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Will photon-counting CT replace conventional CT?

by John R. Fischer, Senior Reporter | January 30, 2023
CT X-Ray
The NAEOTOM Alpha photon-counting CT from Siemens Healthineers (shown here) was the first to receive FDA clearance
With its smaller pixel size and higher spatial resolution, photon-counting CT is generating a lot of excitement. As with any innovation, early adopters are exploring the technology’s potential applications.

Researchers at the University of Dundee in Scotland are investigating the ability of photon-counting CT to differentiate tissue characteristics in patients, as well as to segment bone, blood clots, plaque, hemorrhage, and intracranial tumors.

University of Wisconsin-Madison researchers began scanning humans in December with photon-counting CT. They plan to study the scanner’s reconstruction methods, image presentation workflows, and clinical benefits for specific pathologies and disease types, and use their insights to optimize photon-counting CT for better visualization and utilization.
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Just last week, research published in Radiology: Cardiothoracic Imaging, a journal of the RSNA, showed that photon-counting CT may reduce the amount of contrast needed for CT angiography (CTA) without compromising image quality.

A new kind of detector
Unlike conventional CT scanners, which use scintillating detectors that convert X-ray photons into visible light and then convert that light into electronic signals, photon-counting detectors generate images in a single step. The signals are detected by the energy of the photon and converted together into a digital image.

Scintillation detectors integrate all the signals together. Because of this, they are unable to collect information on each individual photon, limiting resolution and dose efficiency. As a result, scans are comparatively more susceptible to electronic noise and artifacts.

With photon-counting systems, the detector counts and compares each individual photon with energy over a set energy threshold, allowing it to differentiate high-energy photons from low-energy ones. Signals below the energy threshold are discarded. This increases spatial resolution and decreases electronic noise and artifacts. It also reduces radiation exposure to the same or lower levels of conventional CT and speeds up the imaging process.

A 2021 study by Mayo Clinic comparing the two technologies supports this, with the photon-counting scanner able to collect more detailed data about the patient to form images, providing the most useful information for diagnosing and treating them in a personalized fashion.

The end of scintillating detectors?
In November 2021, Siemens Healthineers received FDA clearance for its first photon-counting CT system, the NAEOTOM Alpha. Samsung NeuroLogica followed up a few months later with approval for its OmniTom Elite system. Other leading manufacturers, like GE and Canon, are entering their own research partnerships to evaluate the technology’s diagnostic (and market) potential.

“Although commercial availability has been long-awaited for photon-counting CT systems, it is unlikely that we will see this equipment widely used in the near future due to hospitals’ financial constraints,” Kaitlyn Wilkie, advisor for research and analysis at symplr, wrote in HCB News last year.

In addition to the high cost of capital equipment, providers are already facing financial and operational challenges that have only been made worse by the pandemic and supply chain issues, grappling with decreased revenue streams, a labor shortage, inflation, and rising costs for equipment, parts, and services from vendors.

“I believe that all high-performance systems will move to photon-counting over the next decade, but scanners for small facilities that need a lower price point will keep with the current technology longer,” Dr. Cynthia McCollough, director of Mayo Clinic's CT Clinical Innovation Center and one of the researchers using photon-counting technology, told HCB News. “At some point it will become more cost effective for companies to make only photon-counting detectors (i.e., not to maintain two manufacturing processes/factories). Then we will see the scintillating detectors go away, but it will be a while, I believe.”

Like digital radiography replacing film X-ray, experts agree that the future is photon-counting. It’s just not clear how long it will take to get there.

“Fundamentally any feature that can go on a conventional CT scanner can be put on a photon-counting CT scanner,” McCollough adds. “While products are being launched, there may be a few applications not available yet on photon-counting, but that will be temporary.”

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