IOP PUBLISHING MEASUREMENT SCIENCE AND TECHNOLOGY Meas. Sci. Technol. 19 (2008) 094004 (10pp) doi:10.1088/0957-0233/19/9/094004 Positron imaging techniques for process engineering: recent developments at Birmingham D J Parker, T W Leadbeater, X Fan, M N Hausard, A Ingram and Z Yang University of Birmingham Positron Imaging Centre, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK Received 13 January 2008, in final form 5 June 2008 Published 24 July 2008 Online at stacks.iop.org/MST/19/094004 Abstract For over 20 years the University of Birmingham has been using positron-emitting radioactive tracers to study engineering processes. The imaging technique of positron emission tomography (PET), widely used for medical applications, has been adapted for these studies, and the complementary technique of positron emission particle tracking (PEPT) has been developed. The radioisotopes are produced using the Birmingham MC40 cyclotron, and a variety of techniques are employed to produce suitable tracers in a wide range of forms. Detectors originally designed for medical use have been modified for engineering applications, allowing measurements to be made on real process equipment, at laboratory or pilot plant scale. This paper briefly reviews the capability of the techniques and introduces a few of the many processes to which they have been applied. Keywords: PET, PEPT, radioactive tracers (Some figures in this article are in colour only in the electronic version) 1. Introduction Over the last 25 years, positron emission tomography (PET) has been widely developed as a functional imaging technique in medicine. Detailed information on metabolism is obtained by mapping the concentration of a radioactively-labelled species as a function of time following introduction. The radioisotope used undergoes β + decay, emitting a positron which then annihilates with an electron to produce two 511 keV γ -rays which are emitted almost exactly back-to- back, 180 ◦ apart to within about 0.5 ◦ . A PET scanner, comprising rings of hundreds of small γ -ray detectors operating in coincidence, is used to detect these back-to-back γ -ray pairs. The detected events are binned into histograms (‘sinograms’) representing the total tracer activity along each measured line of response (LOR), from which (after correcting for effects such as attenuation and deadtime) a quantitative map of tracer concentration is obtained by filtered backprojection or iterative reconstruction. The spatial resolution is primarily defined by the size of the individual detector elements and is around 5 mm in the latest generation of clinical PET scanners, while some systems designed for small animal imaging achieve resolution of around 1 mm. Meanwhile the University of Birmingham Positron Imaging Centre has pioneered the use of positron-emitting tracers for studying flow in physics and engineering. The first application was to investigate lubrication of aero-engines in collaboration with Rolls Royce, for which a purpose-built ‘positron camera’ was developed by the Rutherford Appleton Laboratory and commenced operation in 1984 [1]. Shortly afterwards the Birmingham group developed the technique of positron emission particle tracking (PEPT) [2] by which a single tracer particle can be accurately tracked as it moves within the field of view of the positron camera. Whereas measurement of a PET image is relatively slow, requiring acquisition of millions of events, if only a single positron- emitting source is present its location can be determined very quickly by triangulation of only a small number of events (typically around 100 are used), permitting tracking of a fast moving tracer. The original Birmingham positron camera comprised a pair of large area multi-wire proportional chambers operating in coincidence. Its use for PET and PEPT studies of 0957-0233/08/094004+10$30.00 1 © 2008 IOP Publishing Ltd Printed in the UK