We achieved major developments in the PEPT technique in the last 25 years. We now have the ability to use a vast range of tracers, increase experimental speeds whilst ensuring accurate detection and added a modular camera for unusual geometries and increased resolution.
When using the method of indirect activation to fabricate tracer particles, which is necessary for any particle ≤1mm, the fluorine-18 is adsorbed onto the surface of the particle. Fluoride ions are incredibly reactive, as such if the tracer particle is exposed to aqueous solution (most commonly water) the fluoride ions tend to leach from the particle and contaminate the system. If the tracer is to be used in wet conditions it must first be sealed with an insoluble, non-porous coating, this is generally done using acrylic paint. This process is cumbersome for smaller particles and innovative coating methods to overcome this barrier are a major focus for the Centre.
Tracer Particle Size
There is a demand for very small tracer particles that are ≤100µm. This is not impossible but rather the process is limited by the difficulties of handling such particles. 50µm has been achieved in previous studies and the most likely limit due to the capacity of the particle to hold the activity is 10µm. Working towards using very small particles is a primary aim for the Centre.
PEPT will never be able to separate the tracks of two particles which are closer together than the intrinsic spatial resolution (w) of the positron camera, which for most systems is around 6mm so PEPT is unlikely to reveal details of inter-particle collisions. Generally speaking to study different components of a mixed system, it is better to do this sequentially labelling each component in turn. However there is sometimes the desire to track multiple particles within the same system though this is seldom attempted within the Centre.
The algorithm used for PEPT can be extended to track multiple particles provided they remain separated by 2w. This has been done successfully with up to four particles but is computationally intensive. Further research is essential to comprehensibly extend the multiple-particle tracking capabilities within PEPT.