Hepatobiliary MRI: Signal intensity based assessment of liver function correlated to 13C-Methacetin breath test

Abstract

Gadoxetic acid (Gd-EOB-DTPA) is a paramagnetic MRI contrast agent with raising popularity and has been used for evaluation of imaging-based liver function in recent years. In order to verify whether liver function as determined by real-time breath analysis using the intravenous administration of ¹³C-methacetin can be estimated quantitatively from Gd-EOB-DTPA-enhanced MRI using signal intensity (SI) values. 110 patients underwent Gd-EOB-DTPA-enhanced 3-T MRI and, for the evaluation of liver function, a ¹³C-methacetin breath test (¹³C-MBT). SI values from before (SI_pre) and 20 min after (SI_post) contrast media injection were acquired by T1-weighted volume-interpolated breath-hold examination (VIBE) sequences with fat suppression. The relative enhancement (RE) between the plain and contrast-enhanced SI values was calculated and evaluated in a correlation analysis of ¹³C-MBT values to SI_post and RE to obtain a SI-based estimation of ¹³C-MBT values. The simple regression model showed a log-linear correlation of ¹³C-MBT values with SI_post and RE (p < 0.001). Stratified by 3 different categories of ¹³C-MBT readouts, there was a constant significant decrease in both SI_post (p ≤ 0.002) and RE (p ≤ 0.033) with increasing liver disease progression as assessed by the ¹³C-MBT. Liver function as determined using real-time ¹³C-methacetin breath analysis can be estimated quantitatively from Gd-EOB-DTPA-enhanced MRI using SI-based indices.

Figure 1

Liver function analysis in patients with normal liver function (A,B,C) and severely impaired liver function (D,E,F). The patients underwent plain (A,D) and Gd-EOB-DTPA-enhanced HBP (B,E) T1-weighted VIBE sequences with fat suppression, as well as a ¹³C-MBT, over a maximum time span of 60 min (C,F). In the case of the displayed patients, a ¹³C-MBT readout value of 409 µg/kg/h (C) was considered normal liver function (SI_pre, 182.67; SI_post, 441.67; RE, 1.42), while a ¹³C-MBT readout value of 57 µg/kg/h (F) was considered impaired liver function (SI_pre, 258.50; SI_post, 332.83; RE, 0.29). The lesion observed in the liver with impaired function (D,E) was caused by former radiofrequency ablations treatments. The delta-over-baseline (DOB) was assessed inline automatically and describes the increase in the R_PDB-corrected ¹³CO₂:¹²CO₂ ratio to the basal value (blue line). The evaluated ¹³C-MBT value was calculated as the product of the DOB_max, R_PDB, CO₂ production and molar mass of ¹³C-methacetin per body weight. The DOB_max (green line) was defined after an increase in DOB was no longer observable. At the time point 0, the ¹³C-methacetin was applied via bolus injection.

Figure 2

Correlation analysis of SI-based liver function indices to logarithmic values of ¹³C-MBT readout in scatterplots. The SI values obtained without contrast enhancement (SI_pre) show no predictive power for the logarithmic values of ¹³C-MBT (r = 0.213, p = 0.120; A), while the contrast-enhanced SI values (SI_post) show a significant correlation (r = 0.554, p < 0.001; B). A strong linear prediction of logarithmic ¹³C-MBT values can be observed for the relative enhancement (RE) values (r = 0.665, p < 0.001; C).

Figure 3

Boxplot analysis of SI-based indices separated by ¹³C-MBT readout categories. Native SI values (SI_pre; A) show no significant difference between the different ¹³C-MBT readout categories, except for Categories 1 and 2. SI values obtained after contrast enhancement (SI_post; B) and corrected by native SI values (RE; C) show significant differences among the ¹³C-MBT readout categories. *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 4

Representative example of ROI placement in unenhanced (A) and Gd-EOB-DTPA-enhanced VIBE (B) scans of a patient with normal liver function. White circles mark ROIs manually placed at identical places in the right and left lobe of the liver.