echnetium-99m hexakis-2-methoxyisobutyl isoni trile ([@mTcJHEXAMIBI) is a promising new @mTc@ labeled radiophannaceutical for myocardial perfusion imaging (1-3). Initial experimental studies have shown that [99mTcIHEXAMIBI is accumulated in the myocar dium proportional to the distribution of regional myo cardialblood flow, in a manner similar to thallium-201 (201Tl)(4,5). However, unlike @°'Tl, no significant re distributionofthe radiopharmaceuticalwithin the myo cardium occurs: the initial

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... ke pattern remains rel atively fixed over an extended period oftime (6â€"8). HEXAMIBI myocardial imaging in comparison to rest exercise 201T1myocardial imaging and coronary an giographyare presented. METhODS Biodistribution and Safety (Phase I Studies) A total of 17 normal volunteers (16 males, one female) The ParticipatingClinical Centers in the rm Tc]HEXAMIBIPhase I and II Studies The biodistribution, dosimetry, and safety of a new myocardial imaging agent, @â€oeTc-hexakis 2-methoxyisobutyl isonitnle(HEXAMIBI), was evaluatedin 17 normalvolunteersat rest and exercise (Phase I studies). Technetium-99m HEXAMIBI dears rapidly from the blood with good myocardial uptakeandfavorablemyocardial-to-background ratiosfor myocardial imaging.Dosimetryallowsfor administration of up to 30 mCi (1,110 Bq)of [@'Tc]HEXAMlBl. The myocardial imageswere of good qualityand appearedlessgranularwith sharper myocardial wallscomparedto @°1T1 images.Thedinicalefficacyof [1@―1c]HEXAMIBI planar stressand rest imagingwas evaluatedin a multicenterPhaseII clinicaltrial involving38 patients.Of 36 patientswith significant coronaryarterydisease,35 patients(97%)had abnormal @°1T1 stressimages,and32 (89%)hadabnormal [@â€oeTc]HEXAMIBl stressimages (P = N.S.). Technetium-99mHEXAMIBI imagescorrelatedin 31/35 patients(86%) who had either scar or ischemia on @°1T1 images. By segmental myocardial analysis, exact concordancewas obtainedin 463/570myocardial segments(81%).ThismulticenterPhaseI andII studyindicates thatplanar['@â€oeTc]HEXAMIBl stressimaging issafeandcompares well with @°1T1 stressimagingfor detectionof coronaryarterydisease.