title: Quantitative Dose Dependency Analysis of Whole-Brain CT Perfusion Imaging.
abstract: OBJECTIVE
  To quantitatively assess whether decreasing total radiation dose of the image acquisition protocol has an effect on cerebral CT perfusion values in patients with acute stroke.
  
  
  METHODS
  This retrospective study was approved by the institutional ethics committee, and informed consent was waived. Twenty consecutive patients with ischemic stroke who underwent CT perfusion imaging with a 320-detector row CT scanner were included. A standard acquisition protocol was used, which was started 5 seconds after injection of a contrast agent, with a scan at 200 mAs, followed after 4 seconds by 13 scans, one every 2 seconds, at 100 mAs, and then five scans, one every 5 seconds, at 75 mAs. The total examination had an average effective dose of 5.0 mSv. For each patient, a patient-specific digital perfusion phantom was constructed to simulate the same protocol at a lower total dose (0.5-5.0 mSv, with stepped doses of 0.5 mSv). The lowest setting for which the maximum mean difference remained within 5% of the reference standard (at 5.0 mSv) was marked as the optimal setting. At the optimal setting, Pearson correlation coefficients were calculated to assess correlations with the reference values, and paired t tests were performed to compare the means.
  
  
  RESULTS
  At 2.5 mSv, the maximum mean differences in values from those of the reference standard were 4.5%, 5.0%, and 1.9%, for cerebral blood flow, cerebral blood volume, and mean transit time, respectively. Pearson correlation coefficients of perfusion values for white matter and gray matter were 0.864-0.917, and all differences were significant (P < .0001). Paired t tests showed no significant differences between the reference standard and optimal settings (P = .089-.923).
  
  
  CONCLUSIONS
  The total dose of a clinical cerebral CT perfusion protocol can be lowered to 2.5 mSv, with only minor quantitative effects on perfusion values. Dose reduction beyond this point resulted in overestimation of perfusion values.
authors.affiliation: From the Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein 10, 6525 GA, the Netherlands.
authors.forename: Rashindra
authors.initials: R
authors.lastname: Manniesing
authors.affiliation: From the Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein 10, 6525 GA, the Netherlands.
authors.forename: Marcel T H
authors.initials: MT
authors.lastname: Oei
authors.affiliation: From the Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein 10, 6525 GA, the Netherlands.
authors.forename: Bram
authors.initials: B
authors.lastname: van Ginneken
authors.affiliation: From the Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein 10, 6525 GA, the Netherlands.
authors.forename: Mathias
authors.initials: M
authors.lastname: Prokop
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002545:Brain Ischemia / Q000000981:diagnostic imaging*; D002560:Cerebrovascular Circulation; D003287:Contrast Media; D005260:Female; D006801:Humans; D007472:Iohexol / Q000031:analogs & derivatives; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D020521:Stroke / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; C093233:iobitridol; D007472:Iohexol