Lectures > Lecture 5

Lecture 5 by Tom Leadbeater, Dept. of Physics, University of Cape Town, South Africa.

Title: Positron emission imaging of flow dynamics: without all the hard math.

At UCT adapted positron imaging techniques are used to study the dynamics of physical flows and the motion of granules or fluids within engineering and scientific apparatus. In the context of Geoengineering, we have successfully measured flow of (hydrocarbon) fluids through rock cracks and fissures and have vast experience in validating computational models of flows relevant to the minerals industries.  

Conventional positron emission tomography (PET) is rarely used due to the requirements of measuring differential quantities such as velocity, a lack of ability (at UCT) to quantify the measurements through appropriate attenuation corrections, and a reluctance to engage with the difficult mathematics of the inverse problem. Instead, the positron emission detection technologies (adapted for our needs) are used to precisely measure the position of a single point-like source of positron activity, repeatedly at kHz rates. Provided the activity is entrained within the motion of the surrounding particles or fluids (achieved by the construction of a suitable flow-following tracer particle) the resultant trajectory is representative of the dynamic behaviour of the bulk media.  

From the measured tracer trajectory data, residence time distributions corresponding to the localised solids fraction (for a single phase), and differential quantities including velocity and acceleration can be determined pointwise throughout the imaging volume. Under certain conditions, the differential information encoded in the trajectory data can be integrated, forming images equivalent to the corresponding PET image, without the need for the usually applied corrections. Advantageously, as the single point can be located to a precision higher than the spatial resolution of the imaging device (through statistical approaches), the equivalent images are obtained at higher spatial resolution, therefore surpassing the fundamental limits in conventional PET.  

After outlining the basis of the techniques and the UCT facilities we will give detailed examples of the use of positron imaging in geological and minerals applications exemplifying both the conventional use of positron imaging in these fields and demonstrating the benefits of the unconventional approaches pioneered by our laboratory. We will briefly touch on the validation and benchmarking of these techniques using more conventional imaging including X-ray, MRI, and neutron radiography.

Biography: Dr Tom Leadbeater is a senior lecturer in the department of physics at the University of Cape Town. He would normally classify himself as a “general dogsbody of nuclear instrumentation”, although he has almost two decades experience in applying nuclear measurement and imaging techniques to problems in the characterisation of multiphase flows, where he has developed international recognition. He claims to have no working memory, and to be poor at mathematics, but is apparently proficient at applied physics.