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

Purpose 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. Methods 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*. Results 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*. Conclusion 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.