title: Timing-invariant reconstruction for deriving high-quality CT angiographic data from cerebral CT perfusion data.
abstract: OBJECTIVE
  To suggest a simple and robust technique used to reconstruct high-quality computed tomographic (CT) angiographic images from CT perfusion data and to compare it with currently used CT angiography techniques.
  
  
  METHODS
  Institutional review board approval was waived for this retrospective study, which included 25 consecutive patients who had had a stroke. Temporal maximum intensity projection (tMIP) CT angiographic images were created by using prior temporal filtering as a timing-insensitive technique to produce CT angiographic images from CT perfusion data. The temporal filter strength was optimized to gain maximal contrast-to-noise ratios (CNRs) in the circle of Willis. The resulting timing-invariant (TI) CT angiography was compared with standard helical CT angiography, the arterial phase of dynamic CT angiography, and nonfiltered tMIP CT angiography. Vascular contrast, image noise, and CNR were measured. Four experienced observers scored all images for vascular noise, vascular contour, detail of small and medium arteries, venous superimposition, and overall image quality in a blinded side-by-side comparison. Measurements were compared with a paired t test; P ≤ .05 indicated a significant difference.
  
  
  RESULTS
  On average, optimized temporal filtering in TI CT angiography increased CNR by 18% and decreased image noise by 18% at the expense of a decrease in vascular contrast of 3% when compared with nonfiltered tMIP CT angiography. CNR, image noise, vascular noise, vascular contour, detail visibility of small and medium arteries, and overall image quality of TI CT angiograms were superior to those of standard CT angiography, tMIP CT angiography, and the arterial phase of dynamic CT angiography at a vascular contrast that was similar to that of standard CT angiography. Venous superimposition was similar for all techniques. Image quality of the arterial phase of dynamic CT angiography was rated inferior to that of standard CT angiography.
  
  
  CONCLUSIONS
  TI CT angiographic images constructed by using temporally filtered tMIP CT angiographic data have excellent image quality that is superior to that achieved with currently used techniques, but they suffer from modest venous superimposition.
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Heidelberglaan 100, 3508 GA Utrecht, the Netherlands. e.j.smit-3@umcutrecht.nl
authors.forename: Ewoud J
authors.initials: EJ
authors.lastname: Smit
authors.forename: Evert-jan
authors.initials: EJ
authors.lastname: Vonken
authors.forename: Irene C
authors.initials: IC
authors.lastname: van der Schaaf
authors.forename: Adrienne M
authors.initials: AM
authors.lastname: Mendrik
authors.forename: Jan Willem
authors.initials: JW
authors.lastname: Dankbaar
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Horsch
authors.forename: Tom
authors.initials: T
authors.lastname: van Seeters
authors.forename: Bram
authors.initials: B
authors.lastname: van Ginneken
authors.forename: Mathias
authors.initials: M
authors.lastname: Prokop
mesh_terms: D000328:Adult; D002533:Cerebral Angiography / Q000379:methods*; D002561:Cerebrovascular Disorders / Q000000981:diagnostic imaging*; D003287:Contrast Media; D005260:Female; D006801:Humans; D007472:Iohexol / Q000031:analogs & derivatives; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D007472:Iohexol; C038192:iopromide