title: Implementation of automated tube current modulation in PET/CT: prospective selection of a noise index and retrospective patient analysis to ensure image quality.
abstract: Automated tube current modulation (ATCM) has been shown to be a useful tool for reducing CT dose. However, its implementation can be complicated, because the correlation between noise index (NI) settings and noise production can change as parameters are manipulated. The goal was to create a methodology to prospectively select ATCM parameters and retrospectively ensure consistent image quality.
  
  
  METHODS
  An anthropomorphic phantom was scanned at various NIs to determine a baseline NI versus image noise. The noise was measured in SDs of the CT number reported in Hounsfield units. A physician then reviewed 45 studies performed with the same fixed-tube-current protocol to obtain a preferred noise level. The noise level was compared with our phantom baseline scans to find a suitable NI value. This value was implemented in clinical operation. Then, the next 50 patient examinations were retrospectively reviewed to ensure that image quality was maintained to our physician's cutoff noise levels. Radiation dose reductions through tube current reduction were measured for all CT slices of each patient study.
  
  
  RESULTS
  In the phantom study, tube current modulation was observed at an NI of 15. The preferred noise level established in the physician's review correlated with an NI of 20. In our postimplementation analysis, we found that our noise level was 10.75 SDs in Hounsfield units. CT dose reductions of up to 52% were seen.
  
  
  CONCLUSIONS
  We were able to prospectively select an NI for ATCM CT by correlating phantom scans to a physician's preferred noise level while maintaining consistent image quality.
authors.affiliation: Department of Nuclear Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA. James.jackson@mdanderson.org
authors.forename: James
authors.initials: J
authors.lastname: Jackson
authors.forename: Tinsu
authors.initials: T
authors.lastname: Pan
authors.forename: Elena
authors.initials: E
authors.lastname: Tonkopi
authors.forename: Nancy
authors.initials: N
authors.lastname: Swanston
authors.forename: Homer A
authors.initials: HA
authors.lastname: Macapinlac
authors.forename: Eric M
authors.initials: EM
authors.lastname: Rohren
mesh_terms: D001331:Automation; D004553:Electric Conductivity; D005240:Feasibility Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D011446:Prospective Studies; D011786:Quality Control; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*