Feasibility of Single-Source Dual-Energy Computed Tomography for Urinary Stone Characterization and Value of Iterative Reconstructions

Abstract

The purposes of this study were to demonstrate the feasibility and accuracy of single-source dual-energy (DE) computed tomography (CT) with sequential data acquisition and a coregistration motion correction algorithm for urinary stone characterization and to evaluate the value of iterative reconstructions (IRs) in DE imaging. Thirty-five urinary stones were placed in cylindrical phantoms with diameters of 30 and 40 cm. The phantoms were scanned on a 64-section CT machine with a single-source DE protocol consisting of 2 sequential acquisitions at 80 and 140 kilovolt (peak). The phantom was moved between the 80- and 140-kilovolt (peak) scans. Images were reconstructed with weighted filtered back projection (FBP) and with IR, and data were coregistered. Two independent and blinded readers assessed data sets for stone detection, overall image quality, and visibility of stones. Image noise and Hounsfield unit values of the stones were measured, and the DE index was calculated. In addition, the data sets were analyzed on color-coded images using the standard postprocessing software for differentiating uric acid- (UA) from non-UA-containing stones. The motion correction algorithm achieved a good coregistration of the 2 scans with different energy levels. Both readers detected all stones on all data sets with both reconstruction types. The overall image quality was rated significantly higher in IR images in the 40-cm phantom as compared with that in FBP images (P < 0.05), whereas no significant difference was found for the 30-cm phantom. Visibility of stones was rated significantly higher for both the 30- and 40-cm phantoms on IR as compared with that on FBP images, an effect that was pronounced for UA stones (P < 0.05). Noise was significantly reduced by up to 31% in the 40-cm phantom when using IR as compared with FBP (P < 0.001). The DE index was similar in the FBP and IR data sets for the 30- (P = 0.116) and 40-cm phantoms (P = 0.544), being significantly different between UA-containing stones, cystine, and struvite stones as well as stones of other compositions (P < 0.001). The postprocessing software classified all stones correctly as UA- or non-UA-containing stones on color-coded images. In the 40-cm phantom, false-positively colored voxels were found in the FBP data sets, which were not seen when using IR instead. Our study indicates that single-source dual-energy CT with sequential acquisitions at different energy levels and a coregistration motion correction algorithm is feasible and accurate for characterizing urinary stone composition on the basis of phantom evaluation. As compared with reconstructions with FBP, the use of IR in dual-energy CT reduces noise, improves overall image quality and visibility of stones particularly in large phantoms, and helps to avoid false classifications of urinary stones.