title: Accuracy of CT angiography in the assessment of the circle of Willis: comparison of volume-rendered images and digital subtraction angiography.
abstract: BACKGROUND
  Computed tomography angiography (CTA) is increasingly used for non-invasive imaging of the cerebrovascular diseases.
  
  
  OBJECTIVE
  To evaluate the accuracy of CTA in the assessment of the variation of the segment calibers of the circle of Willis.
  
  
  METHODS
  One hundred and 17 patients with acute SAH (51 men and 66 women, mean age 50.9 years) who underwent CTA using a 16 detector-row CT scanner and DSA were evaluated retrospectively. The CTA and DSA studies were performed within 24 h after the onset of symptoms and within 24 h of each other. A total of 819 arterial segments (A-comA, right and left A1 segment, right and left P-com A, and right and left P1 segment) of the circle of Willis were determined to be aplastic (grade 1), hypoplastic (grade 2), or normal-sized (grade 3) by blinded observers evaluating CTA volume-rendered images. The CTA results were then compared with findings on the corresponding DSA images (reference standard).
  
  
  RESULTS
  The overall agreement between CTA and DSA was 92.4%. We had 62 (7.6%) cases of disagreement (58 cases of under-estimation and four cases of over-estimation by CTA) between tow modalities. The sensitivity and specificity of CTA in the detection of aplastic and normal-sized segments were more than 90%. In contrast, subgroup analysis of the hypoplastic segments showed a sensitivity of 52.6% and a specificity of 98.2%.
  
  
  CONCLUSIONS
  CTA is highly accurate in the assessment of anatomical variations of the circle of Willis; however, its sensitivity is limited in depicting hypoplastic segments.
authors.affiliation: Department of Radiology, Kangdong Seong-Sim Hospital, Hallym University College of Medicine, Seoul, Republic of Korea.
authors.forename: Ari
authors.initials: A
authors.lastname: Han
authors.forename: Dae Young
authors.initials: DY
authors.lastname: Yoon
authors.forename: Suk Ki
authors.initials: SK
authors.lastname: Chang
authors.forename: Kyoung Ja
authors.initials: KJ
authors.lastname: Lim
authors.forename: Byung-Moon
authors.initials: BM
authors.lastname: Cho
authors.forename: Yoon Cheol
authors.initials: YC
authors.lastname: Shin
authors.forename: Sam Soo
authors.initials: SS
authors.lastname: Kim
authors.forename: Keon Ha
authors.initials: KH
authors.lastname: Kim
mesh_terms: D015901:Angiography, Digital Subtraction / Q000379:methods*; D002533:Cerebral Angiography / Q000379:methods*; D002941:Circle of Willis / Q000000981:diagnostic imaging*; D003287:Contrast Media; D005260:Female; D006801:Humans; D007472:Iohexol; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D007472:Iohexol