In vivo investigation of myocardial perfusion, metabolism and receptors by positron emission tomography.

Positron emission tomography (PET) is a safe noninvasive visualization technique which gives an accurate and quantitative representation of the spatial distribution of a positron-emitting radionuclide in any desired transverse section of the body. Short-lived positron emitters such as Carbon-11 (half-life:20 min.). Nitrogen-13 (10 min), Fluorine-18 (110 min) or Bromine 75 can be incorporated into biological molecules:amino acids, sugars, fatty acids, hormones and receptor agonists or antagonists. The PET approach may be compared to quantitative autoradiography with the added advantage of allowing in vivo kinetic studies in man, under normal and pathological conditions. Regional myocardial perfusion is measured with rubidium-82, 13N-labelled ammonia, H2(15) O or albumin microspheres labelled with Gallium-68. Regional myocardial metabolism is assessed with 11C-palmitate and 18F-fluorodeoxyglucose. A high and spatially homogenous accumulation of 11C-palmitate is seen in normal myocardium. PET delineates an increased regional accumulation of 18F-2-FDG in ischemic areas while 11C-palmitate accumulation is markedly reduced. Positron Emission Tomography offers a unique opportunity to study receptors in vivo in normal and disease conditions. A potent muscarinic antagonist, 11C-MQNB is used to study the myocardial acetylcholine receptor and beta-blockers, 11C-Pindolol and 11C-CGP 12177 are used to study the beta-adrenergic receptor. The peripheral-type benzodiazepine receptor has been characterized with 11C-PK 11195.