Diagnostic accuracy of iodine quantification and material density imaging with rapid Kilovoltage-switching DECT for small hyperattenuating renal lesions.

Objectives: To assess accuracy of MDI and iodine quantification in distinguishing enhancing renal masses from hyperattenuating cysts, compared with conventional attenuation measurements, given that differentiation between these entities can influence follow-up imaging strategies and surgical decision-making, and to investigate the optimal threshold of iodine concentration using rapid kilovoltage-switching DECT (rsDECT).

Materials and methods: Retrospective study enrolled 126 renal lesions 1-4 cm in size with 10-70 attenuation on pre-contrast CT in patients who underwent rsDECT during the portovenous phase. Two reading sessions (true unenhanced (TUE) + post-contrast (PC) + MDI images versus MDI only images) for the visual assessment of renal mass enhancement were done (with at least 1-month time gap). Measurement of attenuation and iodine concentration within each renal lesion was recorded. Diagnostic accuracies and a threshold of each quantitative parameters were evaluated. Final diagnosis of renal lesions was based on pathological or imaging criteria.

Results: Accuracy of MDI images were 90.5% with TUE + PC + MDI and 88.9% with MDI only. AUC of VUE HU, TUE HU, PC HU, PC VUE HU, PC-TUE HU, absolute and normalized iodine concentration were 0.87, 0.82, 0.96, 0.95, 0.96, 0.97 and 0.95 (all p < 0.001). The optimal absolute iodine concentration threshold was 1.6 mg I/mL, with 91% sensitivity and 92% specificity. This threshold outperformed 0.5 mg I/mL showing 100% sensitivity, 29% specificity) and 2.0 mg I/mL showing 71% sensitivity, 97% specificity.

Conclusion: In characterization of a small (< 4 cm) hyperattenuating renal lesion identified on abdominal CT, post processing MDI with iodine quantification has better or comparable accuracy to attenuation measurement and the specificity of iodine concentration using rsDECT improves with a threshold higher than 0.5 mg I/mL. This could enhance diagnostic workflows for renal lesion assessment using MDI and offer the potential to omit TUE scanning, thereby reducing patient radiation exposure.