title: Aortic CT angiography dose reduction: investigation of optimal noise index and iterative algorithm strength in combination with low kV.
abstract: OBJECTIVE
  The purpose of this study was to optimize an aorta angiographic CT protocol, by investigating the best combination of tube current modulation, iterative algorithm strength and kV reduction.
  
  
  METHODS
  Anthropomorphic phantoms of three sizes were imaged by CT with different values of noise index, of iterative algorithm ASIR percentages and kV in the range 80-120. Quantitative noise and contrast noise ratios were evaluated at different phantom locations. Three radiologists assessed the subjective image quality by comparing the image series with the one acquired with the reference protocol (120 kV, slice thickness 0.625, noise index 28, ASIR 40 %).
  
  
  RESULTS
  Although the highest CNR values were obtained for the 80 kV acquisitions, qualitative scores were higher for 100 and 120 kV at the same noise index. An optimized protocol was established with a NI of 39.2, ASIR 60%, 100 kV for small- and medium-sized patients and 120 kV for large-sized patients, with a dose reduction of 47%.
  
  
  CONCLUSIONS
  When different dose reduction parameters are available, anthropomorphic phantoms of different sizes help to find the optimal combination. For aorta studies, 100 kV with relative high values of noise indexes and iterative levels provides the best balance between dose reduction and image quality.
authors.affiliation: Medical Physics Unit, S.C. Fisica Sanitaria, A.O.U. Città della Salute e della Scienza di Torino, Corso Bramante 88, 10126, Turin, Italy. orampado@cittadellasalute.to.it.
authors.forename: Osvaldo
authors.identifier: http://orcid.org/0000-0003-3078-5438
authors.initials: O
authors.lastname: Rampado
authors.affiliation: Medical Physics Unit, S.C. Fisica Sanitaria, A.O.U. Città della Salute e della Scienza di Torino, Corso Bramante 88, 10126, Turin, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Busso
authors.affiliation: Radiodiagnostic Department, S.C. Radiodiagnostica Ospedaliera, Corso Bramante 88, 10126, Turin, Italy.
authors.forename: Domenica
authors.initials: D
authors.lastname: Garabello
authors.affiliation: Radiodiagnostic Department, S.C. Radiodiagnostica Ospedaliera, Corso Bramante 88, 10126, Turin, Italy.
authors.forename: Ezio
authors.initials: E
authors.lastname: Marengo
authors.affiliation: Radiodiagnostic Department, S.C. Radiodiagnostica Ospedaliera, Corso Bramante 88, 10126, Turin, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Valerio
authors.affiliation: Radiodiagnostic Department, S.C. Radiodiagnostica Ospedaliera, Corso Bramante 88, 10126, Turin, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Capello
authors.affiliation: Radiodiagnostic Department, S.C. Radiodiagnostica Ospedaliera, Corso Bramante 88, 10126, Turin, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Veglia
authors.affiliation: Radiodiagnostic Department, S.C. Radiodiagnostica Ospedaliera, Corso Bramante 88, 10126, Turin, Italy.
authors.forename: Ottavio
authors.initials: O
authors.lastname: Davini
authors.affiliation: Medical Physics Unit, S.C. Fisica Sanitaria, A.O.U. Città della Salute e della Scienza di Torino, Corso Bramante 88, 10126, Turin, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Ropolo
mesh_terms: D000465:Algorithms; D001013:Aorta, Thoracic / Q000000981:diagnostic imaging*; D001027:Aortography / Q000379:methods*; D016477:Artifacts; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed
keywords: Aorta; Computed tomography; Dose optimisation; Iterative reconstruction; Radiation dose