Characterizing Meniscal Calcifications with Photon Counting-Based Dual-Energy Computed Tomography

Meniscal calcifications are associated with meniscal degeneration and osteoarthritis (OA). However, differentiating calcification types, such as basic calcium phosphate (BCP) and calcium pyrophosphate (CPP), remains challenging in vivo. Therefore, assessing new imaging possibilities is crucial in understanding calcification pathologies and their relationship with OA. This study investigated whether dual-energy computed tomography with a photon counting detector (PCD-DECT) can distinguish between BCP and CPP, using Raman spectroscopy as reference.

82 meniscus samples from 41 donors were imaged using PCD-DECT at 120kVp. Data were collected in two energy bins (20-50 keV and 50-120 keV). Raman spectroscopy was used to classify the calcifications as BCP or CPP. Among 82 samples, Raman spectroscopy identified 36 samples with only either BCP or CPP calcifications, which were included in the subsequent analysis. Regression models were used to compare the dual-energy index (DEI) and to assess the low-energy values for corresponding high-energy values between calcification types.

The highest difference observed between BCP and CPP in comparison of low-energy values for corresponding high-energy values was 166HU (95%CI: 73, 259) at high-energy value of 500HU and the difference between DEI values was 0.035 (95%CI: 0.011, 0.059), suggesting a potential difference in the measured parameters of calcification types.

PCD-DECT allowed the measurement of BCP and CPP calcifications ex vivo, suggesting its potential for in vivo applications in the future, which could help understand calcification processes and evaluate the efficacy of disease-modifying drugs targeting calcification inhibition.