title: Time density curve analysis for C-arm FDCT PBV imaging.
abstract: BACKGROUND
  Parenchymal blood volume (PBV) estimation using C-arm flat detector computed tomography (FDCT) assumes a steady-state contrast concentration in cerebral vasculature for the scan duration. Using time density curve (TDC) analysis, we explored if the steady-state assumption is met for C-arm CT PBV scans, and how consistent the contrast-material dynamics in cerebral vasculature are across patients.
  
  
  METHODS
  Thirty C-arm FDCT datasets of 26 patients with aneurysmal-SAH, acquired as part of a prospective study comparing C-arm CT PBV with MR-PWI, were analysed. TDCs were extracted from the 2D rotational projections. Goodness-of-fit of TDCs to a steady-state horizontal-line-model and the statistical similarity among the individual TDCs were tested. Influence of the differences in TDC characteristics on the agreement of resulting PBV measurements with MR-CBV was calculated.
  
  
  RESULTS
  Despite identical scan parameters and contrast-injection-protocol, the individual TDCs were statistically non-identical (p < 0.01). Using Dunn's multiple comparisons test, of the total 435 individual comparisons among the 30 TDCs, 330 comparisons (62%) reached statistical significance for difference. All TDCs deviated significantly (p < 0.01) from the steady-state horizontal-line-model. PBV values of those datasets for which the TDCs showed largest deviations from the steady-state model demonstrated poor agreement and correlation with MR-CBV, compared with the PBV values of those datasets for which the TDCs were closer to steady-state.
  
  
  CONCLUSIONS
  For clinical C-arm CT PBV examinations, the administered contrast material does not reach the assumed 'ideal steady-state' for the duration of scan. Using a prolonged injection protocol, the degree to which the TDCs approximate the ideal steady-state influences the agreement of resulting PBV measurements with MR-CBV.
authors.affiliation: Nuffield Department of Surgical Sciences, University of Oxford, UK m.kamran@oxon.org.
authors.forename: Mudassar
authors.initials: M
authors.lastname: Kamran
authors.affiliation: Nuffield Department of Surgical Sciences, University of Oxford, UK.
authors.forename: James V
authors.initials: JV
authors.lastname: Byrne
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001811:Blood Volume Determination / Q000379:methods*; D001921:Brain / Q000000981:diagnostic imaging*; D002545:Brain Ischemia / Q000000981:diagnostic imaging; D002533:Cerebral Angiography / Q000379:methods*; D002560:Cerebrovascular Circulation; D004621:Embolization, Therapeutic; D005260:Female; D006801:Humans; D006849:Hydrocephalus / Q000000981:diagnostic imaging; D007091:Image Processing, Computer-Assisted; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging / Q000628:therapy
keywords: C-arm flat detector computed tomography; MR perfusion-weighted imaging; Parenchymal blood volume; cerebral blood volume; time density curve