Spectral micro-CT for quantitative analysis of calcification in fibrocartilage

PurposeWe 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 (μCT) system.ApproachTissue samples from 26 patients with osteoarthritis and femoroacetabular impingement were analyzed using a spectral μCT system featuring photon-counting detector with a 62 μm pixel size operating at two energy thresholds. Material decomposition was applied to the μCT 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 μCT analysis, respectively.ResultsThis method provides 3D images with a voxel size of 20 μm over a sample size up to 3 cm. The minimum detectable calcium concentration is 0.24 g/cm3, and calcified structures as small as 49.6 μm 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.ConclusionsThis 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.