Impact of uncertainty in longitudinal T1 measurements on quantification of dynamic contrast-enhanced MRI

The objective of this study was to assess the uncertainty in T-1 measurement, by estimating the repeatability coefficient (RC) from two repeated scans, in normal appearing brain tissues employing two different T-1 mapping methods. All brain MRI scans were performed on a 3T MR scanner in 10 patients who had low grade/benign tumors and partial brain radiation therapy (RT) without chemotherapy, at pre-RT, 3weeks into RT, end RT (6weeks) and 11, 33, and 85weeks after RT. T-1-weighted images were acquired using (1) a spoiled gradient echo sequence with two flip angles (2FA: 5 degrees and 15 degrees) and (2) a progressive saturation recovery sequence (pSR) with five different TR values (100-2000ms). Manually drawn volumes of interest (VOIs) included left and right normal putamen and thalamus in gray matter, and frontal and parietal white matter, which were distant from tumors and received a total of accumulated radiation doses less than 5Gy at 3weeks. No significant changes or even trends in mean T-1 from pre-RT to 3weeks into RT in these VOIs (p0.11, Wilcoxon sign test) allowed us to calculate the repeatability statistics of between-subject means of squares, within-subject means of squares, F-score, and RC. The 2FA method produced RCs in the range of (9.7-11.7)% in gray matter and (12.2-14.5)% in white matter; while the pSR method led to RCs ranging from 10.9 to 17.9% in gray matter and 7.5 to 10.3% in white matter. The overall mean (+/- SD) RCs produced by the two methods, 12.0 (+/- 1.6)% for 2FA and 12.0 (+/- 3.8)% for pSR, were not significantly different (p=0.97). A similar repeatability in T-1 measurement produced by the time efficient 2FA method compared with the time consuming pSR method demonstrates that the 2FA method is desirable to integrate into dynamic contrast-enhanced MRI for rapid acquisition. Copyright (c) 2016 John Wiley & Sons, Ltd.