Feasibility study of spectral computed tomography (CT) with gold as a new contrast agent

Newly developed spectral CTs with a photon-counting and energy-selective detector provide the possibility to obtain additional information about an object’s absorption properties, the footprint of which can be found in the energy spectrum of the detected photons. These new CT systems are capable of yielding valuable insight into the elemental composition of the tissue and open up the way for new CT contrast agents by detecting element-specific K-edge patterns. Gold could be a promising new CT contrast agent. The major goal of this study is to determine the minimum amount of gold that is needed to use it as a spectral CT contrast agent for medical imaging in humans. To reach this goal, Monte Carlo simulations with EGSnrc were performed. The energy-selective detector, on which this study is based, has 6 energy bins and the energy thresholds can be selected freely. First different energy thresholds were analyzed to determine the best energy thresholds with respect to detecting gold. The K-edge imaging algorithm was then applied to the simulation results with these energy bins. The reconstructed images were evaluated with respect to signal-to-noise ratio, contrast-to-noise ratio and contrast. The K-edge imaging algorithm is able to convert the information in the six energy bins into three images, which correspond to the photoelectric effect, Compton scattering and gold content; however, it requires very long computing time. The simulations indicate that at least 0.2w% of gold are required to use it as a CT contrast agent in humans.