Spectral micro-CT for quantitative analysis of calcification in fibrocartilage
This work introduces a quantitative method for assessing calcification in fibrocartilage using spectral micro-computed tomography ($\mu$CT). Tissue samples of hip acetabular labrum from patients with osteoarthritis and femoroacetabular impingement were imaged with a laboratory-based spectral $\mu$CT system equipped with a small-pixel photon-counting detector. The detector operated with two energy thresholds, allowing the simultaneous acquisition of two CT datasets at different X-ray energies. A material decomposition algorithm accounting for the system's spectral response was applied to separate calcium- and water-like components, yielding three-dimensional visualization and quantification of calcified regions within intact paraffin-embedded samples. Unlike the conventional method for calcification assessment based on histology, this spectral \mu CT approach offers volumetric quantification of calcium structures without physical sectioning or staining. The method achieved a voxel size of 20 $\mu$m for samples up to ~3 cm, with a calcium detection threshold of ~0.3 g/cm$^3$ for structures down to 50 $\mu$m. Quantification accuracy was estimated to be 5% by using a calibration phantom. Further comparison with histology demonstrated the correct localization of calcium spatial distributions and a match in the calcium crystal deposition score by providing non-destructive, quantitative 3D calcium maps of preserved tissue samples. This technique complements histology and could enhance the characterization of pathological fibrocartilage calcification in hip joint disorders.