Photon counting imaging method and device with instant retrigger capability

A method for photon counting imaging for single X-ray counting using a layer of photosensitive material, an L×K array photodetector elements arranged ni the layer of the photosensitive material, an N×M array of readout unit cells including amplifying elements, K, L, M and N being numbers greater than or equal to one, at least one readout unit cell for at least one photodetector element, said at least one readout unit cells being controlled via signal processing elements, each said readout unit cell comprising internal signal processing elements allowing to generate a discriminator output signal representing an amplified signal of electron-hole pairs generated by at least one an incident photon in said least one photodetector element, the discriminator output signal being generated by comparing the amplified signal with a predetermined threshold level and the discriminator output signal being generated whenever the amplified signal exceeds the predetermined threshold level with a counter unit registering counts as a function of the discriminator output signal, said method comprising the steps of:

• registering the counts by counting for each signal pulse a number of dead time intervals of a predetermined width corresponding to a width of the signal pulse at the discriminator output by starting a dead time interval whenever the amplified signal initially exceeds the predetermined threshold level;
• and,
• counting directly succeeding dead time intervals for as long as the amplified signal exceeds the predetermined threshold level.

An apparatus for photon counting imaging for single X-ray counting, comprising:

• a layer of photosensitive material;
• an L×K array of photodetector elements arranged in said layer of photosensitive material;
• signal processing elements;
• an N×M array of readout until cells including amplifying elements, K, L, M and N being numbers greater than or equal to one, one or a plurality of readout unit cells for one or a plurality of photodetector elements, said readout unit cells being controlled by said signal processing elements, each said readout unit cell comprising internal signal processing elements allowing to generate a discriminator output signal representing an amplified signal of electron-hole pairs generated by an incident photo or a plurality of incident photons in a respective said photodetector element, said discriminator output signal being generated by comparing the amplified signal with a predetermined threshold level and the discriminator output signal being generated whenever the amplified signal is exceeding the predetermined threshold level;
• a counting unit registering counts as a function of the discriminator output signal;
• and,
• a counting circuit comprising a dead time generation circuit, the dead time having a predetermined width, starting of the dead time being enabled as a function of the discriminator output signal at an input of the dead time generation circuit whenever counting is triggered as a function of the discriminator output signal and delivering a delayed signal at the output of the dead time generation circuit that re-enables a counting process and that re-triggers counting after the dead time if the amplified signal still exceeds the predetermined threshold level.