Optimising imaging parameters in experimental spiral CT

Abstract

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 filled with air or fluid of varying densities to simulate lesions. This was imaged with Siemens Somatom Plus S and GE High Speed Advantage units. 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 mm. The Smartscan program of GE and the reformatting algorithm of Siemens were also analysed. To evaluate the different methods, the phantom lesions were counted by 3 observers. Radiation exposures associated with each technique were also measured.

Results: The images reformatted to a coronal direction were significantly inferior (p < 0.01) to those in other techniques. The use of Smartscan did not influence lesion detection, nor did changes in pitch or increment. Spiral and non-spiral techniques proved to be equal. Radiation exposure was lowest when a greater pitch or the Smartscan program was used.

Conclusion: Radiation exposure in CT can be limited without significantly impairing the image quality by using low-dose techniques. Reformatting to a coronal direction should be used with care as it debases the image quality.