Photon-counting detector CT for bone defect repair: Unveiling the impact of pore size on osseointegration and the advantage over traditional imaging.

PURPOSE: The purpose of this study was to evaluate the role of photon counting detector CT (PCD-CT) in revealing the osseointegration properties of porous polyether ether ketone (PEEK) scaffolds. It was also compared with energy-integrated detector CT (EID-CT) and micro-computed tomography (Micro-CT) to assess the potential and accuracy of PCD-CT in visualizing bone details and evaluating implant-mediated bone regeneration and repair processes.

MATERIALS AND METHODS: PEEK scaffolds with different pore sizes (0, 200, and 400 μm) were implanted into a rabbit tibial defect model. The bone defect model was analyzed by three imaging techniques: EID-CT (SOMATOM Force), PCD-CT (NAEOTOM Alpha) and Micro-CT (ZKKS-MCT-Sharp). Bone structure parameters such as bone volume to tissue volume ratio (BV/TV) and bone surface area to tissue volume ratio (BS/TV) were evaluated. The bone structure parameters obtained using the different imaging techniques were compared to analyze consistency and correlation. In addition, both quantitative and qualitative evaluations of the clarity of the bone-implant interface were conducted.

RESULTS: The BV/TV and BS/TV values tended to increase, while the BS/BV values tended to decrease in all groups as the growth cycle lengthened. Additionally, we found that the location of new bone growth varied with different pore size scaffolds. In 3D reconstructed images, PCD-CT demonstrated superior visualization compared to EID-CT, providing more detailed images of osseointegration. Compared to Micro-CT, although PCD-CT does not provide more detail, it offers a substantially lower radiation dose (Mean dose: 3.306 mGy vs. 642 mGy, p < 0.0001). For the quantitative analysis of bone structure parameters, both EID-CT and PCD-CT analyses showed lower results than Micro-CT. However, PCD-CT values were closer to those of Micro-CT and exhibited better agreement (Bias = 0.009 for BV/TV; Bias = 0.014 for BS/TV; Bias = -0.945 for BS/BV) and stronger correlation (R = 0.849 for BV/TV; R = 0.941 for BS/TV; R = 0.622 for BS/BV) with Micro-CT. Quantitative analysis of scaffold osseointegration edge sharpness showed that PCD-CT (308.4 ± 144.1 Gy value/mm) had higher edge sharpness, which was significantly different from EID-CT (115.4 ± 66.12 Gy value/mm; p < 0.0001) and not significantly different from Micro-CT (286.1 ± 117.6 Gy value/mm; p > 0.05). Observer scores also demonstrated that PCD-CT had better image quality than EID-CT and is comparable to Micro-CT.

CONCLUSIONS: PCD-CT demonstrates significant advantages over conventional imaging techniques in the assessment of osseointegration properties, particularly in the visualization of osseointegration and the accurate measurement of bone structural parameters. The application of PCD-CT not only provides high imaging accuracy but also reduces scanning costs and radiation doses. This reduction in radiation exposure minimizes potential effects on bone metabolism and peripheral muscle function, allowing researchers to reduce the use of experimental animals and track the long-term effects of interventions in the same animal model. Furthermore, PCD-CT enables the accurate in vivo assessment of osseointegration characteristics in large animal models and humans, thereby providing critical guidance for the design and refinement of bone tissue engineering scaffolds. By providing detailed and precise imaging, PCD-CT supports the advancement of regenerative medicine and the clinical translation of innovative biomaterials.