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 HU]; 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 ± 4.1 HU [range, -3 to 12 HU]; solid masses, 89.8 ± 74.1 HU [range, 7-226 HU]; p = 0.04). The correlation was strong to almost perfect (β = 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 = 0.20-0.92). The correlation was strong to almost perfect (β = 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.