Dual Energy Computerized Tomography with a Split Bolus—A 1-Stop Shop for Patients with Suspected Urinary Stones?

Abstract

We evaluated a dual energy, split bolus computerized tomography protocol that provides virtual noncontrast, parenchymal and urographic phases in a single scan. We assessed the sensitivity of the virtual noncontrast phase using this protocol to detect urinary stones compared to the gold standard of the true noncontrast phase. We prospectively enrolled in the study 81 patients who underwent unenhanced single energy computerized tomography at 120 kV/200 mA as well as contrast enhanced dual energy computerized tomography on a Somatom® Definition Flash-CT (tube A 80 kV/233 mA and tube B SN 140 kV/180 mA with 1/0.8 mm slice thickness). For the split bolus protocol 400 mg/ml Iomeron® were injected at 2 time points, that is 15 ml 10 minutes before the scan and 80 ml 65 seconds before the scan. In a consensus reading 2 readers evaluated the presence and diameter of stones on the true and virtual noncontrast phases. Of the 350 stones noted on the true noncontrast phase we found 289 on the virtual noncontrast phase as well as 13 false-positive and 66 false-negative stones. Sensitivity was 98.4%, 89.8% and 82.6% per patient, segment and stone, respectively. The diameter measured on the virtual noncontrast phase corresponded to a mean ± SD 92.5% ± 31.6% of the diameter on the true noncontrast phase. The mean effective dose was 4.8 ± 1.8 and 10.5 ± 3.7 mSv for the true and virtual noncontrast phases, respectively. The proposed protocol allows for combining 3 phases in a single scan while still enabling the detection of urinary stones at high sensitivity. This technique halves the radiation dose and provides the surgeon with better anatomical information on the calyceal system. Therefore, it is a valuable diagnostic tool for kidney stone treatment planning and followup.