Parallel transmit optimized 3D composite adiabatic spectral‐spatial pulse for spectroscopy

Abstract

To develop a 3D composite adiabatic spectral-spatial pulse for refocusing in spin-echo spectroscopy acquisitions and to compare its performance against standard acquisition methods. Methods: A 3D composite adiabatic pulse was designed by modulating a train of parallel transmit-optimized 2D subpulses with an adiabatic envelope. The spatial and spectral profiles were simulated and validated by experiments to demonstrate the feasibility of the design in both single and double spin-echo spectroscopy acquisitions. Phantom and in vivo studies were performed to evaluate the pulse performance and compared with semi-LASER with respect to localization performance, sequence timing, signal suppression, and specific absorption rate. Results: Simultaneous 2D spatial localization with water and lipid suppression was achieved with the designed refocusing pulse, allowing high-quality spectra to be acquired with shorter minimum TE/TR, reduced SAR, as well as adaptation to spatially varying B 0 and B + 1 field inhomogeneities in both prostate and brain studies. Conclusion: The proposed composite pulse can serve as a more SAR efficient alternative to conventional localization methods such as semi-LASER at ultrahigh field for spin echo-based spectroscopy studies. Subpulse parallel-transmit optimization provides the flexibility to manage the tradeoff among multiple design criteria to accommodate different field strengths and applications.

Inter‐subject stability and regional concentration estimates of 3D‐FID‐MRSI in the human brain at 7 T

“…The exclusion of 11 ROIs, predominantly basal brain regions such as brain stem or cerebellum, from further analysis was necessary due to the lack of spectral fit confidence, limiting the mappable brain coverage. This shows that B 0 -and B 1 -field inhomogeneities (the first caused by the proximity to the nasal and auditory cavities, the second by the limitations of single channel transmit coils at 7 T) remain a significant ultra-highfield challenge, which will have to be resolved via hardware improvements [84][85][86] and/or further improved high-resolution approaches. 87 Filtering of outliers based on a set of rigid criteria is insufficient.…”

Ultra-high-field MR in Prostate cancer: Feasibility and Potential

“…Lipid contamination influenced the spectral quality, hindering detection of citrate and indicative of remaining inhomogeneities in the B 1 + field. Effort has also been put into the development of parallel transmit-designed adiabatic spectral-spatial refocusing pulses simultaneously providing both spatial localization and signal suppression insensitive to B0 variations [ 58 ].…”