| Summary: | 碩士 === 國立清華大學 === 原子科學系 === 88 === In PET or SPECT system, the photon transited from the midst of the body passes through more materials than those from the edge of the body does. Therefore, the center of the projection will be attenuated more than the edge of the projection. As a result, in the reconstructed image, the activity in the center section will be less than actual situation, and the activity of the edge section is on the contrary. It’s called attenuation effect. In order to correct this effect, we must compensate the attenuation in the projection data.
Currently, there are two major methods for attenuation correction. First, use a radiation source (ex. Co-60 ) to rotate round the patient body. Second, using Chang’s method, it assume that total attenuation coefficient in the body is constant, which is usually equal to water. Accordingly, we just correct the error from the distance. If the attenuation coefficient is not uniform, the error might be large. So, we focus on the attenuation coefficient in the body and search for new method. How do we know the inner attenuation coefficient distribution? We can calculate unknown inner structure from known standard CT slice, using standard-axis distortion interpolation method. Then, obtaining the body’s attenuation coefficient distribution information, we can repeat Chang’s calculation with adding attenuation coefficient information. In this way, it could increase precision of nuclear medicine image, and also the patients may avoid receiving additional radiation dose.
|
|---|
