Single-photon avalanche diodes are compatible with standard CMOS. It means that photo-multipliers for scintillation
detectors in nuclear medicine (i. e. PET, SPECT) can be built in inexpensive technologies. These
silicon photo-multipliers consist in arrays of, usually passively-quenched, SPADs whose output current is sensed
by some analog readout circuitry. In addition to the implementation of photosensors that are sensitive to singlephoton
events, analog, digital and mixed-signal processing circuitry can be included in the same CMOS chip.
For instance, the SPAD can be employed as an event detector, and with the help of some in-pixel circuitry, a
digitized photo-multiplier can be built in which every single-photon detection event is summed up by a counter.
Moreover, this concurrent processing circuitry can be employed to realize low level image processing tasks. They
can be efficiently implemented by this architecture given their intrinsic parallelism. Our proposal is to operate
onto the light-induced signal at the focal plane in order to obtain a more elaborated record of the detection.
For instance, by providing some characterization of the light spot. Information about the depth-of-interaction,
in scintillation detectors, can be derived from the position and shape of the scintillation light distribution. This
will ultimately have an impact on the spatial resolution that can be achieved. We are presenting the design in
CMOS of an array of detector cells. Each cell contains a SPAD, an MOS-based passive quenching circuit and
drivers for the column and row detection lines.