What is the “washout” of hepatocellular carcinoma as observed on the equilibrium phase CT?: consideration based on the concept of extracellular volume fraction

Abstract

Purpose To verify the hypothesis that extracellular volume fraction (ECV) and precontrast CT density are the main determinants of washout of hepatocellular carcinoma (HCC) at the equilibrium phase CT. Materials and methods Between 2018 and 2020, patients with surgically resected HCC were recruited who had undergone preoperative 4-phase CT. Those larger than 6 cm were excluded to minimize the possibility of intratumoral hemorrhage or degeneration. Two radiologists reviewed the whole images in consensus and divided cases into washout positive and negative groups. Washout positive group at the equilibrium phase was defined as “HCC showing relatively low density as compared to the surrounding background liver (BGL), irrespective of the presence of early enhancement or fibrous capsule”. Several clinico-pathological and radiological features, including ECV and precontrast CT density, were correlated to the presence of washout, using uni- and multi-variable analyses. Results 27 HCC in 24 patients met the inclusion criteria. 22 (82%) and five HCC belonged to washout positive and negative groups, respectively. Univariable analysis revealed ECV of HCC and BGL, ECV difference between HCC and BGL, and presence of fibrous capsule on the equilibrium phase CT were the significant factors. Multivariable analysis showed ECV of HCC and BGL, and precontrast CT density of BGL, were the independently significant factors related to washout, suggesting washout is more likely observed with lower HCC ECV, higher BGL ECV, and higher BGL precontrast CT density. Conclusion Major determinants of washout of HCC may be ECV of HCC and BGL, and precontrast CT density of BGL.

Gallbladder fossa nodularity in the liver as observed in alcoholic liver disease patients: Analysis based on hepatobiliary phase signal intensity on gadoxetate-enhanced MRI and extracellular volume fraction calculated from routine CT data

“…ECV map was generated from pre-contrast and equilibrium phase CT data, according to the previously reported method (14)(15)(16). Just briefly, because ECV is defined as (100-hematocrit) * Δ liver /Δ blood pool, where Δ represents the difference in the CT values between the unenhanced and equilibrium phase (12)(13)(14)(15)(16), ECV map was generated on the dedicated workstation by means of subtracting unenhanced images from equilibrium phase images utilizing a non-linear nonrigid anatomical correction algorithm, and inputting the hematocrit value for each patient (14)(15)(16).…”

“…One radiologist (KS) performed ECV measurement for the rest of the patients. ECV was measured by placing as large an oval-shaped regionof-interest (ROI) as possible on ECV map as generated from pre-contrast and equilibrium phase CT data, as previously reported (14)(15)(16). As for GBFN EVC measurement, ROI was placed in its center.…”

“…ECV of the liver has drawn attention as a biomarker of pathological grades of liver fibrosis (12-16). ECV is (P6) a sum of intravascular and extravascular extracellular spaces, which can be easily calculated from noncontrast and equilibrium phase CT data of routine clinical practice, because the concentration of iodine is considered the same for both intravascular and extravascular spaces at the equilibrium phase (12)(13)(14)(15)(16). We have reported the usefulness of ECV map, which is generated by subtracting precontrast images from equilibrium phase images utilizing a non-linear non-rigid anatomical correction algorithm specifically adjusted to upper abdominal organs (14-16), and promising results have been obtained for the estimation of degree of liver fibrosis (14).…”

“…We hypothesized that, if GBFN represents relatively hyperplastic liver tissue in contrast to fibrotic BGL, gadoxetate uptake, which is a marker of functioning hepatocytes (9)(10)(11), at GBFN should be preserved, as compared to the surrounding fibrotic BGL, at the hepatobiliary phase (HBP) of gadoxetate-enhanced MRI (EOB-MRI). Further, we also hypothesized that the extracellular volume fraction (ECV), which has been reported to be a useful surrogate biomarker for pathological degree of liver fibrosis (12)(13)(14)(15)(16), of GBFN, should be low as compared to that of BGL. The purpose of this study is to further clarify the etiology or mechanism of GBFN, using its HBP signal intensity on EOB-MRI and ECV calculated from CT data relative to those of BGL as analytic indices.…”