Attenuation and Degree of Enhancement With Conventional 120-kVp Polychromatic CT and 70-keV Monochromatic Rapid Kilovoltage-Switching Dual-Energy CT in Cystic and Solid Renal Masses

OBJECTIVE. The purpose of this study was to compare attenuation values (in Hounsfield units) and degree of enhancement (attenuation change) in renal masses using 120-kVp polychromatic (conventional) CT and 70-keV monochromatic dual-energy CT (DECT). MATERIALS AND METHODS. Twenty-two patients with 39 renal masses (24 Bosniak category I and II cysts and 15 solid masses under active surveillance) underwent conventional CT (120-kVp unenhanced and contrast-enhanced CT) and rapid kilovoltage-switching DECT (120-kVp unenhanced CT and 70-keV contrast-enhanced CT). The mean (+/- SD) time between scans was 648 +/- 943 days. A radiologist measured attenuation on matched image sets coregistered between examinations. Absolute attenuation and attenuation change were compared using independent t tests, Pearson correlation, and Bland Altman analysis. RESULTS. There was no difference in attenuation on 120-kVp versus 70-keV contrast-enhanced CT images for cysts (9.5 +/- 5.5 HU [range, -2 to 20 HU] vs 10.1 +/- 4.6 HU [range, -2 to 16 HU]; p = 0.33) and solid masses (110.1 +/- 72.9 HU [range, 35-267 HU] vs 119.1 +/- 73.7 HU [range, 33-265 I IU]; p = 0.04). There also was no difference in attenuation change for 120-kVp contrast-enhanced CT minus 120-kVp unenhanced CT (cysts, 3.5 +/- 3.9 HU [range, -2 to 13 HU]; solid masses, 80.7 +/- 73.3 HU [range, 9-227 HU]; p = 0.45) or for 70-keV contrast-enhanced CT minus 120-kVp unenhanced CT (cysts, 4.3 +/- 41 HU [range, -3 to 12 HU]; solid masses, 89.8 +/- 74.1 I IU [range, 7-226 I IU]; p = 0.04). The correlation was strong to almost perfect (beta = 0.83-0.98) with substantial agreement There was no difference in attenuation of cysts and solid masses comparing 120-kVp acquisitions acquired at different time points (p = 0.200.92). The correlation was strong to almost perfect (beta= 0.72-0.95) with substantial agreement. CONCLUSION. There are no differences in absolute attenuation or degree of enhancement comparing 70-keV monochromatic CT to conventional 120-kVp CT in renal cysts and solid masses.