he artificial prosthesis is widely used today as a measurer of curing hip prosthesis diseases. Its long-lasting functionability is affected heavily by the fitness between the femoral stems and the patient's marrow. However

the off-shelf femoral stems are available only in limited number of models. It usually does not fit individual patient well. There fore

the use of patient-fit artificial prosthesis is recommended. In this article a computer aided system for designing patient-fit intramedullary femoral stems is developed based upon the volume visualization technique. After the 3-D image of the femur is generated

the design of the femoral stem is carried out interactively. The system also simulates the cutted bone and the assembly of the femoral joint with the bone. It gives the doctor a good perspective of the operation before it is really done.Another advantage of the system is that less number of CT-images are needed in 3-D image reconstruction. The CT images are usually taken at relatively large interval

say about 2.0mm. Reducing this distance further is harmful to the health of patients. However

such distance is too large for reconstructing the 3-D image

since the dimension of the voxels must be compatible with it. It leads to a low-resolution image. Therefore

in this system a new interpolating algorithm is developed. The distribution of gray density in the new layers inserted into two given CT layers can be calculated directly from the distribution of gray density on the two known CT layers. With this new interpolating algorithm

the system is suitable for clinic purpose.