Detection of radioactivity on microtiterplates in situ using a photon-counting imager

Abstract A positon-sensitive single-photon counting imaging system, which can determine intensity and location of a light source, has been for the detection of 125 I-labeled Interleukin-1 and [ 3 H]thymidine in 96 wells of a microtier plate (MTP) simultaneously. 4 Bq (1 Bq = 1 Bequerel = 1 disintegration/s), 22 and 150 Bq of 125 I and 3, 10 and 100 Bq of 3 H were visualized and quantified by transforming the radioactivity into light in the visible range by means of Xtalscint, a solid scintillator. After only 1 min of photon accumulation time, the highest radioactivity of both isotopes could be clearly distinguished from background. Photon counts correlate well with radioactivity measured in a beta-counter (for 3 H) and a gamma-counter (for 125 I). The overall counting efficiency was about 5% for 125 I and 3% for 3 H.