title: Precision of dosimetry-related measurements obtained on current multidetector computed tomography scanners.
abstract: OBJECTIVE
  Computed tomography (CT) intrascanner and interscanner variability has not been well characterized. Thus, the purpose of this study was to examine the within-run, between-run, and between-scanner precision of physical dosimetry-related measurements collected over the course of 1 yr on three different makes and models of multidetector row CT (MDCT) scanners.
  
  
  METHODS
  Physical measurements were collected using nine CT scanners (three scanners each of GE VCT, GE LightSpeed 16, and Siemens Sensation 64 CT). Measurements were made using various combinations of technical factors, including kVp, type of bowtie filter, and x-ray beam collimation, for several dosimetry-related quantities, including (a) free-in-air CT dose index (CTDI100,air); (b) calculated half-value layers and quarter-value layers; and (c) weighted CT dose index (CTDIW) calculated from exposure measurements collected in both a 16 and 32 cm diameter CTDI phantom. Data collection was repeated at several different time intervals, ranging from seconds (for CTDI100,air values) to weekly for 3 weeks and then quarterly or triannually for 1 yr. Precision of the data was quantified by the percent coefficient of variation (%CV).
  
  
  RESULTS
  The maximum relative precision error (maximum %CV value) across all dosimetry metrics, time periods, and scanners included in this study was 4.33%. The median observed %CV values for CTDI100,air ranged from 0.05% to 0.19% over several seconds, 0.12%-0.52% over 1 week, and 0.58%-2.31% over 3-4 months. For CTDIW for a 16 and 32 cm CTDI phantom, respectively, the range of median %CVs was 0.38%-1.14% and 0.62%-1.23% in data gathered weekly for 3 weeks and 1.32%-2.79% and 0.84%-2.47% in data gathered quarterly or triannually for 1 yr.
  
  
  CONCLUSIONS
  From a dosimetry perspective, the MDCT scanners tested in this study demonstrated a high degree of within-run, between-run, and between-scanner precision (with relative precision errors typically well under 5%).
authors.affiliation: Department of Bioengineering, Rice University, Houston, Texas 77005, USA. knb2@rice.edu
authors.forename: Kelsey B
authors.initials: KB
authors.lastname: Mathieu
authors.forename: Michael F
authors.initials: MF
authors.lastname: McNitt-Gray
authors.forename: Di
authors.initials: D
authors.lastname: Zhang
authors.forename: Hyun J
authors.initials: HJ
authors.lastname: Kim
authors.forename: Dianna D
authors.initials: DD
authors.lastname: Cody
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*