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Impact of Uncertainty in T1 Measurements On Quantification of Dynamic Contrast Enhanced MRI

M Aryal

M Aryal*, Y Cao , The University of Michigan, Ann Arbor, MI


SU-D-303-3 (Sunday, July 12, 2015) 2:05 PM - 3:00 PM Room: 303

Purpose: Quantification of dynamic contrast enhanced (DCE) MRI requires native longitudinal relaxation time (T1) measurement. This study aimed to assess uncertainty in T1 measurements using two different methods.
Methods and Materials: Brain MRI scans were performed on a 3T scanner in 9 patients who had low grade/benign tumors and partial brain radiotherapy without chemotherapy at pre-RT, week-3 during RT (wk-3), end-RT, and 1, 6 and 18 months after RT. T1-weighted images were acquired using gradient echo sequences with 1) 2 different flip angles (50 and 150), and 2) 5 variable TRs (100-2000ms). After creating quantitative T1 maps, average T1 was calculated in regions of interest (ROI), which were distant from tumors and received a total of accumulated radiation doses < 5 Gy at wk-3. ROIs included left and right normal Putamen and Thalamus (gray matter: GM), and frontal and parietal white matter (WM). Since there were no significant or even a trend of T1 changes from pre-RT to wk-3 in these ROIs, a relative repeatability coefficient (RC) of T1 as a measure of uncertainty was estimated in each ROI using the data pre-RT and at wk-3. The individual T1 changes at later time points were evaluated compared to the estimated RCs.
Results: The 2-flip angle method produced small RCs in GM (9.7-11.7%) but large RCs in WM (12.2-13.6%) compared to the saturation-recovery (SR) method (11.0-17.7% for GM and 7.5-11.2% for WM). More than 81% of individual T1 changes were within T1 uncertainty ranges defined by RCs.
Conclusion: Our study suggests that the impact of T1 uncertainty on physiological parameters derived from DCE MRI is not negligible. A short scan with 2 flip angles is able to achieve repeatability of T1 estimates similar to a long scan with 5 different TRs, and is desirable to be integrated in the DCE protocol.

Funding Support, Disclosures, and Conflict of Interest: Present study was supported by National Institute of Health (NIH) under grant numbers; UO1 CA183848 and RO1 NS064973

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