What is Photon Counting CT?

Photon counting CT converts X-rays directly to electronic signals unlike conventional CT which converts X-rays first to light and then to electronic signals. Direct  conversion allows low energy photons to be differentiated from electronic noise. When data is acquired directly from photons of different energy levels, better contrast-to-noise ratio can be realized. Photon counting CT has a potential for multiple energy reconstructions from the same scan data which enables calcium maps, measurement of extracellular volume and coronary plaque quantification. Decrease in image noise reduces the impact of calcium and metallic artifacts on image quality. Anyone who has seen a CT image of a person with a pacemaker would have noted the blooming effect of the metallic components. Photon counting CT promises lower radiation doses in addition to better resolution.