Direct comparison of a xenon and a solid-state CT detector system: measurements under working conditions

Measurements of various image quality parameters were carried out with two different detector systems in an otherwise unchanged medical computed tomography (CT) scanner. As all other components of the scanner and the image reconstruction system remained identical, the authors were able to quantify the difference in performance between a xenon gas ionization detector and a new solid-state scintillation detector in an isolated fashion. The authors determined noise, spatial resolution, and artifact behavior and assessed the potential for dose reduction. No significant impact of the detector change on absolute CT values of a calibration phantom was observed. Spatial resolution was improved by more than 10% for the solid-state system. As the system's modulation transfer functions were measured with a wire phantom and otherwise unchanged scanner geometry and image reconstruction algorithm, the increase of resolution is explained by the improved temporal response of the solid-state detector. At the same time, noise was reduced by 12% for a 20-cm diameter water phantom. The noise reduction corresponds to a possible reduction of patient dose by 23% for constant image quality, which is in good agreement with our prediction by estimations of both systems total detective quantum efficiency. Also, a significant improvement of scatter rejection was found for the solid-state system.