Highly efficient head‐only magnetic field insert gradient coil for achieving simultaneous high gradient amplitude and slew rate at 3.0T (MAGNUS) for brain microstructure imaging

Abstract

Purpose To develop a highly efficient magnetic field gradient coil for head imaging that achieves 200 mT/m and 500 T/m/s on each axis using a standard 1 MVA gradient driver in clinical whole‐body 3.0T MR magnet. Methods A 42‐cm inner diameter head‐gradient used the available 89‐ to 91‐cm warm bore space in a whole‐body 3.0T magnet by increasing the radial separation between the primary and the shield coil windings to 18.6 cm. This required the removal of the standard whole‐body gradient and radiofrequency coils. To achieve a coil efficiency ~4× that of whole‐body gradients, a double‐layer primary coil design with asymmetric x‐y axes, and symmetric z‐axis was used. The use of all‐hollow conductor with direct fluid cooling of the gradient coil enabled ≥50 kW of total heat dissipation. Results This design achieved a coil efficiency of 0.32 mT/m/A, allowing 200 mT/m and 500 T/m/s for a 620 A/1500 V driver. The gradient coil yielded substantially reduced echo spacing, and minimum repetition time and echo time. In high b = 10,000 s/mm2 diffusion, echo time (TE) < 50 ms was achieved (>50% reduction compared with whole‐body gradients). The gradient coil passed the American College of Radiology tests for gradient linearity and distortion, and met acoustic requirements for nonsignificant risk operation. Conclusions Ultra‐high gradient coil performance was achieved for head imaging without substantial increases in gradient driver power in a whole‐body 3.0T magnet after removing the standard gradient coil. As such, any clinical whole‐body 3.0T MR system could be upgraded with 3‐4× improvement in gradient performance for brain imaging.

Oscillating diffusion‐encoding with a high gradient‐amplitude and high slew‐rate head‐only gradient for human brain imaging

“…In this work, OGSE was evaluated on the microstructure anatomy gradient for neuroimaging with ultrafast scanning (MAGNUS), which is a head‐gradient that is able to simultaneously achieve high gradient amplitudes and slew rates of G max = 200 mT/m and SR max = 500 T/m/s respectively with similar high slew rate threshold for PNS as the Compact 3T head gradient . The effects of gradient performance on OGSE were first evaluated in simulations to determine the achievable b‐values and frequencies.…”

Sensitive detection of extremely small iron oxide nanoparticles in living mice using MP2RAGE with advanced image co-registration

“…In addition, there have been reports that cryoprobes increase SNR up to 40-50% without losing tissue characteristics in vivo [49][50][51] . The human MR scanner hardware also has been improved including main fields of 7T 29,52 , multi-channel RF coils with up to 64 channels 52 , and head only imaging gradient coil 53,54 . The employment of improved MR hardware will significantly increase SNR and spatial resolution.…”

Scan-rescan repeatability of axonal imaging metrics using high-gradient diffusion MRI and statistical implications for study design

“…In addition to the Connectom MRI scanner manufactured by Siemens, other scanner vendors have developed highly efficient gradient coils for clinical use. For example, the MAGNUS gradient developed by General Electric achieves 200 mT/m maximum gradient strength and 500 T/m/s slew rate and will be used for exploring tissue microstructure in patients undergoing clinical 3T MRI ( Foo et al, 2020 ). The higher gradient strengths available on preclinical systems allow the straightforward application of our findings to axon diameter mapping on small-bore systems, as the estimated axon diameter indices should approach the actual values of axon diameters measured on electron microscopy, within the limitations of the pulsed gradient spin echo experimental design and acquisition protocol ( Dyrby et al, 2013 ; Sepehrband et al, 2016 ).…”