title: Optimising imaging parameters in experimental spiral CT.
abstract: OBJECTIVE
  This in vitro study was conducted to analyse lesion detection and relative radiation exposure in different CT techniques.
  
  
  METHODS
  We used a plastic phantom (12 x 8 x 2 cm) containing holes filled with air or fluid of varying densities to simulate lesions. This was imaged with Siemens Somatom Plus S and GE High Speed Advantage units. We varied table feeds (3 and 6 mm/s in Siemens and 3 and 4.5 mm/s in GE) and increments (2 mm and 4 mm) while keeping collimation at 3 mm. The SmartScan program of GE and the reformatting algorithm of Siemens were also analysed. To evaluate the different methods, the phantom lesions were counted by 3 observers. Radiation exposures associated with each technique were also measured.
  
  
  RESULTS
  The images reformatted to a coronal direction were significantly inferior (p < 0.01) to those in other techniques. The use of SmartScan did not influence lesion detection, nor did changes in pitch or increment. Spiral and non-spiral techniques proved to be equal. Radiation exposure was lowest when a greater pitch or the SmartScan program was used.
  
  
  CONCLUSIONS
  Radiation exposure in CT can be limited without significantly impairing the image quality by using low-dose techniques. Reformatting to a coronal direction should be used with care as it debases the image quality.
authors.affiliation: Department of Radiology, Helsinki University Central Hospital, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Tiitola
authors.forename: T
authors.initials: T
authors.lastname: Vehmas
authors.forename: R P
authors.initials: RP
authors.lastname: Kivisaari
authors.forename: L
authors.initials: L
authors.lastname: Kivisaari
mesh_terms: D006801:Humans; D019047:Phantoms, Imaging / Q000706:statistics & numerical data; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data