Measurement of the Disappearance Rate of 75-Se Sodium Selenite in the Eye of the Rat by a CdTe Medical Probe

There are biochemical reasons to attribute a physiological importance to selenium compounds in the constituents of the eye. This could justify a clinical application of 75-Selenium in ophthalmology. Good accuracy and relatively simple technique can be achieved with the aid of a miniature probe capable of working at room temperature and reasonably sensitive to gamma rays in the 100-300 keV region. We have compared the performance of a commercial Si(Li) and an experimental CdTe probe, for the detection of 75-Selenium . A solution of 75-Se sodium selenite was applied dropwise onto the eye and its disappearance rate was then measured with both the Si(Li) and CdTe probes. Because of the low atomic number of silicon, it was not possible to obtain significant results with the Si(Li) probe. On the other hand, the CdTe probe yielded a counting rate sufficiently high to obtain a measurement of the disappearance rate,even with low level activities, in the range of the amounts applicable in clinical diagnosis. Moreover, the higher photoelectric efficiency of the CdTe probe lends itself to the identification and measurement of two or more gamma emitting radionuclides applied simultaneously.