BIOKINETICS AND DOSIMETRY ANALYSIS IN HEALTHY-VOLUNTEERS FOR A 2-INJECTION (REST-STRESS) PROTOCOL OF THE MYOCARDIAL PERFUSION IMAGING AGENTTECHNETIUM-99M LABELED Q3

Background. Trans (N,N'-ethylene bis(acetylacetoneimine)) bis (tris(3- methoxy-1-propyl) phosphine) Tc-99m(III) (Tc-99m-Q3) has been develope d for myocardial perfusion imaging. Biokinetic studies and dosimetry a nalysis have been completed for six healthy volunteers. Methods and Re sults. The same-day two-injection protocol involved (1) an average res t injection of 241 MBq of Tc-99m-Q3 followed by myocardial single-phot on emission computed tomography (SPECT) at 15.0 minutes and a whole bo dy (WB) scan at 1.5 hours; and (2) an average stress injection during treadmill exercise of 744 MBq of Tc-99m-Q3 at 2.4 hours (postrest inje ction) followed by myocardial SPECT and additional WE scans at 1.5, 3. 5, 6.5, and 21 hours poststress injection, Total urine was collected o ver 24 hours. Absolute organ activities were determined by conjugate c ounting methods. The two-injection data were simplified to a one-injec tion equivalent data set to facilitate dosimetry analysis. Decay corre cted average percentage uptake values, plus or minus one standard devi ation, for the myocardium were 1.4% +/- 0.2% at approximately 1.5 hour s for both the postrest and poststress injections. The average biologi c half-time for the myocardium was 26.4 hours. The highest organ uptak e values included the gallbladder with 5.5% +/- 1.9% and the liver wit h 4.1% +/- 1.0% at the 1.5 hours poststress scan time, The sum of all gastrointestinal (GI) tract components was 18.8% +/- 9.4% at approxima tely 6.5 hours poststress injection (before any fecal elimination). Th e total 24 hour urine clearance was 17.1% +/- 2.4%. The gallbladder wa ll and upper large intestine wall received the highest doses at 0.024 and 0.023 mGy/MBq, respectively. Conclusion. The effective dose equiva lent is estimated to be 0.01 mSv/MBq, which for an administration of 1 110 MBq (30 mCi) is less than half that of a standard imaging protocol using 111 MBq (3 mCi) of Tl-201, and comparable to the published esti mates for Tc-99m-labeled sestamibi and Tc-99m-labeled tetrofosmin (als o normalized to 1110 MBq of administered activity). The Tc-99m-Q3 exhi bits myocardium uptake similar to that for these other two Tc-99m agen ts.