Quantitative analysis of liver function: 3D variable-flip-angle versus Look-Locker T1 relaxometry in hepatocyte-specific contrast-enhanced liver MRI.

Abstract

Gd-EOB-DTPA, a liver specific contrast agent with T1- shortening effects, is routinely used in clinical magnetic resonance imaging (MRI) for detection and characterization of focal liver lesions. Gd-EOB-DTPA-enhanced T1 relaxometry has recently received increasing attention as a tool for the quantitative analyses of liver function. However, this T1 relaxometry technique is limited due to various artifacts caused by B1 inhomogeneities and motion artifacts. This study aims to compare two different T1 relaxometry techniques for evaluating liver function as determined using a 13C-methacetin-based breath test (13C-MBT). Ninety-six patients underwent gadoxetic acid-enhanced MRI of the liver at 3T and a 13C-MBT. Two different prototype sequences for T1 relaxometry were used, a 3D VIBE sequence using Dixon water-fat separation and variable-flip-angles (VFA), as well as a 2D Look-Locker sequence (LL). Images were acquired before (T1 pre) and 20 minutes after (T1 post) administration of liver-specific contrast agent to evaluate the reduction rates of T1 relaxation time (rrT1) in accordance with the 13C-MBT outcome. To analyze both MR sequences' performance, the intraclass correlation coefficient (ICC) between four ROI measurements within the same liver and the coefficient of repeatability (CR) were calculated. T1 relaxometry measurements based on MR sequences, VFA, and LL show a constant change in line with impaired liver function progression. Simple regression models showed a log-linear correlation of 13C-MBT values with all evaluated T1 relaxometry measurements (VFA T1post, VFA rrT1, LL T1post, LL rrT1, P<0.001). Both ICC (VFA T1post, LL T1post; 0.75, 0.95) and CR (VFA T1 post, LL T1 post; 179, 101) showed a better agreement between ROI measurements using the LL sequence. Both T1 relaxometry sequences are suitable for the evaluation of liver function based on 13C-MBT. However, the Look-Locker sequence is less susceptible to artifacts and might be more advantageous, especially in patients with impaired liver function.