Positron emission tomography (PET) is a powerful functional imaging technique widely employed for medical diagnostics and research. Although it is most extensively used in clinical oncology, PET is also used for brain diagnostics - e.g., in the study of Alzheimer’s disease - and cardiology. PET scans can be used to diagnose Parkinson’s disease, multiple sclerosis, transient ischemic attack, ALS, Huntington’s disease, stroke, and other nervous system disorders.
In PET, a radioactive tracer that emits low-energy positrons is injected into the subject, and with an appropriate choice of active molecule, collects at sites of interest, typically those corresponding to the disease.
A recent innovation has been the introduction of time of-flight PET. In TOF-PET, the number of ghost intersections, which scales as the square of the number of events, is greatly reduced since the timing information can be used to infer where along the line segment the annihilation occurred.
Traditional PET scanners employ inorganic crystal scintillators - e.g. LYSO - and photomultipliers (PMTs) for gamma-ray detection. In more recent designs, PMTs, which are bulky and expensive, have been replaced by silicon photomultipliers (SiPMs), which reduce the size, cost, and complexity of the readout system. SiPMs have high quantum efficiency and excellent timing resolution.
Within the DarkSide collaboration a new approach to TOF-PET has been developed that is based on liquid argon (LAr) and SiPMs. LAr is an excellent scintillator. At 40,000 photons/MeV its light yield is much larger than that of the scintillating crystals used in standard scanners. Preliminary simulations indicate a resolution of 0.2 cm for the width 2 of the LOR and an overall 0.2-cm resolution following filtered back projection analysis; they also indicate the possibility of reaching sub-cm resolution along the LOR. With these improvements, a better than tenfold reduction of the dose required for a PET scan would be possible.
A significant reduction of the high dose currently required for PET scans would open up new possibilities for the screening of cancer patients. It would enable more frequent PET scans in adult patients and the adoption of PET scans for pediatric cancer patients. It could even make PET brain scans of healthy patients possible, which would enable the study of accumulation of proteins and toxins suspected of being responsible for the onset of Alzheimer and Parkinson diseases.
On these bases, the L’Aquila workshop intends a threefold aim:
• to highlight the state of the art;
• to gather researchers from different disciplines and high-tech industries;
• to launch an action plan.