Clinical applications of ultra-high field magnetic resonance imaging in multiple sclerosis

Central myelin-peripheral myelin junction in trigeminal, facial, and vestibulocochlear nerve: A histo-morphometric study

BACKGROUND

The study aimed to locate the central myelin and peripheral myelin junction (CNS PNS Junction, CPJ) in trigeminal, facial and vestibulocochlear nerves.

METHODS

The cisternal segments of the nerves were cut from the brainstem to the proximal margin of trigeminal ganglia (trigeminal nerve) and internal acoustic meatus (facial and vestibulocochlear nerve) from cadavers. Horizontal sections of H&E stained slides were analysed and histo morphometry was performed. The CPJ was confirmed by immunohistochemistry using monoclonal myelin basic protein antibody.

RESULTS

The mean length of the trigeminal, facial and vestibulocochlear nerves were 13.6 ± 3.1 mm, 12.4 ± 1.9 mm and 11.5 ± 2.0 mm respectively; mean length of the centrally myelinated segment at the point of maximum convexity was 4.1 ± 1.5 mm, 3.7 ± 1.6 mm, 3.6 ± 1.4 mm respectively. Six different patterns were observed fortheCPJ.Utilizing the derived values, the CPJwas located at a distance of 18 - 48% and 17 - 61% of the total length of the nerve in all the cases in trigeminal and facial nerve respectively. In vestibulocochlear nerve, it was located at a distance of about 13 - 54% of the total length of the nerve.

CONCLUSIONS

The location of the CPJ in the vestibulocochlear nerve was midway between the brainstem and internal acoustic meatus which is a novel observation.For all the nerves, the CPJ was located either at or before the half way along the length of the nerve in huge majority (97%); never crossing the 60% of the nerve length.

Adult-onset depletion of sulfatide leads to axonal degeneration with relative myelin sparing

3-O-sulfogalactosylceramide (sulfatide) constitutes a class of sphingolipids that comprise about 4% of myelin lipids in the central nervous system. Previously, our group characterized a mouse with sulfatide's synthesizing enzyme, cerebroside sulfotransferase (CST), constitutively disrupted. Using these mice, we demonstrated that sulfatide is required for establishment and maintenance of myelin, axoglial junctions, and axonal domains and that sulfatide depletion results in structural pathologies commonly observed in Multiple Sclerosis (MS). Interestingly, sulfatide is reduced in regions of normal appearing white matter (NAWM) of MS patients. Sulfatide reduction in NAWM suggests depletion occurs early in disease development and consistent with functioning as a driving force of disease progression. To closely model MS, an adult-onset disease, our lab generated a "floxed" CST mouse and mated it against the PLP-creERT mouse, resulting in a double transgenic mouse that provides temporal and cell-type specific ablation of the Cst gene (Gal3st1). Using this mouse, we demonstrate adult-onset sulfatide depletion has limited effects on myelin structure but results in the loss of axonal integrity including deterioration of domain organization accompanied by axonal degeneration. Moreover, structurally preserved myelinated axons progressively lose the ability to function as myelinated axons, indicated by the loss of the N1 peak. Together, our findings indicate that sulfatide depletion, which occurs in the early stages of MS progression, is sufficient to drive the loss of axonal function independent of demyelination and that axonal pathology, which is responsible for the irreversible loss of neuronal function that is prevalent in MS, may occur earlier than previously recognized.

Improved detection of multiple sclerosis lesions with T2-prepared double inversion recovery at 3T

BACKGROUND AND PURPOSE

Double inversion recovery (DIR) imaging is used in multiple sclerosis (MS) clinical protocols to improve the detection of cortical and juxtacortical gray matter lesions by nulling confounding signals originating from the cerebrospinal fluid and white matter. Achieving a high isotropic spatial resolution, to depict the neocortex and its typically small lesions, is challenged by the reduced signal-to-noise ratio (SNR) determined by multiple tissue signal nulling. Here, we evaluate both conventional and optimized DIR implementations to improve tissue contrast (TC), SNR, and MS lesion conspicuity.

METHODS

DIR images were obtained from MS patients and healthy controls using both conventional and prototype implementations featuring a T2-preparation module (T2P), to improve SNR and TC, as well as an image reconstruction routine with iterative denoising (ID). We obtained quantitative measures of SNR and TC, and evaluated the visibility of MS cortical, cervical cord, and optic nerve lesions in the different DIR images.

RESULTS

DIR implementations adopting T2P and ID enabled improving the SNR and TC of conventional DIR. In MS patients, 34% of cortical, optic nerve, and cervical cord lesions were visible only in DIR images acquired with T2P, and not in conventional DIR images. In the studied cases, image reconstruction with ID did not improve lesion conspicuity.

CONCLUSIONS

DIR with T2P should be preferred to conventional DIR imaging in protocols studying MS patients, as it improves SNR and TC and determines an improvement in cortical, optic nerve, and cervical cord lesion conspicuity.

The Clinical Utility of Magnetic Resonance Imaging According to Field Strength, Specifically Addressing the Breadth of Current State-of-the-Art Systems, Which Include 0.55 T, 1.5 T, 3 T, and 7 T

ABSTRACT

This review provides a balanced perspective regarding the clinical utility of magnetic resonance systems across the range of field strengths for which current state-of-the-art units exist (0.55 T, 1.5 T, 3 T, and 7 T). Guidance regarding this issue is critical to appropriate purchasing, usage, and further dissemination of this important imaging modality, both in the industrial world and in developing nations. The review serves to provide an important update, although to a large extent this information has never previously been openly presented. In that sense, it serves also as a position paper, with statements and recommendations as appropriate.

Variability in subthalamic nucleus targeting for deep brain stimulation with 3 and 7 Tesla magnetic resonance imaging

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective surgical treatment for Parkinson's disease (PD). Side-effects may, however, be induced when the DBS lead is placed suboptimally. Currently, lower field magnetic resonance imaging (MRI) at 1.5 or 3 Tesla (T) is used for targeting. Ultra-high-field MRI (7 T and above) can obtain superior anatomical information and might therefore be better suited for targeting. This study aims to test whether optimized 7 T imaging protocols result in less variable targeting of the STN for DBS compared to clinically utilized 3 T images. Three DBS-experienced neurosurgeons determined the optimal STN DBS target site on three repetitions of 3 T-T2, 7 T-T2*, 7 T-R2* and 7 T-QSM images for five PD patients. The distance in millimetres between the three repetitive coordinates was used as an index of targeting variability and was compared between field strength, MRI contrast and repetition with a Bayesian ANOVA. Further, the target coordinates were registered to MNI space, and anatomical coordinates were compared between field strength, MRI contrast and repetition using a Bayesian ANOVA. The results indicate that the neurosurgeons are stable in selecting the DBS target site across MRI field strength, MRI contrast and repetitions. The analysis of the coordinates in MNI space however revealed that the actual selected location of the electrode is seemingly more ventral when using the 3 T scan compared to the 7 T scans.

Deep Attention and Graphical Neural Network for Multiple Sclerosis Lesion Segmentation from MR Imaging Sequences

The segmentation of multiple sclerosis (MS) lesions from MR imaging sequences remains a challenging task, due to the characteristics of variant shapes, scattered distributions and unknown numbers of lesions. However, the current automated MS segmentation methods with deep learning models face the challenges of (1) capturing the multiple scattered lesions in multiple regions and (2) delineating the global contour of variant lesions. To address these challenges, in this paper, we propose a novel attention and graph-driven network (DAG-Net), which incorporates (1) the spatial correlations for embracing the lesions in distant regions and (2) the global context for better representing lesions of variant features in a unified architecture. Firstly, the novel local attention coherence mechanism is designed to construct dynamic and expansible graphs for the spatial correlations between pixels and their proximities. Secondly, the proposed spatial-channel attention module enhances features to optimize the global contour delineation, by aggregating relevant features. Moreover, with the dynamic graphs, the learning process of the DAG-Net is interpretable, which in turns support the reliability of segmentation results. Extensive experiments were conducted on a public ISBI2015 dataset and an in-house dataset in comparison to state-of-the-art methods, based on the geometrical and clinical metrics. The experimental results validate the effectiveness of the proposed DAG-Net on segmenting variant and scatted lesions in multiple regions.

MRI with ultrahigh field strength and high-performance gradients: challenges and opportunities for clinical neuroimaging at 7 T and beyond

Research in ultrahigh magnetic field strength combined with ultrahigh and ultrafast gradient technology has provided enormous gains in sensitivity, resolution, and contrast for neuroimaging. This article provides an overview of the technical advantages and challenges of performing clinical neuroimaging studies at ultrahigh magnetic field strength combined with ultrahigh and ultrafast gradient technology. Emerging clinical applications of 7-T MRI and state-of-the-art gradient systems equipped with up to 300 mT/m gradient strength are reviewed, and the impact and benefits of such advances to anatomical, structural and functional MRI are discussed in a variety of neurological conditions. Finally, an outlook and future directions for ultrahigh field MRI combined with ultrahigh and ultrafast gradient technology in neuroimaging are examined.

Longitudinal Sodium MRI of Multiple Sclerosis Lesions: Is there Added Value of Sodium Inversion Recovery MRI

BACKGROUND

Sodium enhancement has been demonstrated in multiple sclerosis (MS) lesions.

PURPOSE

To investigate sodium MRI with and without an inversion recovery pulse in acute MS lesions in an MS relapse and during recovery.

STUDY TYPE

Prospective.

SUBJECTS

Twenty-nine relapsing-remitting MS patients with an acute relapse were included.

FIELD STRENGTH/SEQUENCE

A 3D density-adapted radial sodium sequence at 3 T using a dual-tuned (²³ Na/¹ H) head coil.

ASSESSMENT

Full-brain images of the tissue sodium concentration (TSC1, n = 29) and a sodium inversion recovery sequence (SIR1, n = 20) at the beginning of the anti-inflammatory therapy and on medium-term follow-up visits (days 27-99, n = 12 [TSC], n = 5 [SIR]) were measured. Regions of interest (RoIs) with contrast enhancement (T₁ CE+) and without change in T1-weighted imaging (FL + T1n) were normalized (nTSC and nSIR). To gain insight on the origin of the TSC enhancement at time point 1, it is investigated whether the nTSC enhancement of the lesions is accompanied by a change of the respective nSIR. Potential prognostic value of nSIR1 is examined referring to the nTSC progression. STATISTICAL TESTS: nTSC and nSIR were compared regarding the type of lesion and the time point using a one-way ANOVA. Pearson's correlation coefficient was calculated for nTSC over nSIR and for nTSC1-nTSC2 over nSIR1. A P-value <0.05 was considered statistically significant.

RESULTS

At the first measurement, all lesion types showed increased nTSC, while nSIR was decreased in the FL + T₁ n and the T₁ CE+ lesions in comparison to the normal-appearing white matter. For acute lesions, the difference between nTSC at baseline and nTSC at time point 2 showed a significant correlation with the baseline nSIR.

DATA CONCLUSION

At time point 1, nTSC is increased, while nSIR is unchanged or decreased in the lesions. The mean sodium IR signal at baseline correlates with recovery or progression of an acute lesion.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 4.

Utility of 7 Tesla MRI for Preoperative Planning of Endoscopic Endonasal Surgery for Pituitary Adenomas

Objective  There is increasing interest in investigating the utility of 7 Tesla (7 T) magnetic resonance imaging (MRI) for imaging of skull base tumors. The present study quantifies visualization of tumor features and adjacent skull base anatomy in a homogenous cohort of pituitary adenoma patients. Methods  Eighteen pituitary adenoma patients were scanned at 7 T in this prospective study. All patients had reference standard-of-care clinical imaging at either 3 T (7/18, 39%) or 1.5 T (11/18, 61%). Visualization of tumor features and conspicuity of arteries and cranial nerves (CNs) was rated by an expert neuroradiologist on 7 T and clinical field strength MRI. Overall image quality and severity of image artifacts were also characterized and compared. Results  Ability to visualize tumor features did not differ between 7 T and lower field MRI. Cranial nerves III, IV, and VI were better detected at 7 T compared with clinical field strength scans. Cranial nerves III, IV, and VI were also better detected at 7 T compared with only 1.5 T, and CN III was better visualized at 7 T compared with 3 T MRI. The ophthalmic arteries and posterior communicating arteries (PCOM) were better detected at 7 T compared with clinical field strength imaging. The 7 T also provided better visualization of the ophthalmic arteries compared with 1.5 T scans. Conclusion  This study demonstrates that 7 T MRI is feasible at the skull base and identifies various CNs and branches of the internal carotid artery that were better visualized at 7 T. The 7 T MRI may offer important preoperative information that can help to guide resection of pituitary adenoma and reduce operative morbidity.

3 versus 7 Tesla magnetic resonance imaging for parcellations of subcortical brain structures in clinical settings

7 Tesla (7T) magnetic resonance imaging holds great promise for improved visualization of the human brain for clinical purposes. To assess whether 7T is superior regarding localization procedures of small brain structures, we compared manual parcellations of the red nucleus, subthalamic nucleus, substantia nigra, globus pallidus interna and externa. These parcellations were created on a commonly used clinical anisotropic clinical 3T with an optimized isotropic (o)3T and standard 7T scan. The clinical 3T MRI scans did not allow delineation of an anatomically plausible structure due to its limited spatial resolution. o3T and 7T parcellations were directly compared. We found that 7T outperformed the o3T MRI as reflected by higher Dice scores, which were used as a measurement of interrater agreement for manual parcellations on quantitative susceptibility maps. This increase in agreement was associated with higher contrast to noise ratios for smaller structures, but not for the larger globus pallidus segments. Additionally, control-analyses were performed to account for potential biases in manual parcellations by assessing semi-automatic parcellations. These results showed a higher consistency for structure volumes for 7T compared to optimized 3T which illustrates the importance of the use of isotropic voxels for 3D visualization of the surgical target area. Together these results indicate that 7T outperforms c3T as well as o3T given the constraints of a clinical setting.

Developmental venous anomalies in patients with multiple sclerosis: is that a coincidence or an ancillary finding?

PURPOSE

Developmental venous anomalies (DVAs) have been found to be more prevalent in patients with multiple sclerosis (MS). The aim of the study was to compare the prevalence of DVAs in a large population of patients with MS compared with controls and to investigate the correlation of 3D Fluid Attenuated Inversion Recovery (FLAIR) hyperintense signal abnormalities adjacent to DVAs between MS patients and controls having DVAs, as well as DVA potential role in differential diagnosis.

METHODS

Between January 2001 and December 2019, 349 patients who met the McDonald criteria for MS diagnosis (249 females, 100 males, age range 18-70 years) were retrospectively included in the study. All patients and 340 age-matched healthy controls had brain MRIs performed on a 1.5 Tesla MR system. Two radiologists reviewed all images to identify DVAs; their presence was compared between the MS and control groups. Among the subjects having DVAs, age, gender, adjacent FLAIR anomalies, and DVA location were compared between the two groups.

RESULTS

Fifty (14.3%) out 349 patients presented 51 DVAs (35 supratentorial and 16 infratentorial), in comparison to 21/340 (6.2%) controls (P = 0.0005). One patient showed 2 simultaneous DVAs, while 3 patients had coexisting pontine capillary telangiectasias. FLAIR white matter changes adjacent to DVAs were found in 46.2% of patients and in 28.1% of controls (P = 0.0001).

CONCLUSIONS

DVAs demonstrated a higher prevalence in the MS group in comparison to controls. We confirmed the association between DVAs and FLAIR anomalies in MS patients. However, currently there are no evidences that the presence of DVAs may be used in MS differential diagnosis.

A clinically feasible 7-Tesla protocol for the identification of cortical lesions in Multiple Sclerosis

OBJECTIVES

The aim of this study was to evaluate the capability of sequences acquired on a 7-T MRI scanner, within times and anatomical coverage appropriate for clinical studies, to identify cortical lesions (CLs) in patients with Multiple Sclerosis (MS). Furthermore, we aimed to confirm the clinical significance of CL, testing the correlations between gray matter (GM) lesions and clinical scores.

METHODS

A 7-T MRI protocol included 3D-T1-weighted and T2*-weighted sequences. Images were evaluated independently by three readers of different experience, and the number of CLs was recorded. Between-rater concordance was assessed calculating the intraclass correlation coefficient (ICC). Lin's concordance correlation coefficient was used to compare CL detection between sequences, while partial correlations and multivariable regression models were used to study the relationship between CL and clinical data.

RESULTS

Forty MS patients (M/F, 17/23; 44.7 ± 12.6 years) were enrolled in this study, and CLs were identified in 35/40 subjects (87.5%). CL detection rate on 3D-T1-weighted images was significantly correlated with the detection rate on T2*-weighted images (r = 0.99; p < 0.001), with high concordance between readers (ICC ≥ 0.995). CLs were significantly correlated with both motor and cognitive scores (all with p ≤ 0.04).

CONCLUSIONS

CL can be identified over the whole brain at 7-T in MS using a 3D-T1-weighted volume, acquired in a clinically feasible time and with comparable performance to that achievable using the T2*-weighted sequence. Based on the central role of CL in the development of clinical disability, we suggest that 3D-T1-weighted volume may play a role in the evaluation of CL in MS undergoing MRI on ultra-high-field scanners.

KEY POINTS

• Cortical lesions can be identified in a clinically feasible time with a 7-T protocol, which includes a 3D-T1-weighted volume. • Cortical lesions correlated significantly with both motor and cognitive disability in MS patients. • Given their correlation with clinical disability, evaluation of a cortical lesion on a 7-T clinical protocol could help in the management of MS patients.

Anxiety during magnetic resonance imaging of the spine in relation to scanner design and size

INTRODUCTION

Magnetic resonance imaging in closed-bore scanners sometimes provokes anxiety but closed-bore designs have gradually become wider and shorter. Open scanners may be easier to tolerate. The aim was to compare patient anxiety during MRI between bore diameters of 60 cm and 70 cm, and to determine the current level of patient anxiety and experience in open scanners in a clinical setrting.

METHODS

Consecutive patients referred for examination of the spine in 60 cm and 70 cm bores and one open scanner participated. Four established/validated questionnaires, answered before, directly after (N = 155) and one week after (N = 109) the MRI-examination were used, measuring anxiety, fear and depression.

RESULTS

No difference was found in the patient scores of anxiety between the 60 cm and the 70 cm scanners on the examination day. At follow-up, patients in the 70 cm bore rated their examination experience better (p < 0.025), compared to patients in the 60 cm bore. Patients in the open scanner rated higher levels of anxiety (p < 0.001) before, directly after and one week after the examination, compared to the closed bore scanners.

CONCLUSION

Scanners with a 70 cm diameter bore seem more tolerable than those with a 60 cm bore. Patients referred to the open scanner had on average a higher tendency to express anxiety. Still, patient anxiety in MRI is challenging and further research required.

IMPLICATIONS FOR PRACTICE

Patients prefer to be examined in 70 cm bore scanners compared with 60 cm. If open scanners aren't available extended support may be necessary for the most anxious patients.

The Central Vein Sign in Radiologically Isolated Syndrome

BACKGROUND AND PURPOSE

Radiologically isolated syndrome describes asymptomatic individuals with incidental radiologic abnormalities suggestive of multiple sclerosis. Recent studies have demonstrated that >40% of white matter lesions in MS (and often substantially more) have visible central veins on MR imaging. This "central vein sign" reflects perivenous inflammatory demyelination and can assist in differentiating MS from other white matter disorders. We therefore hypothesized that >40% of white matter lesions in cases of radiologically isolated syndrome would show the central vein sign.

MATERIALS AND METHODS

We recruited 20 participants diagnosed with radiologically isolated syndrome after evaluation by a neurologist. We performed 3T MR imaging of the brain and cervical spinal cord. White matter lesions were analyzed for the central vein sign.

RESULTS

Of 391 total white matter lesions, 292 (75%) demonstrated the central vein sign (central vein sign+). The median proportion of central vein sign+ lesions per case was 87% (range, 29%-100%). When the "40% rule" that has been proposed to distinguish MS from other disorders was applied, of 20 participants, 18 cases of radiologically isolated syndrome (90%) had ≥40% central vein sign+ lesions (range, 55%-100%). Two participants (10%) had <40% central vein sign+ lesions (29% and 31%). When the simpler "rule of 6" was applied, 19 participants (95%) met these criteria. In multivariable models, the number of spinal cord and infratentorial lesions was associated with a higher proportion of central vein sign+ lesions (P = .002; P = .06, respectively).

CONCLUSIONS

Most cases of radiologically isolated syndrome had a high proportion of central vein sign+ lesions, suggesting that lesions in these individuals reflect perivenous inflammatory demyelination. Moreover, we found correlations between the proportion of central vein sign+ lesions and spinal cord lesions, a known risk factor for radiologically isolated syndrome progressing to MS. These findings raise the possibility, testable prospectively, that the central vein sign may have prognostic value in distinguishing patients with radiologically isolated syndrome at risk of developing clinical MS from those with white matter lesions of other etiologies.