System Construction And Optimization Of Imaging Quality For Photon Counting Detector

The computed tomography(CT)technique is an indispensable means in modern medical examination by using the X-ray of the subjects at different angles and calculating the distribution of the linear attenuation coefficient in the trial.Currently,the CT system on the market is commonly used as an energy integration detector.In contrast,the photon counting detector utilizes the direct conversion technology,does not need to carry out analog to digital conversion,reduces the electronic reading noise,and has a wide application prospect in the field of CT imaging.However,in the actual application process,the image artifact is much more due to the lack of maturity of the manufacturing process,resulting in more image artifacts in the CT imaging system based on the photon counting detector,and the imaging quality needs to be further improved.This thesis focuses on the construction of CT system platform based on photonic counting detector and the improvement of image quality.The main work is divided into the following three points: 1.Design and construct a CT imaging system based on photon count detector.The energy spectrum CT system platform was built by micro focal spot X-ray and XCounter FX3 photon count detector.Using the data acquisition characteristics of photon count detector,the conventional and fast acquisition modes are designed.The fast acquisition mode was tested,the acquisition parameters were adjusted to ensure the integrity of the acquisition Angle,the motion parameters were adjusted to correct the motion artifacts,and the performance of the two modes were tested.Data preprocessing is optimized by using the data acquisition characteristics of photon count detector.2.In order to improve the quality of reconstructed image,a circular artifact correction method is designed and analyzed by experiments.Firstly,in the sine graph,the average value of all viewing angles is calculated for the direction of the detector channel,and the onedimensional average vector is obtained.by taking the inverse calculation of the average vector,the correction vector of the one-dimensional detector channel is calculated.The detector channel correction vector is multiplied line by line with the sine image at all angles of view,and then Smoothing spline fitting is made by using the sinusoidal image difference diagram before and after vector correction.Finally,the fitted difference map is added to the sinusoidal image after vector correction to realize contrast compensation,and the correction method is optimized according to the data characteristics collected by the conventional acquisition mode.Through the analysis of the standard deviation of the reconstructed water model image,the method in this paper has a good effect of ring artifact correction.3.In order to verify the effectiveness of the CT system based on the photon counting detector,the non-local mean filtering algorithm and the double-energy CT three-material decomposition method are used to carry out the experimental verification on the bone mineral density and the mouse head in the conventional scanning mode and the fast scanning mode respectively.The material decomposition is carried out on the reconstructed image domain by the processing flow after the noise reduction,and good material decomposition results are obtained in different scanning modes.