128‐channel body MRI with a flexible high‐density receiver‐coil array

Abstract

Purpose: To determine whether the promise of high-density many-coil MRI receiver arrays for enabling highly accelerated parallel imaging can be realized in practice. Materials and Methods:A 128-channel body receiver-coil array and custom MRI system were developed. The array comprises two clamshells containing 64 coils each, with the posterior array built to maximize signal-to-noise ratio (SNR) and the anterior array design incorporating considerations of weight and flexibility as well. Phantom imaging and human body imaging were performed using a variety of reduction factors and 2D and 3D pulse sequences. Results:The ratio of SNR relative to a 32-element array of similar footprint was 1.03 in the center of an elliptical loading phantom and 1.7 on average in the outer regions. Maximum g-factors dropped from 5.5 (for 32 channels) to 2.0 (for 128 channels) for 4 ϫ 4 acceleration and from 25 to 3.3 for 5 ϫ 5 acceleration. Residual aliasing artifacts for a right/left (R/L) reduction factor of 8 in human body imaging were significantly reduced relative to the 32-channel array. Conclusion:MRI with a large number of receiver channels enables significantly higher acceleration factors for parallel imaging and improved SNR, provided losses from the coils and electronics are kept negligible.

Three‐dimensional quadrature array coil elements for improved parallel magnetic resonance imaging performance at 1.5 Tesla

“…Dedicated nuclear magnetic resonance (NMR) phased-array coils are required to use these imaging techniques. The recent development of MR systems with up to 128 independent receiver channels (8,9) allows for introducing phased-array coils with a likewise large number of coil elements (10)(11)(12). This way, further reductions in imaging time as well as better signal-to-noise ratios (SNRs) for standard accelerations of up to a factor of four were achieved (13,14).…”

RF encoding using a multielement parallel transmit system

“…Unfortunately, the generation of high spatial frequencies is limited also for phase-dominated RF encoding due to the smooth shape of typical phase transmit profiles. Here, a trend toward higher channel numbers as observed for parallel imaging (see, e.g., (22,23)), probably connected with modified amplifier concepts, might play a role. A separate study shall clarify if an increased transmit channel count is able to generate higher frequencies in phase-transmit profiles.…”

In vivo sensitivity estimation and imaging acceleration with rotating RF coil arrays at 7 Tesla

“…Using a large number of RF coils can increase the SNR and significantly accelerate the imaging process [69][70][71][72]. However, placing a large number of coils in a constrained space will decrease the coil size, leading to a shallower B 1 penetration.…”