Diagnosis of intraocular foreign bodies in multidetector-CT: influence of acquisition parameters on radiation dose and detectability

Purpose: Determination of the influence of acquisition and reconstruction parameters on radiation dose and detectability of intraocular foreign bodies using multidetector CT (MDCT). Materials and Methods: Porcine eyes with intraocular foreign bodies of a 0.3-mm quartz fiber and a 0.1-mm steel wire as well as 0.5 ml of blood in the vitreous were investigated using MDCT. The tube current was 500, 250, 100, and 50 mAs; the collimation was 16 x 0.75 mm and 16 x 1.5 mm; and the pitch was 0.5 and 0.75. Image reconstruction was performed using a soft tissue (H30), a bone algorithm (H60 s), and thin (0.7 and 2 mm, respectively) and thick (2 and 4 mm, respectively) reconstruction increments. The resulting data sets were then used to determine the signal difference to noise ratio (SDNR) between the foreign body and adjacent vitreous. Results: Changes in tube current resulted in a proportional change in the radiation dose but only in the SDNR within a range of 1:2. Reducing the collimation from 1.5 mm to 0.75 mm resulted in a doubling of the SDNR at an approximately identical radiation dose. The series with a lower pitch at the same dose per volume showed a slightly higher SDNR. Reconstruction using a bone algorithm and thin increments resulted in an increase in the mean SDNR by a factor of 1.8 to 2.3. (orig.)