Extracellular volume fraction: CT applications in the abdomen and pelvis Sevtap Arslan, Ilkay S. Idilman, Ali Devrim Karaosmanoglu, Deniz Akata, Mustafa Nasuh Ozmen and Musturay Karcaaltincaba Eur. Radiol. Abdomen 1, 7 (2026). https://doi.org/10.1007/s44501-026-00005-5
Tissue composition has important implications for disease prognosis and treatment planning. Fibrosis and other alterations in the extracellular compartment contribute to chronic organ dysfunction and influence the tumor microenvironment. Imaging techniques have emerged as a valuable noninvasive tool for characterizing these changes (1, 2). CT-derived extracellular volume fraction (CT-ECV) provides a quantitative estimate of the extracellular space based on contrast agent distribution and hematocrit correction, offering a potential imaging biomarker of extracellular compartment alterations. This article provides a synthesis of the technical principles and emerging clinical applications of CT-ECV in the abdomen and pelvis, with a focus on fibrosis assessment, lesion characterization, prognostic stratification, and treatment response. A particular strength is the distinction between applications supported by more mature evidence and those that remain preliminary. The review also addresses the technical standardization and validation needed to translate promising research findings into clinical practice. CT-ECV uses the equilibrium phase to estimate the extracellular volume fraction from the distribution of iodinated contrast between the blood plasma and the tissue extracellular space. Hematocrit correction accounts for the plasma fraction of whole blood (1). Conventional single-energy CT methods derive ECV from changes in tissue and blood-pool attenuation between unenhanced and delayed postcontrast images, whereas spectral CT methods, including dual-energy and photon-counting CT, use tissue-to-blood iodine concentration ratios from a single delayed acquisition (2, 3). Accurate estimation depends on appropriate acquisition timing and consistent measurement technique. Increased CT-ECV indicates extracellular compartment expansion, which may reflect fibrosis, edema, inflammation, or other tissue alterations, and should not be interpreted as a specific marker of any single histopathologic process (1, 2). Among the applications highlighted in this article, hepatic and pancreatic fibrosis assessment have the most mature supporting evidence. In the liver, associations between CT-ECV and histologic fibrosis support its potential for noninvasive tissue characterization (1, 3). In the pancreas, higher parenchymal CT-ECV is associated with greater fibrosis, whereas low values may identify a soft gland susceptible to postoperative pancreatic fistula, a promising link to surgical risk that still lacks prospective validation (2, 4). Validated thresholds and evidence of improved patient outcomes remain necessary for routine implementation. Beyond fibrosis assessment, emerging oncologic applications extend CT-ECV assessment to tumor characterization, prognosis, and treatment response evaluation, but many remain preliminary and rely on small single-center cohorts (2, 5). Some studies have shown a relationship between tumor ECV and stromal composition and histopathologic features, especially in pancreatic, gastric, and colorectal cancers (2, 6). CT-ECV may also contribute to liver tumor characterization. Honda and colleagues reported higher tumor ECV in intrahepatic cholangiocarcinoma than in hepatocellular carcinoma (43.8% vs 31.6%; P < .001). A cutoff of 41.5% yielded 59.0% sensitivity and 90.5% specificity for cholangiocarcinoma, suggesting a potential complementary role alongside conventional enhancement features (7). In rectal cancer, lower post-treatment ECV and greater reductions following neoadjuvant chemoradiotherapy have been associated with pathological complete response (8). In advanced gastric cancer, lower pretreatment ECV independently predicted pathological complete response to preoperative immunochemotherapy (9). However, the direction and clinical significance of these associations vary by tumor type, study population, and treatment setting (2). Variability in acquisition timing, scanner technology, and region-of-interest placement limits comparability across studies and the generalizability of proposed thresholds. Additional delayed imaging may also increase radiation exposure and examination time (2). Standardized acquisition protocols and organ-specific validation remain essential to establish reproducible cutoff values, clinical utility, and the impact of CT-ECV on patient management and decision-making. For ESGAR members, this review provides a practical overview of CT-ECV and its potential to complement morphologic assessment with quantitative tissue characterization. Its clinical relevance lies in relating extracellular compartment alterations to key diagnostic and management questions, including fibrosis assessment, preoperative risk stratification, and evaluation of oncologic treatment response. | References
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November 2026
Dr. Stephanie Trujillo is a Professor of Radiology at Universidad del Rosario in Bogotá, Colombia, where she completed her radiology residency. She currently practices at Fundación Cardioinfantil–LaCardio and Organización Sanitas Internacional in Bogotá. Her clinical and research interests focus on hepatobiliary, pelvic, and gastrointestinal imaging with CT and MRI. She is an ESGAR Young Ambassador and serves as Abdominal Section Editor for the Colombian Journal of Radiology. Comments may be sent to: stetrujillo@lacardio.org
Dr. Ana Villanueva Campos is a radiologist specialized in abdominal and pelvic imaging at HT Medica Hospital Universitario San Rafael in Madrid, Spain. She completed medical school and radiology residency in Spain. After earning the European Diploma in Radiology (EDiR) in 2019, she did two fellowship programs in Sunnybrook Health Sciences Centre (University of Toronto). She is passionate about learning, research and teaching, which has led her to pursue a PhD focused on endometriosis and adenomyosis. Other areas of interest are spectral CT, liver MRI and multisystemic and malabsorptive diseases. Comments may be sent to: Avillanuevacampos10@gmail.com