Lesion detection at seven Tesla in multiple sclerosis using magnetisation prepared 3D-FLAIR and 3D-DIR

Ultra-high-field MR imaging in multiple sclerosis

In multiple sclerosis (MS), MRI is the most important paraclinical tool used to inform diagnosis and for monitoring disease evolution, either natural or modified by treatment. The increased availability of ultra-high-field magnets (7 Tesla or higher) gives rise to questions about the main benefits of and challenges for their use in patients with MS. The main advantages of ultra-high-field MRI are the improved signal-to-noise ratio, greater chemical shift dispersion, and improved contrast due to magnetic susceptibility variations, which lead to increased sensitivity to the heterogeneous pathological substrates of the disease. At present, ultra-high-field MRI is mainly used to improve our understanding of MS pathogenesis. This review discusses the main achievements that have so far come from the use of these scanners, which are: better visualisation of white matter lesions and their morphological characteristics; an improvement in the ability to visualise grey matter lesions and their exact location; the quantification of 'novel' metabolites which may have a role in axonal degeneration; and greater sensitivity to iron accumulation. The application of ultra-high-field systems in standard clinical practice is still some way off since their role in the diagnostic work-up of patients at presentation with clinically isolated syndromes, or in monitoring disease progression or treatment response in patients with definite MS, needs to be established. Additional challenges remain in the development of morphological, quantitative and functional imaging methods at these field strengths, techniques which may ultimately lead to novel biomarkers for monitoring disease evolution and treatment response.

Neuroradiological evaluation of demyelinating disease

Central nervous system inflammatory demyelinating disease can affect patients across the life span. Consensus definitions and criteria of all of the different acquired demyelinating diseases that fall on this spectrum have magnetic resonance imaging criteria. The advances of both neuroimaging techniques and important discoveries in immunology have produced an improved understanding of these conditions and classification. Neuroimaging plays a central role in the accurate diagnosis, prognosis, disease monitoring and research efforts that are being undertaken in this disease. This review focuses on the imaging spectrum of acquired demyelinating disease.

Recommendations to improve imaging and analysis of brain lesion load and atrophy in longitudinal studies of multiple sclerosis

Focal lesions and brain atrophy are the most extensively studied aspects of multiple sclerosis (MS), but the image acquisition and analysis techniques used can be further improved, especially those for studying within-patient changes of lesion load and atrophy longitudinally. Improved accuracy and sensitivity will reduce the numbers of patients required to detect a given treatment effect in a trial, and ultimately, will allow reliable characterization of individual patients for personalized treatment. Based on open issues in the field of MS research, and the current state of the art in magnetic resonance image analysis methods for assessing brain lesion load and atrophy, this paper makes recommendations to improve these measures for longitudinal studies of MS. Briefly, they are (1) images should be acquired using 3D pulse sequences, with near-isotropic spatial resolution and multiple image contrasts to allow more comprehensive analyses of lesion load and atrophy, across timepoints. Image artifacts need special attention given their effects on image analysis results. (2) Automated image segmentation methods integrating the assessment of lesion load and atrophy are desirable. (3) A standard dataset with benchmark results should be set up to facilitate development, calibration, and objective evaluation of image analysis methods for MS.

Quantitative magnetic resonance imaging of cortical multiple sclerosis pathology

Although significant improvements have been made regarding the visualization and characterization of cortical multiple sclerosis (MS) lesions using magnetic resonance imaging (MRI), cortical lesions (CL) continue to be under-detected in vivo, and we have a limited understanding of the causes of GM pathology. The objective of this study was to characterize the MRI signature of CLs to help interpret the changes seen in vivo and elucidate the factors limiting their visualization. A quantitative 3D high-resolution (350 μm isotropic) MRI study at 3 Tesla of a fixed post mortem cerebral hemisphere from a patient with MS is presented in combination with matched immunohistochemistry. Type III subpial lesions are characterized by an increase in T1, T2 and M0, and a decrease in MTR in comparison to the normal appearing cortex (NAC). All quantitative MR parameters were associated with cortical GM myelin content, while T1 showed the strongest correlation. The histogram analysis showed extensive overlap between CL and NAC for all MR parameters and myelin content. This is due to the poor contrast in myelin content between CL and NAC in comparison to the variability in myelo-architecture throughout the healthy cortex. This latter comparison is highlighted by the representation of T1 times on cortical surfaces at several laminar depths.

Multicontrast MR imaging at 7T in multiple sclerosis: highest lesion detection in cortical gray matter with 3D-FLAIR

BACKGROUND AND PURPOSE

7T MR imaging has led to improved detection and classification of cortical MS lesions, mainly based on T2*-weighted gradient-echo sequences. Depiction of cortical GM by using the recommended MS imaging protocol has not yet been investigated at 7T. We aimed to investigate prospectively which recommended sequence for clinical use has the highest value at 7T, in terms of GM and WM lesion detection.

MATERIALS AND METHODS

Thirty-seven patients with MS (mean age, 43.8 years; 25 women) and 7 healthy controls (mean age, 40.4 years; 5 women) underwent multicontrast 7T MR imaging including the recommended clinical 2D-T2WI, 3D-T1WI, 3D-FLAIR, and GM-specific 3D-DIR. Lesions were scored and categorized anatomically by 3 raters, in consensus. The value of sequences was evaluated lesion-wise and patient-wise (Wilcoxon signed-rank test).

RESULTS

At 7T, 3D-FLAIR detected the highest number of total cortical GM lesions (217), 89% more than 3D-DIR and 87% and 224% more than 2D-T2WI and 3D-T1WI. Patient-wise analysis showed that this difference between 3D-FLAIR and 3D-DIR was statistically significant (P<.04), and most pronounced for the number of mixed lesions (P<.03). 3D-FLAIR also detected the highest number of total WM lesions (2605), but the difference with 3D-DIR and 3D-T1WI was not significant.

CONCLUSIONS

When using recommended clinical sequences at 7T, the best way to detect cortical GM lesions is with 3D-FLAIR and not by GM-specific 3D-DIR or by conventional 2D-T2WI and 3D-T1WI sequences.

Cerebral vein changes in relapsing-remitting multiple sclerosis demonstrated by three-dimensional enhanced T₂-weighted angiography at 3.0 T

OBJECTIVE

To investigate characteristics of the internal cerebral veins (ICVs) and their main tributaries and the deep medullary veins (DMVs) in patients with relapsing-remitting MS (RRMS) with enhanced T (2)-weighted angiography imaging (ESWAN).

METHODS

Fifty-three RRMS patients and 53 normal controls underwent conventional MRI and ESWAN. ESWAN venograms were created by performing minimum intensity projections of the phase images, and the resulting venograms were used to observe characteristic vascular changes, including scores of the ICVs and their main tributaries and manifestations of the DMVs. Two experienced radiologists analysed all data.

RESULTS

Patients showed decreased mean scores of the ICVs and their main tributaries compared with controls. The mean score in acute patients was higher than in stable patients. Furthermore, the DMVs diminished and shortened in 48 patients with longer disease duration, whereas the DMVs increased and elongated in 5 patients with shorter disease duration. The penetrating veins were well defined in 30 active lesions, whereas the veins were ill defined in 69 non-active lesions. Interestingly, well-defined penetrating veins were shown in 15 non-active lesions in the stable patients.

CONCLUSIONS

Enhanced T (2)-weighted MR angiography can detect cerebral vein characteristics in relapsing-remitting MS patients, which may provide important information on the pathogenesis of MS.

Clinical application of multi-contrast 7-T MR imaging in multiple sclerosis: increased lesion detection compared to 3 T confined to grey matter

OBJECTIVES

Seven-Tesla MRI demonstrated new pathological features of multiple sclerosis (MS) using T2-weighted sequences. However, a clinical MRI protocol at 7 T has never been investigated. We evaluated the clinical value of 7-T MRI by investigating the sensitivity of lesion detection compared with 3 T.

METHODS

Thirty-eight MS patients and eight healthy controls underwent multi-contrast MRI using 3D T1-weighted (3D-T1w), 2D dual-echo T2-weighted (2D-T2w) and 3D fluid-attenuated inversion recovery (3D-FLAIR) at 3 and 7 T. Images were analysed for focal lesions, which were counted and categorised according to anatomical location. The study was approved by the institutional review board.

RESULTS

Lesion-wise analysis showed increased lesion counts in cortical grey matter (GM) at 7 T of 91, 75 and 238 % for 3D-T1w, 2D-T2w and FLAIR sequences, respectively. Patient-wise analysis confirmed this for 2D-T2w and FLAIR (P < 0.023 and P < 0.001). Seven-Tesla white matter (WM) lesion detection was not increased; 3D-FLAIR even detected significantly more WM lesions at 3 T.

CONCLUSIONS

Using a clinical multi-contrast MRI protocol, increased lesion detection was observed in cortical GM but not in WM. Given the clinical relevance of GM abnormalities, this may have consequences for clinical outcome measures, prognostic classification and future diagnostic criteria incorporating GM abnormalities.

Ultrahigh-field MRI in human ischemic stroke--a 7 tesla study

Introduction

Magnetic resonance imaging (MRI) using field strengths up to 3 Tesla (T) has proven to be a powerful tool for stroke diagnosis. Recently, ultrahigh-field (UHF) MRI at 7 T has shown relevant diagnostic benefits in imaging of neurological diseases, but its value for stroke imaging has not been investigated yet. We present the first evaluation of a clinically feasible stroke imaging protocol at 7 T. For comparison an established stroke imaging protocol was applied at 3 T.

Methods

In a prospective imaging study seven patients with subacute and chronic stroke were included. Imaging at 3 T was immediately followed by 7 T imaging. Both protocols included T1-weighted 3D Magnetization-Prepared Rapid-Acquired Gradient-Echo (3D-MPRAGE), T2-weighted 2D Fluid Attenuated Inversion Recovery (2D-FLAIR), T2-weighted 2D Fluid Attenuated Inversion Recovery (2D-T2-TSE), T2* weighted 2D Fast Low Angle Shot Gradient Echo (2D-HemoFLASH) and 3D Time-of-Flight angiography (3D-TOF).

Results

The diagnostic information relevant for clinical stroke imaging obtained at 3 T was equally available at 7 T. Higher spatial resolution at 7 T revealed more anatomical details precisely depicting ischemic lesions and periinfarct alterations. A clear benefit in anatomical resolution was also demonstrated for vessel imaging at 7 T. RF power deposition constraints induced scan time prolongation and reduced brain coverage for 2D-FLAIR, 2D-T2-TSE and 3D-TOF at 7 T versus 3 T.

Conclusions

The potential of 7 T MRI for human stroke imaging is shown. Our pilot study encourages a further evaluation of the diagnostic benefit of stroke imaging at 7 T in a larger study.

High-field imaging of neurodegenerative diseases

High-field magnetic resonance (MR) imaging is showing potential for imaging of neurodegenerative diseases. 7 T MR imaging is beginning to be used in a clinical research setting and the theoretical benefits of higher signal-to-noise ratio, sensitivity to iron, improved MR angiography, and increased spectral resolution in spectroscopy are being confirmed. Despite the limited number of studies to date, initial results in patients with multiple sclerosis, Alzheimer disease, and Huntington disease show promising additional features in contrast that may help the diagnosis of these disorders.

Inflammation high-field magnetic resonance imaging

Multiple sclerosis (MS) is the most common inflammatory demyelinating disorder of the central nervous system (CNS). MS has been subject to high-field magnetic resonance (MR) imaging research to a great extent during the past years, and much data has been collected that might be helpful in the investigation of other inflammatory CNS disorders. This article reviews the value of high-field MR imaging in examining inflammatory MS abnormalities. Furthermore, possibilities and challenges for the future of high-field MR imaging in MS are discussed.

High field MRI in clinical practice

Magnetic resonance imaging and spectroscopy can provide detailed morphologic, functional and metabolic information that may provide unique biomarkers to assist drug discovery and development. To overcome the inherent low signal to noise of in vivo magnetic resonance applications, stronger magnetic field strengths can be applied that not only boost signal strengths, but can also be used to improve contrast and specificity as well.: