OBJECTIVE. Frequency of acute rejection (AR) after pediatric liver transplant remains high despite progress in immunosuppression. Liver biopsy (LB) is the reference standard for the diagnosis of AR despite its potential for morbidity. The purpose of our study was to evaluate the ability of acoustic radiation force impulse (ARFI) imaging to distinguish AR from other causes of short- and medium-term liver dysfunction and to identify liver transplant cases with normal liver function. MATERIALS AND METHODS. ARFI imaging was used to evaluate shear wave velocity (SWV) after liver transplant in young children. All pediatric liver grafts that had LB and ARFI examination between January 2014 and December 2017 were included in this retrospective study. Results of LB were compared with those of SWV. Collected data included age at biopsy and transplant, sex, weight, height, body mass index, interval between liver transplant and shear wave elastography and LB, kind of graft, type of donor, and diagnosis at transplant. ROC curve analysis was performed to assess the diagnostic performance of SWV. Optimal cutoff of SWV using ARFI imaging in predicting AR was identified using the Youden index. RESULTS. Statistical analysis was performed on 54 children; six of the original 60 were excluded because of confounding alterations or changes in outcome. Median SWV was higher in patients with AR (2.03 m/s; interquartile range [IQR], 1.80-2.45 m/s) compared with those with idiopathic hepatitis (1.33 m/s; IQR, 1.12-1.53 m/s), portal hypertension (1.42 m/s; IQR, 1.32-1.72 m/s), cholangitis (1.56 m/s; IQR, 1.07-1.62 m/s) or normal liver function (1.23 m/s; IQR 1.12-1.29 m/s) at protocol biopsies (all comparisons, p < 0.01). SWV higher than 1.73 m/s was predictive for AR (AUC, 0.966). SWV also showed good diagnostic accuracy in normal liver function (AUC, 0.791). ARFI imaging was not predictive for hepatitis (AUC, 0.402), portal hypertension (AUC, 0.556), or cholangitis (AUC, 0.420). CONCLUSION. ARFI imaging could be routinely used in place of LB in pediatric patients with liver dysfunction after liver transplant, restricting indication and risks of biopsy to selected cases.

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