Adaptive Low-dose CT Reconstruction

Computer tomography(CT) is a common means of modern clinical imaging diagnosis.According to that different organs of the human body have different penetrating and transmittance for X-rays, people use sensitive instruments to measure X-rays those through the body, thereby we can reconstruct the internal cross-section or three-dimensional image of the body, so that doctors can find small lesions.Compared with other diagnostic tools such as magnetic resonance imaging(MRI) and positron emission tomography(PET),CT has high resolution and short scan cycle, it is widely used in the detection of bone,organs,brain,lungs and some other parts.CT image reconstruction is the most important part of the CT technology, the quality of reconstruction image has a relationship to the doctor’s diagonosis. In order to get a more accurate result, people always choose to increase the dose of X-rays to improve image resolution. However, X-rays is harm to human body, its radioactivity will cause death of some normal cells, and it also can increase the possibility of canceration. Therefore, how to minimize the X-rays radiation dose with the high quality of the reconstruction image become the one of research interests in CT imaging.The method to reduce X-rays radiation dose is mainly achieved by reducing the tube current, but low tube current will cause the noise increasing and some artifacts appear,which will affect the doctor’s diagnosis, so how to improve the quality of the reconstruction image at a low-dose is difficult. On the other hand, how to control the radiation dose of CT each time is difficult too. Now, the hospitals give the radiation dose according to the doctor’s experience and judgment, in order to ensure the quality of CT image, doctors often use higher radiation dose than the real needs. What’s more, different doctors have different judgment, they have strong subjective, so it is difficult to form a standard.In this paper, we improve the existing CT reconstruction algorithm, combined ART and TV algorithm better, so that improve the reconstruction image quality in sparse angles.And than integrate the adaptive principle into the reconstruction algorithm, propose the adaptive low-dose CT reconstruction algorithm: starting from a small number of projection angles, increasing the angles of projection gradually, at the same time, judging whether the reconstruction image can meet our standard, stoping while the reconstruction image meet our standard. In this way, we can use the least number of projection angles to get highquality reconstruction image, so that we can reduce the radiation dose. In other words, the computer system will evaluate the quality of the reconstruction image automatically while the projection angles increasing from less to more, it will stop when image meet the requirement. In order to verify the effectiveness of this algorithm, we use models to do some experiments, and results show that the algorithm can achieve the goal of reducing radiation dose.