CT-derived hepatic extracellular volume fraction for the assessment of graft rejection after liver transplantation: a retrospective observational study.

To evaluate the diagnostic performance of hepatic extracellular volume (ECV) fraction derived from delayed single-energy CT for identifying graft rejection in liver transplant recipients and its added value over clinical parameters. This retrospective observational study included consecutive adult liver transplant recipients with available unenhanced and delayed (3-5-min) contrast-enhanced CT examinations. Hepatic ECV was calculated using regions of interest in the liver parenchyma and abdominal aorta, corrected for hematocrit. Patients were stratified by the presence or absence of graft rejection. ECV values were compared using the Mann-Whitney U test. Logistic regression models were constructed to assess predictors of rejection. To avoid multicollinearity, separate MELD-based and laboratory-based clinical models were evaluated, and ECV was added to each model to assess its incremental value. Model performance was evaluated by comparing the area under the receiver operating characteristic curve (AUC). Eighty-four liver transplant recipients were included (21 with rejection and 63 without). Median ECV was 32.4% in the rejection group and 28.7% in the non-rejection group (P = 0.100). ECV alone demonstrated limited diagnostic performance (AUC 0.62). A MELD-based clinical model achieved an AUC of 0.73, which minimally increased to 0.74 after adding ECV (ΔAUC = 0.009; bootstrap P = 0.180). A laboratory-based model achieved an AUC of 0.72 and remained unchanged after adding ECV (ΔAUC = 0.0005; bootstrap P = 1.000). Hepatic ECV derived from delayed CT was not significantly associated with graft rejection and did not improve the diagnostic performance of either MELD-based or laboratory-based clinical models. Despite prior evidence linking increased ECV to hepatic injury and fibrosis, our findings suggest that ECV may not be sensitive to the complex and multifactorial processes underlying graft rejection in liver transplant recipients.