title: Effect of radiographic contrast material exposure on spiral CT attenuation of renal calculi.
abstract: OBJECTIVE
  The authors performed this study to determine whether exposure of renal calculi to radiographic contrast material has an effect on the attenuation values at computed tomography (CT) performed with varying collimation widths.
  
  
  METHODS
  Renal calculi (23 stones of various composition) were scanned with 1-, 3-, and 10-mm collimation. Stones were then exposed to a solution of radiographic contrast material for 5 minutes, washed with water, and rescanned 36 hours later. The reproducibility of the CT attenuation measurements on different days was evaluated by obtaining measurements in a subset of 16 renal stones on 4 different days.
  
  
  RESULTS
  There was no statistically significant change in attenuation after contrast material exposure at narrow collimation. At wider collimation, statistically significant increases were noted in both attenuation and standard deviation. A small amount of variability between readings was noted on different days, with a minimal increase in attenuation each day. Correlation between readings remained very high.
  
  
  CONCLUSIONS
  Exposure of stones to a radiographic contrast material had a statistically significant effect on CT attenuation values only at wide collimation. This may be related to technical factors including volume averaging. Absence of an effect at narrow collimation suggests that the attenuation values of renal stones do not significantly change after exposure to contrast material.
authors.affiliation: Department of Radiology, Clarian/Methodist Hospital of Indiana, Indianapolis 46202, USA.
authors.forename: A G
authors.initials: AG
authors.lastname: Monga
authors.forename: K C
authors.initials: KC
authors.lastname: Saw
authors.forename: J C
authors.initials: JC
authors.lastname: Williams
authors.forename: N S
authors.initials: NS
authors.lastname: Fineberg
authors.forename: J A
authors.initials: JA
authors.lastname: McAteer
authors.forename: J E
authors.initials: JE
authors.lastname: Lingeman
authors.forename: G T
authors.initials: GT
authors.lastname: Chua
mesh_terms: D003287:Contrast Media; D006801:Humans; D007669:Kidney Calculi / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media