I-123 Labeled Radiotracers in Cardiovascular Nuclear Medicine

Radiohalogens (particularly 18F, 34mCl, 77Br, 75Br, 123I, 125I and 211At) produced in a cyclotron are nuclides of choice for radiopharmaceuticals. It has long been recognized that I-123 is the most desirable radioisotope of iodine for in vivo applications. I-123 labeled substrates suitable for imaging the myocardium include receptor binding agents, muscarinic antagonists and analogs of fatty acids. Radioiodinated (I-123) fatty acid analogs have gained significiant attention because of the possibility that these might give quantitative information regarding the regional myocardial metabolic activity by noninvasive scintigraphic methods. Incorporation of tellurium hetero into a carbon skeleton or beta methylation of a long chain phenyl fatty acid tends to prolong the retention of radioactivity in the myocardium of experimental animals. It is recognized that the radioiodine needs to be placed on a phenyl ring attached (in the ¿-position) to a long chain fatty acid for the in vivo stabilityof the C-I-bond. Among the methods of radioiodination of ¿-phenyl fatty acids, a method developed in our laboratory using an organo-thallium intermediate has been found to be simple, efficient, reproducible, and suitable for routine application.