Urinary stone-characterization with Dual Energy
The following question has been sent by Luke Riverstone, Radiographer, Qscan Radiology Clinics, Australia:
We have recently obtained a Siemens DSCT. We performed our first DE KUB the other day and the Dual Energy Software indicated that there was 1 Kidney stone that was of a Uric Acid composition and 1 was of Calcuim composition.
The Radiologist at our institution wanted to know why he should trust the software to determine the compostion of the Stone. He indicated that he would not be mentioning it in his report or to the urologist until he had seen some data on it first.
My Question is: is there any published data on the accuracy of the DE scan in determining the compostion of the Kidney Stones. If not what information can I pass on that will give the confidence in to report based on the finding of the DE scan?
Hatem Alkadhi, M.D., University Hospital Zurich:
Until now, there are two published papers dealing with the topic urinary stone-characterization with dual energy CT. One is an ex-vivo study from Primak et al.: Noninvasive differentiation of uric acid versus non-uric acid kidney stones using dual-energy CT. Acad Radiol. 2007;14:1441-7.
The other study is an ex-vivo and in-vivo study from Graser et al.: Dual energy CT characterization of urinary calculi: initial in vitro and clinical experience. Invest Radiol. 2008;43:112-9.
Both studies could convinsingly demonstrate that dual-energy CT allows to discriminate uric acid stones from other stone types with a high accuracy. Thus, I would be confident in reporting a stone to contain uric acid or not.
Certainly, future in-vivo studies including large patient populations are required to confirm these first experience studies and to assess the true diagnostic performance of dual-energy CT for the differentiation of uric-acid versus non-uric-acid containing stones in comparison with chemical analysis.
Best regards,
Hatem Alkadhi
we’ve done a DE KUB on 10 patients with a proven chemical analysis of one stone. however , if we cange the protocol from the default seimens, some results may be confusing. also i would like to know if any modification can be done so that tiny calculii (which otherwise are not characterised) could be characterised. would a smaller fov in the recon help??
Our experience shows that the reduction of the calculation range is helpful in the depiction of small urinary calculi. This parameter can be set on the advanced definition dialog card. In addition, the limits for calculation can be adjusted. This can be of interest when you examine stones with very low or very high attenuation values. So far – to my knowledge – there is no information on the optimal field of view. On the other hand, the slice acquisition plays an important role. For example Primak et al. showed that the accuracy in the determination of stone compositions depends on the collimation used with dual-source dual-energy CT.