Positron emission tomography of large rock samples using a multiring PET instrument

The technique of positron emission tomography (PET) is well established in the field of medical imaging. Non-medical applications have also been shown to be valuable in the measurement of dynamic chemical processes, specifically in the determination of the characteristics of small rock samples. Since rock is more dense than tissue, the problems of attenuation and scatter are accentuated. However, we are able to show that measurement of porosity in a large rock sample (21.5 cm diameter) is indeed practicable using three-dimensional (3-D) acquisition techniques. Due to multiple scattering of the photons in the rock and the cylindrical symmetry of the experiment, we measured a scatter distribution which is approximately homogeneous, allowing a correction for scattered radiation with a simple method. The problems of determining attenuation coefficients and applying a scatter correction makes absolute quantisation difficult. However, relative changers in porosity within the sample can be measured with a spatial resolution not appreciably different from that in water.