PT  - JOURNAL ARTICLE
AU  - Wasserman, Herman J.
AU  - Klopper, Johannes F.
AU  - Erlank, Petro
TI  - Effect of Technetium-99m on Iodine-131 Thyroid Uptake Measurements
DP  - 1985 Jun 01
TA  - Journal of Nuclear Medicine Technology
PG  - 68--71
VI  - 13
IP  - 2
4099  - http://tech.snmjournals.org/content/13/2/68.short
4100  - http://tech.snmjournals.org/content/13/2/68.full
SO  - J. Nucl. Med. Technol.1985 Jun 01; 13
AB  - Following administration of 2.5–5.0 mCi [99mTc]pertechnetate, several hundred microcuries may be present in the necks of hyperthyroid patients after 6 hr. Coincidence summing of Tc-99m photons may disturb I-131 uptake measurements in such patients if an oral diagnostic dose of I-131 is administered immediately after completion of a [99mTc]pertechnetate scintigram. Using a lower discriminator level of 300 keV, false increases of 10%–50% may occur at 6 hr. The 24-hr uptake is also affected if an I-131 predose measurement is performed after administration of the Tc-99m dose. The authors have shown that these errors may be prevented by using a 1-mm lead filter in front of the scintillation detector. The attenuation of Tc-99m photons by the filter effectively eliminates summation pulses while it reduces the I-131 countrate by approximately 28%.