In vitro analysis of urinary stone composition in dual-energy computed tomography

Purpose
Dual energy computed tomography (DECT) is a new method of computed tomography (CT) imaging, allowing the assessment of not only the object’s morphology, but also its composition. The aim of the study was to evaluate the potential of in vitro DECT evaluation of urinary stones’ chemical composition.

Material and methods
Six samples of surgically removed renal stones were scanned using DECT and analyzed by scanner vendor software. Uric acid stones were marked red and calcium stones white by the software. The real composition of the stones was finally verified using physicochemical laboratory analysis.

Results
In 5 out of 6 samples, the composition of stones in DECT (3 samples identified as uric acid and 2 samples as calcium) was consistent with the physicochemical analysis (3 samples identified as uric acid, 1 as calcium phosphate, 1 as calcium oxalate). In DECT it was not possible to determine more precisely the type of calcium compounds (calcium phosphate vs. calcium oxalate) as established in the physicochemical analysis. In one stone identified in physicochemical analysis as uric acid, DECT detected a composite layered structure containing both uric acid and calcium compounds.

Conclusions
DECT allows uric acid to be distinguished from calcium urinary tract stones, which is crucial in the choice of appropriate therapy. Using the available hardware and software, it was not possible to more accurately distinguish types of calcified stones. Evaluation of the stone type in DECT may be limited in the case of mixed chemical composition.