PREPROCESSING X-RAY TRANSMISSION DATA IN CT SCANNING.

While the reconstruction algorithm utilized in computerized tomography (CT) is important, the overall performance of the system is limited by the quality of the measured transmission data which is used as a basis for the reconstruction process. If the projection values derived from the measured data do not adequately represent the line integrals of the linear attenuation coefficients within the slice being scanned, even a perfect reconstruction algorithm will give rise to a distorted image. Phenomena which tend to deteriorate the quality of the measured data , and hence the final image, include the effective finite dimensions of the scanning aperture, distortions introduced by the detector system such as afterglow, and nonlinearities related to the spectral distribution of x-ray photons used in scanning. Computer methods of preprocessing the x-ray transmission data to minimize these distortions are discussed and illustrated.