Diagnostic performance and feasibility of dual-layer detector dual-energy CT for characterization of urinary stones in patients of different sizes

Background Urinary stones are frequently encountered in urology and are typically identified using non-contrast CT scans. Dual-energy CT (DECT) is a valuable imaging technique that produces material-specific images and allows for precise assessment of stone composition by estimating the effective atomic number (Z(eff)), a capability not achievable with the conventional single-energy CT's attenuation measurement method.Purpose To investigate the diagnostic performance and image quality of dual-layer detector DECT (dlDECT) in characterizing urinary stones in patients of different sizes.Methods All consecutive dlDECT examinations with stone protocol and presence of urinary stones between July 2018 and November 2019 were retrospectively evaluated. Two radiologists independently reviewed 120 kVp and color-overlay Z(eff) images to determine stone composition (reference standard = crystallography) and image quality. The objective analysis included image noise and Z(eff )values measurement.Results A total of 739 urinary stones (median size 3.7 mm, range 1-35 mm) were identified on 177 CT examinations from 155 adults (mean age, 57 +/- 15 years, 80 men, median weight 82.6 kg, range 42.6-186.9 kg). Using color-overlay Z(eff) images, the radiologists could subjectively interpret the composition in all stones >= 3 mm (n = 491). For stones with available reference standards (n = 74), dlDECT yielded a sensitivity of 80% (95%CI 44-98%) and a specificity of 98% (95%CI 92-100%) in visually discriminating uric acid from non-uric acid stones. Patients weighing > 90 kg and <= 90 kg had similar stone characterizability (p = 0.20), with 86% of stones characterized in the > 90 kg group and 87% in the <= 90 kg group. All examinations throughout various patients' weights revealed acceptable image quality. A Z(eff) cutoff of 7.66 accurately distinguished uric acid from non-uric acid stones (AUC = 1.00). Z(eff) analysis revealed AUCs of 0.78 and 0.91 for differentiating calcium-based stones from other non-uric stones and all stone types, respectively.Conclusion dlDECT allowed accurate differentiation of uric acid and non-uric acid stones among patients with different body sizes with acceptable image quality.