Basic and Translational Science Dual Source Computed Tomography: A Novel Technique to Determine Stone Composition Brian R. Matlaga, Satomi Kawamoto, and Elliot Fishman INTRODUCTION Dual source computed tomography (CT), a novel technology that employs two different x-ray sources, may provide an image resolution that has not been possible with conventional single source CT. We tested the ability of dual source CT imaging to distinguish calcium oxalate (CaOx) stones from calcium phosphate (CaP) stones, and both types of calciferous stones from uric acid (UA) stones. METHODS CaOx, CaP, and UA stones were placed in a tissue phantom and imaged with dual source multidetector CT at both 80kV and 140 kV. Hounsfield units (HU) of each stone were recorded for the 140 kV and the 80 kV datasets by drawing regions of interest by circle, hand-drawing, and using a volume calculation method. The differences between, and the ratios of, the HU obtained by the two energy sources were compared among the stone groups. RESULTS Between CaOx and CaP stones, HU differences (80kV-140kV difference, hand-drawing technique: CaOx = 270.7; CaP = 369.5; UA = 11.45; P = 0.020 for CaOx vs. CaP; P  0.001 for CaOx and CaP vs. UA) as well as ratios (140kV:80kV ratio, hand-drawing technique: CaOx = 1.44; CaP = 1.51; UA = 1.04; P = 0.001 for CaOx vs. CaP; P  0.001 for CaOx and CaP vs. UA) were significantly different. There were no significant differences in stone size among the groups. CONCLUSIONS Dual source CT has the ability to distinguish not only between calciferous stones and uric acid stones, but also among stones composed of different calcium salts. Further studies are warranted to confirm these findings in a clinical setting. UROLOGY 72: 1164 –1168, 2008. © 2008 Elsevier Inc. N oncontrast helical computed tomography (CT) is the preferred method for evaluating the majority of patients suspected of harboring urinary calculi. 1 The widespread utilization of CT for this task is due in great part to its ability to rapidly locate the stone in question, gauge its size, and inform the clinician as to associated complicating features such as hydronephrosis. A number of investigators have studied the ability of helical CT to pre- dict stone composition. 2-11 In general, CT has been re- ported to consistently distinguish stones composed of uric acid (UA) from stones composed primarily of calcium. However, the issue of whether CT imaging can distinguish among stones composed of different calcium salts, such as calcium oxalate (CaOx) stones from calcium phosphate (CaP) stones, is an area of open investigation, as published studies have yielded conflicting results. A recent innovation in CT is the development of dual source CT imaging, a novel technology that utilizes two x-ray sources, rather than a single x-ray source as in conventional helical CT. In addition to improved tem- poral resolution, dual source CT scanners have the ability to simultaneously operate the two x-ray sources at differ- ent energy levels, which has the potential to differentiate materials on the basis of their unique energy-dependent profiles. It has been reported that dual source CT imaging may allow tissue differentiation that has not been previ- ously possible with single source CT. 12 We performed a study to test the ability of dual source CT imaging to distinguish stones composed of one calcium salt from stones composed of another calcium salt, as well as from UA stones. MATERIAL AND METHODS Human kidney stones were obtained from a stone analysis laboratory (Beck Analytical Services, Indianapolis, Indiana). The composition of the stones was confirmed by analysis with microscopic visual inspection, chemical reaction, and Fourier transform infrared microspectroscopy. The stones selected for this study were composed of CaOx monohydrate, CaP (hy- droxyapatite), and UA. The intact stones were hydrated in water and placed in a carotid anthropomorphic vascular phantom (Shelly Medical Imaging Technologies, Ontario, Canada). A phantom was em- From the James Buchanan Brady Urological Institute, The Russell H. Morgan Depart- ment of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, Maryland Reprint requests: Brian R. Matlaga, M.D., M.P.H., James Buchanan Brady Urological Institute, The Johns Hopkins University School of Medicine, 600 North Wolfe St, Baltimore, MD 21209. E-mail: bmatlaga@jhmi.edu Submitted: December 11, 2007, accepted (with revisions): March 31, 2008 1164 © 2008 Elsevier Inc. 0090-4295/08/$34.00 All Rights Reserved doi:10.1016/j.urology.2008.03.051