title: Effects of increased image noise on image quality and quantitative interpretation in brain CT perfusion.
abstract: OBJECTIVE
  There is a desire within many institutions to reduce the radiation dose in CTP examinations. The purpose of this study was to simulate dose reduction through the addition of noise in brain CT perfusion examinations and to determine the subsequent effects on quality and quantitative interpretation.
  
  
  METHODS
  A total of 22 consecutive reference CTP scans were identified from an institutional review board-approved prospective clinical trial, all performed at 80 keV and 190 mAs. Lower-dose scans at 188, 177, 167, 127, and 44 mAs were generated through the addition of spatially correlated noise to the reference scans. A standard software package was used to generate CBF, CBV, and MTT maps. Six blinded radiologists determined quality scores of simulated scans on a Likert scale. Quantitative differences were calculated.
  
  
  RESULTS
  For qualitative analysis, the correlation coefficients for CBF (-0.34; P < .0001), CBV (-0.35; P < .0001), and MTT (-0.44; P < .0001) were statistically significant. Interobserver agreements in quality for the simulated 188-, 177-, 167-, 127-, and 44-mAs scans for CBF were 0.95, 0.98, 0.98, 0.95, and 0.52, respectively. Interobserver agreements in quality for the simulated CBV were 1, 1, 1, 1, and 0.83, respectively. For MTT, the interobserver agreements were 0.83, 0.86, 0.88, 0.74, and 0.05, respectively. For quantitative analysis, only the lowest simulated dose of 44 mAs showed statistically significant differences from the reference scan values for CBF (-1.8; P = .04), CBV (0.07; P < .0001), and MTT (0.46; P < .0001).
  
  
  CONCLUSIONS
  From a reference CTP study performed at 80 keV and 190 mAs, this simulation study demonstrates the potential of a 33% reduction in tube current and dose while maintaining image quality and quantitative interpretations. This work can be used to inform future studies by using true, nonsimulated scans.
authors.affiliation: Department of Radiology, Weill Cornell Medical College, New York-Presbyterian Hospital, New York, NY 10065, USA. kjuluru@med.cornell.edu
authors.forename: K
authors.initials: K
authors.lastname: Juluru
authors.forename: J C
authors.initials: JC
authors.lastname: Shih
authors.forename: A
authors.initials: A
authors.lastname: Raj
authors.forename: J P
authors.initials: JP
authors.lastname: Comunale
authors.forename: H
authors.initials: H
authors.lastname: Delaney
authors.forename: E D
authors.initials: ED
authors.lastname: Greenberg
authors.forename: C
authors.initials: C
authors.lastname: Hermann
authors.forename: Y B
authors.initials: YB
authors.lastname: Liu
authors.forename: A
authors.initials: A
authors.lastname: Hoelscher
authors.forename: N
authors.initials: N
authors.lastname: Al-Khori
authors.forename: P C
authors.initials: PC
authors.lastname: Sanelli
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging*; D002533:Cerebral Angiography / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000379:methods*
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