DELAYED IMAGE OF I-123 IOMAZENIL AS A RELATIVE MAP OF BENZODIAZEPINE RECEPTOR-BINDING - THE OPTIMAL SCAN TIME

''Delayed'' single-photon emission tomograpic (SPET) images after an i ntravenous bolus injection of iodine-123 iomazenil have been used as a relative map of benzodiazepine receptor binding. We determined the op timal scan time for obtaining such a map and assessed the errors of th e map. SPET and blood data from six healthy volunteers and five patien ts were used. A three-compartment kinetic model was employed in simula tion studies and analyses of actual data. The simulation studies sugge sted that, in the normal brain, the scan time at which a single SPET I mage best represented the relative receptor binding was 3.0-3.5 h post -injection, This finding was supported by actual data from the volunte ers, The simulation studies also suggested that the optimal scan time was not greatly changed by the variability of the input functions, and that the error in the SPET image contrast in the vicinity of the opti mal scan time was not increased by changes in the tracer kinetics in t he entire brain. The SPET image contrast in the patients at 3.0 h post -injection agreed well with the reference receptor binding estimated b y kinetic analysis, with a mean error of 3.6%, These findings support the use of a single SPET image after bolus injection of [I-123]iomazen il as a relative map of benzodiazepine receptor binding. For this purp ose, a SPET scan time of 3.0-3.5 h post-injection is recommended.