Diagnostic Value of 20 Minute 99mTc Pertechnetate Thyroid Uptake

SummaryFour hour thyroid uptake of orally administered radioiodine was compared with 20 minute uptake of intravenously given 99mTc pertechnetate in 170 patients.Pertechnetate uptake was estimated by counting dots on a rectilinear scan, with appropriate background subtraction. In 22 patients the dot counting method was compared with computer assisted processing of a gamma camera image, using Nuclear Data 50/50 MED Digital Image Processing System. There was good correlation between the two methods, the computer technique is faster and easier, but does not provide, at the same time, a very satisfactory thyroid scan.Optimum interval for measurement of pertechnetate thyroid uptake with the rectilinear scanner is 20—30 minutes after the intravenous dose. When the computer assisted gamma camera can be employed the 10 minute interval would probably be more suitable for differentiation between euthyroid and hyperthyroid patients.For diagnostic accuracy the radioiodine and pertechnetate methods were identical (87% correct), there was quite close correlation between them and both were suitable for T3 suppression and TSH stimulation tests. The pertechnetate method is quicker to complete and provides a scan of the thyroid, but it requires an intravenous injection and is more demanding in personnel and equipment.