Dose optimization of Cd for direct imaging of Cd uptake from culture to root

Suzui, Nobuo; Kawachi, Naoki; Ishii, Satomi; Yamazaki, Haruaki; Fujimaki, Shu

In an effort to understand the mechanism of cadmium (Cd) accumulation in grains, we have conducted noninvasive imaging of Cd in intact rice plants using a positron-emitting tracer imaging system (PETIS) and Cd. Recently, we attempt to obtain the serial images of Cd in underground parts, i.e., roots and culture solutions. In this case, the dosage of Cd should be optimized because the presence of high radioactivity in the field of view (FOV) of PETIS induces the counting loss of annihilation -rays, resulting the underestimation of radioactivity. Thus, in this study, we determined the optimal dosage of Cd for direct imaging of Cd uptake. Cd solution was infused into a flat "phantom" container. This phantom was measured by PETIS for 24 hours while the radioactivity of Cd in FOV decayed to 1/13 of its initial value. In the Cd phantom, the counting loss was diminished after the radioactivity of Cd in FOV decayed to below 8 MBq. On the other hand, we should allow some degree of counting loss at the initial period of imaging in order to obtain the images for kinetic analyses over the longer time period. When 5% of counting loss was allowed, the optimal dosage of Cd for the purpose was determined to be 15 MBq.