Endourology and Stones Dual-energy vs Conventional Computed Tomography in Determining Stone Composition Eric S. Wisenbaugh, Robert G. Paden, Alvin C. Silva, and Mitchell R. Humphreys OBJECTIVE To compare the accuracy between conventional computed tomography (CT) and dual-energy CT (DECT) in predicting stone composition in a blinded, prospective fashion. METHODS A total of 32 renal stones with known composition were scanned in vitro, first using standard CT techniques at 120 kilovolt peak (kV[p]) and then using fast-switched kilovolt DECT at 80 and 140 kilovolt peak (kV[p]). For the DECT scan, a spectral curve was created demonstrating the change of Hounsfield units (HU) across the kiloelectron volt spectrum. The composition of each stone was estimated by comparing each sample curve with curves of known materials. To attempt stone determination using single-energy CT, the HU of each stone was compared with ranges reported in previous studies. The accuracy of each method was compared. RESULTS Included were 27 stones large enough to allow analysis. Single-energy measurements accurately identified 14 of 27 stones of all composition (52%), whereas the DECT spectral curves correctly identified 20 (74%). When analyzed by stone type, single-energy vs DECT correctly identified 12 vs 12 of the 12 uric acid stones, 2 vs 3 of the 6 struvite stones, 0 vs 3 of the 5 cystine stones, and 0 vs 2 of the 4 calcium oxalate stones, respectively. When simply attempting to differentiate uric acid vs nonuric acid stones, single-energy CT could accurately differentiate only 6 of 15 stones as nonuric acid (40%) compared with 14 of 15 stones (93%) for DECT. CONCLUSION DECT appears to be superior to conventional CT in differentiating stone composition and is particularly accurate in differentiating nonuric acid from uric acid stones. UROLOGY -: -e-, 2014. Ó 2014 Elsevier Inc. T he evaluation and treatment of urolithiasis rep- resents a heavy and increasing burden on the United States health care system. The lifetime risk of stone formation exceeds 12% in men and 6% in women and has increased during the last quarter of the 20th century. 1 The estimated annual cost to the United States health care system was $2.1 billion in 2000, not accounting for lost work and productivity. 2 Imaging plays a vital role in the accurate diagnosis of urinary stones. Plain radiography and intravenous urog- raphy were traditionally the imaging modalities of choice; however, the noncontrast computed tomography (CT) scan has now become the gold standard for evaluating patients with symptoms suggestive of urolithiasis. CT has excellent sensitivity and specificity for detecting the presence of stones and is reliable in determining their size and location, which in turn assists in directing treatment. The successful treatment of urolithiasis largely depends on stone composition. For example, that uric acid stones may be managed medically and that certain stone types are resistant to shockwave lithotripsy (SWL) is well established. Ideally, stone composition could be deter- mined at the time of the initial imaging, thereby directing treatment before subjecting the patient to a procedure that may be unnecessary or unsuccessful. This is a major limitation of conventional CT scanning. Dual-energy CT (DECT) is a promising new technology that has the potential to improve our current ability to differentiate stone phenotypes by composition. The limi- tation of conventional “single-energy” scanning is that the Hounsfield unit (HU) value of any object is related to its attenuation coefficient, which depends not only on its composition and density but also on the energy of the photons interacting with it. Therefore, an object’s atten- uation coefficient is not unique at a single energy level and can be indistinguishable from other materials. DECT in- volves scanning at 2 different energy levels, typically 140 and 80 kilovolt peak (kV[p]), thus obtaining a different (typically at a lower energy) attenuation coefficient to help discriminate different material compositions. Three different general configurations are currently used commercially for DECT, each applying a different technique. The Siemens Medical Solutions SOMATOM Definition scanner was the first DECT scanner available. Financial Disclosure: The authors declare that they have no relevant financial interests. From the Department of Urology, Mayo Clinic Arizona, Phoenix, AZ; and the Department of Radiology, Mayo Clinic Arizona, Phoenix, AZ Reprint requests: Eric S. Wisenbaugh, M.D., Mayo Clinic Arizona, 5777 East Mayo Boulevard, Phoenix, AZ 85054. E-mail: eric.wisenbaugh@gmail.com Submitted: July 14, 2013, accepted (with revisions): December 13, 2013 ª 2014 Elsevier Inc. 0090-4295/14/$36.00 1 All Rights Reserved http://dx.doi.org/10.1016/j.urology.2013.12.023