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Photon Detector Breathes New Life Into Conventional CT Imaging

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BETHESDA, Md., Aug. 16, 2022 — The Food and Drug Administration has cleared a photon-counting detector (PCD)-based CT system for clinical use. The system, which has been under development by a team at the Mayo Clinic for a decade, offers an alternative approach to the conversion of x-rays to electrical signals.

Among the benefits of the PCD-CT system, according to its developers, are a reduction in noise compared to traditional CT images, as well as improved spatial resolution.

Cynthia McCollough, director of Mayo Clinic’s CT Clinical Innovation Center, led the work with her team. Though CT imaging has been an immense clinical asset for diagnosing many diseases and injuries, since its introduction into the clinic in 1971, the way that the CT detector converts x-rays to electrical signals has remained essentially the same, according to a release from the National Institutes of Health’s National Institute of Biomedical Imaging and Bioengineering (NIBIB).

A CT scan is obtained when an x-ray beam rotates around a patient, which allows x-rays to pass through the patient. As the x-rays leave the patient, a picture is taken by a detector and the information is transmitted to a computer for further processing.

In contrast, the newly cleared PCD-CT system bypasses a process that requires more than one step. “The photon-counting detector uses a one-step process where the x-ray is immediately transformed into an electrical signal,” McCollough said.
Conventional chest CT image (left) of the human airways compared to the new and improved PCD-CT system. The image produced with the PCD-CT system showed better delineation of the bronchial walls. Preliminary studies showed that the PCD-CT system allowed radiologists to see smaller airways than with standard CT systems. Courtesy of Cynthia McCollough, Mayo Clinic.
Conventional chest CT image (left) of the human airways compared to the new and improved PCD-CT system. The image produced with the PCD-CT system showed better delineation of the bronchial walls. Preliminary studies showed that the PCD-CT system allowed radiologists to see smaller airways than with standard CT systems. Courtesy of Cynthia McCollough/Mayo Clinic.
In the two-step CT process, the energy of the x-ray is not recorded, but with the one-step process, individual x-rays are recorded along with their energy level. As the x-rays rapidly enter the detector, they are counted and sorted according to their energy, which helps identify different materials such as soft tissue, bone, and iodinated blood more easily.

This specific type of imaging is called multi-energy CT imaging. According to McCollough, dual-energy CT requires specialized equipment and is limited to two energies. The photon detector allows the imaging process to start with more “buckets,” she said, into which to sort x-ray energies.

The capability then gives a user the ability to better depict the differences in materials.

Clinical studies showed up to 47% noise reduction with the PCD-CT system. It also lowered the amount of contrast agent needed for CT imaging — conventional CT imaging is effective at visualizing blood vessels and tumors, but contrast agents must be used. Since there is more signal from the contrast agent with the PCD-CT system, study participants required 30% less contrast agent to achieve the same image quality as with conventional CT systems.
Conventional CT (left) image of an inner ear prosthesis compared to PCD-CT system. The structures of the inner ear are composed of tiny bones that are difficult to visualize. Clinicians can get much clearer inner ear images with PCD-CT, which could help with cochlear implants for children. Courtesy of Cynthia McCollough, Mayo Clinic.
Conventional CT (left) image of an inner ear prosthesis compared to PCD-CT system. The structures of the inner ear are composed of tiny bones that are difficult to visualize. Clinicians can get much clearer inner ear images with PCD-CT, which could help with cochlear implants for children. Courtesy of Cynthia McCollough/Mayo Clinic.
Though contrast agents are safe for most patients, it would be best to give a lower dose to some patients if possible.

Studies also showed that the system achieved the best reported resolution for a clinical CT system. “The significantly improved resolution and increased signal are the groundbreaking advantages this CT system has over standard CT,” said Behrouz Shabestari, director of NIBIB’s division of Health Informatics Technologies.

“This is the first major imaging advancement cleared by the FDA for CT in a decade,” Shabestari said. “The impact of this development will be far-reaching and provide clinicians with more detailed information for medical diagnoses.”

McCollough and her team worked with Siemens Healthineers in Forchheim, Germany, and Siemens Medical Solutions in Malvern, Pa., for the last 10 years. Siemens had been working on a prototype PCD-CT system, and with McCollough’s funding from NIBIB the team was able to start scanning patients under Institutional Review Board approval. Over 1100 patients were scanned in these studies, first on a conventional CT system and then with the new PCD-CT scanner, to show the advantages of the new system.

Research on the system was published in Physics in Medicine & Biology (www.doi.org/10.1088/1361-6560/ac155e), Radiology (www.doi.org/10.1148/radiol.212579), and the American Journal of Neuroradiology (www.doi.org/10.3174/ajnr.A7452).

Photonics.com
Aug 2022
medicalimagingbiomedical imagingBiophotonicsphoton sensingphoton sensorCTsensors and detectorsAmericasMayo ClinicNIBIBdiagnosesdiagnosticsclinicalInformaticsx-ray

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