Role of Dual-Energy CT in Evaluating Urinary Stones

Abstract

Objectives: To evaluate the detectability of urinary stones on DECT virtual nonenhanced images and examine the diagnostic performance of dual-energy computed tomography (DECT) in characterization of in vivo renal stone composition.
Methods: Cross-sectional study from 05/2022 to 10/2023, at Nguyen Tri Phuong Hospital, Ho Chi Minh City. DECT images of 197 patients with postsurgical-proven urinary stones were analyzed. All
patients were examined with DECT urography in 3 phases: true nonenhanced (TNE) image, pyelographic phase and excretory phase. The contrast medium in the renal pelvis and ureters was  virtually removed from pyelographic phase and excretory-phase images by using postprocessing software, resulting in virtual nonenhanced (VNE) images. The sensitivity regarding the detection of calculi on VNE images compared with true nonenhanced (TNE) images was determined. Results of the stone compositions were identified on DECT and then were compared to postoperative infrared spectroscopy stone analysis as the standard reference.
Results: The sensitivity, specificity of VNE created from pyelographic phase for detecting urinary stones were 95,4% and 100%. The sensitivity, specificity of VNE created from excretoryphase were 83,2% and 94,6%. Most urinary stones detected on VNE appeared smaller. VNE had a moderate detection rate for small stones (<5mm) with the sensitivity of VNE created from the pyelographic phase was 74,2% and the sensitivity of VNE created from excretory-phase was 31,4%. Most undetected stones were in the urinary calyx with the sensitivity of VNE created from the pyelographic phase was 93,05% and the sensitivity of VNE created from excretory phase was 77,7%. In term of identifying renal stone composition, the accuracy of DECT was 74,1%. The agreement between DECT and infrared spectroscopy was 0,72. The effective atomic number Zeff helped to identified Canxi Oxalate with high accuracy (83,3%). The HU ratio cut off to differentiate Struvite stones from Canxi Oxalate stones was 1.32 with high sensitivity (95%) and high specificity (72%).
Conclusions: VNE can detect large (>5mmmm) calculi with good reliability. VNE created from the pyelographic phase has a higher detectability than VNE created from the excretory phase. DECT was able to determine the composition of urinary tract stones with fair accuracy, especially Canxi oxalate stones. DECT could also differentiate Canxi oxalate stone and Struvite stone.