Single versus multi-detector row CT: comparison of radiation doses and dose profiles

The purpose of this study was twofold: (a) to compare the radiation dose profile between computed tomography (CT) with a single detector row (SD) and with a multi-detector row (MD) and (b) to compare specific organ doses between SD CT and MD CT.

Thermoluminescent dosimeters placed within a 32-cm-diameter cylindrical phantom were used to measure and compare dose profiles from one SD CT scanner and from one MD CT scanner. SD CT scanning parameters were 210 mA, 140 kVp, pitch of 1.0, 5-mm section thickness, and 0.8-second gantry rotation speed. MD CT scanning parameters were 130 mA, 140 kVp, pitch of 0.75, 4 x 5-mm section thickness, 15-mm table feed, and 0.8-second gantry rotation speed. To plot radiation dose profile, doses were measured both in the imaging plane and in the area adjacent to the imaging plane. The resultant data were normalized to achieve constant image noise between MD CT and SD CT. Direct doses to individual organs from primary and scattered radiation were measured with an anthropomorphic phantom containing thermoluminescent dosimeters and with a standard pelvic imaging protocol for both MD CT and SD CT.

MD CT resulted in a dose profile approximately 27% higher than that from SD CT in the plane of imaging (8.0 vs 6.3 mGy) and 69% higher adjacent to the plane of imaging (6.8 vs 4.0 mGy). The individual doses to the kidneys, uterus, ovaries, and pelvic bone marrow were 92%-180% higher with MD CT than with SD CT.

With image noise constant between SD CT and MD CT, the radiation dose profile both inside and outside the plane of imaging was higher with MD CT than with SD CT. Organ dose also was higher with MD CT than with SD CT. This difference should be accounted for in the design of MD CT protocols, especially as MD CT technology becomes more widely available for clinical use.