Characterization of Small Incidental Indeterminate Hypoattenuating Hepatic Lesions: Added Value of Single-Phase Contrast-Enhanced Dual-Energy CT Material Attenuation Analysis

OBJECTIVE. The objective of this study is to determine whether single-phase contrast-enhanced dual-energy CT (DECT) material attenuation analysis improves the characterization of small (< 2.0 cm) incidental indeterminate hypoattenuating hepatic lesions, compared with conventional single-energy CT evaluation. MATERIALS AND METHODS. This retrospective study involved 55 patients (24 men and 31 women; mean [+/- SD] age, 63.9 +/- 15.3 years) with 77 incidental hypoattenuating hepatic lesions (59 benign and 18 malignant lesions) measuring 0.5-2.0 cm who underwent single-phase contrast-enhanced DECT of the abdomen for pain. For each lesion, attenuation measurements were obtained using blended 120-kVp-equivalent images and contrast map images. DECT material attenuation images were used for iodine quantification. Optimal lesion attenuation and iodine concentration threshold values that best distinguished benign lesions from malignant lesions were generated using smooth bootstrapping. The diagnostic accuracy of the optimized thresholds was compared using the Wilcox rank sum test. RESULTS. The optimal mean (+/- standard error) attenuation threshold values that best differentiated benign and malignant lesions were 50.2 +/- 5.2 HU and 11.5 +/- 2.0 HU when blended 120-kVp and contrast map images, respectively, were used. The iodine concentration (expressed as milligrams of iodine per milliliter) differed significantly (p < 0.0001) between benign lesions (0.6 +/- 0.4 mg I/mL) and malignant lesions (1.7 +/- 0.4 mg I/mL). The optimal iodine concentration that best distinguished between benign and malignant lesions was 1.2 +/- 0.1 mg I/mL. The sensitivity, specificity, and AUC value were highest for iodine concentration (0.94, 0.93, and 0.97, respectively), compared with blended images (0.89, 0.70, and 0.81, respectively) and contrast map images (0.94, 0.64, 0.77, respectively). CONCLUSION. Iodine quantification performed using single-phase contrast-enhanced DECT material attenuation images improves the characterization of small (< 2 cm) incidental indeterminate hypoattenuating hepatic lesions, compared with conventional attenuation measurements.