Thursday, March 29, 2012

Caeleste Whitepaper on X-Ray Photon Counting

Caeleste published a white paper on "Photon counting and color X-ray imaging in standard CIS technology".

The 100x100um color X-ray pixel has quite complex functionality:

The counters are charge-based analog ones and the pixel layout is quite compact with 80% metal limited fill factor:


  1. The different energy photons will create several gaussian-like distribution lobes. When the detection quantum efficiency is high, the distribution lobes could be distinguishable by level detector in the pixel. But with scintillator based detection array, the spatial distribution (low MTF) will spread largely these gaussian lobes, so the energy discremination power should be low with a large confusion.

  2. The key with bright, spread-out pulses is pulse rate. Gamma cameras do just fine with a big crystal and a couple of dozen detectors because the centroid of each arriving gamma photon can be readily calculated. However, when simultaneous events occur, the total energy received is too high and the pulse is just discarded.

    In the sort of detector described here, the problems are that simultaneous low-energy events can mimic single high-energy events, that some low energy events will be missed due to the variations in scintillator yield and that some low-yield high-energy events will be counted as low-energy events.

    In addition, as anonymous indicates, trying to detect events by thresholding before centroid calculation will just lead to confusion about the event energy and possibly the event rate.

    Building energy-sensitive detectors is possible using CMOS technology but this is not a very good way to do it. Te nuclear physics people have better ways.

  3. For a 2-level, it's really no need of such complexe detection pixel. A simple 2-shot acquisition can obtain much better result by detecting the real position of the event in order to extract the real energy.

  4. what you say is true... provided that there is time for dual shot, and provided that one can deal with the extra dose the the patient. According to our discussion with pathologist, dual shot is what they do on operation residue, but not on living patient.


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