Study of bone-metal interface in orthopaedic application using spectral CT

This thesis investigates the diagnostic potential of MARS spectral photon counting computed tomography (CT) in assessing musculoskeletal disorders such as bone fractures and crystal arthritis. The hypothesis states that the high spatial resolution, quantitative material specific information and reduced metal artefacts of spectral photon counting CT makes the MARS spectral CT scanner a promising imaging tool to confirm or rule out a diagnosis. Being a new imaging modality, a protocol to scan samples with metal implants has to be optimised, before it can be implemented clinically for patient imaging. I contributed to optimising a protocol for imaging bone-implant specimens. Different biomaterials (titanium and stainless steel) used for fracture fixation were imaged. The artefacts were evaluated in both the energy and material domain. A bone analysis tool for measuring bone morphological parameters such as trabecular thickness and spacing was developed in collaboration with the Human Interface Technology Lab. Bone healing at the bone-metal interface was studied and the results were compared with plain radiographs, dual energy x-ray absorptiometry and clinical single and dual energy CT. The advantages of photon counting spectral CT in the early assessment of bone healing due to reduced artefacts was demonstrated. This thesis also investigated the potential of spectral photon counting CT to differentiate calcium crystals present in phantoms and osteoarthritic human meniscus samples. Our results show that MARS spectral CT can moderately discriminate calcium pyrophosphate (crystals inducing pseudogout) and calcium hydroxyapatite crystals. The results were compared with plain radiographs, polarised light microscopy and x-ray diffraction methods. In conclusion, this thesis demonstrated the clinical potential of MARS preclinical spectral photon counting CT scanner for the non-invasive and non-destructive imaging of bone-metal interfaces, for early assessment of bone healing, and for the detection and characterisation of articular crystals

Study of bone-metal interface in orthopaedic application using spectral CT

This thesis investigates the diagnostic potential of MARS spectral photon counting computed tomography (CT) in assessing musculoskeletal disorders such as bone fractures and crystal arthritis. The hypothesis states that the high spatial resolution, quantitative material specific information and reduced metal artefacts of spectral photon counting CT makes the MARS spectral CT scanner a promising imaging tool to confirm or rule out a diagnosis. Being a new imaging modality, a protocol to scan samples with metal implants has to be optimised, before it can be implemented clinically for patient imaging. I contributed to optimising a protocol for imaging bone-implant specimens. Different biomaterials (titanium and stainless steel) used for fracture fixation were imaged. The artefacts were evaluated in both the energy and material domain. A bone analysis tool for measuring bone morphological parameters such as trabecular thickness and spacing was developed in collaboration with the Human Interface Technology Lab. Bone healing at the bone-metal interface was studied and the results were compared with plain radiographs, dual energy x-ray absorptiometry and clinical single and dual energy CT. The advantages of photon counting spectral CT in the early assessment of bone healing due to reduced artefacts was demonstrated. This thesis also investigated the potential of spectral photon counting CT to differentiate calcium crystals present in phantoms and osteoarthritic human meniscus samples. Our results show that MARS spectral CT can moderately discriminate calcium pyrophosphate (crystals inducing pseudogout) and calcium hydroxyapatite crystals. The results were compared with plain radiographs, polarised light microscopy and x-ray diffraction methods. In conclusion, this thesis demonstrated the clinical potential of MARS preclinical spectral photon counting CT scanner for the non-invasive and non-destructive imaging of bone-metal interfaces, for early assessment of bone healing, and for the detection and characterisation of articular crystals

Assessment of metal implant induced artefacts using photon counting spectral CT

The aim is to perform qualitative and quantitative assessment of metal induced artefacts of small titanium biomaterials using photon counting spectral CT. The energy binning feature of some photon counting detectors enables the measured spectrum to be segmented into low, mid and high energy bins in a single exposure. In this study, solid and porous titanium implants submerged in different concentrations of calcium solution were scanned using the small animal MARS photon counting spectral scanner equipped with a polyenergetic X-ray source operated at 118 kVp. Five narrow energy bins (7-45 keV, 45-55 keV, 55-65 keV, 65-75 keV and 75-118 keV) in charge summing mode were utilised. Images were evaluated in the energy domain (spectroscopic images) as well as material domain (material segmentation and quantification). Results show that calcium solution outside titanium implants can be accurately quantified. However, there was an overestimation of calcium within the pores of the scaffold. This information is critical as it can severely limit the assessment of bone ingrowth within metal structures. The energy binning feature of the spectral scanner was exploited and a correction factor, based on calcium concentrations adjacent to and within metal structures, was used to minimise the variation. Qualitative and quantitative evaluation of bone density and morphology with and without titanium screw shows that photon counting spectral CT can assess bone-metal interface with less pronounced artefacts. Quantification of bone growth in and around the implants would help in orthopaedic applications to determine the effectiveness of implant treatment and assessment of fracture healing