OPTIMIZING IMAGING PARAMETERS IN EXPERIMENTAL SPIRAL CT

Purpose: This in vitro study was conducted to analyse lesion detection and relative radiation exposure in different CT techniques. Material and Methods: We used a plastic phantom (12x8x2 cm) containing holes fi lled with air or fluid of varying densities to simulate lesions. This was imaged with Siemens Somatom Plus S and GE High Speed Advantage uni ts. We varied table feeds (3 and 6 mm/s in Siemens and 3 and 4.5 mm/s in GE) and increments (2 mm and 4 mm) while keeping collimation at 3 m m. The SmartScan program of GE and the reformatting algorithm of Sieme ns were also analysed. To evaluate the different methods, the phantom lesions were counted by 3 observers. Radiation exposures associated wi th each technique were also measured. Results: The images reformatted to a coronal direction were significantly inferior (p<0.01) to those i n other techniques. The use of SmartScan did not influence lesion dete ction, nor did changes in pitch or increment. Spiral and non-spiral te chniques proved to be equal. Radiation exposure was lowest when a grea ter pitch or the SmartScan program was used. Conclusion: Radiation exp osure in CT can be limited without significantly impairing the image q uality by using low-dose techniques. Reformatting to a coronal directi on should be used with care as it debases the image quality.