Extracellular volume fraction, a quantitative imaging measure long validated in cardiology for assessing myocardial fibrosis, is now being applied across the abdomen and pelvis, according to a review published on 2 October 2026 in European Radiology Abdomen. The measure, abbreviated ECV, reflects the proportion of tissue volume occupied by the extracellular space, which includes interstitial fluid, extracellular matrix, and intravascular plasma. Because it rises in conditions involving expansion of that space, such as fibrosis, edema, or inflammation, researchers have begun testing whether computed tomography can capture the same information in the liver, pancreas, spleen, adrenal glands, kidneys, urinary bladder, stomach, colon, and rectum.
The technique rests on a simple physiological assumption. Water-soluble iodinated contrast media diffuse freely between the intravascular compartment and the extravascular extracellular space, so once the contrast agent reaches an equilibrium phase, the relative enhancement of a tissue compared with blood provides an estimate of extracellular expansion. By comparing contrast enhancement in tissue and blood before and after contrast administration, and correcting for the patient’s hematocrit, the calculation yields a quantitative estimate of the extracellular compartment. Since iodinated contrast distributes within plasma but not within red blood cells, hematocrit correction accounts for the intravascular plasma volume and allows more accurate quantification. ECV measurement was originally established using cardiac MRI, where it correlates strongly with histological measures of interstitial fibrosis and predicts adverse cardiovascular outcomes. Because cardiac MRI faces limitations of availability and cost, CT-derived ECV has emerged as a more accessible alternative that correlates strongly with the MRI-based measure.
The technical implementation comes in several forms. Single-energy CT requires two separate scans: a low-dose non-contrast scan to establish baseline attenuation and an equilibrium phase post-contrast scan. The change in tissue attenuation from pre-contrast to equilibrium is divided by the corresponding change in aortic attenuation, multiplied by one minus the hematocrit, and expressed as a percentage. Dual-energy CT and photon-counting CT can instead generate virtual non-contrast images and iodine maps from a single post-contrast acquisition, often eliminating the need for a separate pre-contrast scan and reducing potential errors related to image misregistration. Photon-counting CT additionally offers higher energy resolution for more precise measurements, and both technologies can produce virtual monoenergetic images, with 40 to 50 keV providing optimal contrast-to-noise ratios for ECV assessment.
Across published studies, contrast administration has typically involved non-ionic agents at concentrations of 320, 350, or 370 mg per milliliter, with weight-adjusted dosages ranging from 1.0 to 1.7 mL/kg or fixed iodine loads of 500 to 600 mg/kg, and flow rates between 2.0 and 5.0 mL/s often followed by a saline flush. The timing of the equilibrium phase, the critical imaging window for the calculation, varies considerably in the literature, ranging from approximately 60 seconds to 10 minutes after contrast administration. In rapid spectral CT protocols, a delay of 180 seconds is frequently considered a clinically feasible compromise between workflow efficiency and technical reliability. Notably, one dedicated comparative study demonstrated that 3-minute and 5-minute delayed acquisitions yield statistically equivalent results for hepatic CT-ECV calculation, suggesting the shorter delay can be reliably adopted in routine practice. Standard single-energy protocols typically use a tube voltage of 120 kVp, while dual-energy combinations of 80/140 or 90/150 kVp are common, and reconstructions generally use slice thicknesses of 1.0 to 3.0 mm.
The strongest evidence base concerns the liver. Because hepatic fibrosis reflects expansion of the extracellular space caused by collagen and matrix protein deposition, studies have shown that CT-ECV values increase significantly with advancing fibrosis stages, and the measure has been identified as an independent factor associated with cirrhosis. One study reported cutoff values of 29.46 percent for differentiating cirrhosis from non-cirrhosis, 33.72 percent for distinguishing Child-Pugh class A from B, and 39.53 percent for class B versus C, with corresponding areas under the curve of 0.911, 0.901, and 0.966. Another study reported a cutoff of 38 percent for separating non-significant fibrosis from significant fibrosis, with an area under the curve of 0.698. Fibrosis progression is often spatially heterogeneous: early disease typically appears first in the peripheral areas of the medial and anterior segments, corresponding to the drainage territory of the middle hepatic vein, while the posterior segments are usually involved later and may be more useful for staging severity. Diagnostic performance may also vary by etiology, with alcoholic liver disease showing higher CT-ECV values in advanced fibrosis stages than viral hepatitis or nonalcoholic steatohepatitis, likely reflecting more abundant alcohol-related fibrosis.
Beyond fibrosis staging, hepatic CT-ECV has emerged as a sensitive indicator of functional reserve. Several studies have reported strong positive correlations with established clinical scoring systems, including the Child-Pugh classification, fibrosis-4 index, aspartate aminotransferase to platelet ratio index, albumin-bilirubin score, and model for end-stage liver disease score, with particular utility in distinguishing compensated from decompensated liver disease. In patients with acute decompensation, increased CT-ECV has been identified as an independent risk factor for 90-day disease progression and mortality in acute-on-chronic liver failure. The measure has also been reported as a predictive biomarker for hepatocellular carcinoma development in patients with hepatitis C virus infection following sustained virologic response. Models integrating hepatic and splenic CT-ECV values have been proposed as effective rule-out strategies for high-risk esophagogastric varices, potentially allowing a substantial proportion of low-risk patients to avoid screening endoscopy. In focal liver lesions, intrahepatic cholangiocarcinoma typically demonstrates higher CT-ECV than hepatocellular carcinoma because of its dense fibrotic stroma, and focal nodular hyperplasia generally exhibits higher values than hepatocellular adenoma.
Oncologic applications are expanding but remain more preliminary. In hepatocellular carcinoma, CT-ECV-based nomograms have shown potential for predicting preoperative Ki-67 expression, and higher tumor CT-ECV has been reported as an independent predictor of longer progression-free and overall survival in patients treated with immune checkpoint inhibitors or transarterial chemoembolization. Conversely, one study of liver cancers treated with immune checkpoint inhibitors found that lower tumor CT-ECV was associated with better therapeutic response, a discrepancy the review attributes to differences in study populations, tumor biology, treatment strategies, and clinical endpoints. Elevated CT-ECV has also been identified as an independent predictor of overall and recurrence-free survival in patients with colorectal cancer liver metastases, and emerging evidence suggests it may serve as a noninvasive biomarker for oxaliplatin-induced sinusoidal obstruction syndrome in those patients.
In the pancreas, CT-ECV correlates moderately to strongly with histopathologic fibrosis, shows higher values in advanced disease, and is independently associated with the development of pancreatic ductal adenocarcinoma in patients with pancreatic fibrosis. Tumor CT-ECV has been identified as an independent predictor of overall and progression-free survival in resectable and unresectable pancreatic ductal adenocarcinoma, with lower tumor values associated with lower recurrence-free and overall survival, while high CT-ECV of the noncancerous parenchyma has been linked to significantly worse overall survival. Lower tumor values generally predict better response to chemoradiotherapy, and CT-ECV maps have been explored to improve radiotherapy planning through more accurate gross tumor volume delineation. Preoperative pancreatic CT-ECV also predicts postoperative pancreatic fistula following pancreaticoduodenectomy, with lower values associated with a soft pancreatic texture and limited fibrosis, both well-known risk factors for fistula formation, and lower values have been independently associated with increased risk of post-pancreatectomy acute pancreatitis. One study found CT-ECV significantly higher in autoimmune pancreatitis than in pancreatic ductal adenocarcinoma or normal parenchyma, and high pancreatic CT-ECV has been suggested as a marker of diabetic microangiopathy in type 2 diabetes.
Elsewhere in the abdomen, elevated CT-ECV in colorectal cancer is associated with poorer tumor differentiation, high-grade adenocarcinoma, advanced T stage, nodal involvement, lymphovascular and perineural invasion, and higher grades of tumor budding, while lower post-treatment values and greater reductions after neoadjuvant chemoradiotherapy have been associated with pathological complete response in locally advanced rectal cancer. In gastric cancer, elevated values track with aggressive features and with shorter progression-free and overall survival in patients receiving PD-1 inhibitors, and lower pre-treatment values independently predict pathological complete response after preoperative immunochemotherapy. Adrenal metastases show significantly higher CT-ECV than lipid-poor and lipid-rich adenomas, aldosterone-producing nodules show lower values than nonfunctioning nodules, and in clear cell renal cell carcinoma elevated values are associated with higher pathological grades and have been identified as an independent predictor of recurrence-free survival after surgery. Splenic CT-ECV can differentiate lymphoma-involved from non-involved spleens, outperforming splenic length and visual enhancement assessment, and higher bladder tumor values are associated with advanced stage, high-grade disease, shorter survival, and increased recurrence risk after surgery.
Substantial obstacles remain before routine clinical adoption. The conceptual framework and formulas were developed and validated in cardiac imaging, and the direct transferability of cardiac-derived methodologies to abdominal tissues with different vascular architecture, extracellular matrix composition, perfusion, and heterogeneity remains incompletely established. Evidence maturity differs substantially among applications, with many oncologic findings based on single-center studies with relatively small cohorts and limited external validation. The greatest obstacle is the absence of standardized acquisition protocols and measurement techniques: equilibrium timing, scanner technology, and region-of-interest placement all vary, contributing to inconsistent reported cutoff values and limiting inter-study comparability. Virtual non-contrast images typically underestimate CT attenuation by 5 to 15 HU across soft tissues compared with true non-contrast scans, warranting validation studies within the same patient cohort. Radiation burden is another consideration, since the equilibrium phase is not routinely included in standard diagnostic protocols, though targeted low-dose equilibrium acquisitions have been shown feasible without significant differences in measured values. Most published studies nonetheless report good-to-excellent interobserver and intraobserver reproducibility, with intraclass correlation coefficients exceeding 0.75 to 0.80, and the review’s authors call for multicenter prospective validation, protocol harmonization, reproducible cutoff values, and consensus guidelines before widespread implementation.
Subject of Research: CT-derived extracellular volume fraction as a quantitative imaging biomarker for abdominal and pelvic disease
Article Title: Extracellular volume fraction: CT applications in the abdomen and pelvis
Article References: Arslan, S., Idilman, I. S., Karaosmanoglu, A. D., Akata, D., Ozmen, M. N., & Karcaaltincaba, M. (2026). Extracellular volume fraction: CT applications in the abdomen and pelvis. European Radiology Abdomen, 1(1), Article 7. https://doi.org/10.1007/s44501-026-00005-5
Image Credits: AI Generated
DOI: 10.1007/s44501-026-00005-5
Keywords: extracellular volume fraction, CT-ECV, hepatic fibrosis, pancreatic fibrosis, dual-energy CT, photon-counting CT, quantitative imaging biomarker, liver fibrosis staging, pancreatic ductal adenocarcinoma, colorectal cancer, gastric cancer, tumor microenvironment
News Source: Nathaniel Bowman. (October 28, 2026). CT-Derived Extracellular Volume Fraction Emerges as a Quantitative Biomarker for Abdominal Disease. Scienmag.
