Image of a young female patient lying in a CT machine waiting to have a scan, such as photon-counting CT. Two healthcare professionals can be seen monitoring the scan through a window in the background of the image.
Credit: Sergey Ulanov/Getty Images

Research carried out in Germany and the Netherlands shows photon-counting computed tomography (CT) can be used successfully in the clinic to provide detailed lung scans that require less radiation than standard CT.

“Photon-counting CT is an innovation in CT technology. It involves the direct conversion of incoming photons into electrical charges that are subsequently transferred into a current that is proportional to the energy of the incoming photon,” explain Hoen-oh Shin, a senior physician at the Institute for Diagnostic and Interventional Radiology at the Hannover Medical School, and colleagues in the journal Radiology.

“In addition to improved spatial resolution because of the smaller size of detector pixels and options for spectral imaging, photon-counting CT offers an increased signal of contrast enhancement and better signal-to-noise ratio at lower doses because of the reduction of electronic noise.”

Although this new technology, requiring advanced software but no additional hardware, is now becoming more widely available, data on the routine use of photon-counting CT in the clinic without additional equipment is needed for further evaluation.

In this study, patients needing a CT scan of their lungs were enrolled between late 2021 and June 2022. Those enrolled had two photon-counting CT scans, one when inhaling and one when exhaling. A number of different parameters were measured including: lung structure, ventilation of the lung, and vasculature and perfusion of the parenchyma, which contains the gas-exchanging alveoli.

Overall, 196 patients aged 63 years on average (106 male) were included in the study.  In 85% of this group (n=166), all the suggested parameters were successfully achieved.

“The improvement in the contrast-to-noise ratio and spatial resolution of the pulmonary blood volume images was substantial,” said study senior author Shin in a press statement.

“In my opinion, the most important advantage is the significantly improved spectral resolution, which enables new applications such as functional imaging of the lungs with CT.”

Photon-counting CT can help to better diagnose and predict progression of different lung conditions. For example, it can highlight emphysema and perfusion defects in patients with chronic thromboembolic pulmonary hypertension, which is caused by blood clots in the lungs that are difficult to clear.

Shin and colleagues have used their photon-counting CT protocol in interstitial lung disease, a group of conditions causing lung scarring, and have also used it to scan the lungs of COVID-19 patients.

“With the proposed protocol, we have also been able to answer many other questions related to post-COVID-19 condition, such as the detection of acute and chronic pulmonary emboli on CT angiography, and we are currently investigating whether perfusion changes can be quantified in microvascular damage or inflammatory areas,” said Shin.

The team concluded that while the results are promising, more research is needed on the impact of position and depth of breathing of the patients being scanned. They also call for more work to determine how reproducible the results are.

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