Improved gray-white matter contrast using magnetization prepared fast imaging with steady-state free precession (MP-FISP) brain imaging at 0.55 T.

Abstract

To improve the gray/white matter contrast of magnetization prepared rapid gradient echo (MP-RAGE) MRI at 0.55 T by optimizing the acquisition and sequence kernel parameters. A segmented magnetization prepared rapid gradient echo prototype sequence was implemented with (MP-RAGE*) and without (MP-FISP*) radiofrequency spoiling. Optimized parameters were derived with the assistance of an extended phase graph signal simulation as a function of the relaxation times, the flip angle, the delay times, and the effective inversion time using segmentation. The resulting protocols were compared to the MP-RAGE product sequence offered by the vendor in terms of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). A tissue segmentation reproducibility study was performed on three volunteers for the product MP-RAGE and the MP-FISP*. The MP-RAGE simulation reproduced the parameters already used in the product MP-RAGE on the scanner. An average CNR improvement of 15% for the custom MP-RAGE* over the product MP-RAGE and additional 22% for the MP-FISP* over the MP-RAGE* were observed, which is in accordance with the simulation results. The total improvement, averaged over all volunteers and regions, was 41%. The reproducibility study did not yield a significant difference between MP-RAGE and MP-FISP*. We presented some easy-to-implement adjustments to the MP-RAGE sequence at 0.55 T, which can lead to an overall average improvement of 41% in CNR.