title: Multi-detector row CT: radiation dose characteristics.
abstract: OBJECTIVE
  To determine the dose characteristics of multi-detector row computed tomography (CT) and to provide tabulated dose values and rules of thumb that assist in minimizing the radiation dose at multi-detector row CT.
  
  
  METHODS
  Weighted CT dose index (CTDI100w) values were obtained from three multi-detector row CT scanners (LightSpeed; GE Medical Systems, Milwaukee, Wis) for both head and body CT modes by using standard CT-dose phantoms. The CTDI100w was determined as a function of x-ray tube voltage (80, 100, 120, 140 kVp), tube current (range, 50-380 mA), tube rotation time (0.5-4.0 seconds), radiation profile width (RPW) (5, 10, 15, 20 mm), and acquisition mode (helical high-quality and high-speed modes and axial one-, two-, and four-section modes). Statistical regression was performed to characterize the relationships between CTDI100w and various technique factors.
  
  
  RESULTS
  The CTDI100w (milligray) increased linearly with tube current: in head mode, CTDI100w = (0.391 mGy/mA +/- 0.004) x tube current (milliampere) (r2 = 0.999); in body mode, CTDI100w = (0.162 mGy/mA +/- 0.002) x tube current (milliampere) (r2 = 0.999). The CTDI100w increased linearly with rotation time: in head mode, CTDI100w = (34.7 mGy/sec +/- 0.2) x rotation time (seconds) (r2 = 1.0); in body mode, CTDI100w = (13.957 mGy/sec +/- 0.005) x rotation time (seconds) (r2 = 1.0). The relationship of normalized CTDI100w (milligrays per 100 mAs) with tube voltage followed a power law: in head mode, CTDI100w = (0.00016 mGy/100 mAs. kVp +/- 0.00007) x (tube voltage)(2.5+/-0.1) (r2 = 0.997); in body mode, CTDI100w = (0.000012 mGy/100 mAs. kVp +/- 0.000007) x (tube voltage)(2.8+/-0.1) (r2 = 0.996). In all scanning modes, CTDI100w decreased when RPW increased. CTDI100w was 10% higher in head mode and 13% lower in body mode compared with the value suggested by the manufacturer, which is displayed at the scanner console. When deposited power exceeded 24 kW, CTDI100w increased by 10% as a result of use of the large focal spot.
  
  
  CONCLUSIONS
  The authors provide a set of tables of radiation dose as a function of imaging protocol to facilitate implementation of radiation dose-efficient studies.
authors.affiliation: Department of Radiology, Perfusion and Physiology Analysis Laboratory, Massachusetts General Hospital, 55 Fruit St, Gray Bldg, Rm B238, Boston, MA 02114, USA. lhamberg@partners.org
authors.forename: Leena M
authors.initials: LM
authors.lastname: Hamberg
authors.forename: James T
authors.initials: JT
authors.lastname: Rhea
authors.forename: George J
authors.initials: GJ
authors.lastname: Hunter
authors.forename: James H
authors.initials: JH
authors.lastname: Thrall
mesh_terms: D006257:Head; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D013902:Radiography, Thoracic; D011874:Radiometry / Q000379:methods*; D015898:Tomography Scanners, X-Ray Computed