Three-dimensional biomechanical modeling of vertebrae from radiographs
Templeton, Alistair Kiel
Liebschner, Michael A. K.
Doctor of Philosophy
Three-dimensional modeling has become an important tool for non-destructive evaluation of tissue for experimental and clinical uses. However, its range of applications is limited by its dependence on expensive imaging modalities. The current research explores ordinary radiographs as an alternative for three-dimensional modeling in several applications relating to vertebral fracture detection and treatment. An algebraic reconstruction algorithm was developed to replace CT in the construction of patient-specific vertebral finite element models for the evaluation of fracture risk in elderly individuals. CT-based models have shown far stronger specificity in detecting at-risk osteoporotic vertebrae than DEXA, but have not been adopted into the clinic because of equipment cost, limited reimbursement codes, radiation exposure, and expertise requirements. Our radiograph-based technique was able to replicate biomechanical predictions made from CT scans to within 7% error, providing an improved alternative to DEXA with less interaction required from the operator than traditional modeling. A similar algebraic technique was employed to investigate the internal changes in a vertebral body during compression to fracture. Because testing apparatus are not compatible with traditional 3-D imaging modalities, we evaluated regional changes in apparent density and deformation of the vertebral shell using periodic sets of 4 radiographs. Damage was observable in an internal area of high strain energy density, then propagated across the inferior endplate causing whole bone failure. Vertebroplasty is the most effective treatment of vertebral compression fractures. It is performed with a minimum of planning and evaluation primarily to avoid cement leakage. However, optimization is required to reduce the incidence of post-treatment adjacent vertebral fractures have. We have thus developed a method of reconstructing the bolus shape within the bone based on a series of images acquired with fluoroscopic radiography. The cement volume was calculated with a mean error of 8%, and the location and shape of the bolus were visualized in both two and three dimensions. Three-dimensional imaging modalities allow better visualization and diagnostics and can lead to more precise modeling and optimization of surgical procedures. The techniques presented in this thesis aim to make imaging more accessible and broaden the associated range of applications.
Biomedical engineering; Radiology