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Pediatric Chest MDCT Using Tube Current Modulation: Effect on Radiation Dose with Breast Shielding

¹ Division of Pediatric Radiology, Department of Radiology, Box 3808, Duke University Medical Center, Durham, NC 27710.
² Radiation Safety Division, Duke University Medical Center, Durham, NC.
³ Department of Radiology, University of Arkansas for Medical Sciences and Arkansas Children's Hospital, Little Rock, AR.

OBJECTIVE. The purpose of our study was to assess the effect on radiation dose and image noise during pediatric chest 16-MDCT using automatic tube current modulation and bismuth breast shields.

MATERIALS AND METHODS. Age-based chest 16-MDCT was performed on an anthropomorphic phantom representing a 5-year-old child. Two scans were obtained in each of four sequences: first, without a shield; second, with a 2-ply bismuth shield; third, using automatic tube current modulation with a scout image obtained after placement of the shield; and fourth, using automatic tube current modulation with a scout image obtained before placement of the shield. Metal oxide semiconductor field effect transistor technology was used to measure the radiation dose in 20 organ locations. Effective dose was estimated using the console dose-length product. Noise was measured by recording the SD of Hounsfield units in identical regions of interest.

RESULTS. The bismuth breast shield reduced the dose to the breast by 26%. Shielding and automatic tube current modulation reduced the breast dose by 52%. Multiple organ doses were lowest when the shield was placed after the scout radiograph had been obtained. When the shield was placed after the scout image was obtained, the mean noise in the range of shielding increased from 11.4 to 13.1 H (superior mediastinum) and from 10.0 to 12.8 H (heart) (p < 0.01). Increased noise, however, was near the target noise index (measured in SD of Hounsfield units) of 12.0 H (SD). Using automatic tube current modulation, the effective dose was reduced by 35% when the shield was placed after the scout and by 20% when the shield was present in the scout.

CONCLUSION. The greatest dose reduction is achieved by placing the shield after obtaining the scout image to avoid Auto mA compensation due to density of shield. With this technique, image noise increased but remained close to the target noise index.

Keywords: CT • CT technology • MDCT • pediatric chest CT • phantoms • radiation dose reduction • shielding

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