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Highlights • Multi-shell diffusion MRI is more sensitive than DTI to multiple sclerosis neurodegeneration under clinical settings. • Multi-shell diffusion MRI at high and ultra-high fields is a viable option for imaging tissue changes in multiple sclerosis. • Higher b -values are not beneficial for multiple sclerosis under the tested short-time (10 min acquisition) conditions. Abstract The recent introduction of advanced magnetic resonance (MR) imaging techniques to characterize focal and global degeneration in multiple sclerosis (MS), like the Composite Hindered and Restricted Model of Diffusion, or CHARMED, diffusional kurtosis imaging (DKI) and Neurite Orientation Dispersion and Density Imaging (NODDI) made available new tools to image axonal pathology non-invasively in vivo. These methods already showed greater sensitivity and specificity compared to conventional diffusion tensor-based metrics (e.g., fractional anisotropy), overcoming some of its limitations. While previous studies uncovered global and focal axonal degeneration in MS patients compared to healthy controls, here our aim is to investigate and compare different diffusion MRI acquisition protocols in their ability to highlight microstructural differences between MS and control tissue over several much used models. For comparison, we contrasted the ability of fractional anisotropy measurements to uncover differences between lesion, normal-appearing white matter (WM), gray matter and healthy tissue under the same imaging protocols. We show that: (1) focal and diffuse differences in several microstructural parameters are observed under clinical settings; (2) advanced models (CHARMED, DKI and NODDI) have increased specificity and sensitivity to neurodegeneration when compared to fractional anisotropy measurements; and (3) both high (3 T) and ultra-high fields (7 T) are viable options for imaging tissue change in MS lesions and normal appearing WM, while higher b -values are less beneficial under the tested short-time (10 min acquisition) conditions. [ABSTRACT FROM AUTHOR]

Abstract Perfusion magnetic resonance imaging (MRI) is a promising non-invasive technique providing insights regarding the brain's microvascular architecture in vivo. The scalar perfusion metrics can be used for quantitative diagnostics of various brain abnormalities, in particular, in the stroke cases and tumours. However, conventional MRI-based perfusion approaches such as dynamic contrast-enhanced perfusion imaging or arterial spin labelling have a few weaknesses, for instance, contrast agent deposition, low signal-to-noise ratio, limited temporal and spatial resolution, and specific absorption rate constraints. As an alternative, the intravoxel incoherent motion (IVIM) approach exploits an extension of diffusion MRI in order to estimate perfusion parameters in the human brain. Application of IVIM imaging at ultra-high field MRI might employ the advantage of a higher signal-to-noise ratio, and thereby the use of higher spatial and temporal resolutions. In the present work, we demonstrate an application of recently developed isotropic diffusion weighted sequences to the evaluation of IVIM parameters at an ultra-high 7T field. The used sequence exhibits high immunity to image degrading factors and allows one to acquire the data in a fast and efficient way. Utilising the bi-exponential fitting model of the signal attenuation, we performed an extensive analysis of the IVIM scalar metrics obtained by a isotropic diffusion weighted sequence in vivo and compared results with a conventional pulsed gradient sequence at 7T. In order to evaluate a possible metric bias originating from blood flows, we additionally used a truncated b-value protocol (b-values from 100 to 200 s/mm2 with the step 20 s/mm2) accompanied to the full range (b-values from 0 to 200 s/mm2). The IVIM scalar metrics have been assessed and analysed together with a large and middle vessel density atlas of the human brain. We found that the diffusion coefficients and perfusion fractions of the voxels consisting of large and middle vessels have higher values in contrast to other tissues. Additionally, we did not find a strong dependence of the IVIM metrics on the density values of the vessel atlas. Perspectives and limitations of the developed isotropic diffusion weighted perfusion are presented and discussed. [ABSTRACT FROM AUTHOR]

Purpose: The quality and precision of post‐mortem MRI microscopy may vary depending on the embedding medium used. To investigate this, our study evaluated the impact of 5 widely used media on: (1) image quality, (2) contrast of high spatial resolution gradient‐echo (T1 and T2*‐weighted) MR images, (3) effective transverse relaxation rate (R2*), and (4) quantitative susceptibility measurements (QSM) of post‐mortem brain specimens. Methods: Five formaldehyde‐fixed brain slices were scanned using 7.0T MRI in: (1) formaldehyde solution (formalin), (2) phosphate‐buffered saline (PBS), (3) deuterium oxide (D2O), (4) perfluoropolyether (Galden), and (5) agarose gel. SNR and contrast‐to‐noise ratii (SNR/CNR) were calculated for cortex/white matter (WM) and basal ganglia/WM regions. In addition, median R2* and QSM values were extracted from caudate nucleus, putamen, globus pallidus, WM, and cortical regions. Results: PBS, Galden, and agarose returned higher SNR/CNR compared to formalin and D2O. Formalin fixation, and its use as embedding medium for scanning, increased tissue R2*. Imaging with agarose, D2O, and Galden returned lower R2* values than PBS (and formalin). No major QSM offsets were observed, although spatial variance was increased (with respect to R2* behaviors) for formalin and agarose. Conclusions: Embedding media affect gradient‐echo image quality, R2*, and QSM in differing ways. In this study, PBS embedding was identified as the most stable experimental setup, although by a small margin. Agarose and Galden were preferred to formalin or D2O embedding. Formalin significantly increased R2* causing noisier data and increased QSM variance. [ABSTRACT FROM AUTHOR]

Various approaches to designing unconventional antenna‐based RF probes for obtaining homogeneous 600 MHz B1 magnetic field in 14 T MRI scanners are investigated. Proposed solutions include microstrip patch antennas with engineered multidielectric substrates, acting as surface coils, and systems of vis‐à‐vis placed patch antennas to be used as volume coils with essentially increased Q‐factors compared to those of birdcage coils. Various options of controlling magnetic near fields in antenna systems with flat, cylindrical and cosine‐shaped substrates, as well as with tapered patch electrodes, are demonstrated. Problems of fabricating unconventional microstrip patch antennas for MRI applications are also addressed. [ABSTRACT FROM AUTHOR]

Purpose Most approaches for quantitative susceptibility mapping (QSM) are based on a forward model approximation that employs a continuous Fourier transform operator to solve a differential equation system. Such formulation, however, is prone to high-frequency aliasing. The aim of this study was to reduce such errors using an alternative dipole kernel formulation based on the discrete Fourier transform and discrete operators. Methods The impact of such an approach on forward model calculation and susceptibility inversion was evaluated in contrast to the continuous formulation both with synthetic phantoms and in vivo MRI data. Results The discrete kernel demonstrated systematically better fits to analytic field solutions, and showed less over-oscillations and aliasing artifacts while preserving low- and medium-frequency responses relative to those obtained with the continuous kernel. In the context of QSM estimation, the use of the proposed discrete kernel resulted in error reduction and increased sharpness. Conclusion This proof-of-concept study demonstrated that discretizing the dipole kernel is advantageous for QSM. The impact on small or narrow structures such as the venous vasculature might by particularly relevant to high-resolution QSM applications with ultra-high field MRI – a topic for future investigations. The proposed dipole kernel has a straightforward implementation to existing QSM routines. [ABSTRACT FROM AUTHOR]

Purpose: In this work, a combined body coil array with eight transmit/receive (Tx/Rx) meander elements and with 24 receive‐only (Rx) loops (8Tx/32Rx) was developed and evaluated in comparison with an 8‐channel transmit/receive body array (8Tx/Rx) based on meander elements serving as the reference standard. Methods: Systematic evaluation of the RF array was performed on a body‐sized phantom. Body imaging at 7T was performed in six volunteers in the body regions pelvis, abdomen, and heart. Coil characteristics such as signal‐to‐noise ratio, acceleration capability, g‐factors, S‐parameters, noise correlation, and B1+ maps were assessed. Safety was ensured by numerical simulations using a coil model validated by dosimetric field measurements. Results: Meander elements and loops are intrinsically well decoupled with a maximum coupling value of −20.5 dB. Safe use of the 8Tx/32Rx array could be demonstrated. High gain in signal‐to‐noise ratio (33% in the subject's center) could be shown for the 8Tx/32Rx array compared to the 8Tx/Rx array. Improvement in acceleration capability in all investigations could be demonstrated. For example, the 8Tx/32Rx array provides lower g‐factors in the right–left and anterior–posterior directions with R = 3 undersampling as compared to the 8Tx/Rx array using R = 2. Both arrays are very similar regarding their RF transmit performance. Excellent image quality in the investigated body regions could be achieved with the 8Tx/32Rx array. Conclusion: In this work, we show that a combination of eight meander elements and 24 loop receive elements is possible without impeding transmit performance. Improved SNR and g‐factor performance compared to an RF array without these loops is demonstrated. Body MRI at 7T with the 8Tx/32Rx array could be accomplished in the heart, abdomen, and pelvis with excellent image quality. [ABSTRACT FROM AUTHOR]

Purpose: To implement and validate low-loss ratio-adjustable power splitters (RAPS) for array-compressed parallel transmission (acpTx). Methods: In acpTx, a small number of transmit channels drive a larger number of transmit coils, which are connected via an array compression network that implements optimized coil-tochannel combinations. Previous networks comprised a bank of power splitters, followed by attenuators to implement the amplitudes of the compression weights for each coil, but this resulted in high power dissipation in the network. Recognizing that an acpTx network need only implement relative attenuations between outputs, a RAPS circuit was developed which combines power splitting and relative attenuation, and has low insertion loss. RAPS circuits were experimentally validated and used to build an array compression network for a one-channel- to-four-coil spiral acpTx excitation experiment. Results: Bench tests showed that the RAPS circuits came within 0.05 dB of the desired output ratios, and power dissipation was approximately 0.5 dB (10%). The spiral excitation experiment showed that the ability to optimally drive four coils with a single channel reduced excitation error by 46% compared to driving one coil, without using attenuators in the array compression network. Conclusion: RAPS circuits enable the construction of low-loss array compression networks for parallel transmission. [ABSTRACT FROM AUTHOR]

Deep brain stimulation of the subthalamic nucleus (STN) is a widely performed surgical treatment for patients with Parkinson's disease. The goal of the surgery is to place an electrode centered in the motor region of the STN while lowering the effects of electrical stimulation on the non-motor regions. However, distinguishing the motor region from the neighboring associative and limbic areas in individual patients using imaging modalities was until recently difficult to obtain in vivo . Here, using ultra-high field MR imaging, we have performed a dissection of the subdivisions of the STN of individual Parkinson's disease patients. We have acquired 7 T diffusion-weighted images of seventeen patients with Parkinson's disease scheduled for deep brain stimulation surgery. Using a structural connectivity-based parcellation protocol, the STN's connections to the motor, limbic, and associative cortical areas were used to map the individual subdivisions of the nucleus. A reproducible patient-specific parcellation of the STN into a posterolateral motor and gradually overlapping central associative area was found in all STNs, taking up on average 55.3% and 55.6% of the total nucleus volume. The limbic area was found in the anteromedial part of the nucleus. Our results suggest that 7T MR imaging may facilitate individualized and highly specific planning of deep brain stimulation surgery of the STN. [ABSTRACT FROM AUTHOR]

Introduction: Magnetic resonance imaging (MRI) is of paramount importance for the early diagnosis of multiple sclerosis (MS) and MRI findings are part of the MS diagnostic criteria. There is a growing interest in the use of ultra-high-field strength −7 Tesla- (7T) MRI to investigate,in vivo, the pathological substrate of the disease. Areas covered: An overview of 7T MRI applications in MS focusing on increased sensitivity for lesion detection, specificity of the central vein sign and better understanding of MS pathophysiology. Implications for disease diagnosis, monitoring and treatment planning are discussed. Expert commentary: 7T MRI provides increased signal-to-noise and contrast-to-noise-ratio that allow higher spatial resolution and better detection of anatomical and pathological features. The high spatial resolution reachable at 7T has been a game changer for neuroimaging applications not only in MS but also in epilepsy, brain tumors, dementia, and neuro-psychiatric disorders. Furthermore, the first 7T device has recently been cleared for clinical use by the food and drug administration. [ABSTRACT FROM PUBLISHER]

Purpose: We present the initial in vivo imaging results of an open architecture eight‐channel parallel transmission (pTx) transceive radiofrequency (RF) coil array that was designed and constructed for static and dynamic 7T MRI of the knee and ankle joints. Methods: The pTx coil has a U‐shaped dual‐row configuration (200 mm overall length longitudinally) that allows static and dynamic imaging of the knee and ankle joints at various postures and during active movements. This coil structure, in combination with B1 shimming, allows flexible configuration of B1 transmit profiles, with good homogeneity over 120‐mm regions of interest. This coil enabled high‐resolution gradient echo (e.g., 3D dual‐echo steady state [DESS] and 3D multiecho data image combination [MEDIC]) and turbo spin echo (TSE) imaging (e.g., with proton density weighting [PDw], PDw with fat saturation, and T1 and T2 weightings) with local RF energy absorption rates well below regulatory limits. Results: High‐resolution 2D and 3D image series (e.g., 0.3 mm in‐plane resolution for TSE, 0.47 mm isotropic for DESS and MEDIC) were obtained from the knee and ankle joints with excellent tissue contrast. Dynamic imaging during continuous knee and ankle flexion‐extension cycles were successfully acquired. Conclusion: The new open pTx coil array provides versatility for high‐quality static and dynamic MRI of the knee and ankle joints at 7T. Magn Reson Med 79:1804–1816, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

The hippocampus, like the neocortex, has a morphological structure that is complex and variable in its folding pattern, especially in the hippocampal head. The current study presents a computational method to unfold hippocampal grey matter, with a particular focus on the hippocampal head where complexity is highest due to medial curving of the structure and the variable presence of digitations. This unfolding was performed on segmentations from high-resolution, T2-weighted 7T MRI data from 12 healthy participants and one surgical patient with epilepsy whose resected hippocampal tissue was used for histological validation. We traced a critical image feature composed of the hippocampal sulcus and stratum radiatum lacunosum-moleculare, (SRLM) in these images, then employed user-guided semi-automated techniques to detect and subsequently unfold the surrounding hippocampal grey matter. This unfolding was performed by solving Laplace's equation in three dimensions of interest (long-axis, proximal-distal, and laminar). The resulting ‘unfolded coordinate space’ provides an intuitive way of mapping the hippocampal subfields in 2D space (long-axis and proximal-distal), such that similar borders can be applied in the head, body, and tail of the hippocampus independently of variability in folding. This unfolded coordinate space was employed to map intracortical myelin and thickness in relation to subfield borders, which revealed intracortical myelin differences that closely follow the subfield borders used here. Examination of a histological resected tissue sample from a patient with epilepsy reveals that our unfolded coordinate system has biological validity, and that subfield segmentations applied in this space are able to capture features not seen in manual tracing protocols. [ABSTRACT FROM AUTHOR]

The capacity of functional MRI (fMRI) to resolve cortical columns depends on several factors. These include the spatial scale of the columnar pattern, the point-spread of the fMRI response, the voxel size, and the signal-to-noise ratio (SNR) considering thermal and physiological noise. However, it remains unknown how these factors combine, and what is the voxel size that optimizes fMRI of cortical columns. Here we combine current knowledge into a quantitative model of fMRI of realistic patterns of cortical columns with different spatial scales and degrees of irregularity. We compare different approaches for identifying patterns of cortical columns, including univariate and multivariate based detection, multi-voxel pattern analysis (MVPA) based decoding, and high-resolution imaging and reconstruction of the pattern of cortical columns. We present the dependence of the performance of each approach on the parameters of the imaged pattern as well as those of the data acquisition. In addition, we predict voxel sizes that optimize fMRI of cortical columns under various scenarios. We found that all measures associated with multivariate detection and decoding could be approximately calculated from a measure we termed “multivariate contrast-to-noise ratio” (mv-CNR), which is a function of the contrast-to-noise ratio (CNR) and number of voxels. Furthermore, mv-CNR implied that the optimal voxel width for detection and decoding is independent of changes in response amplitude, SNR and imaged volume that are not caused by changes in voxel size. For regular patterns, optimal voxel widths for detection, decoding and imaging/reconstructing the pattern of cortical columns were approximately half the main cycle length of the organization. Optimal voxel widths for irregular patterns were less dependent on the main cycle length, and differed between univariate detection, multivariate detection and decoding, and reconstruction. We compared the effects of different factors of Gradient Echo fMRI at 3 Tesla (T), Gradient Echo fMRI at 7T, and Spin-Echo fMRI at 7T on the detection, decoding, and reconstruction measures considered and found that in all cases the width of the fMRI point-spread had the most significant effect. In contrast, different response amplitudes and noise characteristics played a relatively minor role. We recommend specific voxel widths for optimal univariate detection, for multivariate detection and decoding, and for high-resolution imaging of cortical columns under these three data-acquisition scenarios. Our study supports the planning, optimization, and interpretation of high-resolution fMRI of cortical columns and the decoding of information conveyed by these columns. [ABSTRACT FROM AUTHOR]

Level Of Evidence: 5 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:282-285. [ABSTRACT FROM AUTHOR]

Purpose To develop short water suppression sequences for 7 T magnetic resonance spectroscopic imaging, with mitigation of subject-specific transmit RF field ( [ABSTRACT FROM AUTHOR]

Objective: Functional parameters can be measured with the help of quantitative non-proton MRI where exact relaxometry parameters are needed. Investigation of $$T_{2}^{*}$$ is often biased by strong partial volume (PV) effects. Hence, in this work a PV correction algorithm approach was evaluated that uses iteratively adapted $$T_{2}^{*}$$ -values and high-resolution structural H data to determine transverse relaxation in non-proton MRI more accurately. Materials and methods: Simulations, a phantom study and in vivo Na, O and Cl MRI measurements of five healthy volunteers were performed to evaluate the algorithm. $$T_{2}^{*}$$ values of grey matter (GM), white matter (WM) and cerebrospinal fluid (CSF) were obtained. Data were acquired at B = 7T with nominal spatial resolutions of (4-7 mm) using a density-adapted radial sequence. The resulting transverse relaxation times were used for quantification of O data. Results: The conducted simulations and phantom study verified the correction performance of the algorithm. For in vivo measured $$T_{2}^{*}$$ values, the correction of PV effects leads to an increase in CSF and to a decrease in GM/WM (Na MRI: long/short GM, WM $$T_{2}^{*}$$ : 36.4 ± 3.1/5.4 ± 0.2, 23.3 ± 2.6/3.5 ± 0.1 ms; Cl MRI: 8.9 ± 1.4/1.0 ± 0.4, 5.9 ± 0.3/0.4 ± 0.1 ms; O MRI: 2.5 ± 0.1, 2.8 ± 0.1 ms). Iteratively corrected in vivo $$T_{2}^{*}$$ values of the O study resulted in improved water content quantification. Conclusion: The proposed iterative algorithm for PV correction leads to more accurate $$T_{2}^{*}$$ values and, thus, can improve accuracy in quantitative non-proton MRI. [ABSTRACT FROM AUTHOR]

Study Design: High-resolution imaging and biomechanical investigation of ex-vivo vertebrae.Objective: The aim of this study was to assess bone microarchitecture of cadaveric vertebrae using ultra-high field (UHF) 7 Tesla magnetic resonance imaging (MRI) and to determine whether the corresponding microarchitecture parameters were related to bone mineral density (BMD) and bone strength assessed by dual-energy x-ray absorptiometry (DXA) and mechanical compression tests.Summary Of Background Data: Limitations of DXA for the assessment of bone fragility and osteoporosis have been recognized and criteria of microarchitecture alteration have been included in the definition of osteoporosis. Although vertebral fracture is the most common osteoporotic fracture, no study has assessed directly vertebral trabecular bone microarchitecture.Methods: BMD of 24 vertebrae (L2, L3, L4) from eight cadavers was investigated using DXA. The bone volume fraction (BVF), trabecular thickness (Tb.Th), and trabecular spacing (Tb.Sp) of each vertebra were quantified using UHF MRI. Measurements were performed by two operators to characterize the inter-rater reliability. The whole set of specimens underwent mechanical compression tests to failure and the corresponding failure stress was calculated.Results: The inter-rater reliability for bone microarchitecture parameters was good with intraclass correlation coefficients ranging from 0.82 to 0.94. Failure load and stress were significantly correlated with BVF, Tb.Sp, and BMD (P < 0.05). Tb.Th was only correlated with the failure stress (P < 0.05). Multiple regression analysis demonstrated that the combination of BVF and BMD improved the prediction of the failure stress from an adjusted R = 0.384 for BMD alone to an adjusted R = 0.414.Conclusion: We demonstrated for the first time that the vertebral bone microarchitecture assessed with UHF MRI was significantly correlated with biomechanical parameters. Our data suggest that the multimodal assessment of BMD and trabecular bone microarchitecture with UHF MRI provides additional information on the risk of vertebral bone fracture and might be of interest for the future investigation of selected osteoporotic patients.Level Of Evidence: N /A. [ABSTRACT FROM AUTHOR]

Purpose To advance the best solutions to two important RF pulse design problems with an open head-to-head competition. Methods Two sub-challenges were formulated in which contestants competed to design the shortest simultaneous multislice (SMS) refocusing pulses and slice-selective parallel transmission (pTx) excitation pulses, subject to realistic hardware and safety constraints. Short refocusing pulses are needed for spin echo SMS imaging at high multiband factors, and short slice-selective pTx pulses are needed for multislice imaging in ultra-high field MRI. Each sub-challenge comprised two phases, in which the first phase posed problems with a low barrier of entry, and the second phase encouraged solutions that performed well in general. The Challenge ran from October 2015 to May 2016. Results The pTx Challenge winners developed a spokes pulse design method that combined variable-rate selective excitation with an efficient method to enforce SAR constraints, which achieved 10.6 times shorter pulse durations than conventional approaches. The SMS Challenge winners developed a time-optimal control multiband pulse design algorithm that achieved 5.1 times shorter pulse durations than conventional approaches. Conclusion The Challenge led to rapid step improvements in solutions to significant problems in RF excitation for SMS imaging and ultra-high field MRI. Magn Reson Med 78:1352-1361, 2017. © 2016 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Background and Purpose: Perform an investigation of the frequency and distribution of leptomeningeal enhancement on postgadolinium magnetization-prepared FLAIR (MPFLAIR) in multiple sclerosis (MS) on 7 Tesla (7T) MRI and to relate this finding to measures of brain structure and lesion volumes.Methods: Twenty-nine participants with MS underwent 7T MRI of the brain. Three healthy volunteers (HVs) were scanned for comparison. Areas of postcontrast leptomeningeal enhancement were identified. Images were segmented for brain structure and lesion volumes. The relationship between leptomeningeal enhancement and clinical and volumetric data was explored.Results: Two patterns of enhancement were found: "nodular" (discrete, spherical nodules at the pial surface or subarachnoid space) and "spread/fill" (appearance of contrast spread through the local subarachnoid space). Twenty-six of 29 (90%) MS participants had at least one focus of leptomeningeal enhancement. Nodular foci were present in 15 of 29 (51%) MS participants. Spread/fill foci were present in 22 of 29 (76%) MS participants. Two HVs had examples of nodular foci, but none had spread/fill enhancement. MS participants with spread/fill foci were older (48.9 years [SD 8.3]) than those without (33.3 years [SD 11.5], P = .005). MS participants with spread/fill foci had reduced cortical gray matter volume compared to those without (P = .020).Conclusions: Leptomeningeal enhancement on postcontrast 7T MPFLAIR is more prevalent than prior reports at 3T-occurring at frequencies closer to histopathologic data. Spread/fill foci are associated with reduced cortical gray matter volumes and may represent blood-meningeal barrier breakdown near sites of meningeal inflammation, whereas nodular foci may be a normal variant. [ABSTRACT FROM AUTHOR]

The basal ganglia (BG) form a network of subcortical nuclei. Functional magnetic resonance imaging (fMRI) in the BG could provide insight in its functioning and the underlying mechanisms of Deep Brain Stimulation (DBS). However, fMRI of the BG with high specificity is challenging, because the nuclei are small and variable in their anatomical location. High resolution fMRI at field strengths of 7 Tesla (T) could help resolve these challenges to some extent. A set of MR protocols was developed for functional imaging of the BG nuclei at 3 T and 7 T. The protocols were validated using a stop-signal reaction task (Logan et al. []: J Exp Psychol: Human Percept Perform 10:276-291). Compared with sub-millimeter 7 T fMRI protocols aimed at cortex, a reduction of echo time and spatial resolution was strictly necessary to obtain robust Blood Oxygen Level Dependent (BOLD) sensitivity in the BG. An fMRI protocol at 3 T with identical resolution to the 7 T showed no robust BOLD sensitivity in any of the BG nuclei. The results suggest that the subthalamic nucleus, as well as the substantia nigra, red nucleus, and the internal and external parts of the globus pallidus show increased activation in failed stop trials compared with successful stop and go trials. Hum Brain Mapp 38:3226-3248, 2017. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

ABSTRACT The hippocampus is one of the most interesting and studied brain regions because of its involvement in memory functions and its vulnerability in pathological conditions, such as neurodegenerative processes. In the recent years, the increasing availability of Magnetic Resonance Imaging (MRI) scanners that operate at ultra-high field (UHF), that is, with static magnetic field strength ≥7T, has opened new research perspectives. Compared to conventional high-field scanners, these systems can provide new contrasts, increased signal-to-noise ratio and higher spatial resolution, thus they may improve the visualization of very small structures of the brain, such as the hippocampal subfields. Studying the morphometry of the hippocampus is crucial in neuroimaging research because changes in volume and thickness of hippocampal subregions may be relevant in the early assessment of pathological cognitive decline and Alzheimer's Disease (AD). The present review provides an overview of the manual, semi-automated and fully automated methods that allow the assessment of hippocampal subfield morphometry at UHF MRI, focusing on the different hippocampal segmentation produced. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Recently, several magnetic resonance imaging contrast mechanisms have been shown to distinguish cortical substructure corresponding to selected cortical layers. Here, we investigate cortical layer and area differentiation by automatized unsupervised clustering of high resolution diffusion MRI data. Several groups of adjacent layers could be distinguished in human primary motor and premotor cortex. We then used the signature of diffusion MRI signals along cortical depth as a criterion to detect area boundaries and find borders at which the signature changes abruptly. We validate our clustering results by histological analysis of the same tissue. These results confirm earlier studies which show that diffusion MRI can probe layer-specific intracortical fiber organization and, moreover, suggests that it contains enough information to automatically classify architecturally distinct cortical areas. We discuss the strengths and weaknesses of the automatic clustering approach and its appeal for MR-based cortical histology.

Ultra-high field (UHF, ≥7 T) tight fit transceiver phased arrays improve transmit (Tx) efficiency ( B1+/√ P) in comparison with Tx-only arrays, which are usually larger to fit receive (Rx)-only arrays inside. One of the major problems limiting applications of tight fit arrays at UHFs is the anticipated increase of local tissue heating, which is commonly evaluated by the local specific absorption rate (SAR). To investigate the tradeoff between Tx efficiency and SAR when a tight fit UHF human head transceiver phased array is used instead of a Tx-only/Rx-only RF system, a single-row eight-element prototype of a 400 MHz transceiver head phased array was constructed. The Tx efficiency and SAR of the array were evaluated and compared with that of a larger Tx-only array, which could also be used in combination with an 18-channel Rx-only array. Data were acquired on the Siemens Magnetom whole body 9.4 T human MRI system. Depending on the head size, positioning and the RF shim strategy, the smaller array provides from 11 to 23% higher Tx efficiency. In general, the Tx performance, evaluated as B1+/√SAR, i.e. the safety excitation efficiency (SEE), is also not compromised. The two arrays provide very similar SEEs evaluated over 1000 random RF shim sets. We demonstrated that, in general, the tight fit transceiver array improves Tx performance without compromising SEE. However, in specific cases, the SEE value may vary, favoring one of the arrays, and therefore must be carefully evaluated. [ABSTRACT FROM AUTHOR]

Recently, several magnetic resonance imaging contrast mechanisms have been shown to distinguish cortical substructure corresponding to selected cortical layers. Here, we investigate cortical layer and area differentiation by automatized unsupervised clustering of high-resolution diffusion MRI data. Several groups of adjacent layers could be distinguished in human primary motor and premotor cortex. We then used the signature of diffusion MRI signals along cortical depth as a criterion to detect area boundaries and find borders at which the signature changes abruptly. We validate our clustering results by histological analysis of the same tissue. These results confirm earlier studies which show that diffusion MRI can probe layer-specific intracortical fiber organization and, moreover, suggests that it contains enough information to automatically classify architecturally distinct cortical areas. We discuss the strengths and weaknesses of the automatic clustering approach and its appeal for MR-based cortical histology. [ABSTRACT FROM AUTHOR]

Purpose The goal of this study was to optimize signal-to-noise ratio (SNR) and parallel receive (Rx) performance of ultrahigh field (UHF) (≥7T) transceiver arrays without compromising their transmit (Tx) efficiency. UHF transceiver head phased arrays with a tight fit improve Tx efficiency in comparison with Tx-only arrays, which are usually larger so that Rx-only arrays can fit inside. However, having ≥16 elements inside a head transceiver array presents decoupling problems. Furthermore, the available number of Tx channels is limited. Methods A prototype of a splittable transceiver phased array was constructed. The array consisted of four flat surface Tx loops positioned in two rows. Each loop could be split into two smaller overlapped Rx loops during reception. Results Experimental data demonstrated that both SNR and parallel reception performance improved substantially by doubling the number of Rx elements from four to eight. Conclusion As a proof of concept, we developed and constructed a novel splittable transceiver phased array that allows doubling of the number of Rx elements while keeping both Tx and Rx elements at the same distance from the subject. Both Tx and Rx performance can be optimized at the same time using this method. Magn Reson Med 76:1621-1628, 2016. © 2015 International Society for Magnetic Resonance in Medicine [ABSTRACT FROM AUTHOR]

Purpose Signal magnitude can robustly be combined using the sum-of-squares approach. Methods have been developed to combine complex images. However, techniques based only on signal phase have not been developed and evaluated. Theory and Methods We performed simulations to demonstrate the effect of noise on coil combination. 32-channel 7 Tesla human gradient echo MRI brain data were collected. We combined phase images based on phase noise leading to spatially selective and coil selective combination of phase images. We compared our selective combination approach to optimal noise distribution and adaptive combination methods. Results We found that selective combination of signal phases leads to improved phase signal-to-noise ratio. Furthermore, a phase shift can be present in combined phase images introduced by the method used to combine multiple channel phases. Conclusion Mapping of signal phase from ultra-high field MRI data undoubtedly provides a wealth of information about the ageing brain and the effects of neurodegenerative disorders. Measurement of signal phase is essential in frequency shift mapping and in quantitative susceptibility mapping. The method used to combine signal phase should be informed by an understanding of the noise distribution in signal phase at the individual channel level. Magn Reson Med 76:1469-1477, 2016. © 2015 International Society for Magnetic Resonance in Medicine [ABSTRACT FROM AUTHOR]

The aim of this study is to compare the current state of lesion identification, the BI-RADS classification and the contrast-enhancement behavior at 7T and 3T breast MRI in the same patient group. Twenty-seven patients with thirty suspicious lesions were selected for this prospective study and underwent both 7T and 3T MRI. All examinations were rated by two radiologists (R1 and R2) independently on image quality, lesion identification and BI-RADS classification. We assessed sensitivity, specificity, NPV and PPV, observer agreement, lesion sizes, and contrast-enhancement-to-noise ratios (CENRs) of mass lesions. Fifteen of seventeen histopathological proven malignant lesions were detected at both field strengths. Image quality of the dynamic series was good at 7T, and excellent at 3T (P = 0.001 for R1 and P = 0.88 for R2). R1 found higher rates of specificity, NPV and PPV at 7T when compared to 3T, while R2 found the same results for sensitivity, specificity, NPV and PPV for both field strengths. The observers showed excellent agreement for BI-RADS categories at 7T (κ = 0.86) and 3T (κ = 0.93). CENRs were higher at 7T (P = 0.015). Lesion sizes were bigger at 7T according to R2 (P = 0.039). Our comparison study shows that 7T MRI allows BI-RADS conform analysis. Technical improvements, such as acquisition of T2w sequences and adjustment of B1+ field inhomogeneity, are still necessary to allow clinical use of 7T breast MRI. [ABSTRACT FROM AUTHOR]

Introduction: The subthalamic nucleus, substantia nigra, and globus pallidus, three nuclei of the human basal ganglia, play an important role in motor, associative, and limbic processing. The network of the basal ganglia is generally characterized by a direct, indirect, and hyperdirect pathway. This study aims to investigate the mesoscopic nature of these connections between the subthalamic nucleus, substantia nigra, and globus pallidus and their surrounding structures. Methods: A human post mortem brain specimen including the substantia nigra, subthalamic nucleus, and globus pallidus was scanned on a 7 T MRI scanner. High resolution diffusion weighted images were used to reconstruct the fibers intersecting the substantia nigra, subthalamic nucleus, and globus pallidus. The course and density of these tracks was analyzed. Results: Most of the commonly established projections of the subthalamic nucleus, substantia nigra, and globus pallidus were successfully reconstructed. However, some of the reconstructed fiber tracks such as the connections of the substantia nigra pars compacta to the other included nuclei and the connections with the anterior commissure have not been shown previously. In addition, the quantitative tractography approach showed a typical degree of connectivity previously not documented. An example is the relatively larger projections of the subthalamic nucleus to the substantia nigra pars reticulata when compared to the projections to the globus pallidus internus. Discussion: This study shows that ultra-high field post mortem tractography allows for detailed 3D reconstruction of the projections of deep brain structures in humans. Although the results should be interpreted carefully, the newly identified connections contribute to our understanding of the basal ganglia. [ABSTRACT FROM AUTHOR]

Objectives: To assess the detectability of vasculitic changes of the superficial cranial arteries with contrast-enhanced 7 T MRI in three patients with GCA and intraindividual comparison with 3 T MRI. Methods: Three patients (two female, one male) with suspected GCA underwent contrast-enhanced T1-weighted high-resolution MRI at 3 T and 7 T magnetic field strength. The clinical diagnosis, based on criteria of the American College of Rheumatology, was confirmed by biopsy of the superficial temporal artery after MRI. MR images were visually assessed for detection of vasculitic mural contrast enhancement and vessel wall thickening of the superficial cranial arteries. Results: Both 3 T and 7 T MRI allows for visualisation of mural inflammatory changes and assessment of the vasculitic involvement pattern. Image quality of 7 T MRI was rated superior to image quality of 3 T MRI scans. Conclusions: 7 T MR imaging of vasculitic changes in patients with GCA is possible, and suggests superior image quality. Larger patient studies are necessary to quantify the diagnostic advantages of 7 T MRI. [ABSTRACT FROM AUTHOR]

Objective To perform non-enhanced (NE) magnetic resonance imaging (MRI) of the small bowel at 7 Tesla (7 T) and to compare it with 1.5 Tesla (1.5 T). Material and methods Twelve healthy subjects were prospectively examined using a 1.5 T and 7 T MRI system. Coronal and axial true fast imaging with steady-state precession (TrueFISP) imaging and a coronal T2-weighted (T2w) half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence were acquired. Image analysis was performed by 1) visual evaluation of tissue contrast and detail detectability, 2) measurement and calculation of contrast ratios and 3) assessment of artifacts. Results NE MRI of the small bowel at 7 T was technically feasible. In the vast majority of the cases, tissue contrast and image details were equivalent at both field strengths. At 7 T, two cases revealed better detail detectability in the TrueFISP, and better contrast in the HASTE. Susceptibility artifacts and B 1 inhomogeneities were significantly increased at 7 T. Conclusion This study provides first insights into NE ultra-high field MRI of the small bowel and may be considered an important step towards high quality T2w abdominal imaging at 7 T MRI. [ABSTRACT FROM AUTHOR]

Objectives: The use of 7 Tesla (T) magnetic resonance imaging (MRI) has recently shown great potential for high-resolution soft-tissue neuroimaging and visualization of microvascularization in glioblastoma (GBM). We have designed a clinical trial to explore the value of 7 T MRI in radiation treatment of GBM. For this aim we performed a preparatory study to investigate the technical feasibility of incorporating 7 T MR images into the neurosurgical navigation and radiotherapy treatment planning (RTP) systems via qualitative and quantitative assessment of the image quality. Materials and methods: The MR images were acquired with a Siemens Magnetom 7 T whole-body scanner and a Nova Medical 32-channel head coil. The 7 T MRI pulse sequences included magnetization-prepared two rapid acquisition gradient echoes (MP2RAGE), T2-SPACE, SPACE-FLAIR and gradient echo sequences (GRE). A pilot study with three healthy volunteers and an anthropomorphic 3D phantom was used to assess image quality and geometrical image accuracy. Results: The MRI scans were well tolerated by the volunteers. Susceptibility artefacts were observed in both the cortex and subcortical white matter at close proximity to air-tissue interfaces. Regional loss of signal and contrast could be minimized by the use of dielectric pads. Image transfer and processing did not degrade image quality. The system-related spatial uncertainty of geometrical distortion-corrected MP2RAGE pulse sequences was ≤2 mm. Conclusion: Integration of high-quality and geometrically-reliable 7 T MR images into neurosurgical navigation and RTP software is technically feasible and safe. [ABSTRACT FROM AUTHOR]

Intra-axonal accumulation of sodium ions is one of the key mechanisms of delayed neuro-axonal degeneration that contributes to disability accrual in multiple sclerosis. In vivo sodium magnetic resonance imaging studies have demonstrated an increase of brain total sodium concentration in patients with multiple sclerosis, especially in patients with greater disability. However, total sodium concentration is a weighted average of intra- and extra-cellular sodium concentration whose changes reflect different tissue pathophysiological processes. The in vivo, non-invasive measurement of intracellular sodium concentration is quite challenging and the few applications in patients with neurological diseases are limited to case reports and qualitative assessments. In the present study we provide first evidence of the feasibility of triple quantum filtered (23)Na magnetic resonance imaging at 7 T, and provide in vivo quantification of global and regional brain intra- and extra-cellular sodium concentration in 19 relapsing-remitting multiple sclerosis patients and 17 heathy controls. Global grey matter and white matter total sodium concentration (respectively P < 0.05 and P < 0.01), and intracellular sodium concentration (both P < 0.001) were higher while grey matter and white matter intracellular sodium volume fraction (indirect measure of extracellular sodium concentration) were lower (respectively P = 0.62 and P < 0.001) in patients compared with healthy controls. At a brain regional level, clusters of increased total sodium concentration and intracellular sodium concentration and decreased intracellular sodium volume fraction were found in several cortical, subcortical and white matter regions when patients were compared with healthy controls (P < 0.05 family-wise error corrected for total sodium concentration, P < 0.05 uncorrected for multiple comparisons for intracellular sodium concentration and intracellular sodium volume fraction). Measures of total sodium concentration and intracellular sodium volume fraction, but not measures of intracellular sodium concentration were correlated with T2-weighted and T1-weighted lesion volumes (0.05 < P < 0.01) and with Expanded Disability Status Scale (P < 0.05). Thus, suggesting that while intracellular sodium volume fraction decrease could reflect expansion of extracellular space due to tissue loss, intracellular sodium concentration increase could reflect neuro-axonal metabolic dysfunction. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this study was to determine the feasibility of muscle BOLD (mBOLD) imaging at 7 Tesla (T) by comparing the changes in R2* of muscle at 3 and 7T in response to a brief period of tourniquet-induced ischemia. Methods Eight subjects (three male), aged 29.5 ± 6.1 years (mean ± standard deviation, SD), 167.0 ± 10.6 cm tall with a body mass of 62.0 ± 18.0 kg, participated in the study. Subjects reported to the lab on four separate occasions including a habituation session, two MRI scans, and in a subset of subjects, a session during which changes in blood flow and blood oxygenation were quantified using Doppler ultrasound (U/S) and near-infrared spectroscopy (NIRS) respectively. For statistical comparisons between 3 and 7T, R2* rate constants were calculated as R2* = 1/ T2*. Results The mean preocclusion R2* value was greater at 7T than at 3T (60.16 ± 2.95 vs. 35.17 ± 0.35 s−1, respectively, P < 0.001). Also, the mean Δ R2*END and Δ R2*POST values were greater for 7T than for 3T (−2.36 ± 0.25 vs. −1.24 ± 0.39 s−1, respectively, Table 1). Conclusion Muscle BOLD contrast at 7T is as much as six-fold greater than at 3T. In addition to providing greater SNR and CNR, 7T mBOLD studies may offer further advantages in the form of greater sensitivity to pathological changes in the muscle microcirculation. Magn Reson Med 75:1333-1340, 2016. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Visual snow syndrome (VSS) is a neurological disorder characterized by a range of continuous visual disturbances. Little is known about the functional pathological mechanisms underlying VSS and their effect on brain network topology, studied using high-resolution resting-state (RS) 7 T MRI. Forty VSS patients and 60 healthy controls underwent RS MRI. Functional connectivity matrices were calculated, and global efficiency (network integration), modularity (network segregation), local efficiency (LE, connectedness neighbors) and eigenvector centrality (significance node in network) were derived using a dynamic approach (temporal fluctuations during acquisition). Network measures were compared between groups, with regions of significant difference correlated with known aberrant ocular motor VSS metrics (shortened latencies and higher number of inhibitory errors) in VSS patients. Lastly, nodal co-modularity, a binary measure of node pairs belonging to the same module, was studied. VSS patients had lower modularity, supramarginal centrality and LE dynamics of multiple (sub)cortical regions, centered around occipital and parietal lobules. In VSS patients, lateral occipital cortex LE dynamics correlated positively with shortened prosaccade latencies (p = .041, r = .353). In VSS patients, occipital, parietal, and motor nodes belonged more often to the same module and demonstrated lower nodal co-modularity with temporal and frontal regions. This study revealed reduced dynamic variation in modularity and local efficiency strength in the VSS brain, suggesting that brain network dynamics are less variable in terms of segregation and local clustering. Further investigation of these changes could inform our understanding of the pathogenesis of the disorder and potentially lead to treatment strategies., (© 2022 The Authors. Human Brain Mapping published by Wiley Periodicals LLC.)

Transient ischemic attack (TIA) has gained significant attention recently due to the increased incidence of subsequent stroke. However, there are many nonvascular clinical mimics of TIA, creating a need for improved biomarkers to identify a vascular origin. Following the recent approval of ultra-high field (UHF) 7T MRI in clinical practice, several clinical studies have highlighted its added utility in neuroimaging compared to lower-field 1.5T and 3T MRI, particularly in epilepsy and multiple sclerosis. Our case series of three patients with TIA illustrates that 7T MRI can depict small areas of intracortical microhemorrhages and microinfarctions, which could not be resolved with 3T or 1.5T MRI. There are currently no reports of intracortical localization of microhemorrhages in patients with TIA. This discovery may enhance our understanding and characterization of cerebrovascular abnormalities in TIAs. In addition, UHF imaging could potentially be utilized to distinguish transient neurological episodes secondary to cerebrovascular events from other differential considerations. Our cases highlight the underestimation of imaging abnormalities in cases of TIA and support the potential expanded application of clinical 7T to assess patients with TIA. Future studies are necessary at 7T redundant to determine the true incidence of such lesions in TIA and to examine the correlation between cortical microhemorrhages and subsequent ischemic stroke, hemorrhagic events, and neurocognitive impairment.