Advanced application and validation of a phantom-less quantitative computed tomography system on site-specific bone density assessment

Abstract

Osteoporosis, as a silent epidemic, imposes significant health and economic burdens through its severe complication of osteoporotic fractures. The diagnosis of osteoporosis and assessment of its effects are crucial for preventive strategies and early interventions to minimize associated risks. Bone mineral density (BMD) remains the primary diagnostic indicator, with quantitative computed tomography (QCT) recognized as the most accurate and advanced measurement tool. However, clinical applications of QCT in orthopedic diagnostics remain underexplored. This thesis focuses on two objectives: first, implementing phantom-less QCT (PL-QCT) for BMD assessment at clinically relevant sites including spinal endplates, spinal pedicles, and proximal humerus; second, validating the precision and accuracy of PL-QCT measurements across imaging devices and novel anatomical applications.

In the evaluation of vertebral bodies, PL-QCT was employed to measure site-specific BMD variations and their spatial correlation with cage subsidence following interbody fusion. Concurrent cross-device reliability testing revealed reliability of BMD measurement on the PL-QCT. The methodology demonstrated high precision, with intra-scanner variability of 1.61 mg/cm³ and inter-brand variability of 2.64 mg/cm³. Importantly, L1-L3 vertebral BMD measurements from all scanners satisfied the ±5 mg/cm³ bias criterion, confirming technical consistency across imaging devices. Comparative analysis of pedicle screw planning methods highlighted the advantages of PL-QCT-based software over conventional freehand techniques. The PL-QCT approach generated screws with larger dimensions (length: 48.65 ± 5.99 mm vs. 44.78 ± 2.99 mm; thickness: 7.39 ± 0.42 mm vs. 6.1 ± 0.27 mm) and higher surgical safety rates, with 85.1% of software-planned screws achieving the highest safety classification compared to 64.9% in freehand plans. These results underscore the potential for PL-QCT to enhance preoperative planning accuracy. Building upon the relationship between endplate BMD and subsidence risk, a biomechanical customization framework was developed for patient-specific interbody cages. Through analysis of BMD-modulus correlations, optimal structural parameters were identified as irregularity (IR) = 1 and porosity (CP) = 43.86%–51.63%. Computational simulations demonstrated that cages designed with these parameters achieved modulus compatibility with patient-specific endplate BMD requirements. Validation study on the proximal humerus compared PL-QCT with phantom-based QCT (PB-QCT), revealing strong agreement between the two methods. The mean BMD difference was 1.0 mg/cm³ (P > 0.05), supported by a high correlation coefficient (R² = 0.9723). Both modalities exhibited comparable short-term reproducibility, confirming their clinical equivalence in cancellous bone assessment on the proximal humerus. In conclusion, this thesis establishes PL-QCT as a robust and versatile tool for orthopedic diagnostics and personalized treatment strategies. The developed methodologies for BMD quantification, surgical planning optimization, and implant customization address critical gaps in osteoporosis management and biomechanical engineering. These findings provide a foundation for advancing evidence-based clinical practices through enhanced bone quality assessment and precision medicine approaches.