Program Information
Characterizing B1 Inhomogeneities in DCE MRI
H Gach1*, N Mason2 , (1) Washington University in St. Louis, St. Louis, MO, (2) University of Pittsburgh, Pittsburgh, PA
Presentations
TU-H-206-3 (Tuesday, August 2, 2016) 4:30 PM - 6:00 PM Room: 206
Purpose: Dynamic Contrast Enhanced (DCE) MRI is a valuable technique for measuring perfusion and permeability characteristics of tumors. Exogenous contrast concentrations are calculated based on changes in T₁ measured using fast 3D gradient echo (FLASH) sequences. However, the slab selective pulses used in 3D MRI may result in B₁ inhomogeneities across the volume of interest that can lead to errors in T₁ and thus the estimated gadolinium concentration. We compared three FLASH DCE sequences (GRE, TWIST, and VIBE) to determine their signal homogeneity across slices and the accuracy in calculating T₁ using acquisitions with variable flip angles.
Methods: The sequences were tested at 3 T on a Siemens mMR (VB20P) using a doped water phantom 3.75 g/L NiSO₄-6H₂O + 5 g/L NaCl (T₁ = 104 ms) and a 2% agar, 0.67% NaCl phantom (T₁ = 1.71 s). 2D EPI B₁ maps and inversion recovery T₁ maps were acquired for ground truth. 3D MRI was acquired at different flip angles to generate a T₁ map. Regions of interest were drawn to measure signal inside the phantoms as a function of slice position. The T₁ for each slice ROI was fit to the FLASH steady-state model of magnetization.
Results: Based on the data, GRE gave the most uniform signal homogeneity and T₁ values in the middle slices of the 3D volume. The 3D VIBE sequence had the largest region of signal inhomogeneity compared to the 3D GRE and TWIST sequences. VIBE’s B₁ inhomogeneity is inconsistent at low flip angles. However, VIBE resulted in more slices with T₁ values similar to the ground truth.
Conclusion: The central 1/3 of the slices yielded signals that result in T₁ fits consistent with the ground truth. However, the remaining slices required some form of B₁ inhomogeneity correction for quantitative DCE analysis.
Funding Support, Disclosures, and Conflict of Interest: The research was supported in part by NIH NCI Grant R01CA159471.
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