In Vivo Thyroid 125I Monitoring with Radioluminography

The counting features of an in vivo thyroid monitoring system with an imaging plate (IP) were investigated by using an anthropomorphic thyroid-neck phantom. The realistic thyroid phantoms loaded with 125I solution were embedded in a neck phantom. The IP was fixed on the neck phantom and exposed to 125I photons emitted from the thyroid phantom by changing the pre-thyroid tissue thickness at the front of the thyroid. A clear thyroid image was obtained at short tissue thicknesses. A region of interest (ROI) was set so that the ROI contained the thyroid image. The count within the ROI was regarded as the number of 125I photons detected by the IP. The IP counting efficiency was about 0.6% at maximum. Monitoring with IP has the advantage of allowing the worker to move freely during the monitoring period by wearing the IP on his neck. Radioluminography with IP has shown itself to be useful when monitoring thyroid 125I.