Experimental analysis of high-speed gamma-ray tomography performance

High-speed gamma-ray tomography (HSGT) based on multiple fan-beam collimated radioisotope sources has proved to be an efficient and fast method for cross sectional imaging of the dynamics in different industrial processes. The objective of the tomography system described here is to identify the flow regime of gas/liquid pipe flows. The performance of such systems is characterized by the spatial resolution, the speed of response and the measurement resolution of the attenuation coefficient. The work presented here is an experimental analysis of how the measurement geometry and the reconstruction method affect the error of the reconstructed pixel values. These relationships are well established for medical x-ray tomography where high intensity x-ray tubes are used as sources. For radioisotope sources, however, the radiation intensity is limited, which causes the measurement uncertainty, i.e. the Poisson noise, to be considerably higher. In addition, the influence of scattered radiation is more severe in a multiple source radioisotope system compared to that of x-ray systems. A computer-controlled flexible geometry gamma-ray tomograph has been developed to acquire experimental data for different fan-beam measurement geometries, and these data have subsequently been used for image reconstruction using seven different iterative image reconstruction algorithms. The results show that the reconstruction algorithms perform cross sectional images with different quality and that there is virtually nothing to be gained by using more than seven sources for flow regime classification of multiphase pipe flow consisting of gas, oil and water.