2D multislice MP2RAGE sequence for fast T mapping at 7 T: Application to mouse imaging and MR thermometry.

Purpose: To develop a 2D radial multislice MP2RAGE sequence for fast and reliable T mapping at 7 T in mice and for MR thermometry.

Methods: The 2D-MP2RAGE sequence was performed with the following parameters: TI -TI -MP2RAGE = 1000-3000-9000 ms. The multiple dead times within the sequence were used for interleaved multislice acquisition, enabling one to acquire six slices in 9 seconds. The excitation pulse shape, inversion selectivity, and interslice gap were optimized. In vitro comparison with the inversion-recovery sequence was performed. The T variations with temperature were measured on tubes with T ranging from 800 ms to 2000 ms. The sequence was used to acquire T maps continuously during 30 minutes on the brain and abdomen of healthy mice.

Results: A three-lobe cardinal sine excitation pulse, combined with an inversion slice thickness and an interslice gap of respectively 150% and 50% of the imaging slice thickness, led to a SD and bias of the T measurements below 1% and 2%, respectively. A linear dependence of T with temperature was measured between 10°C and 60°C. In vivo, less than 1% variation was measured between successive T maps in the mouse brain. In the abdomen, no obvious in-plane motion artifacts were observed but respiratory motion in the slice dimension led to 6% T underestimation.

Conclusion: The multislice MP2RAGE sequence could be used for fast whole-body T mapping and MR thermometry. Its reconstruction method would enable on-the-fly reconstruction.