Dual Energy Computed Tomography Cannot Effectively Differentiate Between Calcium Pyrophosphate and Basic Calcium Phosphate Diseases in the Clinical Setting

Background: Recent reports suggested that dual-energy CT (DECT) may help discriminate between different types of calcium phosphate crystals in vivo, which would have important implications for the characterization of crystal deposition occurring in osteoarthritis. Purpose: Our aim was to test the hypothesis that DECT can effectively differentiate basic calcium phosphate (BCP) from calcium pyrophosphate (CPP) deposition diseases. Methods: Discarded tissue after total knee replacement specimens in a 71 year-old patient with knee osteoarthritis and chondrocalcinosis was scanned using DECT at standard clinical parameters. Specimens were then examined on light microscopy which revealed CPP deposition in 4 specimens (medial femoral condyle, lateral tibial plateau and both menisci) without BCP deposition. Regions of interest were placed on post-processed CT images using Rho/Z maps (Syngo.via, Siemens Healthineers, VB10B) in different areas of CPP deposition, trabecular bone BCP (T-BCP) and subchondral bone plate BCP (C-BCP). Results: Dual Energy Index (DEI) of CPP was 0.12 (SD ​= ​0.02) for reader 1 and 0.09 (SD ​= ​0.03) for reader 2, The effective atomic number (Zeff) of CPP was 10.83 (SD ​= ​0.44) for reader 1 and 10.11 (SD ​= ​0.66) for reader 2. Nearly all DECT parameters of CPP were higher than those of T-BCP, lower than those of C-BCP, and largely overlapping with Aggregate-BCP (aggregate of T-BCP and C-BCP). Conclusion: Differentiation of different types of calcium crystals using DECT is not feasible in a clinical setting.