title: Calcium stone fragility is predicted by helical CT attenuation values.
abstract: OBJECTIVE
  Helical CT has become the preferred method for imaging urinary calculi, and so it would be useful if data from helical CT could also be used to predict the number of shockwaves (SWs) needed to break a given stone.
  
  
  METHODS
  We measured the number of SWs required to comminute calcium stones in vitro.
  
  
  RESULTS
  The SW requirement correlated with stone size (volume, weight, diameter) and with helical CT attenuation values when the scans were performed at 3-mm collimation. When CT scans were performed at 1-mm collimation, the number of SWs needed for comminution did not correlate with helical CT attenuation values. This result indicates that the correlation with 3-mm scans was attributable to volume-averaging effects, in which smaller stones yield smaller attenuation values. That is, attenuation values from helical CT at larger beam collimation widths contain information about stone size that can be exploited to predict the fragility of calcium stones. We observed that for calcium stones, the number of SWs to comminution was generally less than half the stone CT attenuation value in Hounsfield units. This "half-attenuation rule" predicted the number of SWs needed to complete fragmentation for 95% of calcium stones (24/24 calcium oxalate monohydrate, 13/13 hydroxyapatite, 8/10 brushite stones).
  
  
  CONCLUSIONS
  This in vitro study suggests that it may be possible to predict effective SW dose using helical CT prior to lithotripsy.
authors.affiliation: Methodist Hospital Institute of Kidney Stone Disease, Indianapolis, Indiana, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Saw
authors.forename: J A
authors.initials: JA
authors.lastname: McAteer
authors.forename: N S
authors.initials: NS
authors.lastname: Fineberg
authors.forename: A G
authors.initials: AG
authors.lastname: Monga
authors.forename: G T
authors.initials: GT
authors.lastname: Chua
authors.forename: J E
authors.initials: JE
authors.lastname: Lingeman
authors.forename: J C
authors.initials: JC
authors.lastname: Williams
mesh_terms: D006801:Humans; D007669:Kidney Calculi / Q000000981:diagnostic imaging*; D008096:Lithotripsy / Q000009:adverse effects / Q000379:methods*; D011237:Predictive Value of Tests; D014057:Tomography, X-Ray Computed