness in the presence of noise. In vivo data were processed and analyzed using this method. Both simulations and in vivo results show that most streaking artifacts inside the susceptibility map caused by the ill-defined inverse filter were suppressed by the iterative approach. In simulated data, the bias toward lower mean susceptibility values inside vessels has been shown to decrease from around 10% to 2% when choosing an appropriate threshold value for the proposed iterative method. Typically, three iterations are sufficient for this approach to converge and this process takes less than 30 s to process a 512×512×256 dataset. This iterative method improves quantification of susceptibility inside vessels and reduces streaking artifacts throughout the brain for data collected from a single-orientation acquisition. This approach has been applied to vessels alone as well as to vessels and other structures with lower susceptibility to generate whole brain susceptibility maps with significantly reduced streaking artifacts.

Assessing abnormal iron content in the deep gray matter of patients with multiple sclerosis versus healthy controls

BACKGROUND AND PURPOSE

It is well known that patients with MS tend to have abnormal iron deposition in and around the MS plaques, in the basal ganglia and the THA. In this study, we used SWI to quantify iron content in patients with MS and healthy volunteers.

MATERIALS AND METHODS

Fifty-two patients with MS were recruited to assess abnormal iron content in their basal ganglia and THA structures. One hundred twenty-two healthy subjects were recruited to establish a baseline of normal iron content in deep GM structures. Each structure was separated into 2 regions: a low-iron-content region and a high-iron-content region. The average phase, the percentage area, and the total phase of the high-iron-content region were evaluated. A weighting was also assigned to each subject depending on the level of iron content and its deviation from the normal range.

RESULTS

A clear separation between iron content in healthy subjects versus patients with MS was seen. For healthy subjects 13% and for patients with MS 65% showed an iron-weighting factor >3 SDs from the normal mean (P < .05). The results for those patients younger than 40 years are even more impressive. In these cases, only 1% of healthy subjects and 67% of patients with RRMS showed abnormally high iron content.

CONCLUSIONS

Iron-weighting factors in the basal ganglia, THA, and the midbrain appeared to be abnormal in roughly two-thirds of patients with MS as measured by SWI.

Improving detection of siderotic nodules in cirrhotic liver with a multi-breath-hold susceptibility-weighted imaging technique

PURPOSE

To evaluate the role of abdominal susceptibility-weighted imaging (SWI) in the detection of siderotic nodules in cirrhotic liver.

MATERIALS AND METHODS

Forty patients with pathologically identified liver cirrhosis and 40 age/sex-matched normal controls underwent T1-, T2-, T2*-weighted imaging and SWI at 3T. Two radiologists prospectively analyzed all magnetic resonance imaging (MRI) studies. Siderotic nodules detected by each imaging technique were counted for comparison. The conspicuity of siderotic nodules was assessed using a scale from 1 to 3 (1, weak; 2, moderate; 3, prominent).

RESULTS

The number of siderotic nodules detected by SWI (3863) was significantly greater than that of T1-weighted imaging (262, P < 0.001), T2-weighted imaging (842, P < 0.001), and T2*-weighted imaging (2475, P < 0.001). No suspected siderotic nodules were detected in normal controls by any imaging technique.

CONCLUSION

SWI appears to provide the most sensitive method to detect siderotic nodules in cirrhotic liver.

Different iron-deposition patterns of multiple system atrophy with predominant parkinsonism and idiopathetic Parkinson diseases demonstrated by phase-corrected susceptibility-weighted imaging

BACKGROUND AND PURPOSE

MSA-P and IPD have similar clinical presentations that may complicate accurate clinical diagnosis. Different iron-deposition patterns of those 2 diseases have been demonstrated in histopathology. The aim was to demonstrate the different iron-deposition patterns of MSA-P and IPD by using SWI phase images.

MATERIALS AND METHODS

Sixteen patients with IPD, 8 with MSA-P, and 44 age-matched healthy controls underwent SWI of brain. The different phase shifts as well as the high iron percentage of the area in several gray nuclei were statistically evaluated. The putamen was divided into 4 subregions for further analysis.

RESULTS

Patients with MSA-P had significantly higher iron deposition in the putamen and PT compared with those with IPD (P < .05). Moreover, ROC curves indicated slightly more sensitivity in differentiating MSA-P from IPD, by means of the high-iron-deposition-percentage area than the average phase shift (putamen: AUC = 0.88 versus 0.78; PT: AUC = 0.79 versus 0.62). Moreover, the lower inner region of the putamen was the most valuable subregion in differentiating MSA-P from IPD among the 4 subregions (AUC = 0.92 and 0.91 for high-iron-percentage area and average phase shift, respectively).

CONCLUSIONS

Higher iron deposition in the putamen and PT may differentiate MSA-P from IPD, but the lower inner region of the putamen may be better compared with the PT and other subregions of the putamen. Moreover, the high iron percentage makes it possible to detect smaller increases in iron content more confidently in comparison with average phase shift.

Susceptibility mapping as a means to visualize veins and quantify oxygen saturation

PURPOSE

To create an orientation-independent, 3D reconstruction of the veins in the brain using susceptibility mapping.

MATERIALS AND METHODS

High-resolution, high-pass filtered phase images usually used for susceptibility weighted imaging (SWI) were used as a source for local magnetic field behavior. These images were subsequently postprocessed using an inverse procedure to generate susceptibility maps of the veins. Regularization and interpolation of the data in k-space of the phase images were used to reduce reconstruction artifacts. To understand the effects of artifacts, and to fine-tune the methodology, simulations of blood vessels were performed with and without noise.

RESULTS

With sufficient resolution, major veins in the brain could be visualized with this approach. The usual geometry-dependent phase dipole effects are removed by this processing, leaving basically images of the veins. Different sized vessels show a different level of contrast depending on their partial volume effects. Vessels that are 8 mm or 16 mm in size show quantitative values expected for normal oxygen saturation levels. Smaller vessels show smaller values due to errors in the methodology and due to partial volume effects. Larger vessels show a bias toward a reduced susceptibility approaching 90% of the expected value. Limitations of the method and artifacts related to different sources of errors are demonstrated.

CONCLUSION

Susceptibility maps can successfully create venograms of the brain with varying levels of contrast-to-noise depending on the size of the vessel. Partial volume effects render this approach more useful as an imaging tool or a visualization tool, although certain larger vessels have measured susceptibilities close to expected values associated with normal blood oxygen saturation levels.

Iron stores and cerebral veins in MS studied by susceptibility weighted imaging

AIM

In this paper, we seek to determine whether the iron deposition as seen by susceptibility weighted imaging (SWI) in the basal ganglia and thalamus of patients with multiple sclerosis is greater than the iron content measured in normal subjects (individuals unaffected by multiple sclerosis). As increased iron content may result from increased venous pressure, such information would add credence to the concept of Zamboni et al (1) that MS is caused by chronic cerebrospinal venous insufficiency.

METHODS

Fourteen MS patients were recruited for this study with a mean age of 38 years ranging from 19 to 66 year-old. A velocity compensated 3D gradient echo sequence was used to generate SW images with a high sensitivity to iron content. We evaluated iron in the following structures: substantia nigra, red nucleus, globus pallidus, putamen, caudate nucleus, thalamus and pulvinar thalamus. Each structure was broken into two parts, a high iron content region and a low iron content region. The measured values were compared to previously established baseline iron content in these structures as a function of age.

RESULTS

Twelve of fourteen patients had an increase in iron above normal levels and with a particular pattern of iron deposition in the medial venous drainage system that was associated with the confluence of the veins draining that structure.

CONCLUSION

Iron may serve as a biomarker of venous vascular damage in multiple sclerosis. The backward iron accumulation pattern seen in the basal ganglia and thalamus of most MS patients is consistent with the hypothesis of venous hypertension.

Evaluation of traumatic subarachnoid hemorrhage using susceptibility-weighted imaging

BACKGROUND AND PURPOSE

SWI is an MR imaging technique that is very sensitive to hemorrhage. Our goal was to compare SWI and CT to determine if SWI can show traumatic SAH in different parts of the subarachnoid space.

MATERIALS AND METHODS

Twenty acute TBI patients identified by CT with SAH underwent MR imaging scans. Two neuroradiologists analyzed the CT and SWI data to decide whether there were SAHs in 8 anatomical parts of the subarachnoid space.

RESULTS

Fifty-five areas with SAH were identified by both CT and SWI. Ten areas were identified by CT only and 13 by SWI only. SAH was recognized on SWI by its very dark signal intensity surrounded by CSF signal intensity in the sulci or cisterns. Compared with the smooth-looking veins, SAH tended to have a rough boundary and inhomogeneous signal intensity. In many instances, blood in the sulcus left an area of signal intensity loss that had a "triangle" shape. SWI showed 5 more cases of intraventricular hemorrhage than did CT.

CONCLUSIONS

SAH can be recognized by SWI through its signal intensity and unique morphology. SWI can provide complementary information to CT in terms of small amounts of SAH and hemorrhage inside the ventricles.

Characterizing the mesencephalon using susceptibility-weighted imaging

BACKGROUND AND PURPOSE

The mesencephalon is involved in a number of human neurodegenerative disorders and has been typically imaged with T1-, T2- and T2*-weighted methods. Our aim was to collect high-contrast susceptibility-weighted imaging (SWI) data to differentiate among and within the basic mesencephalic structures: namely, the red nucleus, substantia nigra, and crus cerebri.

MATERIALS AND METHODS

High-resolution SWI, 3D T1-weighted, and T2-weighted data were collected to study contrast in the mesencephalon at 1.5T and 4T. Contrast between structures was calculated for SWI high-pass (HP)-filtered-phase, T1 gradient-echo, and spin-echo T2-weighted data.

RESULTS

SWI HP-filtered-phase data revealed similar contrast for the red nucleus and substantia nigra when compared with T2-weighted imaging. However, SWI was able to show structures within the red nucleus, substantia nigra, and medial geniculate body that were invisible on T2-weighted imaging. T1-weighted imaging, on the other hand, did not reveal measurable contrast for any of the structures of interest. SWI HP-filtered-phase data at 4T agreed well with india ink-stained cadaver brain studies, which appear to correlate with capillary density.

CONCLUSIONS

With SWI, it is possible to create better anatomic images of the mesencephalon, with improved contrast compared with conventional T1- or T2-weighted sequences.

Susceptibility-weighted imaging: technical aspects and clinical applications, part 2

SUMMARY

Susceptibility-weighted imaging (SWI) has continued to develop into a powerful clinical tool to visualize venous structures and iron in the brain and to study diverse pathologic conditions. SWI offers a unique contrast, different from spin attenuation, T1, T2, and T2* (see Susceptibility-Weighted Imaging: Technical Aspects and Clinical Applications, Part 1). In this clinical review (Part 2), we present a variety of neurovascular and neurodegenerative disease applications for SWI, covering trauma, stroke, cerebral amyloid angiopathy, venous anomalies, multiple sclerosis, and tumors. We conclude that SWI often offers complementary information valuable in the diagnosis and potential treatment of patients with neurologic disorders.

Susceptibility-weighted imaging: technical aspects and clinical applications, part 1

Susceptibility-weighted imaging (SWI) is a new neuroimaging technique, which uses tissue magnetic susceptibility differences to generate a unique contrast, different from that of spin density, T1, T2, and T2*. In this review (the first of 2 parts), we present the technical background for SWI. We discuss the concept of gradient-echo images and how we can measure local changes in susceptibility. Armed with this material, we introduce the steps required to transform the original magnitude and phase images into SWI data. The use of SWI filtered phase as a means to visualize and potentially quantify iron in the brain is presented. Advice for the correct interpretation of SWI data is discussed, and a set of recommended sequence parameters for different field strengths is given.

Aerosol delivery in ventilated newborn pigs: an MRI evaluation

Pulmonary deposition of inhaled drugs in ventilated neonates has not been studied in vivo. The objective of this study was to evaluate pulmonary delivery of gadopentetate dimeglumine (Gd-DTPA) following nebulization in ventilated piglets using magnetic resonance imaging. Seven ventilated piglets (5 +/- 2 d old, weight 1.8 +/- 0.5 kg) were scanned in the Bruker/Siemens 4T magnetic resonance scanner using T1 weighted spin-echo sequence. Aerosols of Gd-DTPA were generated continuously using the MiniHeart jet nebulizer. Breath-hold coronal images were obtained before and every 10 min during aerosolized Gd-DTPA for 90 min. Signal intensity (SI) changes over the lungs, kidneys, liver, skeletal muscle, and heart were evaluated. A significant increase in SI was observed in the lungs, kidney, and liver at 10, 20, and 40 min respectively after start of aerosol. At the end of 90 min, the SI increased by 95%, 101%, and 426% over the right lung, left lung, and kidney, respectively. A much smaller increase in SI was observed over the liver. In conclusion, we have demonstrated effective pulmonary aerosol delivery within 10 min of contrast nebulization in ventilated piglets. Contrast visualization in the kidneys within 20 min of aerosol initiation reflects alveolar absorption, glomerular filtration and renal concentration.

Susceptibility-weighted MR imaging: a review of clinical applications in children

Susceptibility-weighted imaging (SWI) is a high-spatial-resolution 3D gradient-echo MR imaging technique with phase postprocessing that accentuates the paramagnetic properties of blood products such as deoxyhemoglobin, intracellular methemoglobin, and hemosiderin. It is particularly useful for detecting intravascular venous deoxygenated blood as well as extravascular blood products. It is also quite sensitive to the presence of other substances such as iron, some forms of calcification, and air. We have used this technique in the past several years to study a wide variety of pediatric neurologic disorders. We present a review with selected case histories to demonstrate its clinical usefulness in the improvement of the following: 1) detection of hemorrhagic lesions seen in various conditions, including traumatic brain injury and coagulopathic or other hemorrhagic disorders; 2) detection of vascular malformations such as cavernous angiomas, telangiectasias, or pial angiomas associated with Sturge-Weber syndrome; 3) demonstration of venous thrombosis and/or increased oxygen extraction in the setting of infarction, hypoxic/anoxic injury, or brain death; 4) delineation of neoplasms with hemorrhage, calcification, or increased vascularity; and 5) depiction of calcium or iron deposition in neurodegenerative disorders. SWI has provided new understanding of some of these disease processes. It is hoped that as SWI becomes more widely available, it will provide additional diagnostic and prognostic information that will improve the care and outcome of affected children.

Multimodality imaging of cortical and white matter abnormalities in Sturge-Weber syndrome

BACKGROUND AND PURPOSE

Impaired cortical venous outflow and abnormal deep venous collaterals are common in Sturge-Weber syndrome (SWS), but their relation to brain metabolism and function is poorly understood. In this study, advanced MR imaging techniques, such as susceptibility-weighted imaging (SWI) and diffusion tensor imaging (DTI), were applied in conjunction with positron-emission tomography (PET), to assess cortical and white matter structural abnormalities and their relation to cortical glucose metabolism and cognitive functions in children with unilateral SWS.

MATERIALS AND METHODS

Thirteen children (age, 1.5-10.3 years) with unilateral SWS underwent MR imaging with SWI and DTI, glucose metabolism PET, and comprehensive neuropsychologic assessment prospectively. The MR imaging and PET images were coregistered and cortical regions showing decreased glucose metabolism were compared with locations of SWI signal intensity abnormalities, changes in white matter water diffusion, and cognitive functions.

RESULTS

SWI detected both cortical abnormalities (n=8) and deep transmedullary veins (n=9), including those in young children with no cortical SWI signal intensity changes. These veins were often located under cortex adjacent to hypometabolic regions. DTI showed abnormal water diffusion both under hypometabolic cortex and in adjacent white matter with collateral veins. Cognitive dysfunction was associated with abnormal water diffusion in the posterior white matter.

CONCLUSIONS

Transmedullary venous collaterals can be detected early by SWI and persist in white matter adjacent to damaged cortex in children with SWS. Microstructural white matter damage extends beyond cortical abnormalities and may contribute to cognitive impairment. SWI and DTI can be incorporated into clinical MR imaging acquisitions to objectively assess microstructural abnormalities at different stages of SWS.

Imaging cerebral amyloid angiopathy with susceptibility-weighted imaging

Gradient-echo (GE) imaging is recognized as a means to detect hemorrhagic changes in cerebral amyloid angiopathy (CAA). However, almost 25% of patients with CAA do not show microhemorrhages on T2* GE imaging. We applied a new imaging method, susceptibility weighted imaging (SWI), to evaluate the presence of microhemorrhages. In a suspected case of CAA, where cognitive effects are also present, we show that SWI is much more sensitive in detecting microhemorrhages than conventional methods.

Diffuse axonal injury in children: clinical correlation with hemorrhagic lesions

An inception cohort of 40 children and adolescents with traumatic brain injury and suspected diffuse axonal injury were studied using a new high-resolution magnetic resonance imaging susceptibility-weighted technique that is very sensitive for hemorrhage. A blinded comparison was performed between the extent of parenchymal hemorrhage and initial clinical variables as well as outcomes measured at 6 to 12 months after injury. Children with lower Glasgow Coma Scale scores (< or =8, n = 30) or prolonged coma (>4 days, n = 20) had a greater average number (p = 0.007) and volume (p = 0.008) of hemorrhagic lesions. Children with normal outcomes or mild disability (n = 30) at 6 to 12 months had, on average, fewer hemorrhagic lesions (p = 0.003) and lower volume (p = 0.003) of lesions than those who were moderately or severely disabled or in a vegetative state. Significant differences also were observed when comparing regional injury to clinical variables. Because susceptibility-weighted imaging is much more sensitive than conventional T2*-weighted gradient-echo sequences in detecting hemorrhagic diffuse axonal injury, more accurate and objective assessment of injury can be obtained early after insult, and may provide better prognostic information regarding duration of coma as well as long-term outcome.