1. Figure 16c. Determination of chemical composition of renal stones in two different patients who presented with flank pain. (a, b) Axial dual-source DEdual-energy CT images, material-specific for calcium (a) and uric acid (b). (c) Illustration shows the dual-energy indexes for different stones. Kidney stones are classified as uric acid and non–uric acid stones on the basis of the dual-energy attenuation ratio. Uric acid renal stones are red (1 in a) and a non–uric acid calculus is blue (2 in b). Note that stones with uric acid composition have lower dual-energy indexes than do non–uric acid stones.