Dianna M. Ehrhart Bardo MD, Presenter: Nothing to Disclose

Jane Asamoto RT, BS, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Steven Utrup MS, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Dava Smith, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Jeffrey Harold Yanof PhD, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

X-ray dose reduction in the pediatric population is paramount due to the relatively high absorption per kilogram in the small body habitués and the greater radiosensitivity of rapidly growing tissue. The purpose of this study was to quantify x-ray dose reductions for infant examinations afforded by advances in MDCT source collimation and beam filtration.

Five infants (ages less then 18 months) were scanned on a Brilliance iCT 256 slice CT (Philips Healthcare) with 8 cm detector width, rotation speeds up to 220 rpm, and a combination of special features applicable to infant x-ray dose reduction. The collimator assembly automatically switches to an infant-sized bow-tie filter (38% of adult size) to shape and decrease beam intensity and dose as measured with standard CTDI phantoms. Dynamic source collimation was also automatically deployed at the start and end of all helical scans (three cases) to decrease longitudinal “over-ranging.”   The dose savings with dynamic collimation was estimated with a computational model that accounts for the collimator width and blade velocity. These features were combined with wide collimation settings (4 and 8 cm) to increase z-axis geometric efficiency. The axial scanning mode (two cases) was used with 80 mAs and 80 kVp for cardiovascular studies with one high-speed (220 rpm), wide collimation (8 cm) tube rotation thereby decreasing x-ray dose and motion artifact.

Use of the infant sized bow-tie filter reduced body CTDIvol dose by 22% and head CTDIvol by 14% relative to phantom measurements with the adult size filter. The average percentage dose savings with dynamic collimation ranged from 17 to 28% (scan lengths range, 6.1 to 11.2 cm) compared with static collimation. Scan collimations of 8 and 4 cm resulted in z-axis geometric dose efficiency of 96.4% and 93.0 %, respectively. The single rotation axial technique resulted in a dose range of CTDIvol=2.0 to 3.6 mGy, DLP= 12.8 to 23.0 mGy*cm, and ED=0.50 to 0.90 mSv (age-specific conversion factor=0.039).

Preliminary results indicate that advances in MDCT source collimation and beam filtration for axial or helical scanning can reduce infant x-ray dosage without compromising image quality.

Advances in MDCT combined with special low-dose strategies can help manage doses ALARA for routine and advanced applications within the pediatric and adult patient populations.

Bardo, D, Asamoto, J, Utrup, S, Smith, D, Yanof, J, Evaluation of Infant Radiation Dose Reduction with Enhanced Source Collimation and Beam Filtration for MDCT.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8003477.html