Utility of material-specific fat images derived from rapid-kVp-switch dual-energy renal mass CT for diagnosis of renal angiomyolipoma

Abstract

Background Renal angiomyolipoma (AML) are benign masses that require detection of macroscopic fat for accurate diagnosis. Purpose To evaluate fat material-specific images derived from dual-energy computed tomography (DECT) to diagnose renal AML. Material and Methods This retrospective case-control study evaluated 25 renal AML and 44 solid renal masses (41 renal cell carcinomas, three other tumors) imaged with rapid-kVp-switch DECT (120 kVp non-contrast-enhanced [NECT], 70-keV corticomedullary [CM], and 120-kVp nephrographic [NG]-phase CECT) during 2017–2018. A radiologist measured attenuation (Hounsfield Units [HU]) on NECT, CM-CECT, NG-CECT, and fat concentration (mg/mL) using fat-water base-pair images. Results At NECT, 100% (44/44) non-AML and 4.0% (1/25) AML measured >–15 HU. At CM-CECT and NG-CECT, 24.0% (6/25) and 20.0% (5/25) AML measured >–15 HU (size 6–20 mm). To diagnose AML, area under receiver operating characteristic curve (AUC) using –15 HU was: 0.98 (95% confidence interval [CI] 0.98–1.00) NECT, 0.88 (95% CI 0.79–0.91) CM-CECT, and 0.90 (95% CI 0.82–0.98) NG-CECT. At DECT, fat concentration was higher in AML (163.7 ± 333.9 [–553.0 to 723.5] vs. –2858.1 ± 460.3 [–2421.2 to –206.0] mg/mL, P<0.001). AUC to diagnose AML using ≥–206.0 mg/mL threshold was 0.98 (95% CI 0.95–1.0) with sensitivity/specificity of 92.0%/96.7%. Of AML, 8.0% (2/25) were incorrectly classified; one of these was fat-poor. AUC was higher for fat concentration compared to HU measurements on CM-CECT and NG-CECT ( P=0.009–0.050) and similar to NECT ( P=0.98). Conclusion DECT material-specific fat images can help confirm the presence of macroscopic fat in renal AML which may be useful to establish a diagnosis if unenhanced CT is unavailable.