Gamma sensor technology

In oncology, radioactive tracers are often used, which attach themselves to tumour cells. This makes them easy to locate, for example in a PET-CT or SPECT scan. However, it is difficult to find these lesions during surgery, as they are visually and tactilely almost indistinguishable from the surrounding tissue. Gamma cameras can be used to detect the tumours, but without anatomical image information.

At IMT, we are researching ways to localise radioactively labelled cells in ultrasound images. Our approach is to work with photodiodes that are as simple and inexpensive as possible.

The aim of this research is to develop a low-cost device that can be used endoscopically during surgery to find radioactively labelled tumour cells. To this end, a suitable basic sensor type in the form of a photodiode was identified, a specific sensor was selected and the entire signal processing chain was examined in detail. The device constructed on the basis of the findings was then characterised using, among other things, a 137Cs radiation source, whose activity lies in the range of labelled degenerated lymph nodes.

It was found that it is possible to build a suitable detector with an efficiency of around 1.2% for a price in the lower double-digit euro range. The sensor head fits into a cylinder with an outer diameter of 12 mm and a length of 25 mm. Further findings relate to the relevant parameters for the specific selection of a PIN photodiode, which is used here as a sensor, and to numerous possibilities for improving the device.

The work is being continued in the AiF-funded international research project ULTRACLEAR.

Based on simple photodiodes, the IMT has been working on the development of a detection concept that uses a small number of gamma detectors to achieve three-dimensional localisation of a gamma radiation source and combines the results with ultrasound data.
 A localisation algorithm was developed that determines robust position estimates from the sensor measurements despite measurement noise. To this end, an optimised arrangement of six sensors was determined for which the localisation algorithm achieves the highest possible accuracy. This was predicted in simulations and then validated using a test setup. The test setup uses near-infrared (NIR) as a substitute for gamma radiation in order to reduce development time. With this test setup, an NIR radiation source with unknown radiation power could be localised at a distance of up to 6 cm in front of the sensor system with a spatial deviation of 3.64±1.66 mm on average. In addition, a visualisation concept was developed that combines the sensor data from the developed sensor system and an ultrasound system and displays it at a rate of 3 images per second.

• Mayer Th, Pohlner G, Starflinger J, Pott PP, Combined Gamma radiation source detector and Ultrasound Imaging System: proof of concept and first results, Computers in Biology and Medicine, 19:193:110378, 2025 10.1016/j.compbiomed.2025.110378
• Sorysz J, Heryan K, Krombach G, Friebe M, Pott PP, Novel and Inexpensive Gamma Radiation Sensor – Initial Concept and Design, International Journal of Computer Assisted Radiology and Surgery, 18, 1987–1990, 2023 https://doi.org/10.1007/s11548-023-03003-z
• Behling M, Wezel F, Pott PP, Miniature low-cost γ-radiation sensor for localization of radioactively marked lymph nodes, Part H: Journal of Engineering in Medicine, 2021 https://doi.org/10.1177/09544119211058918