title: CT brain perfusion: A static phantom study of contrast-to-noise ratio and radiation dose.
abstract: BACKGROUND
  Computed tomography perfusion (CTP) is increasingly employed in the diagnosis and management of ischaemic stroke but radiation dose can be significant and optimising contrast-to-noise ratio (CNR) is challenging. This study aimed to quantify and optimise the balance between CNR as a surrogate for image quality and radiation dose.
  
  
  METHODS
  A perspex head phantom with vials of dilute contrast agent was scanned using a Siemens Definition Flash 128-slice scanner. The CTP protocol exposure parameters were adjusted over 70-120 kVp and 150-285 mAs. Measurements were obtained for the average dose per slice, Hounsfield Units (HU) for iodinated contrast agent, and the image noise for background regions of perspex. The CNR was measured as a function of the volumetric CT dose index (CTDIvol) and kVp.
  
  
  RESULTS
  A change from 120 to 80 kVp, achieved the same CNR with 60% reduction in dose. Alternatively, for the same dose, the change from 120 to 80 kVp improved CNR by +58%. A change from 80 to 70 kVp while operating at the same CNR, led to 13% reduction in dose. Alternatively, maintaining the same dose while changing from 80 to 70 kVp improved the CNR by +7%.
  
  
  CONCLUSIONS
  Lower beam energies achieved the same CNR with less dose, or improved CNR at the same dose. A reduction from 80 kVp to 70 kVp may be clinically useful to optimise CTP acquisitions.
authors.affiliation: Department of Radiology, Royal Melbourne Hospital and University of Melbourne, Parkville, Victoria, Australia.|South Australian Medical Imaging, Flinders Medical Centre, Bedford Park, South Australia, Australia.|School of Physics and Astronomy, Monash University, Clayton, Victoria, Australia.
authors.forename: Stewart M
authors.initials: SM
authors.lastname: Midgley
authors.affiliation: Department of Radiology, Royal Melbourne Hospital and University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Damien L
authors.identifier: http://orcid.org/0000-0002-2241-8702
authors.initials: DL
authors.lastname: Stella
authors.affiliation: Department of Medicine and Neurology, Royal Melbourne Hospital and University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Bruce Cv
authors.initials: BC
authors.lastname: Campbell
authors.affiliation: Department of Radiology, Royal Melbourne Hospital and University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Francesca
authors.initials: F
authors.lastname: Langenberg
authors.affiliation: Department of Radiology, Royal Melbourne Hospital and University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Paul F
authors.initials: PF
authors.lastname: Einsiedel
mesh_terms: D002561:Cerebrovascular Disorders / Q000000981:diagnostic imaging*; D006801:Humans; D059906:Neuroimaging / Q000379:methods*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: CT brain perfusion; contrast-to-noise ratio; radiation dose