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Multi-Slice T2-weighted MR imaging is a fundamental technique in brain imaging but suffers from field inhomogeneities at ultra-high field systems. In this work we present a pulse design method which provides slab-selective universal pulses with phase-coherent excitation profiles over selected brain regions. Applied in a 3D variable flip angle turbo-spin-echo (TSE) sequence, the pulses achieve superior SNR compared to multi-slice TSE imaging and B1 + field inhomogeneity mitigation.

We present a versatile high-resolution whole-brain multiparametric/susceptibility mapping protocol at 7T, introducing interleaved fly-back skipped-CAIPI 3D-EPI. To overcome the impeding limitations of B1 + inhomogeneity, universal pTX pulses for excitation and magnetization transfer saturation are employed. Within 17 minutes scan time, 0.6mm isotropic whole-brain MT-/PD-/T1-weighted magnitude and phase images at four echo times and corresponding quantitative parameter maps are obtained. Supplementary output, like SWI and MPRAGElike images can be generated as well. Scan efficiency is high and geometric distortions are negligible. Optionally, the interleaved fly-back acquisition allows a separate analysis of two monopolar readout images.

CEST imaging benefits from the increased spectral resolution at ultra-high field. Due to the inhomogeneous RF field, a B1 correction is necessary, which requires repeated measurements. The number of required repetitions can be reduced to two by using a ptx-based saturation scheme, like MIMOSA. We present an alternative saturation scheme that is based on PUSH saturation and universal pulses, which we name PUSHUP. Using this approach, we could reduce the inhomogeneity of the CEST saturation as effectively as MIMOSA while being more SAR efficient.

Purpose We present a time-efficient water-selective, parallel transmit RF excitation pulsedesign for ultra-high field applications. Methods The proposed pulse design method achieves flip angle homogenization at ultrahigh fields by employing spatially non-selective kT-points pulses. In order tointroduce water-selection, the concept of binomial pulses is applied. Due to thecomposite nature of kT -points, the pulse can be split into multiple binomial sub-pulse blocks shorter than half the precession period of fat, that are playedout successively. Additional fat precession turns, that would otherwise impairthe spectral response, can thus be avoided. Bloch simulations of the proposedinterleaved binomial kT-points pulses were carried out and compared in terms ofduration, homogeneity, fat suppression and pulse energy. For validation, in vivoMP-RAGE and 3D-EPI data were acquired. Results Simulation results show that interleaved binomial kT-points pulses achieve shorter total pulse durations, improved flip angle homogeneity and more robustfat suppression compared to available methods. Interleaved binomial kT-pointscan be customized by changing the number of kT-points, the sub-pulse duration and the order of the binomial pulse. Using shorter sub-pulses, the number ofkT-points can be increased and hence better homogeneity is achieved, while still maintaining short total pulse durations. Flip angle homogenization and fatsuppression of interleaved binomial kT-points pulses is demonstrated in vivo at 27T, confirming Bloch simulation results. Conclusion In this work, we present a time efficient and robust parallel transmission technique for non-selective water excitation with simultaneous flip angle homogenizationat ultra-high field.

We present a time-efficient water-selective, parallel transmit RF excitation pulse design for ultra-high field applications.The proposed pulse design method achieves flip angle homogenization at ultra-high fields by employing spatially nonselectivemml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:mrowmml:mik/mml:mi/mml:mrowmml:mrowmml:miT/mml:mi/mml:mrow/mml:msub/mml:mrowmml:annotation$$ {\mathrm{k}}_T $$/mml:annotation/mml:semantics/mml:math-points pulses. In order to introduce water-selection, the concept of binomial pulses is applied. Due to the composite nature ofmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:mrowmml:mik/mml:mi/mml:mrowmml:mrowmml:miT/mml:mi/mml:mrow/mml:msub/mml:mrowmml:annotation$$ {\mathrm{k}}_T $$/mml:annotation/mml:semantics/mml:math-points, the pulse can be split into multiple binomial subpulse blocks shorter than half the precession period of fat, that are played out successively. Additional fat precession turns, that would otherwise impair the spectral response, can thus be avoided. Bloch simulations of the proposed interleaved binomialmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:mrowmml:mik/mml:mi/mml:mrowmml:mrowmml:miT/mml:mi/mml:mrow/mml:msub/mml:mrowmml:annotation$$ {\mathrm{k}}_T $$/mml:annotation/mml:semantics/mml:math-points pulses were carried out and compared in terms of duration, homogeneity, fat suppression and pulse energy. For validation, in vivo MP-RAGE and 3D-EPI data were acquired.Simulation results show that interleaved binomialmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:mrowmml:mik/mml:mi/mml:mrowmml:mrowmml:miT/mml:mi/mml:mrow/mml:msub/mml:mrowmml:annotation$$ {\mathrm{k}}_T $$/mml:annotation/mml:semantics/mml:math-points pulses achieve shorter total pulse durations, improved flip angle homogeneity and more robust fat suppression compared to available methods. Interleaved binomialmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:mrowmml:mik/mml:mi/mml:mrowmml:mrowmml:miT/mml:mi/mml:mrow/mml:msub/mml:mrowmml:annotation$$ {\mathrm{k}}_T $$/mml:annotation/mml:semantics/mml:math-points can be customized by changing the number ofmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:mrowmml:mik/mml:mi/mml:mrowmml:mrowmml:miT/mml:mi/mml:mrow/mml:msub/mml:mrowmml:annotation$$ {\mathrm{k}}_T $$/mml:annotation/mml:semantics/mml:math-points, the subpulse duration and the order of the binomial pulse. Using shorter subpulses, the number ofmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:mrowmml:mik/mml:mi/mml:mrowmml:mrowmml:miT/mml:mi/mml:mrow/mml:msub/mml:mrowmml:annotation$$ {\mathrm{k}}_T $$/mml:annotation/mml:semantics/mml:math-points can be increased and hence better homogeneity is achieved, while still maintaining short total pulse durations. Flip angle homogenization and fat suppression of interleaved binomialmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:mrowmml:mik/mml:mi/mml:mrowmml:mrowmml:miT/mml:mi/mml:mrow/mml:msub/mml:mrowmml:annotation$$ {\mathrm{k}}_T $$/mml:annotation/mml:semantics/mml:math-points pulses is demonstrated in vivo at 7T, confirming Bloch simulation results.In this work, we present a time efficient and robust parallel transmission technique for nonselective water excitation with simultaneous flip angle homogenization at ultra-high field.

Objectives GABA is the most important inhibitory neurotransmitter. Thus, variation in its concentration is connected to a wide variety of diseases. However, the low concentration and the overlap of more prominent resonances hamper GABA quantification using MR spectroscopy. The hippocampus plays a pivotal role in neurodegeneration. Susceptibility discontinuities in the vicinity of the hippocampus cause strong B0 inhomogeneities, impeding GABA spectroscopy. The aim of this work is to improve the reproducibility of hippocampal GABA+ MRS. Methods The GABA+/total creatine ratio in the hippocampus was measured using a MEGA-sLASER sequence at 7 Tesla. 10 young healthy volunteers participated in the study. A dedicated pre-processing approach was established. Spectral quantification was performed with Tarquin. The quantification parameters were carefully adjusted to ensure optimal quantification. Results An inter-subject coefficient of variation of the GABA+/total creatine of below 15% was achieved. Additional to spectral registration, which is essential to obtain reproducible GABA measures, eddy current compensation and additional difference artifact suppression improved the reproducibility. The mean FWHM was 23.1 Hz (0.078 ppm). Conclusion The increased spectral dispersion of ultra-high-field spectroscopy allows for reproducible spectral quantification, despite a very broad line width. The achieved reproducibility enables the routine use of hippocampal GABA spectroscopy at 7 Tesla.

(Meyer MF, Knezic K, Jansen S, Klünter HD, Pracht ED, Grosheva M. Effects of freediving on middle ear and eustachian tube function. Diving and Hyperbaric Medicine. 2020 December 20;50(4):350–355. doi: 10.28920/dhm50.4.350-355. PMID: 33325015.) Introduction: During descent in freediving there is exposure to rapidly increasing pressure. Inability to quickly equalise middle ear pressure may cause trauma to the ear. This study aimed to evaluate the occurrence of pressure-related damage to the middle ear and the Eustachian tube during freediving and to identify possible risk factors. Methods: Sixteen free divers performed diving sessions in an indoor pool 20 metres’ freshwater (mfw) deep. During each session, each diver performed four own free dives and up to four safety dives. Naso- and oto-endoscopy and Eustachian tube function tests were performed on the right and left ears before diving, between each session and after the last session. The otoscopic findings were classified according to the Teed classification (0 = normal tympanic membrane to 4 = perforation). Additionally, ENT-related complaints were assessed using a questionnaire. Results: Participants performed 317 dives (on average 20 dives per diver, six per session). The average depth was 13.3 mfw. Pressure-related changes (Teed 1 and 2) were detected in 48 % of ears. Teed level increased significantly with an increasing number of completed sessions (P < 0.0001). Higher pressure-related damage (Teed 2) occurred in less experienced divers, was associated with significantly lower peak pressures in the middle ear and led to more ear-related symptoms. A preference for the Frenzel technique for middle ear pressure equalisation during freediving was shown. Conclusions: Pressure exposure during freediving had a cumulative effect on the middle ear. Factors such as diving depth, diving experience and number of diving sessions correlated with the occurrence of higher Teed levels.

Purpose To investigate the impact of accelerated, single-shot 3D-GRASE acquisition on quantitative arterial spin labeling (ASL) with multiple and single post-labeling delay (PLD) in terms of perfusion-weighted SNR per unit scan time (TSNRPW ) and quantification accuracy. Methods Five subjects were scanned on a 3T MRI scanner using the pseudo-continuous arterial spin labeling (PCASL) technique with a 3D-GRASE imaging sequence capable of parallel imaging acceleration. A 3-inversion pulse background suppression was simulated and implemented in the sequence. Three time-matched single PLD measurements, a segmented one without acceleration, 1 with conventional GRAPPA, and 1 with CAIPIRINHA sampling, were used to compare TSNRPW . Three time-matched multiple PLD measurements with the identical imaging parameters were additionally evaluated (no acceleration vs. CAIPIRINHA sampling vs. CAIPIRINHA sampling with doubled number of PLDs). Cerebral blood flow and arterial transit time fit uncertainties were compared and used as a quality measure. Results The single PLD measurements show an 11% TSNRPW increase using CAIPIRINHA sampling instead of GRAPPA sampling, while the non-accelerated scan exhibits 35% higher TSNRPW compared to the GRAPPA scan. However, taking advantage of the increased number of averages for multiple PLD acquisitions, a 14%/16% (gray matter) and 34%/36% (white matter) reduction of CBF fit uncertainty is observed with CAIPIRINHA sampling (6 PLDs/12 PLDs) compared to no acceleration. Conclusion Accelerated single-shot 3D-GRASE with PCASL allows for smaller quantification uncertainties than time-matched segmented acquisitions. Corresponding single-shot acquisitions with acceptable blurring and no intra-volume motion render state-of-the-art ASL methods in a clinically feasible time possible.

Purpose The aim of this project was to develop a GRAPPA-based reconstruction for wave-CAIPI data. Wave-CAIPI fully exploits the 3D coil sensitivity variations by combining corkscrew k-space trajectories with CAIPIRINHA sampling. It reduces artifacts and limits reconstruction induced spatially varying noise enhancement. The GRAPPA-based wave-CAIPI method is robust and does not depend on the accuracy of coil sensitivity estimations. Methods We developed a GRAPPA-based, noniterative wave-CAIPI reconstruction algorithm utilizing multiple GRAPPA kernels. For data acquisition, we implemented a fast 3D magnetization-prepared rapid gradient-echo wave-CAIPI sequence tailored for ultra-high field application. The imaging results were evaluated by comparing the g-factor and the root mean square error to Cartesian CAIPIRINHA acquisitions. Additionally, to assess the performance of subcortical segmentations (calculated by FreeSurfer), the data were analyzed across five subjects. Results Sixteen-fold accelerated whole brain magnetization-prepared rapid gradient-echo data (1 mm isotropic resolution) were acquired in 40 seconds at 7T. A clear improvement in image quality compared to Cartesian CAIPIRINHA sampling was observed. For the chosen imaging protocol, the results of 16-fold accelerated wave-CAIPI acquisitions were comparable to results of 12-fold accelerated Cartesian CAIPIRINHA. In comparison to the originally proposed SENSitivity Encoding reconstruction of Wave-CAIPI data, the GRAPPA approach provided similar image quality. Conclusion High-quality, wave-CAIPI magnetization-prepared rapid gradient-echo images can be reconstructed by means of a GRAPPA-based reconstruction algorithm. Even for high acceleration factors, the noniterative reconstruction is robust and does not require coil sensitivity estimations. By altering the aliasing pattern, ultra-fast whole-brain structural imaging becomes feasible.

INTRODUCTION: We investigated in a prospective, observational trial the feasibility of using the Eustachian tube function test (ETFT) to measure the effect of repetitive pressure exposure during open seawater dives on Eustachian tube function. METHODS: The study included 28 adult divers during six consecutive days of diving in the Red Sea. Participants underwent otoscopy and ETFT before the first dive, between each dive and after the last dive. ETFT included regular tympanometry (R-tymp), tympanometry after Valsalva (V-tymp) and after swallowing (S-tymp). The R-tymp was obtained as 'baseline' peak pressure. After a Valsalva, the peak pressure should shift (positively), revealing a positive shift of the tympanic membrane. This pressure shift is defined here as R-V(dP). The changes in compliance and peak pressure were recorded and correlated with otoscopic findings and diving experience. Middle ear barotrauma was scored using the Edmonds modified TEED scale. RESULTS: The 28 participants performed 437 dives. Positive shift of pressure in the middle ear was evident with significant changes from day one to day three (P < 0.0001). Divers with barotrauma showed significantly lower values of R-tymp peak pressure and significantly higher negative R-V(dP), compared to divers with normal otoscopic findings (P < 0.05). Diving experience significantly correlated with R-tymp peak pressure and prevalence of middle ear barotrauma. CONCLUSIONS: Significant changes in middle ear pressure and pressure equalization from repeated pressure exposure in saltwater were seen using ETFT. Repetitive, multi-day diving led to significantly decreased compliance and increased R-tymp peak pressure (overpressure) in the middle ear. Most profound changes were observed in less and intermediate experienced divers.

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., SDS is supported by a NARSAD Young Investigator Grant (Grant #25104) and by the European Research Council through a Marie Skłodowska-Curie Individual Fellowship (Grant #749506). MB is supported by the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013/ERC Grant Agreement #319456). This work was also supported by a grant from Federal Ministry for Education and Research (BMBF, KKNMS, project MSNetworks) to SG and FZ. AR is supported by Netherlands Organisation for Scientific Research through a VIDI grant (#14637).

Demonstration of a 3D version of the DREAM sequence (3DREAM) for rapid 3D flip angle and B 1 + mapping of the human brain.A rectangular non-selective STE preparation is followed by a 3D readout with a Cartesian center-out spiral phase encoding order. This enables parallel imaging acceleration in both phase encoding dimensions as well as early capture of the prepared magnetization. B 1 + mapping of the whole human head is demonstrated on a 7T system at a nominal resolution of 5 mm with and without parallel imaging acceleration. Artifacts caused by the different signal decay of the FID and STE signal during the long imaging train is suppressed by appropriate filtering of the FID image. Remaining blurring can be controlled by adjusting the echo train length and readout flip angle.3DREAM provides a whole-brain flip angle map in a few seconds or individual maps for an 8-channel array in about a minute.

Purpose The fluid attenuated inversion recovery sequence is a pillar technique to detect brain lesions in MRI. At ultrahigh field, the lengthening of T1 often advocates a T2 -weighting preparation module to regain signal and contrast between tissues, which can be affected by transmit RF field inhomogeneity. In this note, we report an extension of a previous fluid attenuated inversion recovery study that now incorporates the T2 preparation with parallel transmission calibration-free universal pulses to mitigate the problem. Methods The preparation consisted of a 90°-τ-180° -τ-90° module to implement an effective inversion in the CSF and a saturation in the brain tissues. Care was taken for the pulses to have the desired phase relationship in every voxel by appropriate pulse design. The RF pulse design made use of the kT -point parametrization and was based on a database of 20 B1 + and ΔB0 maps previously acquired on different subjects at 7 T. Simulations and experiments on 5 volunteers, not contained in the database, were performed for validation. Results Simulations reported very good inversion efficiency for the preparation module with 8% variation, with respectively 4 and 6 times less power and specific absorption rate than for the adiabatic version. Experiments revealed fluid attenuated inversion recovery images free of B1 + artifacts. Conclusion This work contributes further to the panel of 3D sequences validated and now available with universal pulses at 7 T. The drop in power and specific absorption rate demand compared with adiabatic pulses in the T2 preparation leads to more freedom for the design of the readout train.

The fluid attenuated inversion recovery sequence is a pillar technique to detect brain lesions in MRI. At ultrahigh field, the lengthening of TThe preparation consisted of a 90°-τ-180Simulations reported very good inversion efficiency for the preparation module with 8% variation, with respectively 4 and 6 times less power and specific absorption rate than for the adiabatic version. Experiments revealed fluid attenuated inversion recovery images free of BThis work contributes further to the panel of 3D sequences validated and now available with universal pulses at 7 T. The drop in power and specific absorption rate demand compared with adiabatic pulses in the T

PURPOSE: The aim of this project was to implement an ultra-high field (UHF) optimized double inversion recovery (DIR) sequence for gray matter (GM) imaging, enabling whole brain coverage in short acquisition times ( ≈5 min, image resolution 1 mm(3) ).METHODS: A 3D variable flip angle DIR turbo spin echo (TSE) sequence was optimized for UHF application. We implemented an improved, fast, and specific absorption rate (SAR) efficient TSE imaging module, utilizing improved reordering. The DIR preparation was tailored to UHF application. Additionally, fat artifacts were minimized by employing water excitation instead of fat saturation.RESULTS: GM images, covering the whole brain, were acquired in 7 min scan time at 1 mm isotropic resolution. SAR issues were overcome by using a dedicated flip angle calculation considering SAR and SNR efficiency. Furthermore, UHF related artifacts were minimized.CONCLUSION: The suggested sequence is suitable to generate GM images with whole-brain coverage at UHF. Due to the short total acquisition times and overall robustness, this approach can potentially enable DIR application in a routine setting and enhance lesion detection in neurological diseases. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Research on molluscan specimens is increasingly being carried out using high-throughput molecular techniques. Due to their efficiency, these technologies have effectively resulted in a strong bias towards genotypic analyses. Therefore, the future large-scale correlation of such data with the phenotype will require a significant increase in the output of morphological studies. Three-dimensional (3D) scanning techniques such as magnetic resonance imaging (MRI) or computed tomography (CT) can achieve this goal as they permit rapidly obtaining digital data non-destructively or even entirely non-invasively from living, fixed, and fossil samples. With a large number of species and a relatively complex morphology, the Mollusca would profit from a more widespread application of digital 3D imaging techniques. In order to provide an overview of the capacity of various MRI and CT techniques to visualize internal and external structures of molluscs, more than twenty specimens ranging in size from a few millimeters to well over one meter were scanned in vivo as well as ex vivo. The results show that all major molluscan organ systems can be successfully visualized using both MRI and CT. The choice of a suitable imaging technique depends primarily on the specimen’s life condition, its size, the required resolution, and possible invasiveness of the approach. Apart from visual examples derived from more than two dozen scans, the present article provides guidelines and best practices for digital 3D imaging of a broad range of molluscan taxa. Furthermore, a comprehensive overview of studies that previously have employed MRI or CT techniques in malacological research is given.

To investigate the impact of accelerated, single-shot 3D-GRASE acquisition on quantitative arterial spin labeling (ASL) with multiple and single post-labeling delay (PLD) in terms of perfusion-weighted SNR per unit scan time (TSNRPW ) and quantification accuracy.Five subjects were scanned on a 3T MRI scanner using the pseudo-continuous arterial spin labeling (PCASL) technique with a 3D-GRASE imaging sequence capable of parallel imaging acceleration. A 3-inversion pulse background suppression was simulated and implemented in the sequence. Three time-matched single PLD measurements, a segmented one without acceleration, 1 with conventional GRAPPA, and 1 with CAIPIRINHA sampling, were used to compare TSNRPW . Three time-matched multiple PLD measurements with the identical imaging parameters were additionally evaluated (no acceleration vs. CAIPIRINHA sampling vs. CAIPIRINHA sampling with doubled number of PLDs). Cerebral blood flow and arterial transit time fit uncertainties were compared and used as a quality measure.The single PLD measurements show an 11% TSNRPW increase using CAIPIRINHA sampling instead of GRAPPA sampling, while the non-accelerated scan exhibits 35% higher TSNRPW compared to the GRAPPA scan. However, taking advantage of the increased number of averages for multiple PLD acquisitions, a 14%/16% (gray matter) and 34%/36% (white matter) reduction of CBF fit uncertainty is observed with CAIPIRINHA sampling (6 PLDs/12 PLDs) compared to no acceleration.Accelerated single-shot 3D-GRASE with PCASL allows for smaller quantification uncertainties than time-matched segmented acquisitions. Corresponding single-shot acquisitions with acceptable blurring and no intra-volume motion render state-of-the-art ASL methods in a clinically feasible time possible.