CNR improvement of MP2RAGE from slice encoding directional acceleration

Abstract

Purpose: While MP2RAGE shows the potential to generate B1 insensitive T1 contrast, the long TR of MP2RAGE (≥6s at 7T) is essential to provide the large dynamic range of apparent T1 relaxation for dual inversion time acquisitions. We present a 2 direction (2D) accelerated MP2RAGE, which provides an increased flip angle while maintaining similar dynamic recovery as 1D accelerated MP2RAGE.

Method: Simulations were conducted to optimize 2D accelerated MP2RAGE parameters and healthy subjects were scanned with 1D and 2D accelerated MP2RAGE at 7T. Images were compared visually and contrast to noise (CNR) between brain tissues was measured.

Result: Simulations showed that CNR is primarly determined by the TR, followed by the number of the first partition encoding steps in MP2RAGE. Keeping TR constant, a smaller number of partition encoding steps increases the achievable maximal CNR. In-vivo 2D MP2RAGE improves CNR between white and gray matters by 9% when compared to 1D accelerated MP2RAGE with identical voxel size.

Conclusion: We presented 2D accelated MP2RAGE at 7T with the increased flip angle. We show that this leads to CNR improvement, and consequently a reduction of scan time to be compared to 1D accelerated MP2RAGE.

Keywords: 2D acceleration; 7T; MP2RAGE; MPRAGE; SPIRiT; ultra-high filed.