CEA-Leti in France has designed a new generation of PCDM to be integrated into an X-ray CT scanner prototype. The PCDM module has been integrated into a prototype scanner from Siemens Healthineers and shown increased spatial resolution, reducing X-ray exposure to patients, improving image quality by lowering image noise and artifacts, and by distinguishing multiple contrast agents.
X-ray PCDMs based on cadmium telluride (CdTe) allow simultaneous acquisition of high-spatial-resolution and multi-energy images. Higher spatial resolution improves image quality by using a small-pixel size detector, while image noise can obscure features, and artifacts can mimic them. Detecting the energy of all the photons on the sensor provides colour images and allows a precise determination of the atomic number of any chemical elements present in the body.
“The successful early collaboration with CEA-Leti allowed Siemens Healthineers to prototype what the med- tech company sees as the future of detector modules for whole-body CT,” said Jean-Michel Casagrande, the project manager for medical X-ray imaging at CEA-Leti.
X-ray CT scanners use computer-processed combinations of many X-ray measurements taken from different angles to produce cross-sectional images of scanned objects. Current X-ray CT scanners produce images with energy-integrating detectors (EIDs) where the X-ray photons are first converted into visible light using scintillator material, then visible photons produce electronic signals using a photodiode. PCDMs instead directly convert X-ray photons into electronic signals with a higher conversion yield using CdTe pxiels.
While an EID registers the total energy deposited in a pixel during a fixed period of time, a PCDM counts each photon. This improves the contrast-to-noise ratio of the image, and the energy classification of the detected photons can be used to produce a colour image that allows a precise determination of the atomic number of any chemical elements and a distinction of multiple contrast agents present in the body.
The higher spatial resolution from the smaller pixel size generates clearer images of very-fine structures, such as small airways in the lungs, trabeculae in bones, and thin wires in coronary stents than current scanner technology.
Next: Integrating the X-ray sensor
“The idea of Siemens Healthineers to integrate PCDMs in the future generation of X-ray CT scanners was new and no available technology existed when CEA-Leti began working on this,” said Loick Verger, industrial partnership manager for X-ray imaging at CEA-Leti. “The technical challenge – low noise at a very high counting rate, two energy classifications, and sufficient maturity to be integrated in an X-ray CT scanner – was tremendous.”
CEA-Leti used its simulation tools to design the geometry of the detector, chose a semiconductor based on CdTe, designed the electronic readout circuit, and then was able to propose a reliable CdTe electronic assembly technology.
Researchers at the Mayo Clinic in the US have evaluated Siemens Healthineers’ photon-counting detector system’s performance in phantoms, cadavers, animals, and humans. “Images of more than 300 patients produced with this technology consistently demonstrated that the theoretical benefits of this type of detector technology yield a number of important clinical benefits,” said Cynthia McCollough, professor of Medical Physics and Biomedical Engineering at the Mayo Clinic.
“Publications by our research team have shown improved spatial resolution, decreased radiation or iodine contrast dose requirements, and decreased levels of image noise and artifacts,” she said. “Additionally, the ability to simultaneously acquire multiple 150-micron-resolution datasets, each representing a different energy spectrum, is anticipated to lead to new clinical applications.”
Research papers showed it was possible to use the higher resolution of the sensor to reduce the radiation dose by up to 85 percent.
“It is extremely rewarding to see the exquisite images that can be made using the technologies of the detector module that we developed,” said Verger. “Seeing for ourselves the clinical benefits of all our R&D efforts motivates our entire team to continue the development of cutting-edge technologies for improving healthcare.”
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