In-vivo thyroid 125I monitoring method using imaging plate.

A new in vivo thyroid monitoring system was devised with radioluminography using an imaging plate. The counting features of the system were investigated by using a neck-thyroid phantom. A clear thyroid image was obtained at thin prethyroid tissue thicknesses and short distances between IP and neck surface. The characteristic 125 I thyroid image made it possible to visually confirm that the thyroid definitely accumulated 125 I. The counting efficiency in 100×cps Bq -1 of the imaging plate system was determined by setting a region of interest on the thyroid image resulting in a maximum efficiency of 0.5%. The higher efficiency was obtained for thinner tissue thickness overlaying the thyroid, smaller thyroids, and shorter distances between the imaging plate and neck surface. The imaging plate thyroid monitoring system was sensitive to thyroid 125 I. Its minimum detection limit of 23 Bq for a 10-min measurement was considerably lower than the annual thyroid burden limit of 300 kBq.