New detectors for PET imaging

Monte Carlo simulation (Geant4) of a TMBi PET scanner
© EIMI/K. Schäfers

Project title: Characterization of the particle drift behavior of a novel PET detector concept using heavy dielectric organometallic liquids
Principal investigators: Christian Weinheimer, Klaus Schäfers
Project time: 11/2017 - 12/2018
Project code: FF-2017-19

In this project, physicists at the Cells-in-Motion Cluster of Excellence are aiming to develop new detectors for positron emission tomography (PET). Looking inside patients by means of whole-body imaging plays an important role in clinical and experimental medicine. PET equipment can capture labelled molecules with high spatial and temporal resolution, showing for example where centres of inflammation are located in the body or where diseases are developing. Today’s PET scanners can be improved even further, though. One of the reasons for this is that modern PET detectors always make a compromise: their aim is to resolve very fine structures – with smallest possible radiation doses for the patient and measuring times as short as possible – and at the same time provide exact information of labelled molecules. The CiM researchers are now looking to see whether other detectors can do a better job with this compromise.

Today’s detectors normally consist of so-called scintillation crystals which can capture gamma energy and locate its source. The CiM researchers are now testing whether using PET detectors with a liquid known as TriMethyl Bismuth (TMBi) provides any advantages over those using conventional crystals. Researchers in France have recently shown that detectors can be developed with TMBi which allow a significantly better position reconstruction by measuring in addition to the ionisation the so-called Cherenkov radiation. The challenge, however, is to produce TMBi of such extreme purity that measuring is actually possible.

This is exactly where the research project – headed by medical physicist Prof. Klaus Schäfers and particle physicist Prof. Christian Weinheimer – comes in. In three sub-projects, the two researchers intend to analyse the properties of a detector on the basis of TMBi. To this end, they first want to incorporate a special purification for TMBi by technologies that they also use in the XENON1T experiment (distillation, molecular filters and ultra-high vacuum technology). After this, they aim to test a first drift chamber by using the principle of an ionization chamber and analysing the drift behaviour of the electrical charges generated in the detector. As soon as the principle is seen to function, the researchers want to develop a liquid-filled detector prototype to be used in PET.

This project provides the basis for further developments of larger-scale whole-body PET detectors, or for a new generation of small-animal PET systems. This, in turn, is the basis for new applications in molecular imaging.