title: Diagnostic yield of delayed phase imaging in CT angiography of the head and neck: a retrospective study.
abstract: OBJECTIVE
  To evaluate how often delayed images, obtained during neurovascular CTA, provide unique information relative to early phase imaging alone.
  
  
  METHODS
  Informed consent was waived by the institutional review body for this study. Neurovascular CTAs from January through June 2009 were searched to identify those with delayed phase imaging. Reports were reviewed to identify cases where delayed images provided potentially unique information. The studies with potentially unique information were re-interpreted to determine if the information was indeed unique.
  
  
  RESULTS
  645 CTAs with delayed phase imaging were identified. There were 324 men and 310 women (median age 67 years; range 20-96 years). 59 studies (59/645: 9.1%) had findings on the delayed images. There were 13 cases with hemorrhage, with 4 showing progression on delayed views. Of the remaining 46 cases, 28 had occlusion of a vessel that did not reconstitute on the delayed images, 6 had occlusion of a vessel that did reconstitute on the delayed images, 7 had a string sign which was unchanged on the delayed views and 5 had no abnormal findings. Thus in 10 cases the findings were unique to the delayed images (10/645: 1.55%). Four showed active bleeding, three showed proximal occlusion with distal internal carotid filling from ophthalmic collaterals, two showed pial vessels filling distal to proximal MCA occlusion, and one showed retrograde vertebral artery filling due to subclavian steal. 95% confidence limits of the expected incidence of unique information from the delayed phase images are 0.6%-2.5%.
  
  
  CONCLUSIONS
  Obtaining delayed phase imaging for neurovascular CTA should be an active decision and not the default protocol. This avoids imaging with little, if any value. If delayed images had not been obtained in our cohort, no detriment in patient management would have occurred.
authors.affiliation: Massachusetts General Hospital, Department of Radiology, Boston, Massachusetts, United States of America.
authors.forename: Debbie L
authors.initials: DL
authors.lastname: Bennett
authors.affiliation: Brigham and Women's Hospital, Department of Radiology, Boston, Massachusetts, United States of America.
authors.forename: Leena M
authors.initials: LM
authors.lastname: Hamberg
authors.affiliation: The University of Texas MD Anderson Cancer Center, Diagnostic Radiology, Houston, Texas, United States of America.
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.affiliation: Massachusetts General Hospital, Department of Radiology, Boston, Massachusetts, United States of America.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Hirsch
authors.affiliation: Massachusetts General Hospital, Department of Radiology, Boston, Massachusetts, United States of America.
authors.forename: R Gilberto
authors.initials: RG
authors.lastname: González
authors.affiliation: Massachusetts General Hospital, Department of Radiology, Boston, Massachusetts, United States of America.
authors.forename: George J
authors.initials: GJ
authors.lastname: Hunter
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000792:Angiography; D005260:Female; D006257:Head / Q000098:blood supply* / Q000000981:diagnostic imaging*; D006470:Hemorrhage / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000098:blood supply* / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D055815:Young Adult