Advances in the world of physics often quickly lead to advances in the world of medical diagnostics. From the moment Wilhelm Röntgen discovered X-rays he was using them to look through his wife’s hand.
A lot of the physics principles at the foundation of MAX IV are also at the foundation of medical imaging technologies such as nuclear magnetic resonance imaging, x-ray computed tomography and positron emission tomography.
Positron emission spectroscopy is more commonly known as PET imaging. It’s a method used to study metabolic processes in the body as a research tool but also to diagnose disease. An important use today is in the diagnosis of metastases in cancer patients, but it can also be used to diagnose certain types of dementia.
In PET, a positron-emitting radionuclide is injected into a patient and travels around the body until it accumulates somewhere, depending on the chemical composition. For example, the fluorine-18 radionuclide when bound to deoxyglucose accumulates in metabolically active cells which is useful for finding metastases. The radionuclide is unstable and emits positrons which is the antimatter equivalent of an electron. When a positron and an electron inevitably meet, they annihilate one another, producing two pulses of gamma radiation traveling in opposite directions. By placing a detector around a patient, it is possible to measure the gamma radiation and convert the signal into something that can be more easily measured. These detectors are made up of materials known as scintillators which take high energy radiation and emit lower energy radiation that can be detected using fast photodetectors – photomultiplier tubes.
A team of researchers visiting FinEstBeAMS from the University of Tartu study scintillators and want to understand the fundamentals of this process better in order to improve their performance. Marco Kirm, the lead investigator explained that the problem with the scintillators used today is that they are too slow for high-resolution TOF PET imaging. In today’s PET machine, although it’s possible to precisely identify the direction that a gamma ray was traveling, the time resolution is not high enough to determine the distance that it traveled. With better time resolution of scintillators, it would be possible to determine the distance by time-of-flight (TOF) technique which relies on the time difference of the arrival of a pair of gamma rays detected by scintillators at opposite sides of the detector. The goal is to achieve a 10 picosecond time resolution (Biograph SIEMENS provides currently 250 picoseconds), which corresponds to 1.5 mm spatial resolution and thus, better image quality. This would allow medical staff to determine the location of the annihilation event more precisely and know where the metastases are. As a result better treatment of patients will be achieved.
Marco Kirm is currently performing experiments at FinEstBeAMS to develop scintillators that operate using ultrafast intrinsic emissions. This novel concept may allow technological breakthroughs which would give millimetre resolution in the TOF PET scans compared to the centimetre resolution that exists today. He was very impressed with the time-resolution at FinEstBeAMS, as short as 40 picosecond pulses generated by MAX IV storage rings, as well as the available energy range of the FinEstBeAMS beamline which is important for proper characterisation of new scintillator materials. Kirm also expressed a strong interest of research team that in the future, when they need even shorter pulses to study processes for detectors with higher sub-picosecond time resolution, it would be great to use the FemtoMAX beamline at MAX IV, commenting that it is extremely useful to have all of these experimental stations in the same facility.