Quantitation of benzodiazepine receptor binding with PET [C-11]iomazenil and SPECT [I-123]iomazenil: preliminary results of a direct comparison in healthy human subjects

Although positron emission tomography (PET) and single photon emission comp uted tomography (SPECT) are increasingly used for quantitation of neurorece ptor binding, almost no studies to date have involved a direct comparison o f the two. One study found a high level of agreement between the two techni ques, although there was a systematic 30% increase in measures of benzodiaz epine receptor binding in SPECT compared with PET. The purpose of the curre nt study was to directly compare quantitation of benzodiazepine receptor bi nding in the same human subjects using PET and SPECT with high specific act ivity [C-11]iomazenil and [I-123]iomazenil, respectively. All subjects were administered a single bolus of high specific activity iomazenil labeled wi th C-11 or I-123 followed by dynamic PET or SPECT imaging of the brain. Art erial blood samples were obtained for measurement of metabolite-corrected r adioligand in plasma. Compartmental modeling was used to fit values for kin etic rate constants of transfer of radioligand between plasma and brain com partments. These values were used for calculation of binding potential (BP = B-max/K-d) and product of BP and the fraction of free non-protein-bound p arent compound (V3'). Mean values for V3' in PET and SPECT were as follows: temporal cortex 23 +/- 5 and 22 +/- 3 ml/g, frontal cortex 23 +/- 6 and 22 +/- 3 ml/g, occipital cortex 28 +/- 3 and 31 +/- 5 ml/g, and striatum 4 +/ - 4 and 7 +/- 4 ml/g. These preliminary findings indicate that PET and SPEC T provide comparable results in quantitation of neuroreceptor binding in th e human brain. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.