We have developed and evaluated a specially designed flat panel imaging system for CT imaging, which consists of a conventional flat panel sensor attached to a thick scintillator. A timing interface co-ordinates acquisition by the imaging system and pulsing of the linear accelerator. With this interface, as little as one accelerator pulse (0.023 cGy at the isocentre) can be used to form projection images. Different CT phantoms, irradiated by a 6 MV x-ray beam, have been imaged to evaluate the performance of the system. The phantoms have been mounted on a rotating stage and rotated while 360 projection images are acquired in 48 s. CT images have been reconstructed using the Feldkamp cone-beam reconstruction algorithm. Using a 16 cGy irradiation, contrast resolution is ~1% for 30 mm diameter objects and spatial resolution is 1.2 mm for high contrast structures. The reconstructed image intensities are linear with electron density between 0.001 – 2.16 g/cm
3
and the reconstruction time for 512 x 512 x 512 reconstructed datasets is 6 minutes.
Images of an anthropomorphic phantom show that using a total dose of 16 cGy, soft-tissue structures such as the heart, lung, kidneys and liver are visible in the reconstructed images.
Research supported by Varian Medical Systems.