Can a dual-energy computed tomography predict unsuitable stone components for extracorporeal shock wave lithotripsy?

Abstract

Purpose: To assess the potential of dual-energy computed tomography (DECT) to identify urinary stone components, particularly uric acid and calcium oxalate monohydrate, which are unsuitable for extracorporeal shock wave lithotripsy (ESWL).

Materials and methods: This clinical study included 246 patients who underwent removal of urinary stones and an analysis of stone components between November 2009 and August 2013. All patients received preoperative DECT using two energy values (80 kVp and 140 kVp). Hounsfield units (HU) were measured and matched to the stone component.

Results: Significant differences in HU values were observed between uric acid and nonuric acid stones at the 80 and 140 kVp energy values (p<0.001). All uric acid stones were red on color-coded DECT images, whereas 96.3% of the nonuric acid stones were blue. Patients with calcium oxalate stones were divided into two groups according to the amount of monohydrate (calcium oxalate monohydrate group: monohydrate≥90%, calcium oxalate dihydrate group: monohydrate<90%). Significant differences in HU values were detected between the two groups at both energy values (p<0.001).

Conclusions: DECT improved the characterization of urinary stone components and was a useful method for identifying uric acid and calcium oxalate monohydrate stones, which are unsuitable for ESWL.

Keywords: Calcium oxalate; Uric acid; Urinary calculi; X-ray computed tomography.

Fig. 1. (A) Uric acid and nonuric acid stones in color-coded images. Dual-energy computed tomography had excellent sensitivity and accuracy for differentiating uric acid from nonuric acid stones. Uric acid stones are red in the color-coded image (a), and nonuric acid stones are blue (b) (arrow). (B) Measuring Hounsfield unit (HU) values using the region of interest (ROI) method. One radiological specialist drew a circular ROI along the inner edge of the stone to measure the HU value. An HU value of 946.33 was determined for the left uretero-vesical junction stone.

Fig. 2. Mean Hounsfield unit (HU) values for stones based on the energy used. Different HU values were measured on 80 and 140 kVp images of each stone. CaOM, calcium oxalate monohydrate; CaOD, calcium oxalate monohydrate+dihydrate; Carbonate, carbonate apatite.