Photon-counting detectors advance CT technology

October 04, 2022
CT X-Ray
From the October 2022 issue of HealthCare Business News magazine

By Kaitlyn Wilkie

Improving image quality and dose efficiency have always been top priorities in the development of new imaging systems to improve diagnostics and patient care. Photon-counting detectors (PCDs) are the newest major advancement for CT systems. These detectors have already been used for several years in nuclear imaging.

In September 2021, Siemens Healthineers received FDA approval for the NAEOTOM Alpha, the first photon-counting CT system cleared for the U.S. market. Neurologica received FDA approval for its photon-counting CT system, the OmniTom Elite with PCD, in March 2022. What makes these systems unique among other CT systems on the market is the PCD, which allows for spectral imaging. Conventional CT systems use third-generation digital radiography (DR) detectors. The PCD’s advantages are its ability to provide increased spatial resolution, decrease electronic noise, and reduce radiation exposure compared to DR detectors.

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How PCDs operate, and their benefits
The DR detectors first convert X-ray photons into visible light, which is then converted into electronic signals. These signals are measured by the energy of the detected photon, with high-energy photons creating stronger signals and low-energy photons creating weaker signals. The electronic signals are then converted into a digital image. The DR detector integrates all these signals and does not provide any information regarding the individual photons detected. Due to this integration of signals, high-energy photons contribute more to the resulting image than low-energy photons and the integration also provides information that is not useful (the electronic noise shown in an image).

In comparison, PCDs do not require the conversion of X-rays to visible light and do not integrate all the electronic signals together. The X-ray photons are directly absorbed by a semiconductor and create electronic signals. These detectors count the number of individual photons with energy that is over a set energy threshold, and each detected photon is compared to the energy threshold. The electronic signal from each photon is proportional to that photon’s energy.

Photon-counting detectors can produce better image quality by providing increased spatial resolution, decreased electronic noise, and can also reduce radiation exposure compared to DR detectors. For CT systems with DR detectors, low-dose scans tend to have noticeable electronic noise and artifacts. A PCD will interpret these signals on a low-dose scan as a low-energy photon, and if that energy is below the energy threshold, the signal will be excluded. Less electronic noise on images allows a photon-counting CT system to provide the same or better image quality as a conventional CT system using a lower dose. Also, eliminating the need to convert X-rays to light before converting to an electronic signal makes the imaging process quicker, reducing the patient’s radiation exposure. The capture of information for each detected photon as well as the speed of this process results in images with improved resolution. This technology will be highly beneficial for cardiac imaging and other exams that require fast scans, or for exams where details of small structures are difficult to capture using a conventional CT system.

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