2D multislice MP2RAGE sequence for fast T₁ mapping at 7 T: Application to mouse imaging and MR thermometry

Abstract

Purpose:To develop a 2D radial multislice MP2RAGE sequence for fast and reliable T 1 mapping at 7 T in mice and for MR thermometry. Methods: The 2D-MP2RAGE sequence was performed with the following parameters: TI 1 -TI 2 -MP2RAGE TR = 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 1 variations with temperature were measured on tubes with T 1 ranging from 800 ms to 2000 ms. The sequence was used to acquire T 1 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 1 measurements below 1% and 2%, respectively. A linear dependence of T 1 with temperature was measured between 10°C and 60°C. In vivo, less than 1% variation was measured between successive T 1 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 1 underestimation. Conclusion: The multislice MP2RAGE sequence could be used for fast wholebody T 1 mapping and MR thermometry. Its reconstruction method would enable onthe-fly reconstruction.