Gemstone spectral imaging dual-energy computed tomography: a novel technique to determine urinary stone composition

Abstract

Objective: To assess the capability of determining the chemical composition of urinary stones using dual-energy spectral computed tomography (CT).

Materials and methods: A total of 116 urinary stones with a known chemical composition determined by infrared spectroscopy were scanned using both gemstone spectral imaging and conventional polychromatic imaging (at 120 kVp) in vitro. The CT numbers of each stone were recorded from the 11 sets of monochromatic images (40-140 keV, 10-keV interval) and 120-kVp polychromatic images. The differences between the CT numbers obtained in the 12 sets were compared among the stone groups.

Results: The 116 urinary stones were classified into 7 groups: uric acid (n = 16), cystine (n = 10), brushite (n = 17), weddellite (n = 14), whewellite (n = 24), carbapatite (n = 12), and struvite (n = 23). The paired CT numbers (at 120 kVp and 50 keV, respectively) of each stone group were as follows: uric acid, 469.11 ± 69.83 and 474.06 ± 40.55 Hounsfield units (HU); cystine, 564.81 ± 97.71 and 839.58 ± 92.14 HU; brushite, 1830.94 ± 59.19 and 2787.41 ± 306.07 HU; weddellite, 1438.09 ± 191.12 and 2100.79 ± 202.32 HU; whewellite, 1493.48 ± 259.90 and 2321.39 ± 367.23 HU; carbapatite, 1784.58 ± 106.42 and 2513.86 ± 189.09 HU; and struvite, 833.037 ± 9.91 and 1123.24 ± 267.70 HU. The differences in the CT numbers at 120 kVp and 50 keV among the groups were statistically significant by binary comparison (P <.05), except for those at 120 kVp between uric acid and cystine (P = .121), whewellite and weddellite (P = .280), and brushite and carbapatite (P = .419).

Conclusion: Gemstone spectral imaging dual-energy CT provides a novel method to better characterize pure urinary stones using the CT numbers at 50 keV.