Image characteristics and effective dose estimation of a cone beam CT using a video-fluoroscopic system

We developed a cone-beam CT system to acquire volume data of high-contrast objects, such as bone, lung and blood vessels (enhanced by contrast agents), that were amenable to 3D image processing. An X-ray tube and a large-area detector were mounted on a frame and rotated around an object in 12 seconds. The large-area detector consisted of a fluorescent plate and a CCD (charge-coupled device) video camera. While the X-ray tube was rotated around the object, X-ray pulses were generated, and 360 projected images were collected in a 12-second scan. A 256×256×256 matrix image was reconstructed using a parallel processor with a reconstruction time of 6 minutes. Image characteristics, such as spatial resolution, image noise and distortion, were evaluated by phantoms and compared with those of helical CT. Organ or tissue doses by the scan were determined by an in-phantom measurement. The effective dose recommended by the International Commission on Radiological Protection's Publication 60 (ICRP60) was evaluated using the organ or tissue doses. The results showed an isotropic resolving power of less than 1.6 mm and no distortion of the images, though they showed larger image noise and effective dose than that of helical CT