Program Information
B1 Inhomogeneity Correction for Measuring T1 From DCE MRI
H Gach1*, N Mason2, H Wang1, C Tsien1, T Benzinger1, C Robinson1 (1) Washington University in St. Louis, St. Louis, MO, (2) University of Pittsburgh, Pittsburgh, PA
Presentations
TU-H-206-6 (Tuesday, August 2, 2016) 4:30 PM - 6:00 PM Room: 206
Purpose: 3D MRI sequences typically used in DCE MRI suffer from B1 inhomogeneities associated with the slab-selective RF pulse. B₁ inhomogeneities affect the calculation of tissue T₁ often used to solve the two-compartment model. Previously, the inhomogeneities were corrected based on Bloch equation simulations of the RF pulse. However, the RF pulse specification may not be readily available or the simulation may not represent the actual scan conditions. The objective of this work was to directly measure B₁ inhomogeneities and apply an inhomogeneity correction to minimize quantification errors in T₁ fitting.
Methods: We used a 3D GRE sequence with varied flip angles (2-30⁰) to measure T₁-weighted signals in phantoms at 3 T on a Siemens mMR. 2D EPI B₁ maps were acquired to measure the B₁ inhomogeneity associated with the RF coils. Inversion recovery T1 maps were acquired for ground truth. Two B₁ inhomogeneity correction methods were compared: 1) A 3D segmented EPI sequence measured the RF slab selective excitation profile; and 2) The T₁’s of phantom standards were used to normalize the 3D GRE images.
Results: Only the central 1/3 of the 3D GRE slices yielded accurate T₁ values without correction. The slice profiles measured with 3D EPI were consistent between measurements made with different flip angles. The two correction approaches resulted in similar T₁ values for at least 2/3 of the slices. Approach 2 yielded more slices with values comparable to the ground truth. However, Approach 1 resulted in less error than Approach 2 for the upper 2/3 of the slices.
Conclusion: Using a phantom standard with a short T₁ allowed us to shorten the acquisition time of the 3D EPI sequence to less than 1 minute or increase spatial resolution. The B₁ inhomogeneity correction technique requires further testing in vivo for DCE MRI studies.
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