Bone stiffness and strength at the distal radius can be determined using photon-counting CT

Estimating bone strength aids in osteoporotic fracture risk assessment. Bone strength is usually calculated with a high-resolution CT; however, this modality has limited clinical utility. We demonstrated that clinical photon-counting CT can also be used for bone strength quantification, which facilitates the use of this information in clinical decision-making.

Quantification of bone strength and microarchitecture at the distal radius with high-resolution peripheral quantitative computed tomography (HR-pQCT) can predict osteoporotic fracture risk independently of dual-energy X-ray absorptiometry. Photon-counting CT (PCCT) is a novel imaging technique with larger fields of view, shorter acquisition times, and similar resolution when compared to HR-pQCT. This study aimed to compare the stiffness and strength of the distal radius computed from PCCT and HR-pQCT images.

We evaluated a 10.2 mm section of the distal radius from eight cadaveric forearms scanned with PCCT and HR-pQCT at 0.11 mm and 0.061 mm voxel size, respectively. All CT images were converted to voxel-based linear finite element models. Two material models were used: a segmentation-based model with a fixed Young's modulus of 10 GPa for bone elements, and a density-based model where Young's modulus was assigned on a voxel-by-voxel basis, based on its gray value. Poisson's ratio was set to 0.3 for all elements. Axial compression at 1% apparent strain was applied to quantify stiffness; strength was quantified with the Pistoia criterion. In addition, load sharing between cortical and trabecular bone was quantified.

We found strong correlations between PCCT and HR-pQCT-derived bone stiffness, strength, and cortical and trabecular proportion for segmentation-based models (R² > 0.911; p < 2e-4). Correlation and agreement were higher for density-based models (R² > 0.977; p < 4e-6).

We demonstrated that PCCT can estimate bone strength with high accuracy and agreement when compared to HR-pQCT. These findings highlight PCCT's potential in assessing fracture risk in osteoporosis. At the same time, PCCT's large field of view enables broader usage, at sites different from peripheral limbs.