title: Effect of automatic tube current modulation on radiation dose and image quality for low tube voltage multidetector row CT angiography: phantom study.
abstract: OBJECTIVE
  To evaluate the effect of automatic tube current modulation on radiation dose and image quality for low tube voltage computed tomography (CT) angiography.
  
  
  METHODS
  An anthropomorphic phantom was scanned with a 64-section CT scanner using following tube voltages: 140 kVp (Protocol A), 120 kVp (Protocol B), 100 kVp (Protocol C), and 80 kVp (Protocol D). To achieve similar noise, combined z-axis and xy-axes automatic tube current modulation was applied. Effective dose (ED) for the four tube voltages was assessed. Three plastic vials filled with different concentrations of iodinated solution were placed on the phantom's abdomen to obtain attenuation measurements. The signal-to-noise ratio (SNR) was calculated and a figure of merit (FOM) for each iodinated solution was computed as SNR(2)/ED.
  
  
  RESULTS
  The ED was kept similar for the four different tube voltages: (A) 5.4 mSv +/- 0.3, (B) 4.1 mSv +/- 0.6, (C) 3.9 mSv +/- 0.5, and (D) 4.2 mSv +/- 0.3 (P > .05). As the tube voltage decreased from 140 to 80 kVp, image noise was maintained (range, 13.8-14.9 HU) (P > .05). SNR increased as the tube voltage decreased, with an overall gain of 119% for the 80-kVp compared to the 140-kVp protocol (P < .05). The FOM results indicated that with a reduction of the tube voltage from 140 to 120, 100, and 80 kVp, at constant SNR, ED was reduced by a factor of 2.1, 3.3, and 5.1, respectively, (P < .001).
  
  
  CONCLUSIONS
  As tube voltage decreases, automatic tube current modulation for CT angiography yields either a significant increase in image quality at constant radiation dose or a significant decrease in radiation dose at a constant image quality.
authors.affiliation: Department of Diagnostic, Interventional and Pediatric Radiology, Inselspital, Bern University Hospital, University of Bern, Freiburgstrasse, Bern, Switzerland. sschindera@aol.com
authors.forename: Sebastian T
authors.initials: ST
authors.lastname: Schindera
authors.forename: Rendon C
authors.initials: RC
authors.lastname: Nelson
authors.forename: Terry
authors.initials: T
authors.lastname: Yoshizumi
authors.forename: Greta
authors.initials: G
authors.lastname: Toncheva
authors.forename: Giao
authors.initials: G
authors.lastname: Nguyen
authors.forename: David M
authors.initials: DM
authors.lastname: DeLong
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Szucs-Farkas
mesh_terms: D000792:Angiography / Q000295:instrumentation / Q000379:methods*; D001822:Body Burden; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control; D011835:Radiation Protection / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011874:Radiometry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*