Compound analysis of gallstones using dual energy computed tomography--results in a phantom model

The potential of dual energy computed tomography (DECT) for the analysis of gallstone compounds was investigated. The main goal was to find parameters, that can reliably define high percentage (>70%) cholesterol stones without calcium components.

35 gallstones were analyzed with DECT using a phantom model. Stone samples were put into specimen containers filled with formalin. Containers were put into a water-filled cylindrical acrylic glass phantom. DECT scans were performed using a tube voltage/current of 140 kV/83 mAs (tube A) and 80 kV/340 mAs (tube B). ROI-measurements to determine CT attenuation of each sector of the stones that had different appearance on the CT images were performed. Finally, semi-quantitative infrared spectroscopy (FTIR) of these sectors was performed for chemical analysis.

ROI-measurements were performed in 45 different sectors in 35 gallstones. Sectors containing >70% of cholesterol and no calcium component (n=20) on FTIR could be identified with 95% sensitivity and 100% specificity on DECT. These sectors showed typical attenuation of -8+/-4 HU at 80 kV and +22+/-3 HU at 140 kV. Even the presence of a small calcium component (<10%) hindered the reliable identification of cholesterol components as such.

Dual energy CT allows for reliable identification of gallstones containing a high percentage of cholesterol and no calcium component in this pre-clinical phantom model. Results from in vivo or anthropomorphic phantom trials will have to confirm these results. This may enable the identification of patients eligible for non-surgical treatment options in the future.