title: The effect of varying user-selected input parameters on quantitative values in CT perfusion maps.
abstract: OBJECTIVE
  Deconvolution-based software can be used to calculate quantitative maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) from first-pass computed tomography perfusion (CTP) datasets. The application of this software requires the user to select multiple input variables. The purpose of this study was to investigate the degree to which both major and minor variations of these user-defined inputs would affect the final quantitative values of CBF, CBV, and MTT.
  
  
  METHODS
  A neuroradiologist constructed CBF, CBV, and MTT maps using standard methodology with commercially available software (GE Functool Version 1.9s) from CTP datasets of three acute stroke patients. Each map was reconstructed multiple times by systematically and independently varying the following parameters: postenhancement and preenhancement cutoff values, arterial and venous region-of-interest (ROI) placement, and arterial and venous ROI size. The resulting quantitative CTP values were compared using identical ROIs placed at the infarct core.
  
  
  RESULTS
  Major variations of either arterial ROI placement or arterial and venous ROI size had no significant effect on the mean CBF, CBV, and MTT values at the infarct core (p > .05). Even minor variations, however, in the choice of venous ROI placement or in pre- and postenhancement cutoff values significantly altered the quantitative values for each of the CTP maps, by as much as threefold.
  
  
  CONCLUSIONS
  Even minor variations of user-defined inputs can significantly influence the quantitative, deconvolution-based CTP map values of acute stroke patients. Although quantitation was robust to the choice of arterial ROI placement and arterial or venous ROI size, it was strongly dependent on the choice of venous ROI location and pre- and postenhancement cut-off values. Awareness of these results by clinicians may be important in the creation of quantitatively accurate CTP maps.
authors.affiliation: Department of Radiology, Weill Medical College of Cornell University, New York Presbyterian Hospital, 520 East 68th Street, Starr Pavilion, Starr-630, New York, NY 10021, USA. pcs9001@med.cornell.edu
authors.forename: Pina C
authors.initials: PC
authors.lastname: Sanelli
authors.forename: Michael H
authors.initials: MH
authors.lastname: Lev
authors.forename: James D
authors.initials: JD
authors.lastname: Eastwood
authors.forename: R Gilberto
authors.initials: RG
authors.lastname: Gonzalez
authors.forename: Ting Y
authors.initials: TY
authors.lastname: Lee
mesh_terms: D000328:Adult; D001811:Blood Volume Determination; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D020244:Infarction, Middle Cerebral Artery / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*