• 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 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.

Martin Sjölin 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.

Mats Persson received his MSc in Engineering Physics in 2011 and his PhD in Physics in 2016, both from KTH Royal Institute of Technology in Stockholm. His PhD work was centered on photon-counting spectral CT imaging with a photon-counting silicon strip detector. After working as a postdoc at Stanford University and as a visiting postdoc at General Electric Research Center, he returned to KTH in 2020 where he is now an Assistant Professor of Physics. His research interests are focused on image reconstruction and mathematical performance modeling for photon-counting spectral CT.