the bone marrow as part of routine scanning while adding morphological details.
Source: Courtesy of University Hospital Pilsen, Pilsen, Czech Republic
Traditional CT scanning has operated like a camera with old-style film – capturing the overall intensity of X-rays passing through the body. Photon-counting CT represents a fundamental shift, working more like a modern digital camera that captures each particle of light individually.
This fundamental change in how we capture medical images represents one of the most significant advances in CT technology since its invention in the 1970s.
The technology employs special crystals made of cadmium telluride that can detect and count individual X-ray photons as they pass through the body. Think of it as the difference between measuring rainfall by looking at how wet the ground is (traditional CT) versus counting individual raindrops as they fall (photon-counting CT).
Each X-ray photon creates a tiny electrical pulse when it hits the detector. The size of this pulse corresponds to the photon’s energy level – similar to how different colours of light have different energy levels. This energy information, previously lost in conventional CT, provides crucial details about the tissues the X-ray passed through.
The detector elements in photon-counting CT are also much smaller than traditional systems. Using the rainfall analogy, it’s like having many small cups to catch rain rather than a few large buckets. This increased precision leads to sharper images with finer detail.
A key advantage is the system’s ability to differentiate between materials based on how they affect X-rays of different energies. For example, it can better distinguish between calcium in bones and iodine used as a contrast agent in blood vessels – a task that challenged conventional CT scanners.
The technology eliminates electronic noise – unwanted background signals that can blur images – by only counting X-ray photons above a certain energy threshold. This is similar to how noise-cancelling headphones filter out background noise to deliver clearer sound.
The result is clearer images with up to 40% less radiation exposure and contrast medium use. This makes CT scanning available to more patients, including those who previously couldn’t undergo scans due to radiation concerns or kidney problems that made contrast agents risky.
The enhanced capabilities of photon-counting CT are opening up new possibilities in medical imaging. The technology is particularly valuable for:
- Cardiac imaging: Allowing clear visualisation of heavily calcified coronary arteries and stents that were previously difficult to assess
- Lung imaging: Providing extremely detailed views of small airways and blood vessels
- Oncology: Enabling better characterisation of tumours and monitoring of treatment response
- Orthopaedics: Offering unprecedented detail of bone microstructure and small fractures
- Paediatric imaging: Reducing radiation exposure while maintaining high image quality
- Emergency care: Allowing whole-body trauma assessment in under three seconds with exceptional detail
