In-field examination of root-microbial interactions using SPECT imaging

Abstract

A Compton camera SPECT imager was simulated using GEANT4 to determine its feasibility for imaging roots and microbes within soil. The simulated detector was composed of a polystyrene scatter detector (as an approximation of plastic scintillator) and a GAGG scintillator crystal absorber detector. Various detector configurations were explored. It was found that the detector has reasonable e ciency up to depths of 15 cm to 35 cm depending on the saturation of the soil for 511 keV photons. The optimal spacing between the scatter and absorber detectors was found to be 5 cm or less. It was also found that a scatter detector thickness of 5 cm will have a higher e ciency (by around 0:6%) than a thickness of 2 cm, but a thicker scatter detector will make the detector less portable and will also deteriorate the resolution of the detector. The calculated scattering angles using the energy deposited within the detector were compared to the truth angles that were calculated using initial momentum and scattered direction. The reconstructed angles from energy deposition appear to be similar to the true values. The energies of the scattered photons and scattered electrons for di erent scattering angles also appear to match the expected values quite closely. The Compton camera method appears to be quite promising for imaging near surface in-field roots and microbes within soil.