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Lee JY et al, 2016: Stone heterogeneity index as the standard deviation of Hounsfield units: A novel predictor for shock-wave lithotripsy outcomes in ureter calculi.

Lee JY, Kim JH, Kang DH, Chung DY, Lee DH, Do Jung H, Kwon JK, Cho KS.
Department of Urology, Soonchunhyang University Seoul Hospital, Soonchunhyang University College of Medicine, Seoul, Korea.
Department of Urology, Incheon Red Cross Hospital, Incheon, Korea.
Department of Urology, Severance Check-Up, Yonsei University Health System, Seoul, Korea.
Department of Urology, Gangnam Severance Hospital, Urological Science Institute, Yonsei University College of Medicine, Seoul, Korea.

Abstract

We investigated whether stone heterogeneity index (SHI), which a proxy of such variations, was defined as the standard deviation of a Hounsfield unit (HU) on non-contrast computed tomography (NCCT), can be a novel predictor for shock-wave lithotripsy (SWL) outcomes in patients with ureteral stones. Medical records were obtained from the consecutive database of 1,519 patients who underwent the first session of SWL for urinary stones between 2005 and 2013. Ultimately, 604 patients with radiopaque ureteral stones were eligible for this study. Stone related variables including stone size, mean stone density (MSD), skin-to-stone distance, and SHI were obtained on NCCT. Patients were classified into the low and high SHI groups using mean SHI and compared. One-session success rate in the high SHI group was better than in the low SHI group (74.3% vs. 63.9%, P = 0.008). Multivariate logistic regression analyses revealed that smaller stone size (OR 0.889, 95% CI: 0.841-0.937, P < 0.001), lower MSD (OR 0.995, 95% CI: 0.994-0.996, P < 0.001), and higher SHI (OR 1.011, 95% CI: 1.008-1.014, P < 0.001) were independent predictors of one-session success. The radiologic heterogeneity of urinary stones or SHI was an independent predictor for SWL success in patients with ureteral calculi and a useful clinical parameter for stone fragility.

Sci Rep. 2016 Apr 1;6:23988. doi: 10.1038/srep23988. 

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Comments 1

Peter Alken on Sunday, 20 November 2016 09:45

I wonder why the group around Williams who has been working on CT and stones since years (1,2,3) has never jumped on that issue. At least in their 2007 publication they looked at stone heterogeneity subjectively determined by four blinded observers. Their conclusion was: “When stones were graded by appearance on helical CT, classification was repeatable and homogeneous stones required more SW’s for comminution than did heterogeneous stones (1,702 ± 993 SW/g, compared to 907 ± 773). Stone fragility normalized to stone size did not correlate with Hounsfield units (P = 0.85). In conclusion, COM stones of homogeneous structure require almost twice as many SW’s to comminute than stones of similar mineral composition that exhibit internal structural features that are visible by CT. This suggests that stone fragility in patients could be predicted using pre-treatment CT imaging. The findings also show that Hounsfield unit values of COM stones did not correlate with stone fragility. Thus, it is stone morphology, rather than X-ray attenuation, which correlates with fragility to
SW’s in this common stone type.” (2). These results seem to be confirmed by the present publication. The present authors do not quote this publication but they must have been aware of Williams work as they quote reference1 and another publication by Williams from 2003.

In the present publication the difference of the one-session success rate in the high SHI group compared to the low SHI group (74.3% vs. 63.9%, P = 0.008) is not very impressive but the authors state ”SHI can be readily measured using the currently available PACS without additional equipment”. So it is easy to try and find out.

1 Williams JC Jr, et al. High resolution detection of internal structure of renal calculi by helical computerized tomography. J Urol. 2002 Jan;167(1):322-6.
2 Zarse CA, et al. CT visible internal stone structure, but not Hounsfield unit value, of calcium oxalate monohydrate (COM) calculi predicts lithotripsy fragility in vitro. Urol Res. 2007 Aug;35(4):201-6.
3 Williams JC Jr et al. Fragility of brushite stones in shock wave lithotripsy: absence of correlation with computerized tomography visible structure. J Urol. 2012 Sep;188(3):996-1001.

I wonder why the group around Williams who has been working on CT and stones since years (1,2,3) has never jumped on that issue. At least in their 2007 publication they looked at stone heterogeneity subjectively determined by four blinded observers. Their conclusion was: “When stones were graded by appearance on helical CT, classification was repeatable and homogeneous stones required more SW’s for comminution than did heterogeneous stones (1,702 ± 993 SW/g, compared to 907 ± 773). Stone fragility normalized to stone size did not correlate with Hounsfield units (P = 0.85). In conclusion, COM stones of homogeneous structure require almost twice as many SW’s to comminute than stones of similar mineral composition that exhibit internal structural features that are visible by CT. This suggests that stone fragility in patients could be predicted using pre-treatment CT imaging. The findings also show that Hounsfield unit values of COM stones did not correlate with stone fragility. Thus, it is stone morphology, rather than X-ray attenuation, which correlates with fragility to SW’s in this common stone type.” (2). These results seem to be confirmed by the present publication. The present authors do not quote this publication but they must have been aware of Williams work as they quote reference1 and another publication by Williams from 2003. In the present publication the difference of the one-session success rate in the high SHI group compared to the low SHI group (74.3% vs. 63.9%, P = 0.008) is not very impressive but the authors state ”SHI can be readily measured using the currently available PACS without additional equipment”. So it is easy to try and find out. 1 Williams JC Jr, et al. High resolution detection of internal structure of renal calculi by helical computerized tomography. J Urol. 2002 Jan;167(1):322-6. 2 Zarse CA, et al. CT visible internal stone structure, but not Hounsfield unit value, of calcium oxalate monohydrate (COM) calculi predicts lithotripsy fragility in vitro. Urol Res. 2007 Aug;35(4):201-6. 3 Williams JC Jr et al. Fragility of brushite stones in shock wave lithotripsy: absence of correlation with computerized tomography visible structure. J Urol. 2012 Sep;188(3):996-1001.
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