Measurement of cerebral blood flow by the autoradiographic method with N-isopropyl-4-[I-123] iodoamphetamine: comparison of radiopharmaceuticals marketed by different companies in Japan

Abstract

Iodine-123-labeled N-isopropyl-4-iodoamphetamine (IMP) is used as a tracer for the measurement of cerebral blood flow (CBF) by single-photon emission computed tomography (SPECT). Two IMP products, IMP(A) (Nihon Medi-Physics Co., Ltd.) and IMP(B) (FUJIFILM RI Pharma Co., Ltd.), produced by different radiopharmaceutical companies are marketed for clinical use in Japan. Although no significant difference in whole-body distribution between the two products has been reported, a significant difference in the radioactivity of the octanol-extracted fraction in whole blood between the two products has been reported in humans. In this study, CBF values obtained by the autoradiographic (ARG) method obtained from both IMP(A) and IMP(B) were compared in the same human subjects. SPECT studies were performed on 6 healthy subjects with the use of both IMP(A) and IMP(B). Standard input functions used in the ARG method were obtained for both IMP(A) and IMP(B) from 5 additional healthy subjects. Significant differences were found between CBF values when SPECT data with IMP(A) was combined with the standard input function for IMP(B) (37.7 +/- 3.7 mL/100 g/min at a mid-scan time of 30 min) and SPECT data with IMP(B) was combined with the standard input function for IMP(A) (50.7 +/- 8.9 mL/100 g/min). Nearly the same CBF values were found when SPECT data with IMP(A) was combined with the standard input function for IMP(A) (43.1 +/- 4.4 mL/100 g/min) and SPECT data with IMP(B) was combined with the standard input function for IMP(B) (44.2 +/- 7.6 mL/100 g/min). Our results suggest that the appropriate standard input function should be used, according to the IMP product used, in the calculation of CBF by the ARG method.