Study On Gating Control Of True Photon Number Breathing Motion Based On PET / CT Detection Loop

The main degrading factor in the quality of PET/CT (Positron Emission Tomography/Computed Tomography) image of the thorax and upper abdomen is respiratory motion. Thus, it is especially important to exploring an effective method to reduce this effect in clinical.To improve the image quality, we presents a new respiratory motion gating method based on the detector ring true coincidence event, which use the feature that the distribution of detector ring true coincidence event will change with the movement of the object to gating the raw data. On the PET/CT simulation platform, we use GATE (Geant4 Application Tomographic Emission) software package simulates realistic PET/CT scanner, and respectively builds geometry phantom and NCAT (NURBs Cardiac Torso) phantom to simulate lung motion. Next, we process the simulation raw data with the method proposed in this paper and use the processed data to reconstruction the 3-D image. Finally, make qualitative and quantitative evaluation of the gating image, motion image and static image.The evaluation results show that compared with the motion-blurred image, the shape, size and position of the gating image is closer to those of the static image. In the coronal image, the quality of the gating image is better than that of the motion-blurred image; in the sagittal image, the line profile curve of the gating image is more similar to those of the static image, which is better than those of the motion-blurred image. The simulation results demonstrate that the proposed method reduce the motion artifact of PET/CT image effectively, making the lung cancer image more accurate, furthermore, effectively overcoming the limitations of some motion correction methods.In addition, gating threshold value selection will directly affect the quality level of respiratory motion gating, which is the key to realize the method of respiratory motion correction. Based on the study of the respiratory motion correction method of the detector ring true coincidence event, in this paper, we present a method to automatically determine the threshold value according to the relationship of the slope rate between the adjacent absolute errors.We building geometry phantom for respiratory motion simulation through the PET/CT simulation platform, respectively using the proposed method and the manually threshold value determination method to process the simulation data. Next, we apply the gating thresholds to the respiratory motion correction method of the detector ring true coincidence event, obtaining the results of gating correction, and evaluating all the results.The evaluation results show that the parameters of the image quality evaluation of the proposed method are superior to the manually threshold value determination, and the line profile curve is closer to the stationary state. The experimental results demonstrate that the proposed method can efficiently and automatically determine the gating threshold value, and overcome the limitation of the method of manually determining threshold value.