Evaluation of Renal/Ureteric Calculus Composition using Dual-Energy Computed Tomography: A Cross-sectional Study

Introduction: Urolithiasis is a commonly encountered health problem, and knowledge of the chemical composition of stones is crucial in deciding the management approach and preventing recurrence. Pre-operative assessment of stone composition has become possible after the introduction of Dual-Energy Computed Tomography (DECT). Aim: To compare the accuracy of DECT with biochemical analysis of postoperative stone samples. Materials and Methods: A cross-sectional study was conducted in the Department of Radiodiagnosis, Mysore Medical College and Research Institute, Mysore, Karnataka, India, between January 2020 to June 2021 on 35 patients who met the inclusion and exclusion criteria. All the patients underwent a non contrast DECT scan of the Kidneys, Ureters and Bladder (KUB) on a 128-slice twin beam single-source DECT scanner. The stone composition was determined using pre-programmed software and was correlated with biochemical analysis. Proportions were compared using chi-square test of significance. The sensitivity and specificity of DECT was determined. Results: Amongst the total 35 patients (mean age of 45.7±14.89 years, 23 patients males and 12 patients females) and 36 calculi analysed, The most frequently encountered calculus in the urinary tract was calcium oxalate n=24 (66.7%). The second most common calculus was Uric Acid (UA) n=5 (13.9%). The DECT findings regarding chemical composition of calculus were confirmed by Fourier Transformation Infrared Spectroscopy (FTIRS). The mean Dual-Energy (DE) ratio for oxalate, UA, hydroxyapatite, cystine and mixed stones was found to be 1.18, 1.01, 1.39, 1.09 and 1.11, respectively. DECT was found to be highly sensitive and specific in the diagnosis of calculi composition based on their DE ratio. It was found to be 95.8% sensitive and 100% specific for differentiating calcium oxalate stones from non oxalate stones and 100% sensitive and 96.8% specific for differentiating UA stones from non UA stones. Conclusion: DECT has high diagnostic accuracy in the pre- operative determination of urinary calculus composition which will guide in management, as UA stones are open to medical therapy while most of the non UA stones need surgical intervention.