A Research On Digital Subtraction Angiography (DSA) Image Processing System

In this paper, the author studies the kernel arithmetic of the digital subtraction image processing in digital subtraction angiography system. The content mainly involved in the image pre-processing, which includes de-noise and registration on the live image sequence and the mask image, the digital subtraction arithmetic and the image post-processing, which includes the image quantization and enhancement.In the de-noise part, the author firstly proved that the SNR of the live image can be improved by integrating several images. Because the subtraction images are image sequences, which related to time, so in the arithmetic realization, different images are integrated after assigning different weight that is convenient for optimization. Dues to several factor result in motion artifacts that will make diagnoses to be difficult, the registration is essential. The author has a theory analysis on registration and its limitations, and then provides two schemes, one is manual registration and the other is automatic registration. In the automatic registration, the template registration is selected to deliver the automatic global registration. And the similarity measurement is based on the histogram' entropy of differences-based measures which makes the registration to be robust and efficient for real-time digital subtraction. According to the X-ray image's mathematic model, the author provides two kind of subtraction mode: directly subtraction and logarithmic substation. In the image quantization and enhancement section, the non-linear gray mapping based on histogram specification and the enhancement digital filter in spatial domain is applied to the result digital subtraction images. The final image's quantity is suitable for commercial use.The DSA image processing system which the author have developed can be used as the image processing prototype model in the digital subtraction angiography system, according to the new arithmetic achieved by software it can be changed to hardware implement to the whole-one DSA system, on the other hand, it can be directly applied to the reconstruction of old X-ray machines to the new DSA system and based on this system, more applications on DSA can be developed.