Research On The3D Iterative Reconstruction Algorithm Of Cone-beam CT

X-ray computed tomography (CT) is a technique to noninvasively acquire the inner structure information utilizing the attenuation of X-ray passing through objects. This technology has been widely used in medical diagnosis and industrial nondestructive detection. In recent years, cone-beam CT has been more widely used in medicine and industry, and owing to the advantages as high spatial resolution, low radiation and fast scanning speed, becomes the future development trend of CT technology one. With the development of oral medicine, dentistry special cone-beam CT has been applied widely. Oral CT can be reflect the tissue from different angles, and found in more subtle lesions on bone tissue condition, temporomandibular joint accurate assessment of the situation, for help doctors make more accurate clinical diagnosis plays an important role.The image reconstruction algorithm is an important part of CT technology. There are two kinds of basic reconstruction algorithms:analytic algorithm and iterative algorithm. The analytic algorithm is generally adopted in CT, because it can quickly reconstruct the image with high quality. But the analytic algorithm can’t suit the incomplete and noise projections situation, while the iterative algorithm can reconstruct better image for this situation. This thesis focused on three iterative algorithms include:algebraic reconstruction technique(ART), simultaneous algebraic reconstruction technique(SART) and expectation maximization algorithm(EM). Also studied ordered subset algorithm(OSEM). ART algorithm which is based on solution of algebraic linear equations algorithm, the formula is derived from the least-squares method. EM algorithm formula is based on the X-ray photons Poisson statistical distribution of the maximum likelihood function derived.Finally, using the simulation data and the actual data collected from oral CT imaging system following three points to explain the differences between the three kinds of iterative algorithm:(1) Under the complete projection data, three types of iterative algorithms can get high quality rebuilding image;(2) Under the incomplete projection data, OS-EM algorithm reconstruction image relative to the ART algorithm and SART algorithm has certain advantages;(3) Under the condition of the projection data containing noises, ART algorithm is affected by noise is bigger, but the OS-EM algorithm and SART algorithm has a certain resistance to noise.