Study Of The Scatter Correction Method In CBCT System Based On Moving Blocker

With the fast development and wide use of the CT technology in clinical, we need faster and more precise CT scan technology. In some advanced CBCT scan system, it is easy to catch a pot of the cone-beam ray source and large size detector, and the spiral cone-beam CT scan technology becomes a hot issue in this area. However, because of the interaction between the X-ray and the imaged objects, lots of scatter signals are been induced when X-ray goes through the imaged objects. And these scatter signals can impact the quality of the reconstructed image significantly. So far, the large illumination size of the cone-beam scan technology which widely used in present clinical aggravates the impact, which comes from the interaction between the X-ray and the human tissue. The following reconstruction process enlarges this influence. So it is necessary to make a scatter correction before reconstruction.To remove the scatter signals from the projection images, this article uses an attenuation grid method which is used in the clinical, and according to this method, the article put forward a sphere grid aiming to reducing scatter signals in the scan system. The globe of sphere grid is located on the X-ray source, and there are lead strip, which are uniform arrangement, on the sphere grid. Additionally, in this article, I introduce a moving blocker method to obtain a complementary projection image, which can estimate scatter signals distribution more reliable.Based on the grid method, this article utilizes the ray-cast method to segment the imaged object, and then calculate the attenuation to obtain the projection data; then in the simulation of scatter process, this article combines the ray-cast method and probability model to simulate the scatter process when the X-ray goes through the imaged objects. We can calculate the scatter signals distribution via the interposition between the X-ray source and the detector. Later on, this article makes up the missing pixels during the scatter process. We can extract the scatter signals from the mixed signals on the detector. In the end, we can obtain the 3-D image through reconstruction.This article uses the sphere grid and the traditional flat grid to correct the scatter signals on one same 3-D image, and compare the effect of these two methods. Result shows that, due to the inconsistent attenuation of the X-ray by the flat grid, the reconstruction image, which is reconstructed using flat grid method, introduce lots of ring artifacts. Additionally, this article compares the influence on the efficiency used Lead strip and Lead blocker. Results show that: the reconstruction image which is corrected by Lead strip is more reliable because of the in-conformity reduction of Lead strip.