Correlation of In Vivo and Ex Vivo Photon-Counting CT in Knee Osteoarthritis

Overview

This study demonstrates a strong correlation and agreement between in vivo and ex vivo photon-counting CT (PCCT) assessments of subchondral trabecular bone characteristics in patients with knee osteoarthritis (OA). Key bone parameters including bone volume fraction, trabecular thickness, attenuation, and sclerosis area were reliably measured using PCCT, supporting its use for non-invasive longitudinal bone evaluation in OA.

Background

Osteoarthritis involves changes in subchondral bone morphology and density, such as sclerosis and cyst formation, which are important in disease progression. Conventional CT lacks sufficient resolution to accurately depict trabecular bone microstructure in vivo, limiting longitudinal studies. Photon-counting CT (PCCT) offers ultra-high-resolution imaging capabilities comparable to ex vivo micro-CT methods, potentially enabling detailed in vivo bone assessment. Validating the correlation between in vivo and ex vivo PCCT imaging is essential to establish PCCT as a reliable tool for studying bone changes in knee OA.

Data Highlights

Key Findings

• In vivo PCCT imaging of subchondral trabecular bone shows strong correlation with ex vivo PCCT measurements in knee OA patients.
• Bone volume fraction and trabecular thickness measured in vivo closely match ex vivo values after image registration and thresholding.
• Trabecular attenuation in Hounsfield Units in healthy and sclerotic bone regions is comparable between in vivo and ex vivo PCCT scans.
• Manual segmentation of subchondral sclerosis areas demonstrates good agreement between in vivo and ex vivo imaging.
• PCCT provides ultra-high-resolution imaging with clinically acceptable radiation doses, enabling detailed bone microstructure assessment in vivo.

Clinical Implications

Photon-counting CT enables non-invasive, high-resolution assessment of subchondral bone microstructure in patients with knee osteoarthritis, facilitating longitudinal studies of disease progression and treatment effects. This imaging modality may support the evaluation of bone-targeting therapies and improve understanding of bone's role in OA pathophysiology. Clinicians can consider PCCT as a valuable tool for monitoring structural bone changes without the need for invasive biopsies.

Conclusion

The study validates that in vivo PCCT imaging reliably reflects ex vivo bone microstructural characteristics in knee OA, supporting its use for non-invasive longitudinal bone assessment. PCCT holds promise for advancing research and clinical management of osteoarthritis through detailed bone evaluation.

References

1. INKA Trial NCT05172843 -- Weight loss and knee arthroplasty surgery in knee OA
2. Siemens Healthineers -- Naeotom Alpha Photon-Counting CT Scanner
3. ITK-SNAP -- Image Registration Software
4. 3D Slicer -- Open Source Software for Medical Image Computing