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

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. [ABSTRACT FROM AUTHOR]