Monte Carlo simulations of GeoPET experiments: 3D images of tracer distributions (¹⁸F, ¹²⁴I and ⁵⁸Co) in Opalinus Clay, anhydrite and quartz

Understanding conservative flow and reactive tracer transport processes in soils and rock formations requires quantitative visualization methods in 3D+t. After a decade of research and development we established the GeoPET as a non-destructive method with unrivalled sensitivity and selectivity, without physical and chemical impact, and with due spatial and temporal resolution by applying Positron Emission Tomography (PET), a nuclear medicine imaging method, to dense rock material. Requirements for reaching the physical limit of image resolution of nearly 1 mm are a high-resolution PET- camera, like our ClearPET scanner (Raytest), and appropriate correction methods for scatter and attenuation of 511 keV - photons in the dense geological material, which are by far more significant than in human and small animal body tissue (water).
Here we present data from Monte Carlo simulations, considering all involved nuclear physical processes of the measurement with the ClearPET-system, that allows us to quantify the sensitivity of the method and the scatter fractions in geological media as function of material (quartz, Opalinus clay and anhydrite compared to water), PET isotope (18F, 58Co and 124I), and system parameters. Comparison of simulated data with measured images indicates the limits of the method and provides procedures for image quality improvement, including a scatter correction method by subtracting projections of simulated scattered coincidences from experimental data sets prior to image reconstruction with an iterative reconstruction process.