title: Radiation Dose Reduction in 4D Cerebral CT Angiography by Individualized Estimation of Cerebral Circulation Time.
abstract: The novel technique of 4D CTA for dynamic assessment of the intracranial vessels has a greater radiation burden than conventional CTA. Previous descriptions of the technique used a fixed-duration exposure protocol. This study examines the potential for dose reduction by individualizing exposure time to patient physiology by the use of time-enhancement curve techniques as previously applied in CT angiography and venography.
  
  
  
  4D-CTA examinations performed at our institution were retrospectively reviewed. Scan protocols used a test-bolus scan with either a subjective estimate of the main acquisition timing (estimated-duration method) or a quantitative measure (measured-duration method). The estimated-duration method used peak arterial enhancement to determine the start of exposure, with the duration chosen at the radiologist's discretion. The measured-duration method used arterial and venous time-enhancement curves to determine exposure start and duration. Exposure duration, study adequacy, quality score, and maximum venous enhancement were compared among groups.
  
  
  
  One hundred fifty-one examinations used the estimated-duration method, and 53 used measured-duration. The measured-duration method used a shorter exposure time (10 versus 15.8 seconds; P < .001). There was no statistically significant difference in the study adequacy rate, subjective quality score, or maximum venous enhancement. The radiation dose was reduced by 51% in the measured-duration method (3021 mGy × cm, 6.9 mSv, versus 1473 mGy × cm, 3.4 mSv). Both methods showed good agreement with DSA (κ = 0.88 for estimated-duration, κ = 1.0 for measured duration).
  
  
  
  Exposure time in 4D-CTA can be reduced with dual time-enhancement curves to match exposure to physiology without degrading study adequacy or quality.
authors: From the Department of Neuroradiology, The Walton Centre, Liverpool, United Kingdom. Mark.radon@thewaltoncentre.nhs.uk.
authors: M R
authors: 0000-0002-8904-9331
authors: MR
authors: Radon
authors: From the Department of Neuroradiology, The Walton Centre, Liverpool, United Kingdom.
authors: A
authors: 0000-0002-3687-5752
authors: A
authors: Chandran
authors: From the Department of Neuroradiology, The Walton Centre, Liverpool, United Kingdom.
authors: M
authors: 0000-0003-4004-0640
authors: M
authors: Bhojak
authors: From the Department of Neuroradiology, The Walton Centre, Liverpool, United Kingdom.
authors: K V
authors: 0000-0001-9334-2031
authors: KV
authors: Das
mesh_terms: D001921:Brain / Q000098:blood supply* / Q000000981:diagnostic imaging*; D000072226:Computed Tomography Angiography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D012189:Retrospective Studies; D012680:Sensitivity and Specificity