Characterization of Small Focal Renal Lesions: Diagnostic Accuracy with Single-Phase Contrast-enhanced Dual-Energy CT with Material Attenuation Analysis Compared with Conventional Attenuation Measurements

Abstract

Purpose To determine whether single-phase contrast material-enhanced dual-energy material attenuation analysis improves the characterization of small (1-4 cm) renal lesions compared with conventional attenuation measurements by using histopathologic analysis and follow-up imaging as the clinical reference standards. Materials and Methods In this retrospective, HIPAA-compliant, institutional review board-approved study, 136 consecutive patients (95 men and 41 women; mean age, 54 years) with 144 renal lesions (111 benign, 33 malignant) measuring 1-4 cm underwent single-energy unenhanced and contrast-enhanced dual-energy computed tomography (CT) of the abdomen. For each renal lesion, attenuation measurements were obtained; attenuation change of greater than or equal to 15 HU was considered evidence of enhancement. Dual-energy attenuation measurements were also obtained by using iodine-water, water-iodine, calcium-water, and water-calcium material basis pairs. Mean lesion attenuation values and material densities were compared between benign and malignant renal lesions by using the two-sample t test. Diagnostic accuracy of attenuation measurements and dual-energy material densities was assessed and validated by using 10-fold cross-validation to limit the effect of optimistic bias. Results By using cross-validated optimal thresholds at 100% sensitivity, iodine-water material attenuation images significantly improved specificity for differentiating between benign and malignant renal lesions compared with conventional enhancement measurements (93% [103 of 111]; 95% confidence interval: 86%, 97%; vs 81% [90 of 111]; 95% confidence interval: 73%, 88%) (P = .02). Sensitivity with iodine-water and calcium-water material attenuation images was also higher than that with conventional enhancement measurements, although the difference was not statistically significant. Conclusion Contrast-enhanced dual-energy CT with material attenuation analysis improves specificity for characterization of small (1-4 cm) renal lesions compared with conventional attenuation measurements. RSNA, 2017 Online supplemental material is available for this article.

Virtual Unenhanced Images at Dual-Energy CT: Influence on Renal Lesion Characterization

“…We demonstrated a size-specific dose reduction on average of 51%, and this reduction was higher for the dual-source DE CT (65% vs 44%). This is in accordance with previous renal lesion imaging studies (6,11,12,17,(30)(31)(32). However, approaches maintaining diagnostic performance should always precede dose reduction, as this may only lead to inconclusive examinations.…”

“…Our final single-center retrospective study population was composed of 293 patients. The study patients are part of a large retrospective DE CT database, of which 85 patients have been reported in previously published studies (12)(13)(14) from our institution. In patients with multiple renal lesions (n = 86), up to five of the smallest lesions (1.0 cm) in each patient were included because small lesions represent the biggest challenge for characterization in clinical practice.…”

Renal Lesion Characterization with Spectral CT: Determining the Optimal Energy for Virtual Monoenergetic Reconstruction

“…We did not assess the diagnostic performance of iodine concentration for renal lesion characterization. There is accumulating evidence to suggest that direct quantification of iodine concentrations has several important benefits, including improved sensitivity in the detection of lesion vascularity (24,30), decreased reader interpretation times (24,31,32), and higher quantitative value due to the lack of variability from differences in ROI positioning during conventional measurements of lesion enhancement (33). We excluded renal lesions smaller than 10 mm in size; these results may not extend to assessment of subcentimeter renal lesions due to increased susceptibility of small lesions to pseudoenhancement.…”

ACR Appropriateness Criteria® Indeterminate Renal Mass

“…Several studies have demonstrated that dual-energy CT can improve the differentiation between nonenhancing cysts and low-level-enhancing tumors [8][9][10][11]. Dual-energy CT with reconstruction of virtual monochromatic images has been shown to decrease or overcome renal cyst pseudoenhancement [12].…”