Purpose: There has been recent clinical interest in identifying gout (monosodium urate – MSU) vs. calcium deposits in the pericardium using dual energy CT (DECT). The unique challenge arises from the small size of the lesion in the fast-moving heart. This study was designed using a dynamic heart phantom and DECT with gated cardiac acquisition to evaluate identification of pericardial MSU in the presence of calcium lesions.
Methods: The phantom was designed using two batches of kidney stones returned from clinical pathology; one was 80% MSU and 20% calcium oxalate (CaOx), while the other was 100% CaOx. The stones of size 1 - 4mm were loaded into separate 5mm polypropylene tubes, which were also filled with water and sealed. The tubes were inserted into a dynamic cardiac phantom with fillable epicardial coronary artery tracks. The phantom was controlled to execute the manufacturer’s cardiac motion pattern at 60 bpm and 90 bpm. It was also kept stationary in combination with synthetic ECG. Imaging was performed on a Siemens Force CT using a DECT retrospectively-gated cardiac protocol at 70% R-to-R peak. For temporal and spatial resolution, the pitch defaulted to 0.19, the rotation time was 0.25 sec, and the tube voltages were 90 and 150(Sn) kVp. Images were reconstructed to thickness of 0.5 mm (Bv36) and processed on dual-energy software to distinguish calcium and MSU. The material decomposition parameters were chosen to maximize MSU identification without false positives from CaOx.
Results: An average MSU volume (cc) of 0.18 and 0.17 was determined for the stationary and 60 bpm images, respectively. The MSU volume averaged 0.12 for 90 bpm images. The software correctly identified all MSU stones.
Conclusion: This study shows potential for differentiating pericardial MSU and calcium in vivo, although our findings suggest that quantifying cardiac MSU is affected by lesion motion.