Recent Advances in Functional Liver Volumetry: Emphasis on 99mTc-GSA SPECT/CT Fusion Imaging.

Functional assessment of the future liver remnant (FLR) has become increasingly important for improving the safety of major hepatectomy. Conventional evaluation based on computed tomography (CT) volumetry estimates anatomical liver volume but does not fully reflect the functional capacity of the remnant liver, particularly in patients with underlying liver disease or those receiving preoperative therapy. In recent years, functional liver volumetry using technetium-99 m-labeled galactosyl human serum albumin (99mTc-GSA) scintigraphy combined with single-photon emission computed tomography/computed tomography (SPECT/CT) fusion imaging has emerged as a reliable method for quantitative assessment of regional liver function. This review summarizes recent advances in functional liver volumetry with particular focus on 99mTc-GSA SPECT/CT fusion imaging and its clinical applications in patients undergoing major hepatectomy. Functional imaging enables simultaneous evaluation of FLR volume and function and has demonstrated superior predictive value for post-hepatectomy liver failure compared with volumetric assessment alone. Functional imaging has also clarified important aspects of liver regeneration following portal vein embolization, hepatic vein embolization, and associating liver partition and portal vein ligation for staged hepatectomy, demonstrating that functional recovery often exceeds or precedes volumetric hypertrophy. Our studies using 99mTc-GSA SPECT/CT further demonstrated that functional liver regeneration after hepatectomy occurs earlier than volumetric regeneration and that factors such as liver fibrosis, chemotherapy exposure, and hepatic venous congestion influence regional functional recovery. Integration of functional volumetry into preoperative planning can improve risk stratification and optimize surgical decision-making.