Liver functional assessment using time-associated change in the liver-to-spleen signal intensity ratio on enhanced magnetic resonance imaging: a retrospective study

Abstract

Abstract Background Liver-to-spleen signal intensity ratio (LSR) is evaluated by magnetic resonance imaging (MRI) in the hepatobiliary phase, and has been reported as a useful radiological assessment of regional liver function. However, LSR is a passive (non-time-associated) liver functional assessment, but not a dynamic (time-associated) assessment. Moreover, LSR has several limitations such as dose bias of contrast medium and the timing bias of imaging. Previous studies have reported the advantages of time-associated liver functional assessment as a precise assessment of liver function. For instance, the indocyanine green (ICG) disappearance rate, which is calculated from the serum ICG concentration at multiple time points, reflects a precise preoperative liver function for predicting post-hepatectomy liver failure without the dose bias of ICG or the timing bias of blood sampling. The aim of this study was to develop a novel time-associated radiological assessment of liver function. Methods A total of 279 pancreatic cancer patients were evaluated for investigating fundamental time-associated changes of LSR in normal liver. We defined the time-associated radiological assessment of liver function, calculated using information on LSR from four time points, as the “LSR increasing rate” (LSRi). We then investigated correlations between LSRi and previous liver functional parameters. Furthermore, we evaluated how timing bias and protocol bias affect LSRi. Results Significant correlations were observed between LSRi and previous liver functional parameters such as total bilirubin, Child-Pugh grade, and albumin-bilirubin grade (P < 0.001 each). Conversely, the protocol bias of MRI acquisitions does not significantly affect LSRi. Moreover, considerably high correlations were observed between LSRi calculated by four time points and that calculated by three time points (r > 0.973 each), indicating that the timing bias of imaging was minimal. Conclusions This is the first report to propose time-associated assessment of radiological liver function. Changes in LSR over time may provide a superior preoperative assessment of regional liver function for predicting post-hepatectomy liver failure than any other radiological liver functional assessments using the hepatobiliary phase alone.