Spectral micro-CT for quantitative analysis of calcification in fibrocartilage.

PURPOSE: We describe a method for the quantitative analysis of calcification structures in fibrocartilage samples from human hip acetabular labrum, using a lab-based spectral micro-computed tomography ( μ CT ) system. APPROACH: Tissue samples from 26 patients with osteoarthritis and femoroacetabular impingement were analyzed using a spectral μ CT system featuring photon-counting detector with a 62    μ m pixel size operating at two energy thresholds. Material decomposition was applied to the μ CT images to separate calcium and water-like components, resulting in the 3D spatial distribution and quantification of calcium deposits within the tissue. Results were compared with histological analysis using Alizarin Red™ staining. Two calcium crystal deposition scores on a four-grade scale were assigned based on histological and μ CT analysis, respectively. RESULTS: This method provides 3D images with a voxel size of 20    μ m over a sample size up to 3 cm. The minimum detectable calcium concentration is 0.24    g / cm 3 , and calcified structures as small as 49.6    μ m in diameter were identified. The quantification accuracy was validated using a hydroxyapatite calibration phantom. Across the complete sample set, spectral µCT grading demonstrated significant correlation (Spearman correlation coefficient ρ = 0.67 ) and substantial agreement (weighted Cohen's coefficient κ = 0.70 ) with histological assessment. Moreover, the calcification spatial distribution exhibited very good consistency with histological results, supporting the method validity. CONCLUSIONS: This approach offers a nondestructive and reproducible alternative to histology for assessing calcification in joint tissue, providing quantitative 3D mapping of calcium concentration in intact samples without the need for staining or physical sectioning.