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The measurements of bone macro- and microstructures provide major insight into bone health and risk fracture. The accuracy of these measurements is limited when Conventional CT is used. However, CT technology has advanced with the introduction of photon-counting detectors that offer significant improvements in spatial resolution. This advancement offers potential improvements in resolving trabecular microstructures, and the quantification of bone through current or emerging biomarkers. Additionally, the spectral separation available in photon-counting CT (PCCT) may further aid in quantification. The purpose of this study was to objectively investigate PCCT capabilities in accurate quantification of bone macro- and micro-structures. To do so, 5 human bone specimens were scanned using a PCCT scanner (NAEOTOM Alpha, Siemens) and an energy-integrating CT (EICT) (FORCE, Siemens). Each specimen was imaged at a CTDIvol of 4 and 8mGy, and then reconstructed with 2 matrix sizes and at least 2 kernels. For PCCT, a 70keV virtual mono-energetic image series was acquired to evaluate the potential benefits of spectral maps. The same specimens were also scanned using a high-resolution peripheral quantitative CT to provide a ground truth for the bone metrics. Each image series was analyzed in terms of bone mineral density (BMD) and trabecular bone volume to total bone volume. PCCT demonstrated major improvements (5.5% compared to 17% error for EICT) in quantifying bone microstructures (BV/TV). However, the BMD measurements remained similar across imaging conditions and scanners, and did not significantly change by the PCCT spatial resolution enhancement. For BV/TV measurements, PCCT T3D was the most accurate when the sharpest kernel available and 1024-matrix size for (error: 5.53%±4.72%) were used. Similarly, EICT images were the most accurate for BV/TV measurements (error: 16.70%±10.55%) when a medium-sharpness kernel and 1024-matrix size were used. The overall results suggest that PCCT technology can further improve trabecular bone measurements and thus enhance the clinical decision making for patients with bone disease.
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