Clinical applications of 7T MRI in the brain

AbstractThis review illustrates current applications and possible future directions of 7Tesla (7T) Magnetic Resonance Imaging (MRI) in the field of brain MRI, in clinical studies as well as clinical practice. With its higher signal-to-noise (SNR) and contrast-to-noise ratio (CNR) compared to lower field strengths, high resolution, contrast-rich images can be obtained of diverse pathologies, like multiple sclerosis (MS), brain tumours, aging-related changes and cerebrovascular diseases. In some of these diseases, additional pathophysiological information can be gained compared to lower field strengths. Because of clear depiction of small anatomical details, and higher lesion conspicuousness, earlier diagnosis and start of treatment of brain diseases may become possible. Furthermore, additional insight into the pathogenesis of brain diseases obtained with 7T MRI could be the basis for new treatment developments. However, imaging at high field comes with several limitations, like inhomogeneous transmit fields, a higher specific absorption rate (SAR) and, currently, extensive contraindications for patient scanning. Future studies will be aimed at assessing the advantages and disadvantages of 7T MRI over lower field strengths in light of clinical applications, specifically the additional diagnostic and prognostic value of 7T MRI

7 T renal MRI: challenges and promises

The progression to 7 Tesla (7 T) magnetic resonance imaging (MRI) yields promises of substantial increase in signal-to-noise (SNR) ratio. This increase can be traded off to increase image spatial resolution or to decrease acquisition time. However, renal 7 T MRI remains challenging due to inhomogeneity of the radiofrequency field and due to specific absorption rate (SAR) constraints. A number of studies has been published in the field of renal 7 T imaging. While the focus initially was on anatomic imaging and renal MR angiography, later studies have explored renal functional imaging. Although anatomic imaging remains somewhat limited by inhomogeneous excitation and SAR constraints, functional imaging results are promising. The increased SNR at 7 T has been particularly advantageous for blood oxygen level-dependent and arterial spin labelling MRI, as well as sodium MR imaging, thanks to changes in field-strength-dependent magnetic properties. Here, we provide an overview of the currently available literature on renal 7 T MRI. In addition, we provide a brief overview of challenges and opportunities in renal 7 T MR imaging

FLAIR images at 7 Tesla MRI highlight the ependyma and the outer layers of the cerebral cortex.

Objectives: Fluid-attenuated inversion recovery (FLAIR) imaging is an important clinical ‘work horse’ for brain MRI and has proven to facilitate imaging of both intracortical lesions as well as cortical layers at 7 T MRI. A prominent observation on 7 T FLAIR images is a hyperintense rim at the cortical surface and around the ventricles.We aimed to clarify the anatomical correlates and underlying contrast mechanisms of this hyperintense rim. Materials and Methods: Two experiments with post-mortem human brain tissue were performed. FLAIR and T2-weighted imageswere obtained at typical in vivo (0.8mmisotropic) and high resolution (0.25mmisotropic). At one location the cortical surfacewas partly removed, and scanned again. Imagingwas followed by histological and immunohistochemical analysis. Additionally, several simulations were performed to evaluate the potential contribution from an artifact due to water diffusion. Results: The hyperintense rim corresponded to the outer – glia rich – layer of the cortex and disappeared upon removal of that layer. At the ventricles, the rim corresponded to the ependymal layer, and was not present at white matter/fluid borders at an artificial cut. The simulations supported the hypothesis that the hyperintense rim reflects the tissue properties in the outer cortical layers (or ependymal layer for the ventricles), and is not merely an artifact, although not all observations were explained by the simulated model of the contrast mechanism. Conclusions: 7 T FLAIR seems to amplify the signal from layers I–III of the cortex and the ependyma around the ventricles. Although diffusion of water from layer I into CSF does contribute to this effect, a long T2 relaxation time constant in layer I, and probably also layer II–III, is most likely themajor contributor, since the rimdisappears upon removal of that layer. This knowledge can help the interpretation of imaging results in cortical development and in patients with cortical pathology

3D black blood VISTA vessel wall cardiovascular magnetic resonance of the thoracic aorta wall in young, healthy adults: reproducibility and implications for efficacy trial sample sizes: a cross-sectional study

Background: Pre-clinical detection of atherosclerosis enables personalized preventive strategies in asymptomatic individuals. Cardiovascular magnetic resonance (CMR) has evolved as an attractive imaging modality for studying atherosclerosis in vivo. Yet, the majority of aortic CMR studies and proposed sequences to date have been performed at 1.5 tesla using 2D BB techniques and a slice thickness of 4-5 mm. Here, we evaluate for the first time the reproducibility of an isotropic, T1-weighted, three-dimensional, black-blood, CMR VISTA sequence (3D-T1-BB-VISTA) for quantification of aortic wall characteristics in healthy, young adults. Methods: In 20 healthy, young adults (10 males, mean age 31.3 years) of the AMBITYON cohort study the descending thoracic aorta was imaged with a 3.0 T MR system using the 3D-T1-BB-VISTA sequence. The inter-scan, inter-rater and intra-rater reproducibility of aortic lumen, total vessel and wall area and mean and maximum wall thickness was evaluated using Bland-Altman analyses and Intraclass Correlation Coefficients (ICC). Based on these findings, sample sizes for detecting differences in aortic wall characteristics between groups were calculated. Results: For each studied parameter, the inter-scan, inter-rater and intra-rater reproducibility was excellent as indicated by narrow limits of agreement and high ICCs (ranging from 0.76 to 0.99). Sample sizes required to detect a 5 % difference in aortic wall characteristics between two groups were 203, 126, 136, 68 and 153 per group for lumen area, total vessel area and vessel wall area and for mean and maximum vessel wall thickness, respectively. Conclusion: The 3D-T1-BB-VISTA sequence provides excellent reproducibility for quantification of aortic wall characteristics and can detect small differences between groups with reasonable sample sizes. Hence, it may be a valuable tool for assessment of the subtle vascular wall changes of early atherosclerosis in asymptomatic populations

No evidence of microbleeds in ALS patients at 7 Tesla MRI

There have been several reports about disruption of the blood-spinal cord barrier (BSCB) and blood-brain barrier (BBB) in SOD1 mutant mice. Pathologically, microbleeds and hemosiderine deposits were found. We investigated patients with ALS for the occurrence of cerebral microbleeds with 7 Tesla MRI. Twelve patients with ALS and 12 age- and sex-matched healthy controls were studied. We performed T2*-weighed imaging which enables whole-brain in vivo detection of cerebral microbleeds and hemosiderin deposits in humans. No microbleeds were found in patients with ALS

Distribution and natural course of intracranial vessel wall lesions in patients with ischemic stroke or TIA at 7.0 tesla MRI

Objectives: Previous studies using intracranial vessel wall MRI techniques showed that over 50 % of patients with ischemic stroke or TIA had one or more intracranial vessel wall lesions. In the current study, we assessed the preferential location of these lesions within the intracranial arterial tree and their potential changes over time in these patient groups. Methods: Forty-nine patients with ischemic stroke (n = 25) or TIA (n = 24) of the anterior cerebral circulation underwent 7.0 T MRI, including a T1-weighted magnetization-preparation inversion recovery turbo-spin-echo (MPIR-TSE) sequence within one week and approximately one month after symptom onset. Intracranial vessel wall lesions were scored for multiple locations within the arterial tree and differences between one-week and one-month images. Results: At baseline, 132 intracranial vessel wall lesions were found in 41 patients (84 %), located primarily in the anterior cerebral circulation (74 %), with a preferential location in the distal internal carotid artery and M1 and M2 segments of the middle cerebral artery. During follow-up, presence or enhancement patterns changed in 14 lesions (17 %). Conclusions: A large burden of intracranial vessel wall lesions was found in both the anterior and posterior cerebral circulation. Most lesions were found to be relatively stable, possibly indicating a more generalized atherosclerotic process. Key points: • Intracranial vessel wall lesions are present in patients with varying cerebrovascular diseases. • Intracranial vessel wall 7.0 T MRI provides information on preferential location and natural course. • Distal ICA and M1 and M2 segments of MCA are predilection sites. • 83 % of lesions found remained stable, possibly indicating more generalized atherosclerosis

Myelin contrast across lamina at 7T, ex-vivo and in-vivo dataset

In this article we report the complete data obtained in-vivo for the paper: "Lines of Baillarger in vivo and ex-vivo: myelin contrast across lamina at 7T MRI and histology" (Fracasso et al., 2015) [1]. Single participant data (4 participants) from the occipital lobe acquisition are reported for axial, coronal and sagittal slices; early visual area functional localization and laminar profiles are reported. Data from whole brain images are reported and described (5 participants), for axial, coronal and sagittal slices. Laminar profiles from occipital, parietal and frontal lobes are reported. The data reported in this manuscript complements the paper (Fracasso et al., 2015) [1] by providing the full set of results from the complete pool of participants, on a single-participant basis. Moreover, we provide histological images from the ex-vivo sample reported in Fracasso et al. (2015) [1]