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Largo R et al, 2015: Predictive value of low tube voltage and dual-energy CT for successful shock wave lithotripsy: an in vitro study.

Largo R, Stolzmann P, Fankhauser CD, Poyet C, Wolfsgruber P, Sulser T, Alkadhi H, Winklhofer S.
Department of Urology, University Hospital Zürich, University of Zürich, Zürich, Switzerland.
Institute of Diagnostic and Interventional Radiology, University Hospital Zürich, Raemistrasse 100, 8091, Zürich, Switzerland.
Institute of Diagnostic and Interventional Radiology, University Hospital Zürich, Raemistrasse 100, 8091, Zürich, Switzerland.
Department of Radiology and Biomedical Imaging, University of California San Francisco, 505 Parnassus Ave, M-372, Box 0628, San Francisco, CA, 94143-0628, USA.

Abstract

This study investigates the capabilities of low tube voltage computed tomography (CT) and dual-energy CT (DECT) for predicting successful shock wave lithotripsy (SWL) of urinary stones in vitro. A total of 33 urinary calculi (six different chemical compositions; mean size 6 ± 3 mm) were scanned using a dual-source CT machine with single- (120 kVp) and dual-energy settings (80/150, 100/150 Sn kVp) resulting in six different datasets. The attenuation (Hounsfield Units) of calculi was measured on single-energy CT images and the dual-energy indices (DEIs) were calculated from DECT acquisitions. Calculi underwent SWL and the number of shock waves for successful disintegration was recorded. The prediction of required shock waves regarding stone attenuation/DEI was calculated using regression analysis (adjusted for stone size and composition) and the correlation between CT attenuation/DEI and the number of shock waves was assessed for all datasets. The median number of shock waves for successful stone disintegration was 72 (interquartile range 30-361). CT attenuation/DEI of stones was a significant, independent predictor (P < 0.01) for the number of required shock waves with the best prediction at 80 kVp (β estimate 0.576) (P < 0.05). Correlation coefficients between attenuation/DEI and the number of required shock waves ranged between ρ = 0.31 and 0.68 showing the best correlation at 80 kVp (P < 0.001). The attenuation of urinary stones at low tube voltage CT is the best predictor for successful stone disintegration, being independent of stone composition and size. DECT shows no added value for predicting the success of SWL. 

Urolithiasis. 2015 Sep 21. [Epub ahead of print]

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Comments 1

Hans-Göran Tiselius on Monday, 30 November 2015 10:35

The radiological density of urinary tract stones expressed in Hounsfield units has proven useful for roughly predicting stone composition and SWL fragility. With dual energy CT (DECT) this possibility has been refined. The authors of this report introduced a dual-energy index (DEI). Their interesting finding was that the disintegration of stones was possible to predict by the attenuation/DEI quotient, but not by information on stone composition. These results were obtained in vitro and only further experience will disclose whether these experimental results will correspond to results during clinical SWL.

The radiological density of urinary tract stones expressed in Hounsfield units has proven useful for roughly predicting stone composition and SWL fragility. With dual energy CT (DECT) this possibility has been refined. The authors of this report introduced a dual-energy index (DEI). Their interesting finding was that the disintegration of stones was possible to predict by the attenuation/DEI quotient, but not by information on stone composition. These results were obtained in vitro and only further experience will disclose whether these experimental results will correspond to results during clinical SWL.
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