Fig. 1
Simplified schematic of algorithm used in DECT scans for the evaluation of gout. The algorithm separates the chemical composition of compounds based on their different attenuations at 80 kV and 150 kV (with additional tin (Sn) filter). Three materials (MSU, soft tissue and calcium) can be differentiated from each other. For simplicity, only the range of different concentrations of pure calcium in water is depicted. Materials above the cut-off DECTratio are classified as calcium (i.e. material with high Zeff), and materials below the cut-off DECTratio are classified as MSU depositions and colour-coded green (i.e. materials with low Zeff). A HU cut-off differentiates soft tissues (with Zeff similar to MSU) from MSU depositions. Mixed tissues (such as calcified dense tissues of calcified MSU depositions) may lead to misinterpretations of DECT examinations: as illustrated by the light grey area. DECT, dual-energy computed tomography; MSU, monosodium urate; Zeff, effective atomic number