Members of the Proteus team, led by Proteus Co-Investigator Prof. Robert R. Thomson and Postdoctoral Researcher Dr Mike Tanner (Heriot Watt University), have completed the first steps in developing a camera that can ‘see’ through the human body. The camera is designed to help doctors track medical tools that are inserted into a patient in order to investigate a range of internal conditions. The new device is able to detect sources of light from inside, such as the illuminated tip of the endoscope’s long flexible tube. Until now, it has not been possible to track where an endoscope is located in the body in order to guide it to the right place without using X-rays or other expensive methods
Usually, light scatters or bounces off body tissue rather than travelling straight through. While this can reveal a wealth of information about internal structure it makes conventional through-tissue imaging practically impossible, as the scattering results in a blurred image and loss of information.
Taking advantage of single photon detection solves this problem. Not only does it give the camera a high sensitivity towards observing the small number of photons passing through tissue, but it also records the time they take to arrive onto the sensor. Light which is highly scattered travels a longer distance and therefore takes more time to reach the camera. Conversely, a small fraction of the light scatters relatively little and travels in a nearly direct (or ballistic) path to the camera, arriving much sooner. Operating the camera in a mode similar to a video camera, the early arrival of this so-called ‘ballistic light’ can be separated from the later, scattered light – a concept known as ‘ballistic imaging’. By detecting the first photons, it is possible to determine where the light source is located inside the body.
The prototype demonstrations have already shown that a point light source can be located through tissue approximately 20 cm thick under normal lighting conditions using the ballistic imaging technique. The camera will be further developed to enable clinicians to locate inserted medical devices at the bedside, visualising both the tip and length of the device.