INTRODUCTION: In liver MR imaging using gadoxetic acid disodium (Gd-EOB-DTPA), multiphasic dynamic imaging including arterial, portal, transitional and hepatobiliary phases during a separate breath-holding has been widely used to detect and characterize hepatic lesions. Additionally, some studies showed that the signal intensity (SI) of the hepatic parenchyma in the hepatobiliary phase (HBP) was related to the severity of hepatic fibrosis and could be used to estimate the liver function. The recent introduction of compressed sensing (CS) combined with a self-gating technique enables continuous multiphasic dynamic MR imaging during free-breathing for several minutes, allowing for the evaluation of the continuous signal change of the hepatic parenchyma over time. However, there have been no studies evaluating the relationship between the continuous signal change of the liver and the hepatic contrast enhancement effect in the HBP. The purpose of this study was to investigate the relationship between the hepatic contrast enhancement effect in the HBP and the hepatic contrast enhancement parameters based on data of continuous signal changes obtained by free-breathing continuous multiphasic dynamic EOB-MR imaging using CS and self-gating technique. METHODS: Our study included 96 patients who underwent free-breathing continuous multiphasic dynamic EOB-MR imaging of the liver using CS and self-gating technique due to HCC, hemangioma, or liver metastases. Free-breathing continuous dynamic T1-weighted images were obtained every 11 seconds for about 5 minutes including 1 precontrast and 28 post-contrast phases. The injection of contrast materials was started just after the completion of the precontrast phase acquisition. Finally, HBP images were obtained 20 min. after the contrast injection as 30th phase images. The region of intensity (ROI) was set as large as possible at two locations in the right lobe and one in the left lobe, avoiding blood vessels, and the SI of each temporal phase was measured at the same location. The average of the SI of the three ROIs was taken as the signal intensity for each time phase. Several contrast enhancement parameters based on data of continuous signal changes were calculated to evaluate the enhancement effects of the liver parenchyma. The contrast enhancement ratio (CER) from phase X to phase y was calculated as follows: CERy-x: (SIy -SIx)/SIx. The gradient of the regression line was also calculated if necessary. We have calculated CER4-pre (arterial enhancement rate), CER7-5 (portal-arterial enhancement rate), CER7-pre (portal enhancement rate), CER28-pre (5min early hepatocyte enhancement rate), CER28-7 (early hepatocyte-portal enhancement rate), and CERHBP-pre (20min hepatocyte enhancement rate). For the gradient of a regression line (Gradienty-x : the gradient from the phase X to the phase Y), we calculated Gradient4-2 (arterial transit gradient), Gradient7-4 (portal transit gradient), Gradient7-2 (arterioportal transit gradient), Gradient28-7 (early hepatocytic transit gradient). According to the severity of liver fibrosis (F0-F2, F3-F4), patients can be divided into two groups with sufficient or insufficient liver enhancement based on CERHBP-pre with a cutoff value of 0.7031. Then, each parameter was compared between these two groups. In addition, age, gender, total bilirubin, prothrombin time, albumin, and eGFR were also compared between the two groups (Wilcoxon's rank sum test). A nonparametric test was also performed to determine the effect of each item on the SI of the HBP (Spearman's rank sum correlation coefficient). RESULTS: In the analysis of the arterioportal phases (phases 1-7), CER7-pre in the sufficient HBP enhancement group was significantly higher than that in the insufficient HBP enhancement group (0.50 vs 0.44, p<0.001) while the differences in CER4-pre, Gradient4-2, Gradient7-4 and Gradient7-2 were not significant between the two groups. Regarding 5min early hepatocyte phase (phases 1-28) analysis, significant differences were observed in CER28-pre, CER28-7 and Gradient28-7 between the two groups (0.64 vs 0.47, 0.10 vs 0.03, 1.27 vs 0.27, all p<0.001). The parameters of blood sampling (total bilirubin, prothrombin time, albumin, and eGFR) showed significant differences between the two groups (p=0.049~0.004). For the strength of correlation between hepatic contrast enhancement effect in the 20min HBP and each parameter, CER7-pre, CER28-pre, CER28-7, and Gradient28-7 had higher correlation coefficients, compared with total bilirubin, prothrombin time, albumin, and eGFR. CER28-pre showed the highest correlation coefficient (0.838). (Table 1-3). DISCUSSION: Our study showed that CER7-pre, CER28-pre and CER28-7 were significantly well correlated with hepatic contrast enhancement effect in the 20min HBP, compared with the blood sampling parameters. In addition, CER7-pre, CER28-pre and CER28-7 were significantly higher in the sufficient HBP enhancement group than in the insufficient HBP enhancement group. These facts suggested that the CER in the portal phase and 5min early hepatocyte phase (CER7-pre, CER28-pre and CER28-7) may help estimate the sufficient 20min HBP enhancement, and that these parameters may be used to shorten the timing of imaging the HBP. CONCLUSION: In the analysis of the hepatic contrast enhancement parameters based on continuous data of the signal changes over time obtained by free-breathing continuous multiphasic dynamic EOB-MR imaging using CS and self-gating technique, CER in the portal phase and 5min early hepatocyte phase had significant correlation with hepatic contrast enhancement effects in the 20min HBP, and showed significant difference between sufficient and insufficient HBP enhancement groups, suggesting that sufficient 20min HBP enhancement may be estimated by the CER in the portal phase and 5min early hepatocyte phase.

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References

REFERENCES: References should use the suggested style below. 1. C Besa , M Wagner, et al. Detection of Liver Fibrosis Using Qualitative and Quantitative MR Elastography Compared to Liver Surface Nodularity Measurement, Gadoxetic Acid Uptake, and Serum Markers. J Magn Reson Imaging. 2018; 47: 1552-1561