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Ahn SH et al, 2015: Can a dual-energy computed tomography predict unsuitable stone components for extracorporeal shock wave lithotripsy?

Ahn SH, Oh TH, Seo IY.
Department of Urology, Institute of Wonkwang Medical Science, Wonkwang University School of Medicine, Iksan, Korea.

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.

Korean J Urol. 2015 Sep;56(9):644-9. doi: 10.4111/kju.2015.56.9.644. Epub 2015 Sep 8

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Comments 1

Hans-Göran Tiselius on Friday, 04 December 2015 10:39

With the described CT-protocol the authors were successful to discriminate between uric acid (UA) stones and calcium oxalate monohydrate (COM) stones. Obviously DECT is very useful for diagnosis of HU-stones, which otherwise only can be indirectly identified by their absence on the scout image of standard NCCT images. The use of DECT with the higher radiation exposure might be justified in those cases inasmuch as elimination of HU-stones can be accomplished by oral chemolysis and accordingly without the fluoroscopy during stone removal.

The value of identifying stones composed of COM might, in my mind, be most important for the largest stones, when stone removal with methods other than SWL should be considered. The expression “shockwave resistant stones” only means that the stones will require greater total SW-energy and usually repeated treatment sessions (depending on the stone size). But most stones can be successfully disintegrated with SWL, also COM-stones if repeated sessions can be accepted [1].

Reference
1. Tiselius HG,Chaussy CG (2012) Aspects on how extracorporeal shockwave lithotripsy should be carried out in order to be maximally effective. Urological Research 40: 433-446.

With the described CT-protocol the authors were successful to discriminate between uric acid (UA) stones and calcium oxalate monohydrate (COM) stones. Obviously DECT is very useful for diagnosis of HU-stones, which otherwise only can be indirectly identified by their absence on the scout image of standard NCCT images. The use of DECT with the higher radiation exposure might be justified in those cases inasmuch as elimination of HU-stones can be accomplished by oral chemolysis and accordingly without the fluoroscopy during stone removal. The value of identifying stones composed of COM might, in my mind, be most important for the largest stones, when stone removal with methods other than SWL should be considered. The expression “shockwave resistant stones” only means that the stones will require greater total SW-energy and usually repeated treatment sessions (depending on the stone size). But most stones can be successfully disintegrated with SWL, also COM-stones if repeated sessions can be accepted [1]. Reference 1. Tiselius HG,Chaussy CG (2012) Aspects on how extracorporeal shockwave lithotripsy should be carried out in order to be maximally effective. Urological Research 40: 433-446.
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