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Jan 29, 2022, 9:06:10 AM
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Spectral photon counting CT (computed tomography)

Session chair: Ballabriga , Rafael (CERN, Switzerland); Danielsson , Mats (KTH, Stockholm, Sweden); Kachelrieß , Marc (German Cancer Research Center (DKFZ), X-Ray Imaging and CT, Heidelberg, Germany); Persson , Mats (KTH, Stockholm, Sweden); Wang , Adam S. (Stanford University, Stanford, USA)
Shortcut: SC-04
Date: Saturday, 16 October, 2021, 8:00 AM - 2:30 PM
Room: SC-02
Session type: Short Course

This course provides a comprehensive overview of photon counting CT imaging from basic principles to the state of the art: clinical applications of the technology, detector design, ASIC design, and CT image formation algorithms. The course is designed for engineers and physicists who wish to gain or deepen the knowledge on this emerging field of research.


Click on an contribution to preview the abstract content.

8:00 AM SC-04-01

Technology and clinical applications. Main differences between Energy Integrating and Photon Counting. Improvements of PC technology and their impact on clinical applications (#1471)

M. Kachelrieß1

1 German Cancer Research Center (DKFZ), X-Ray Imaging and CT, Heidelberg, Baden-Württemberg, Germany


  • Photon energy weighting
  • Material specific imaging
  • Small pixel effect
  • Iodine effect
  • High spatial resolution imaging
  • Improved CNR and contrast-enhanced imaging
  • Material-selective imaging 
  • Low dose imaging and dose reduction potentials
  • Energy resolving capabilities used for artifact reduction
  • Novel contrast agents and multi contrast agent imaging

Prof. Dr. Marc Kachelrieß is chair of the division of X-Ray Imaging and CT of the German Cancer Research Center (DKFZ), Heidelberg, Germany. After finishing his diploma in theoretical physics he started his PhD research on metal artifact reduction in CT in 1995. In 2002 Marc Kachelrieß completed all post-doctoral lecturing qualifications (habilitation) for Medical Physics and in 2005 he was appointed Professor of Medical Imaging at the University of Erlangen-Nürnberg. Since 2009 Marc Kachelrieß additionally holds an Adjunct Associate Professor position at the Department of Radiology at the University of Utah, USA. In 2014 Marc Kachelrieß was appointed full Professor of X-Ray Imaging and CT at the German Cancer Research Center (DKFZ) in Heidelberg, Germany. His research interests are basic algorithmic and physics aspects of tomographic imaging with ionizing radiation, with a focus on x-ray computed tomography.

Keywords: Short Course
9:15 AM SC-04-02


9:30 AM SC-04-03

Lecture 2: Mats Persson and Mats Danielsson (#1472)

M. Persson1, M. Danielsson1

1 KTH, Stockholm, Sweden



  • Description of systems under evaluation.
  • Detector design configuration: Materials (Si, CdTe/CZT), geometry
  • Detector Physics 
  • Limitations of real Detectors (Conversion efficiency, Charge Diffusion that leads to charge sharing, Fluorescence, Charge Trapping, Noise, Pile-up),
  • Relationship between detector design and image quality
  • Imaging figures of merit. Definition and practical measurement (CNR, DQE, NEQ, MTF, NPS).

Mats Persson of KTH 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 centered on image reconstruction and mathematical performance modeling for photon-counting spectral CT.

Mats Danielsson of KTH received his MSc in Engineering Physics from the Royal Institute of Technology in Stockholm in 1990. From then until 1996 he pursued research with the CPLEAR experiment at CERN, the European Facility for Nuclear Research in Geneva, Switzerland. He received his Ph.D. 1996 with the thesis titled First Direct Measurement of T-violation, based on the first measurement of violation of the Time symmetry. From 1996 to 1998 Mats Danielsson worked as a postdoc at Lawrence Berkeley National Laboratory, Berkeley, USA on research in detectors and integrated electronics for x-ray imaging. From 1999 up to now he has been employed at the KTH Royal Institute of Technology in Stockholm where he currently holds a position as Professor and heads the research group in medical imaging. Together with Staffan Holmin at Karolinska Institutet Mats Danielsson took the initiative to MedTechLabs that was approved in 2017 by the Stockholm city council and he is now co-director for its research program in imaging and minimal invasive techniques. Mats Danielsson further co-founded Sectra Mamea AB (sold to Philips in 2011), C-RAD (listed at Nasdaq) and Prismatic Sensors. Mats Danielsson holds around 50 patents and is co-author of over 100 peer reviewed scientific publications in journals such as Medical Physics, Physics in Medicine and Biology, Journal of Medical Imaging and Nature and the articles have been referenced more than 4000 times.

Keywords: Short Course
11:00 AM SC-04-04

Lunch Break

11:30 AM SC-04-05

Pulse Processing Application Specific Integrated Circuits (ASICs) for the readout of semiconductor detectors (#1473)

R. Ballabriga1

1 CERN, Geneva, Switzerland


  • The ideal detector
  • Sensor limitations (Very brief description for completeness. Most of the discussion on this will be covered in Lecture 2)
    • Sensor
      • Absorption efficiency
      • Fluctuations in the number of generated charge carriers
      • Charge diffusion
      • Partial charge deposition due to Fluorescence and Compton Scattering
      • Charge trapping in the semiconductor material (use small pixel effect)
    • Interface
      • Ballistic deficit
    • Readout electronics
      • Electronics noise
      • Threshold offset and gain dispersion between pixels
      • Cross talk
      • Pulse pile-up
    • Review of ASICs with emphasis on Photon Counting CT
      • Digitization methods
      • Count rate
      • On chip correction algorithms for spectral fidelity
      • Power consumption

Rafael Ballabriga is a graduate of the Ramon Llull University in Barcelona (BSc 2000, MSc 2002). In 2004, he joined CERN microelectronics group, Geneva (Switzerland), in the framework of the CERN Doctoral Student Program to work in the design and characterization of hybrid pixel detectors.

Rafael Ballabriga received the IEEE NPSS Best Student Paper Award in 2006. He defended his PhD thesis entitled “The Design and Implementation in 0.13um CMOS of an Algorithm Permitting Spectroscopic Imaging with High Spatial Resolution for Hybrid Pixel Detectors” in 2009 for which he received the best thesis award of the Ramon Llull university doctoral programme 2009-2010. In 2013 he received the IEEE Nuclear and Plasma Sciences Society Radiation Instrumentation Early Career Award.

Rafael Ballabriga has coached younger designers in the design of front-ends in CMOS technologies. Holds three patents and has authored or co-authored more than 70 peer-reviewed journal publications.

Keywords: Short Course
12:30 PM SC-04-06


12:45 PM SC-04-07

CT Image generation fundamentals / Task-based performance (#1474)

A. S. Wang1

1 Stanford University, Stanford, United States of America


  • CT Image generation fundamentals.
    • Algorithms: Optimal energy weighting, Material decomposition, Virtual monoenergetic
      • Projection domain
      • Image domain
    • Reconstruction
      • FBP
      • Iterative
    • Noise reduction
    • AI-based processing
    • Performance analysis
      • Spatial resolution
      • Noise
      • DQE
      • Reduced artifacts
  • Task-based performance
Adam Wang, PhD is an Assistant Professor of Radiology and, by courtesy, Electrical Engineering at Stanford University, where he leads the Advanced X-ray and CT Imaging lab. His research interests include photon counting CT, spectral x-ray imaging, novel x-ray/CT systems and algorithms, and AI applied to image acquisition, processing, and reconstruction. Before joining the Stanford faculty in 2018, Dr. Wang completed his PhD at Stanford in 2012, on the topic of maximizing the information content of spectral x-ray imaging. He then completed a postdoctoral fellowship at Johns Hopkins University in 2014, on iterative reconstruction and image registration of cone-beam CT for image-guided surgery. Afterwards, Dr. Wang was a Senior Scientist at Varian Medical Systems (2014-2018), developing systems and algorithms for image-guided radiation therapy.

Keywords: Short Course
2:00 PM SC-04-08


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