DWI/ADC in response assessment after local-regional treatment of HCC - Pearls and Pitfalls

Many patients with hepatocellular carcinoma (HCC) present with advanced-stage disease or multifocal tumors which make them unsuitable for radical treatment options. In such cases, locoregional therapy (LRT) such as transarterial chemoembolization (TACE), transarterial radioembolization (TARE) can be used as a bridge to liver transplantation or to downstage borderline tumors. However, post treatment response assessment can be very difficult, especially in the case of TARE. The recently updated Liver Imaging Reporting and Data System treatment response algorithm (LI-RADS TRA) 2024 guidelines has included ancillary features of mild-moderate T2 signal intensity and diffusion restriction into the assessment algorithm. Diffusion-weighted imaging (DWI) would be particularly important in post-TARE assessment as early response assessment using traditional size and enhancement criteria can be challenging following TARE. However, the interpretation of restricted diffusion in post-treatment imaging can be challenging as DWI can be affected by various factors such as inflammatory changes, haemorrhage, or T2-relaxation time of the surrounding parenchyma. In this review article, we provide an overview of the advantages and challenges in the use of DWI to interpret treatment response after LRT.