Michael Devin Rivers-Bowerman MD,MSc, Presenter: Nothing to Disclose

Arash Eftekhari MD, Abstract Co-Author: Nothing to Disclose

Kristopher Thomas Kang BA, Abstract Co-Author: Nothing to Disclose

Karl Krzymyk, Abstract Co-Author: Employee, Siemens AG

Silvia D. Chang MD, Abstract Co-Author: Nothing to Disclose

Savvas Nicolaou MD, Abstract Co-Author: Nothing to Disclose

Jiamin Zheng, Abstract Co-Author: Nothing to Disclose

Ben Chew, Abstract Co-Author: Nothing to Disclose

The objective of this in vitro study was to determine if the chemical composition of small urinary stones can be determined with dual energy computed tomography (DECT) KUB at 100/140 kVp using a tin filter separation method.

Thirty urinary stones, ten each of uric acid (UA), cystine (CYS), and calcium oxalate (CaOX) were scanned in a 16 cm acrylic CT body phantom. DECT datasets were acquired with a SOMATOM Definition Flash unit (Siemens Medical Solutions, Germany) with the following parameters: tube A/B voltage, 100/140 kVp; tube A/B current, 46/40 mAs; collimation, 0.6 mm; CTDIvol, 3.9 mGy; DLP, 74 mGy•cm. Images were axially reconstructed with a D30f kernel for dual energy viewing and a modified two-material decomposition algorithm was applied to the datasets for stone analysis. One reader blinded to stone composition performed region-of-interest (ROI) measurements to calculate the DECT overlay value for each stone. DECT results were then compared with the actual chemical composition of the stones as determined by IR spectroscopy. Mean colour overlay values were evaluated with the ANOVA test. Pair-wise comparisons were corrected for multiple hypothesis testing using the Bonferroni method and significance was taken at P ≤ 0.05.  

Mean (standard deviation (SD), range) stone diameter was 2.0 (0.6, 1.2-4.0) mm. Modified two-material decomposition correctly identified the chemical composition of 53% (n = 16/30) of stones. Stones less than 2 mm in diameter (n = 14) were not characterized by the decomposition algorithm. Mean (SD) overlay values in Hounsfield units (HU) for stones greater than 2 mm in diameter were -13.3 (0.7) for UA, 23.9 (1.9) for CYS, and 42.7 (2.5) for CaOX. ANOVA testing of group overlay means yielded P < 0.001. With Bonferroni-adjusted pair-wise comparisons, we found that the chemical composition of stones greater than 2 mm could be resolved using overlay values alone (P < 0.05).

The chemical compositions of stones greater than 2 mm in diameter are reliably determined with DECT at 100/140 kVp using overlay values.

DECT overlay values at 100/140 kVp can be used to identify stone types responsive to urinary alkalinization with the potential to streamline patient management at the time of imaging.

Rivers-Bowerman, M, Eftekhari, A, Kang, K, Krzymyk, K, Chang, S, Nicolaou, S, Zheng, J, Chew, B, In Vitro Characterization of Urinary Stones Less than 4 mm in Diameter with Dual-Energy CT.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11014159.html