This course explains the principles of photon counting detectors for spectral x-ray imaging. Typical technical implementations are described and fundamental differences to energy integrating systems are pointed out. In particular, the issues of high-rate handling and the effect of detector cross talk on energy resolution are described. Requirements on electronics for spectral imaging in computed tomography is also discussed.
A second objective of the course is to describe how energy sensitive counting detectors make use of the energy sampling of the linear attenuation coefficients of the background and target materials for any given imaging task; methods like material basis decomposition and optimal energy weighting will be explained.
The second objective highlights the interesting fact that while the spatial-frequency descriptor of signal-to-noise-ratio transfer (DQE) of a system gives a complete characterization of performance for energy integrating (and pure photon counting) systems, it fails to characterize multibin systems since a complete description of the transfer characteristics requires specification of how the information of each energy bin is handled. The latter is in turn dependent on the imaging case at hand which shows that there is no such thing as an imaging case independent system DQE for photon counting multibin systems. We also suggest how this issue could be resolved.
describe the fundamental operating principles of photon counting detectors for spectral x-ray imaging
distinguish between the proposed detector materials in terms of their main physical limitations/challenges to high-rate energy resolved photon counting
list essential requirements on read-out electronics and predict effect on image quality if not fulfilled
explain the physical origin of pile-up and separate between the effects of decreased energy resolution and loss of counts
explain the physical origins of cross-talk and how it degrades performance, both in terms of resolution and noise
compute optimal weights for the energy bins
illustrate how poor choice of weights results in inferior image quality
perform material basis decomposition and explain why noise in decomposed images is a poor figure-of-merit
distinguish between system DQE and task dependent DQE and suggest solutions to allow comparison at system level between multibin energy resolved systems and other solutions
Scientists, engineers, or managers who wish to learn more about basic strengths and challenges of photon counting detectors for spectral x-ray imaging, how the data is treated and how performance can be quantified.
Mats E. Danielsson
has been developing photon counting x-ray detectors for medical imaging for 15 years and his research has resulted in detector systems in worldwide clinical use. He received his Ph.D. in experimental physics in 1996 based on work at CERN, Geneva and later did his postdoc at Lawrence Berkeley National Laboratory. In 2006 he was appointed Professor at KTH Royal Institute of Technology in Stockholm, Sweden, where he heads the physics of medical imaging research group. Dr. Danielsson is a lifetime member of SPIE.
has worked with the development of photon-counting spectral x-ray detectors since 2011. He has worked on several topics related to photon-counting spectral detectors, including: energy calibration, geometric calibration, count-rate performance, sampling and digital data compression. Martin received his PhD from KTH Royal Institute of Technology, Sweden, in 2016 with the thesis “Methods of image acquisition and calibration for x-ray computed tomography”. His current research is focused on the design and development of spectral photon-counting detectors suitable for clinical CT.
Attendee testimonial: Great course, summarized the research into photon counting detectors well as well as providing some interesting open questions in the field.