Hepatic lesion detectability on dual energy computed tomography imaging : phantom study

Abstract

The purpose of this study is to determine the hepatic lesion detectability in abdomen from various phantom sizes by dual-energy computed tomography (DECT) imaging and to investigate the factors affecting the detectability of hepatic lesion in abdomen by dual-energy CT in phantom study. The anthropomorphic liver with nodule inserted phantom with extension rings simulating the small, medium, and large patients were scanned under DECT acquisitions by varying three kVp combinations (80/-,90/-, and 100/Sn150-kVp). The series of 40-,50-,60-, and 70-keV VMI were generated from DECT data set. All images were used to assess the task-based image quality; task transfer function (TTF), noise power spectrum (NPS), and detectability index (d’) with the diagnostic task to detect 15 mm diameter hyperattenuating hepatic lesion based on clinical task of hepatocellular carcinoma (HCC) detection in CT imaging. In addition, the accuracy of iodine quantification in DECT for various kVp combinations was performed by using the customized 3D- printed liver nodule phantom. The result showed that the TTF increased as increasing the VMI energy level from 40-70 keV and the maximum values of 50%TTF (f50) was found at 70 keV VMI. The noise magnitude increased as increasing the phantom size and decreasing the VMI-energy and when the kV on x-ray tube A increased. The results of d’ demonstrated that as increased phantom sizes and decreased the energy level , the d’ decreased. The measured iodine concentrations with DECT were strongly related to the true concentrations with the percentages of iodine quantification error within ±20% for concentration at 2.0-5.0 mgI/cc in all kV combinations. In conclusion, for the small phantom, the imaging condition yields the highest d’ was at the 70keV-VMI acquired with 80/Sn150 kV. For the medium and large phantom sizes, the highest d’ was at the 70keV-VMI acquired by 100/Sn150 kV. The percentage of iodine quantification error in the range of 2.0-5.0 mgI/cc was within ±20% in all kV combination settings.