Comparative evaluation of image quality from 3 computed tomography (CT) simulation scanners

Abstract

Introduction: Today, radiation therapy is moving towards increased radiation dose to the tumour as a result of 3D conformal RT (3DCRT) and intensity modulated RT (IMRT), which have been made possible by advances in volumetric-based image planning with digital imaging systems like computed tomography (CT). Treatment planning for such radiation therapy requires superior CT image quality. Purpose: Our goal was to evaluate and compare image quality of 3 unique CT simulation scanners available at our center for both axial and helical modes of scanning. These scanners included a conventional 70cm bore single slice scanner from Philips Medical Systems, a large 85cm bore single slice scanner also from Philips, and a 70cm bore multi-slice scanner from GE Medical Systems. Methods: Image quality was evaluated in terms of image noise, low contrast detectability (LCD), limiting spatial resolution (Modulation transfer function) and slice thickness accuracy in accordance with guidelines set out by the AAPM. A commercially available CatphanÒ phantom was used to characterize image quality for both axial and helical modes of scanning. Results and Discussion: Image quality was generally comparable for all scanners. Limiting spatial resolution and slice thickness (ST) accuracy were comparable for all three scanners for both scanning modes. The multi-slice unit was superior in terms of noise content, resulting in improved visualization of small, low contrast objects, which is of significant clinical importance, particularly for soft tissue delineation. In addition, the multi-slice unit optimizes volume coverage speed and longitudinal resolution without compromising image quality, a significant advantage for the radiation oncology environment.