Positron emission tomography (PET) is a medical imaging modality which measures the three-dimensional distribution of a positron emitting substance inside a patient or animal. Before such a PET scan, the patient or animal is injected with a biologically active molecule which contains a radioactive positron-emitting isotope (the tracer).
The positron annihilates with an electron from the patient’s body, thus producing two photons which propagate through the body in opposite directions. These photons are detected outside the body using a ring of PET detectors. From the detection points a line of response can be assumed along which the annihilation took place. With this information a quantitative cross-section image of the radiotracer distribution inside the patient's body can be reconstructed. Despite the quantitative character of PET images, they lack detailed anatomic information. To overcome this problem other imaging modalities like MRI are used to get anatomic information and to fuse both images.
Our group developed the world’s first small-animal PET/MRI insert on basis of fully digital silicon photomultipliers (dSiPM). A small-animal high resolution PET scanner uses crystal scintillators with a very small pitch. Light-sharing over a larger area of the sensor tile is employed to identify the crystal rod in which the gamma scintillated. Photon counts and time stamps are collected from several sensors and have to be combined to obtain the location, time and energy of the gamma. We are working on the development of calibration methods and crystal identification algorithms. Additionally, we are investigating new scintillator geometries and concepts for a possible future generation of PET scanners. For these development of future detector concepts, simulation studies and small proof-of-concept lab setups go hand in hand.