Abstract: To produce an image of a component of part of an engineering structure such as an aero-engine using a positron emission tomography (PET) technique it is proposed to provide the component or part of the structure of interest with a surface coating containing a radioisotope labelling material. The radioisotope label may be provided by applying a film of lacquer, paint or the like containing the isotope, or the component etc. may be bombarded by suitably energetic ions in order to induce a reaction in which a selected isotope is produced.

Abstract: A representation of oil flow in a gas turbine engine is obtained by injecting a compatible radioactive isotope label into the engine oil flow and detecting the radiation emitted from within the body with detectors mounted outside the body to produce signals representative of the quantity and direction of the radiation; the detector output signals are compensated for attenuation on passing through the engine in accordance with attenuation signals derived from a representation of the spatial distribution of the engine and of its materials, and signals from non-viable directions are discounted. The compensated detector output signals are used to generate a number of focal-plane tomograms from which an image in a desired plane may be re-constructed. The image may be formed on a background of the engine in the relevant plane generated from the representation thereof.

Abstract: Carrier particles, e.g., of metal or metal oxide, are doped with a positron-emitting isotope and injected into fluid flowing in a body, such as a gas turbine engine. The positrons decay on coming to rest, giving two gamma rays which are detected, and a 3D image is built up. The particles are capable of stopping a portion of the positions before they escape from the particles into the surroundings; thus the gamma rays indicate more accurately the position at which the positron was emitted, and give a clearer image.