Extracellular volume fraction: CT applications in the abdomen and pelvis

Extracellular volume fraction (ECV) is a quantitative imaging biomarker that reflects expansion of the extracellular compartment and has been extensively validated in cardiac imaging. More recently, CT-derived ECV (CT-ECV) has emerged as a promising tool for evaluating a broad spectrum of abdominal diseases involving the liver, pancreas, spleen, adrenal glands, kidneys, urinary bladder, stomach, colon, and rectum. Current evidence demonstrates that CT-ECV correlates with histopathological measures of fibrosis, functional reserve, tumor microenvironment, prognosis, and treatment response across multiple abdominal applications. However, substantial heterogeneity exists among published studies regarding acquisition protocols, equilibrium phase timing, scanner technologies, ROI methodologies, and reported cutoff values, limiting inter-study comparability and widespread clinical implementation. The strongest evidence currently supports hepatic and pancreatic fibrosis assessment, whereas many oncologic applications remain preliminary and require further validation. This review summarizes single-energy, dual-energy, and photon-counting CT acquisition protocols, discusses the current evidence for abdominal CT-ECV applications, and highlights key limitations, challenges, and future directions for clinical adoption. Question Current abdominal imaging lacks a validated noninvasive biomarker capable of quantifying extracellular matrix expansion across different organs and diseases. Findings Current evidence indicates that CT-ECV correlates with fibrosis severity, tumor microenvironment, prognosis, and treatment response across multiple abdominal organs. Relevance statement CT-ECV may complement routine abdominal CT by providing quantitative tissue characterization and supporting personalized patient management, but broader standardization and validation are required before widespread clinical implementation.