Regional dynamics of N-isopropyl-(123I)p-iodoamphetamine in human brain

Regional cerebral dynamics of N-isopropyl-(123I)p-iodoamphetamine (IMP) in the human brain were studied using a multi-detector single photon emission computed tomography (SPECT) scanner in 35 subjects both normal and with a variety of neurological conditions. Distribution of IMP in the brain was also compared with regional cerebral blood flow (CBF) measured by positron emission tomography (PET) in 15 of these 35 cases. A significant regional difference in temporal changes of radioactivity was observed among normal brain structures. A rapid increase with early washout of the tracer was shown in the cerebellum and the occipital cortex, while the basal ganglia revealed a relatively slow increase and prolonged retention, indicating the regional difference in extraction and/or retention of IMP among the cerebral tissues. In cases with unilateral hypoperfusion, the percentage of the activity in the lesion to that in the contralateral normal cortex on the early SPECT was correlated well with that on CBF measured by PET (r = 0.870, p less than 0.001). However, the contrast on the SPECT image decreased with time after injection; 84.0 +/- 7.4% on the SPECT at 5-20 min scan, 87.6 +/- 7.6% at 35-50 min scan and 96.2 +/- 6.3% at 5 hr scan. In a case with a brain tumor having high blood flow documented by PET, increased accumulation of IMP was observed in the tumor on the early images obtained within 20 min followed by a rapid washout. These findings suggested altered extraction and/or retention of IMP in normal and diseased tissues, and these factors should be considered for the assessment of distribution and redistribution of IMP.