Brain and whole body distribution of N-isopropyl-4-iodoamphetamine (I-123) in humans: comparison of radiopharmaceuticals marketed by different companies in Japan.
OBJECTIVE
Iodine-123 (123I)-labeled N-isopropyl-4-iodoamphetamine (IMP) has been used as a cerebral blood flow (CBF) tracer for single-photon emission computed tomography (SPECT). An autoradiographic (ARG) method has been developed for the quantitation of CBF by IMP and SPECT. Two IMPs (IMPA and IMPB) produced by different radiopharmaceutical companies are marketed in Japan. In the present study, whole-body distributions including brain and blood of the two IMPs were compared in the same human subjects.


METHODS
Two brain SPECT studies using IMPA or IMPB were performed on separate days in six young healthy men. Whole-body scans were also obtained with a large field-of-view single-head gamma camera. One-point arterial blood sampling was performed at 10 min after injection of IMP to measure both the radioactivity concentrations of whole blood and of octanol-extracted components.


RESULTS
No significant differences between the two tracers were observed in body distribution, tracer kinetics in brain, or regional distribution in brain. However, the octanol extraction fraction in blood was significantly different between the two tracers. Radiochemical purity was slightly but significantly different between the tracers.


CONCLUSIONS
In the ARG method, arterial input function is determined by calibration of a standard input function with the radioactivity concentration of arterial whole blood. Because the standard input function in the ARG method was obtained using IMPA, the standard input function obtained for IMPB should be used when CBF is calculated by the ARG method with IMPB.
Ito
Hiroshi
H
Department of Nuclear Medicine and Radiology, Division of Brain Sciences, Institute of Development, Aging and Cancer, Tohoku University. hito@nirs.go.jp
Sato
Tachio
T
Odagiri
Hayato
H
Inoue
Kentaro
K
Shidahara
Miho
M
Suhara
Tetsuya
T
Hatazawa
Jun
J
Fukuda
Hiroshi
H
D000328:Adult; D001345:Autoradiography / Q000379:methods; D001921:Brain / Q000187:drug effects* / Q000473:pathology; D006801:Humans; D007457:Iodine Radioisotopes; D020367:Iofetamine; D007564:Japan; D008297:Male; D019275:Radiopharmaceuticals; D013997:Time Factors; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods; D051598:Whole Body Imaging
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D020367:Iofetamine