Dual-Source Dual-Energy CT Evaluation of Complex Cystic Renal Masses

OBJECTIVE. The purpose of this study was to assess the value of dual-source dual-energy CT in the evaluation of complex cystic renal masses. SUBJECTS AND METHODS. Seventy patients underwent contrast-enhanced dual-energy CT that included true unenhanced images acquired in single-energy mode, corticomedullary phase images acquired in dual-energy mode, and nephrographic phase images acquired in single-energy mode. Virtual unenhanced, blended weighted-average, and color-coded iodine overlay images were reconstructed. The acceptance level and image quality of virtual and true unenhanced images were evaluated. Contrast enhancement on both true unenhanced or blended weighted-average images and color-coded iodine overlay images was evaluated with both calculation in regions of interest and use of confidence level scales. Radiation dose parameters were estimated. RESULTS. Virtual unenhanced images of 70 lesions (97.2%) and true unenhanced images of 72 lesions (100%) were judged acceptable (p = 0.5). The mean quality score of virtual unenhanced images was 2.0 +/- 0.7 and of true unenhanced images was 1.5 +/- 0.5 (p < 0.001). Mean contrast enhancement measured on true unenhanced and blended weighted-average images was 45.9 +/- 15.9 HU (range, 21-78 HU) and on color-coded iodine overlay images was 47.3 +/- 16.8 HU (range, 22-75 HU) with no significant differences. Enhancement was excluded on color-coded iodine overlay images with a significantly (p < 0.03) higher level of confidence than it was on true unenhanced and blended weighted-average images. The mean dose reduction with use of a combined dual-and single-energy dual-phase CT protocol was 29.1% +/- 11.9% (p < 0.001). CONCLUSION. Dual-source dual-energy CT is a reliable imaging technique in the evaluation of complex cystic renal masses. True unenhanced images can be replaced by virtual unenhanced images with considerable radiation dose reduction. The color-coded iodine overlay technique is a useful tool for both excluding and identifying endocystic enhancement.