Citations

PurposeTo build and evaluate a small‐footprint, lightweight, high‐performance 3T MRI scanner for advanced brain imaging with image quality that is equal to or better than conventional whole‐body clinical 3T MRI scanners, while achieving substantial reductions in installation costs.MethodsA conduction‐cooled magnet was developed that uses less than 12 liters of liquid helium in a gas‐charged sealed system, and standard NbTi wire, and weighs approximately 2000 kg. A 42‐cm inner‐diameter gradient coil with asymmetric transverse axes was developed to provide patient access for head and extremity exams, while minimizing magnet‐gradient interactions that adversely affect image quality. The gradient coil was designed to achieve simultaneous operation of 80‐mT/m peak gradient amplitude at a slew rate of 700 T/m/s on each gradient axis using readily available 1‐MVA gradient drivers.ResultsIn a comparison of anatomical imaging in 16 patients using T2‐weighted 3D fluid‐attenuated inversion recovery (FLAIR) between the compact 3T and whole‐body 3T, image quality was assessed as equivalent to or better across several metrics. The ability to fully use a high slew rate of 700 T/m/s simultaneously with 80‐mT/m maximum gradient amplitude resulted in improvements in image quality across EPI, DWI, and anatomical imaging of the brain.ConclusionsThe compact 3T MRI system has been in continuous operation at the Mayo Clinic since March 2016. To date, over 200 patient studies have been completed, including 96 comparison studies with a clinical 3T whole‐body MRI. The increased gradient performance has reliably resulted in consistently improved image quality.

PurposeTo investigate the feasibility of substantially reducing acoustic noise while performing diffusion tensor imaging (DTI) on a compact 3T (C3T) MRI scanner equipped with a 42‐cm inner‐diameter asymmetric gradient.MethodsA‐weighted acoustic measurements were made using 10 mT/m‐amplitude sinusoidal waveforms, corresponding to echo‐planar imaging (EPI) echo spacing of 0.25 to 5.0 ms, on a conventional, whole‐body 3T MRI and on the C3T. Acoustic measurements of DTI with trapezoidal EPI waveforms were then made at peak gradient performance on the C3T (80 mT/m amplitude, 700 T/m/s slew rate) and at derated performance (33 mT/m, 10 to 50 T/m/s) for acoustic noise reduction. DTI was acquired in two different phantoms and in seven human subjects, with and without gradient‐derating corresponding to multi‐ and single‐shot acquisitions, respectively.ResultsSinusoidal waveforms on the C3T were quieter by 8.5 to 15.6 A‐weighted decibels (dBA) on average as compared to the whole‐body MRI. The derated multishot DTI acquisition noise level was only 8.7 dBA (at 13 T/m/s slew rate) above ambient, and was quieter than non‐derated, single‐shot DTI by 22.3 dBA; however, the scan time was almost quadrupled. Although derating resulted in negligible diffusivity differences in the phantoms, small biases in diffusivity measurements were observed in human subjects (apparent diffusion coefficient = +9.3 ± 8.8%, fractional anisotropy = +3.2 ± 11.2%, radial diffusivity = +9.4 ± 16.8%, parallel diffusivity = +10.3 ± 8.4%).ConclusionThe feasibility of achieving reduced acoustic noise levels with whole‐brain DTI on the C3T MRI was demonstrated. Magn Reson Med 79:2902–2911, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Abstract Aims This study was designed to evaluate the safety, tolerability and haemodynamic effects of BMS-986231, a novel second-generation nitroxyl donor with potential inotropic, lusitropic and vasodilatory effects in patients hospitalized with decompensated heart failure and reduced ejection fraction (HFrEF). Methods and results Forty-six patients hospitalized with decompensated HFrEF were enrolled into four sequential dose-escalation cohorts in this double-blind, randomized, placebo-controlled Phase 2a study. Patients with baseline pulmonary capillary wedge pressure (PCWP) of ≥20 mmHg and a cardiac index of ≤2.5 L/min/m2 received one 6-h i.v. infusion of BMS-986231 (at 3, 5, 7 or 12 µg/kg/min) or placebo. BMS-986231 produced rapid and sustained reductions in PCWP, as well as consistent reductions in time-averaged pulmonary arterial systolic pressure, pulmonary arterial diastolic pressure and right atrial pressure. BMS-986231 increased non-invasively measured time-averaged stroke volume index, cardiac index and cardiac power index values, and decreased total peripheral vascular resistance. There was no evidence of increased heart rate, drug-related arrhythmia or symptomatic hypotension with BMS-986231. Analyses of adverse events throughout the 30-day follow-up did not identify any toxicities specific to BMS-986231, with the potential exception of infrequent mild-to-moderate headaches during infusion. There were no treatment-related serious adverse events. Conclusions BMS-986231 demonstrated a favourable safety and haemodynamic profile in patients hospitalized with advanced heart failure. Based on preclinical data and these study's findings, it is possible that the haemodynamic benefits may be mediated by inotropic and/or lusitropic as well as vasodilatory effects. The therapeutic potential of BMS-986231 should be further assessed in patients with heart failure.

PurposeTo investigate the effect of the asymmetric gradient concomitant fields (CF) with zeroth and first‐order spatial dependence on fast/turbo spin‐echo acquisitions, and to demonstrate the effectiveness of their real‐time compensation.MethodsAfter briefly reviewing the CF produced by asymmetric gradients, the effects of the additional zeroth and first‐order CFs on these systems are investigated using extended‐phase graph simulations. Phantom and in vivo experiments are performed to corroborate the simulation. Experiments are performed before and after the real‐time compensations using frequency tracking and gradient pre‐emphasis to demonstrate their effectiveness in correcting the additional CFs. The interaction between the CFs and prescan‐based correction to compensate for eddy currents is also investigated.ResultsIt is demonstrated that, unlike the second‐order CFs on conventional gradients, the additional zeroth/first‐order CFs on asymmetric gradients cause substantial signal loss and dark banding in fast spin‐echo acquisitions within a typical brain‐scan field of view. They can confound the prescan correction for eddy currents and degrade image quality. Performing real‐time compensation successfully eliminates the artifacts.ConclusionsWe demonstrate that the zeroth/first‐order CFs specific to asymmetric gradients can cause substantial artifacts, including signal loss and dark bands for brain imaging. These effects can be corrected using real‐time compensation. Magn Reson Med 79:1354–1364, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

PurposeImaging gradients result in the generation of concomitant fields, or Maxwell fields, which are of increasing importance at higher gradient amplitudes. These time‐varying fields cause additional phase accumulation, which must be compensated for to avoid image artifacts. In the case of gradient systems employing symmetric design, the concomitant fields are well described with second‐order spatial variation. Gradient systems employing asymmetric design additionally generate concomitant fields with global (zeroth‐order or B0) and linear (first‐order) spatial dependence.MethodsThis work demonstrates a general solution to eliminate the zeroth‐order concomitant field by applying the correct B0 frequency shift in real time to counteract the concomitant fields. Results are demonstrated for phase contrast, spiral, echo‐planar imaging (EPI), and fast spin‐echo imaging.ResultsA global phase offset is reduced in the phase‐contrast exam, and blurring is virtually eliminated in spiral images. The bulk image shift in the phase‐encode direction is compensated for in EPI, whereas signal loss, ghosting, and blurring are corrected in the fast‐spin echo images.ConclusionA user‐transparent method to compensate the zeroth‐order concomitant field term by center frequency shifting is proposed and implemented. This solution allows all the existing pulse sequences—both product and research—to be retained without any modifications. Magn Reson Med 79:1538–1544, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

AbstractMedical devices increasingly depend on software. While this expands the ability of devices to perform key therapeutic and diagnostic functions, reliance on software inevitably causes exposure to hazards of security vulnerabilities. This article uses a recent high‐profile case example to outline a proactive approach to security awareness that incorporates a scientific, risk‐based analysis of security concerns that supports ongoing discussions with patients about their medical devices.

PurposeTo investigate the effects on echo planar imaging (EPI) distortion of using high gradient slew rates (SR) of up to 700 T/m/s for in vivo human brain imaging, with a dedicated, head‐only gradient coil.Materials and MethodsSimulation studies were first performed to determine the expected echo spacing and distortion reduction in EPI. A head gradient of 42‐cm inner diameter and with asymmetric transverse coils was then installed in a whole‐body, conventional 3T magnetic resonance imaging (MRI) system. Human subject imaging was performed on five subjects to determine the effects of EPI on echo spacing and signal dropout at various gradient slew rates. The feasibility of whole‐brain imaging at 1.5 mm‐isotropic spatial resolution was demonstrated with gradient‐echo and spin‐echo diffusion‐weighted EPI.ResultsAs compared to a whole‐body gradient coil, the EPI echo spacing in the head‐only gradient coil was reduced by 48%. Simulation and in vivo results, respectively, showed up to 25–26% and 19% improvement in signal dropout. Whole‐brain imaging with EPI at 1.5 mm spatial resolution provided good whole‐brain coverage, spatial linearity, and low spatial distortion effects.ConclusionOur results of human brain imaging with EPI using the compact head gradient coil at slew rates higher than in conventional whole‐body MR systems demonstrate substantially improved image distortion, and point to a potential for benefits to non‐EPI pulse sequences. J. Magn. Reson. Imaging 2016;44:653–664.

PurposeTo characterize peripheral nerve stimulation (PNS) of an asymmetric head‐only gradient coil that is compatible with a commercial high–channel‐count receive‐only array.MethodsTwo prototypes of an asymmetric head‐only gradient coil set with a 42‐cm inner diameter were constructed for brain imaging at 3T with maximum performance specifications of up to 85 mT/m and 708 T/m/s. Tests were performed in 24 volunteers to measure PNS thresholds with the transverse (x = left–right; y = anterior–posterior [A/P]) gradient coils of both prototypes. Fourteen of these 24 volunteers were also tested for the z‐gradient PNS in the second prototype and were scanned with high–slew‐rate echo planar imaging (EPI) immediately after the PNS tests.ResultsFor both prototypes, the y‐gradient PNS threshold was markedly higher than the x‐gradient threshold. The z‐gradient threshold was intermediate between those for the x‐ and y‐coils. Of the 24 volunteers, only two experienced y‐gradient PNS at 80 mT/m and 500 T/m/s. All volunteers underwent the EPI scan without PNS when the readout direction was set to A/P.ConclusionMeasured PNS characteristics of asymmetric head‐only gradient coil prototypes indicate that such coils, especially in the A/P direction, can be used for fast EPI readout in high‐performance neuroimaging scans with substantially reduced PNS concerns compared with conventional whole body gradient coils. Magn Reson Med 76:1939–1950, 2016. © 2015 International Society for Magnetic Resonance in Medicine