American Journal of Neuroradiology 27:2221-2225, November-December 2006
© 2006 American Society of Neuroradiology
HEAD & NECK
Optimization of Z-Axis Automatic Exposure Control for Multidetector Row CT Evaluation of Neck and Comparison with Fixed Tube Current Technique for Image Quality and Radiation Dose
a From the Department of Radiology, Emory University Hospital, Atlanta, Ga
Address correspondence to Patricia A. Hudgins, MD, Department of Radiology, Emory University Hospital, 1364 Clifton Rd NE, Atlanta, GA 30322; e-mail: patricia.hudgins{at}emoryhealthcare.org
BACKGROUND AND PURPOSE: Z-axis automatic exposure control (AEC) technique automatically adjusts tube current based on size of body region scanned. The purpose of the current study was to compare diagnostic acceptability, noise, and radiation exposure of multidetector row CT (MDCT) of neck performed with z-axis AEC and with fixed current.
MATERIALS AND METHODS: Two study groups of 26 patients each underwent MDCT of neck using z-axis AEC with 8 noise index (NI), 150–440 mA, and 10 NI, 75–440 mA, respectively. A control group consisting of another 26 patients underwent MDCT of neck with fixed-current technique (300 mA). Objective noise and mean tube current-time products (mA · s) were recorded. Two radiologists evaluated images for diagnostic acceptability and subjective noise on a 5-point scale.
RESULTS: All CT examinations of study and control groups were diagnostically acceptable, though objective noise was significantly more with z-axis AEC (shoulder: NI 8, 20.6 ± 6.2 HU; NI 10, 22.2 ± 4.6 HU) than with fixed current (16.2 ± 6 HU) (P = .01). There was no significant difference between AEC and fixed current in diagnostic acceptability and subjective noise (P = .22–.42). AEC resulted in significant radiation dose reduction (NI 8, 186.3 ± 20.5 mA · s; NI 10, 158.1 ± 21.2 mA · s), compared with fixed current (235 ± 21.8 mA · s).
CONCLUSION: Z-axis AEC resulted in similar subjective noise and diagnostic acceptability, with radiation dose reduction of 21% for NI of 8 and 33% for NI of 10, respectively, for MDCT evaluation of neck, compared with those of fixed current technique.
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