Abstract
Introduction and Aims: CT is one of the most versatile and useful medical imaging modalities for computer assisted surgery (CAS) and monitoring bone remodelling. However, the high radiation dosage hinders its widespread use. We describe a method for generating smooth and accurate Finite Element (FE) meshes using CT data with reduced radiation exposure.
Method: We have performed serial CT assisted osteodensitometry measurement on seven patients who had a total hip replacement. FE models were generated automatically with cubic Hermite basis functions for both geometry and density. The meshes were fitted to the geometric and density data sets using least square’s fitting. Density was displayed over the surface of the elements using a colour spectrum. The effect of reducing radiation dosage was studied by generating five different types of FE meshes from each patient with different numbers of CT slices. The different mesh types were generated by varying the gap between slices.
Results: The mesh with the smallest number of CT slices used seven CT scans, with the gap between slices of 3cm on average while the mesh with the largest number of slices used 22 scans with the gap of 0.8cm. For the mesh with the largest number of CT slices, the average error after the geometric fitting was less than 0.5mm. The average error for the density fitting was 70.2 mg/ml. When expressed as the percentage to the overall density data range (0 ~ 1500 mg/ml), the average error was 4.7%. Meshes generated with a smaller number of CT slices had larger errors, and this increased as the number of slices used decreased. The error in geometry dropped dramatically (more than 50%) when more than 10 slices were used, whereas the error in density decreased approximately linearly as the number of slices increased. Overall, it was possible to generate realistic and smooth meshes with a geometrical error of less than 1.5mm and a density error less than 7% using 10 CT slices.
Conclusion: One strength of the current study is that we have used cubic Hermite elements, which requires much less information in generating FE meshes without sacrificing too much accuracy. Our study has shown that we can generate realistic and smooth meshes with about 10 CT slices of the proximal femur. This is important to enhance the power of CT in clinical applications.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
At least one of the authors is receiving or has received material benefits or support from a commercial source.
