Single Photon Emission Computerised Tomography, a non-destructive imaging technique particularly employed for medical diagnoses, has been adapted and applied for the first time to the study of two-dimensional reaction rate distributions within lightly activated nuclear fuel pins. This paper describes the details of the experimental method in this new context. The tomographic equipment built to measure projections of reaction products distributed within fuel pins irradiated in the central LWR test zone of the zero-power research reactor PROTEUS is first described, together with the measurement method adopted. This is followed by the presentation of a procedure based on the use of well-chosen, smooth basis functions to reconstruct the within-pin distributions from the measured projections. Finally, typical results obtained are shown and discussed