Dual energy CT characterization of urinary calculi: Initial in vitro and clinical experience

Objective: The purpose of this study is to assess the accuracy of dual energy CT (DECT) in the characterization of renal and ureteral stones. Material and Methods: Twenty-four renal calculi of known variable composition were scanned on a dual-source CT scanner (Somatorn Definition; Siemens Medical Solutions, Forchheim, Germany) in dual energy (DECT) mode. Scan parameters for DECT were: tube potentials, 80 and 140 kV; tube current, 342 and 76 mA . s; collimation, 14 X 1.2 mm(2). Dual energy properties of calculi were used to differentiate between uric acid (UA) and other calculi. Differentiation was based on a 3-material decomposition implemented in the dual energy software (Syngo VA 11; Siemens Medical Solutions). Color coding was used to display different types of stones and their DECT properties were characterized with density measurements at both photon energies. Subsequently, 20 consecutive patients with known or suspected uroliths were scanned using identical scan parameters. Stone size and material were assessed in DECT and compared with the chemical analyses of stones after mechanical extraction. Results: With DECT characterization, differentiation of UA from other calculi was possible. Additionally, differentiation between cystine and struvite stones was shown to be feasible in vitro. In the patient cohort, DECT correctly characterized 4 UA calculi, 4 mixed, multiple calcified, and I cystine stone. The calculi were displayed in specific colors, ie, UA stones in red and calcified stones in blue. Conclusion: With dual energy CT techniques, the UA, cystine, struvite, and mixed renal calculi can be differentiated from other types of stones in vitro and in vivo. This is of clinical relevance as UA uroliths may be treated pharmacologically rather than with surgical extraction or extracorporal shockwave lithotripsy.