EVALUATION OF TC-99M EXAMETAZIME STABILIZED WITH COBALT CHLORIDE AS ABLOOD-FLOW TRACER IN FOCAL CEREBRAL-ISCHEMIA

A protocol has been devised to effectively ex tend the limited post-re constitution shelf life of technetium-99m exametazime as a radiopharma ceutical for imaging cerebral blood flow (CBF) distribution. The poten tial of Tc-99m-exametazime stabilised with cobalt chloride for imaging CBF distribution as late as 4 h after reconstitution has been examine d in ischaemic and nonischaemic tissue in halothane-anaesthetised cats . Focal cerebral ischaemia was produced by permanent middle cerebral a rtery occlusion. The relationship between Tc-99m-exametazime uptake an d retention and CBF (assessed with [C-14]iodoantipyrine 10 min after f irst radiopharmaceutical administration) was determined in the same ti ssue section with double label autoradiography. Over the CBF range 0 - 80 ml 100 g(-1) min(-1), the uptake of Tc-99m-exametazime (quantitati vely and topographically) was linearly related to CBF irrespective of whether the Tc-99m-labelled tracer was unstabilised (and administered within 10 min of reconstitution) or was stabilised with cobalt chlorid e (and administered up to 240 min after reconstitution). For levels of CBF in excess of 80 mi 100 g(-1) min(-1) the excellent topographical relationship between Tc-99m-exametazime distribution and CBF is mainta ined but quantitatively, Tc-99m-exametazime underestimates CBF to a si milar degree in animals receiving stabilised and unstabilised Tc-99m-e xametazime. The presence of the stabiliser, cobalt chloride, extends g reatly the period over which Tc-99m-exametazime can be used after reco nstitution to generate images of CBF distribution in normal and ischae mic cerebral tissue.