Low dose MDCT of the wrist--an ex vivo approach

The primary objective of this study was to evaluate, if in multidetector computed tomography (MDCT) of the wrist a good image quality can be maintained while radiation dose is substantially reduced. In a second approach one solely parameter change that allows for the best trade-off between dose reduction and image quality should be identified. Twenty wrist specimens were examined with a 16-slice MDCT in different parameter combinations: 120 and 100 kV, 100, 70 and 40 electronic mAs, pitch factor 0.9 and 1.5. Images were reconstructed in four standard planes (slice thickness 1.0mm, increment 0.5mm, hard kernel) resulting into a total number of 960 images. Two observers evaluated image quality in a blinded and randomized consensus scheme. Detail quality of corticalis, spongiosa, articular surface and soft tissues was graded according to a four-point scale (1 = excellent, 2 = good, 3 = sufficient, and 4 = poor). The scan protocol with the best trade-off between radiation exposure and image quality had a parameter constellation of 100 kV, 70 electronic mAs (78 effective mAs) and a pitch of 0.9 (DLP 63 mGycm). This represented a dose reduction of 55%. A solely decrease of voltage lead to a dose reduction of 36% without any loss of image quality. An increase of the pitch factor to 1.5 and a decrease from 70 to 40 mAs caused the most distinct impairment of image quality. In MDCT of the wrist good image quality could be maintained while radiation dose was considerably reduced. A reduction of voltage offers the best result for a solely parameter change.