Photon-counting CT vs. conventional detector technologies
Photon-counting computed tomography (CT) is rapidly moving from research into routine clinical practice, offering significant improvements in image quality and diagnostic performance over conventional energy-integrating detector (EID) CT systems. However, users should avoid treating the technology as just a replacement for existing scanners, according to Cynthia McCollough, PhD, professor of medical physics and biomedical engineering and director of the CT Clinical Innovation Center and X-ray Imaging Core at Mayo Clinic and a former president of the American Association of Physicists in Medicine (AAPM).
She spoke to Cardiovascular Business following a session on the topic at the SCCT2026, the Society of Cardiovascular Computed Tomography (SCCT) annual meeting. McCollough said the most important distinction is not the underlying physics, but how the technology can improve patient care.
"The technical differences ultimately matter because of the differences they make in the clinical images," she said.
Unlike conventional EID systems, photon-counting CT detectors count individual X-ray photons and measure their energy, enabling inherent spectral imaging while improving spatial resolution, reducing image noise and increasing iodine signals. These capabilities allow clinicians to better visualize anatomy while potentially lowering both radiation dose and contrast requirements. While Siemens was first to market photon-counting CT (PCCT) systems, GE Healthcare recently gained FDA clearance for its new workhorse photon scanner.
Neusoft and Canon Medical are also working on photon-counting scanners and displayed them at the Radiological Society of North American (RSNA) 2025 meeting last November.
McCollough said users evaluating the growing number of commercially available systems should focus on how vendors balance key imaging characteristics, including spatial resolution, image quality, noise and radiation dose. She also recommended examining the clinical experience from early adopter sites to determine whether technical improvements with the scanners translated into meaningful clinical benefits.
Most promising application of PCCT is cardiac CT
Photon-counting CT can substantially reduce calcium blooming and metal streaking artifacts, allowing physicians to better visualize coronary artery lumens to evaluate patients with heavily calcified vessels, coronary stents and other metal artifacts from implantable electrophysiology devices, valves and other devices. The improved spatial resolution also enables the detection of much smaller coronary calcifications than previously possible. This can help improve accuracy with coronary calcium scoring (CAC) exams.
"An Agatston score of zero might become non-zero," McCollough explained. "Zero versus not zero is the sign that you do or don't have coronary artery disease. So seeing even smaller calcifications is a really big deal."
Because photon-counting systems directly measure photon energies, they also offer inherent spectral imaging capabilities. Radiologists can selectively emphasize or suppress materials such as iodine, calcium or metal, to improve tissue characterization and reduce artifacts from implanted devices.
The technology also inherently increases iodine contrast, allowing either lower contrast doses or improved image quality using standard contrast volumes.
"For the same sharpness, you get lower noise. If you're happy with the noise level you have at a certain sharpness, you can dial down the dose," she explained.
Despite these advantages, McCollough cautioned that facilities should not simply transfer protocols from conventional CT scanners onto photon-counting systems because they might not translate as intended.
"You don't want to drive this like your conventional scanner. You need to start from scratch," she explained.
Instead, users should begin with vendor-recommended protocols and gradually optimize them as they gain experience. Photon-counting CT takes advantage of sharper reconstruction kernels, higher spatial resolution and spectral imaging in ways that conventional CT protocols do not, she said.
Although photon-counting CT systems currently carry higher price tags than conventional scanners, McCollough said organizations should evaluate the technology based on its overall clinical value rather than equipment cost alone. Mayo Clinic uses photon-counting CT scanners as routine workhorse systems, though she acknowledged many health systems may initially reserve them for high-value applications at a central hospital. In addition to coronary CT angiography, she highlighted the clinical impact from clearer imaging for cochlear implants, musculoskeletal, lung and pancreatic imaging as areas where the technology provides notable benefits.
McCollough also said photon-counting CT could improve advanced post-processing applications, including coronary plaque analysis and CT-derived fractional flow reserve (FFR-CT) because of its clearer visualization of the vessel lumen. However, she added, imaging centers need to verify that software vendors have validated their algorithms on photon-counting datasets.
Looking ahead, she believes the technology is still in its early stages and more clinical experience is needed to fully understand the impact on patient outcomes to justify the extra cost. However, she said the improved noninvasive coronary imaging will likely reduce unnecessary invasive cardiac catheterizations, creating downstream savings that could help offset the higher capital investment costs.
"If you can save people going to the cath lab because you can show on the CT that they've got normal vessels, you are saving money for the health system and for the patient," she said. "The price tag of the scanner isn't the only financial consideration."
Dave Fornell has covered healthcare for more than 17 years, with a focus in cardiology and radiology. Fornell is a 5-time winner of a Jesse H. Neal Award, the most prestigious editorial honors in the field of specialized journalism. The wins included best technical content, best use of social media and best COVID-19 coverage. Fornell was also a three-time Neal finalist for best range of work by a single author. He produces more than 100 editorial videos each year, most of them interviews with key opinion leaders in medicine. He also writes technical articles, covers key trends, conducts video hospital site visits, and is very involved with social media. E-mail: [email protected]