title: Reduced-dose CT: effect on reader evaluation in detection of pulmonary embolism.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the effect of reduction in radiation dose on CT detection of pulmonary embolism.
  
  
  METHODS
  Emergency department patients were evaluated for pulmonary embolism with standard and simulated reduced-dose CT angiography. Simulated lower-dose CT angiograms obtained at 90, 45, 22, and 10 mAs(eff) were reconstructed by mathematical addition of noise to the standard dose (180 mAs(eff)) data from the images of 18 patients with and 20 patients without pulmonary embolism. Four radiologists blinded to the study parameters separately interpreted each CT angiogram. Dose trends for subjective measures (diagnostic certainty, image quality, and perceived technical limitations) were evaluated, test characteristics for the detection of pulmonary embolism were computed, and clot burden was measured.
  
  
  RESULTS
  Readers indicated significant reductions in diagnostic certainty (p < 0.02) and image quality (p < 0.02) and an increase in perceived technical limitations (p < 0.01) as the simulated radiation dose was decreased. These subjective measures also showed significant adverse dose trends when the mAs(eff) was reduced (p < 0.001). At reduced radiation doses, the sensitivity and positive predictive value for detection of pulmonary embolism diminished significantly. The sensitivity was 0.94 (lower bound of 0.95 CI, 0.92); specificity, 0.99 (lower bound of 0.95 CI, 0.98); positive predictive value, 0.95 (lower bound of 0.95 CI, 0.92); and negative predictive value, 0.99 (lower bound of 0.95 CI, 0.97). All patients had a low to moderate clot burden.
  
  
  CONCLUSIONS
  Reduction in dose for CT angiography in the detection of pulmonary embolism has a significant adverse effect on readers' subjective assessment of diagnostic confidence and image quality. Detection of pulmonary embolism also decreases as the tube current dose is reduced.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Boston, MA, USA.
authors.forename: John D
authors.initials: JD
authors.lastname: MacKenzie
authors.forename: Javier
authors.initials: J
authors.lastname: Nazario-Larrieu
authors.forename: Tianxi
authors.initials: T
authors.lastname: Cai
authors.forename: M Stephen
authors.initials: MS
authors.lastname: Ledbetter
authors.forename: Maria Alejandra
authors.initials: MA
authors.lastname: Duran-Mendicuti
authors.forename: Philip F
authors.initials: PF
authors.lastname: Judy
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Rybicki
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000792:Angiography / Q000379:methods*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging*; D011829:Radiation Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*