Image reconstruction in CT fluoroscopy requires the computer to provide very fast reconstructions of images in order to provide immediate and accurate spatial and anatomical feedback during a procedure. This is achieved by:
- use of a small reconstruction matrix – e.g. 256 x 256 (compared with conventional 512 x 512 matrix)
- arithmetic and logical operations performed in parallel in the array processor
- speed enhanced by high-speed internal buses
- reconstruction limited to a circular area
- no corrections made for beam hardening or other artifacts
- modified reconstruction algorithms
CT fluoroscopy uses a partial (or incremental) reconstruction technique, which means that data from the last 360 degree set is reconstructed and displayed after every N° (30°/45°/60°) of tube motion. A frame rate of 6-12 frames per second is generally used. The delay between each image displayed depends on frame rate and N°. For example, for 60 degree updates and 6 frames per second, the image is updated every 0.17 seconds (compared with conventional fluoroscopy which is around 25 frames per second). Because of this, a relatively high level of noise will be apparent in soft tissues.