The future is Spectral Photon Counting

Photon counting represents the next generation of CT hardware technology. It is an area of significant research both in academia and in the industry that promises to deliver improvements in ultra high resolution, enhanced dose efficiency, and Spectral always on. While systems are currently available for research and patient use, there are still limitations to full routine clinical adoption. At the same time, with its quantitative and analytical imaging technology photon counting is the future of CT.

The promises of Spectral Photon Counting Technology

Photon counting technology high image quality

Ultra High Resolution enabled by significant improvement in resolution. Commercially available systems enable spatial resolution of up to 40 lp/cm.¹

Enhanced Dose efficiency by enabling the possibility to use less dose and get more information from each photon. Commercially available systems allow for dose reduction of 32% compared to dual-source CT. ²

Photon counting technology with additional information

Spectral always on through detector-based multi-energy acquisition and analysis capabilities.

Photon Counting Detectors

Christoph Herrmann, Philips Research, “Detection principle of Photon Counting Detectors”⁴

Unlike the integrated detectors used in conventional scanners, Spectral Photon Counting Detectors are made of CZT (Cadmium Zinc Telluride) semiconductors. The first layer of semiconductor of thickness from 2 to 3mm, allows, by absorbing a photon, to form electron-hole pairs. These detectors are connected to an electronic system (ASIC) composed of parallel channels allowing successively to model the signal and to amplify it so that it is sorted by energy level. The photons are then discriminated in 2 to 8 energy levels chosen beforehand. Operation of the detectors is summarized in the video.³

The importance of photon counting technology

In contrast to CT, spectral photon counting systems (SPCCT) doesn’t just capture the volume of photons that make it through – it also measures the energy of each photon. As a result, much like we perceive different photon energy levels as different colors of light, SPCCT enables clinicians to ‘see’ X-rays in full color.⁵

Multi-Energy CT images can be acquired with different technologies and scan modes
Source-based techniques require two data sets while detection-based techniques achieve it in one scan
Advanced use case: It will be possible to see separation of different materials allowing for targeted contrast agents

Challenges with current designs

Protocol Optimization Workflow

Protocol Optimization Workflow

Protocol optimization is a long-stated goal in CT. Mistakes in protocol selection can lead to non-diagnostic imaging requiring rescans. While there is a promise of a universal protocol, current Photon Counting systems "further complicate this landscape by offering more parameters to tune in the form of bin thresholds." Additionally, commercially available PCCT currently do not have AI noise reduction algorithms which may be necessary to enable both high resolution and low dose imaging.
Cardiac Imaging

Cardiac Imaging

Cardiac imaging is one of the most exciting areas of potential Photon Counting applications. Commercially available PCCT and Spectral systems have been able to demonstrate reduction in blooming artifacts and the ability to visualize the lumen inside the stent. However, currently available Photon Counting systems experience limitations when imaging in ultra high-resolution including lack of spectral data and one-beat acquisition, reduced z-axis coverage, limited scan types, and increased exam times and raw data size.
Large data handling

Large data handling

Photon counting systems generate a lot of data. It is estimated the data rates range from 2-35 times higher than conventional CT. The sizeable amount of data generated by these scanners, which includes larger matrix size ultra-high-resolution images and spectrally derived images, will require improvements in data storage, interpretation, and radiology workflow management.
Neuro Imaging

Neuro Imaging

Studies show the quality of Monoenergetic Reformats (MERs) on commercially available PCCT significantly different from those of the DECT and are inferior in every image-quality parameter. Additionally, due to the lack of an artifact reduction algorithm, artifacts below the calvarium and in the posterior fossa still underperformed when compared to conventional CT.
Number of spectral results

Number of spectral results

Commercially available photon counting systems offer 4 spectral results. By comparison, commercially available Spectral CT systems offer 10 unique results, enabling further analysis in areas such as bone marrow edema, coronary artery disease, and proton therapy planning. Learn more

Philips pioneers research into next generation of CT imaging

As part of an EU-funded consortium, Philips is pioneering research into the next generation of CT imaging: Spectral Photon Counting CT (SPCCT).

Philips’ clinical prototype is the world’s first full-field-of-view SPCCT system, and has recently been installed at Lyon University Hospital, France.⁷

Read further

Photon Counting is a work in progress, not FDA cleared.

Spectral Photon Counting CT is a new imaging modality based on the usual CT concept with the key difference of energy resolving detector technology. The additional spectral information can be used for material separation and can deliver additional, new contrast with clinically relevant new information.

Pr Philippe Douek, MD, PhD

Professor at Hospices Civils de Lyon

More from the world of Spectral Detector CT

Sources

1. NAEOTOM Alpha

2. Photon-counting CT bests DSCT for reducing abdominal radiation dose (auntminnie.com)

3. Photon Counting Detectors for a higher spatial resolution

4. Christoph Herrmann, Philips Research, “Detection principle of Photon Counting Detectors”
Photon Counting Detectors for a higher spatial resolution (spectralphotoncountingct.com)

5. Imaging Physics: Update on Multienergy CT: Physics, Principles, and Applications. Prabhakar Rajiah, MBBS, et al. RSNA.org

6. Photon Counting CT: Clinical Applications and Future Developments
    ISCT: Just how great is photon-counting CT?
    Photon-counting CT: Scouting for Quantitative Imaging Biomarkers
    MDPI: Image-Quality Assessment of Polyenergetic and Virtual Monoenergetic Reconstructions of Unenhanced CT Scans of the Head

7. Philips pioneers research into next generation of CT imaging - News | Philips
SPCCT – Imaging all the Photons

8. Prof Philippe Douek, MD, PhD, Professor at Hospices Civils de Lyon (PDF) Spectral Photon Counting CT European Project

Photon Counting Clinical Images courtesy of Lyon, Hospices Civils de Lyon