Abstract
This thesis investigates MARS spectral CT technology for preclinical orthopaedic applications to assess cartilage and bone health simultaneously. As the population ages, the economic, social, and health burden of osteoarthritis (OA) and osteoporosis are growing. OA is a disabling joint disease accompanied by the degradation of cartilage and changes in subchondral bone. In 2010, the total financial costs of OA were about $2.25 billion so that it has the sixth largest disability burden in New Zealand. It is quite difficult to visualise the cartilage quality without opening up the joint. Osteoporosis is a disabling bone disease characterized by low bone density and thinning of cortical and trabecular bone that causes poor bone quality and easily fractured bones. Osteoporotic fractures are estimated to cost $3B annually by 2020 in NZ. Determining bone sites at risk of fracture is difficult in clinical practice at present therefore osteoporosis treatment monitoring remains difficult.
Despite significant developments, current modalities for musculoskeletal imaging have limited success for OA and osteoporosis due to high cost, high radiation dose, low spatial resolution, inability to quantify tissue types and contrast media, and failure to reduce artefacts such as beam hardening and partial volume effect. Photon counting spectral CT allows for quantification and differentiation of multiple materials simultaneously at high spatial resolution. This thesis is presented in two parts, with the first half focusing on preclinical studies on cartilage imaging, and the second half focusing on preclinical studies on bone imaging.
Quantitative cartilage imaging using spectral CT was demonstrated using healthy bovine cartilage and osteoarthritic human cartilage samples. I have used contrast media to quantify cartilage health and distinguish cartilage from the subchondral bone. I have established two methods on spectral CT to measure bone structure and density simultaneously. These methods were applied to demonstrate the potential of the spectral CT for bone quality assessment on the bone samples excised from the sheep proximal tibia and human femoral neck. Then the MARS measurements were compared with existing imaging modalities and validated by histology. The challenges I faced in this thesis were that spectral CT technology is immature and current software for measuring density and structure is not suited yet for this particular purpose, so further work is still required to exploit smaller voxel size and more user-friendly analysis.
In conclusion, proof of concept for the new imaging technique has been developed for simultaneous quantitative imaging of articular cartilage and bone using a MARS small animal scanner. This technology can be utilised (i) as a basis for developing clinical scanning protocols on human spectral CT scanners when available and (ii) facilitate monitoring and testing of treatment methods to improve cartilage and bone health which in turn can lead to reduce burden and improve the quality of life.