The number of projection affects the reconstruction quality in computed tomography system. Larger projection number
will lead to better reconstruction quality. Infinite projections can reconstruct the specimen without mathematical error.
On the other hand, less projection number can reduce the radiation dose, save time and keep the patients comfortable.
The optimal number of projection compromises both the mathematical accuracy and real-life requirement. The purpose
of this paper is to find the relationship between the projection number and the reconstruction quality. A micro-CT system
is developed to validate the relationship between projection number and reconstruction quality. But the actual precision
and signal to noise ratio is hard to find in experiments, because the sample are not standard whose physical
characteristics are certain. We can only provide limited projection number and get relative reconstruction quality in the
experiment. Half-scan method can reduce radiation dose, and it can achieve better results with sufficient sampling.
In this paper a practical, automated contour segmentation technique for digital radiography image is described. Digital
radiography is an imaging mode based on the penetrability of x-ray. Unlike reflection imaging mode such as visible light
camera, the pixel brightness represents the summation of the attenuations on the photon thoroughfare. It is not
chromophotograph but gray scale picture. Contour extraction is of great importance in medical applications, especially in
non-destructive inspection. Manual segmentation techniques include pixel selection, geometrical boundary selection and
tracing. But it relies heavily on the experience of the operators, and is time-consuming. Some researchers try to find
contours from the intensity jumping characters around them. However these characters also exist in the juncture of bone
and soft tissue. The practical way is back to the primordial threshold algorithm. This research emphasizes on how to find
the optimal threshold. A high resolution digital radiography system is used to provide the oriental gray scale image. A
mouse is applied as the sample of this paper to show the feasibility of the algorithm.