The use of radio-iodinated toluidine blue for myocardial scintigrams.

A lthough heart disease is the principal cause of death in many countries and its diagnosis is of major importance, methods for direlct visualization of the myocardium in intact subjects are few. The roentgenogram of the heart shows the myocardium plus other tissues, especially the blood contained in the cardiac cavities, as a single shadow. Various techniques show cavities and vessels rather than the myocardium itself. On the basis of the important earlier studies which had demonstrated mycvardial uptake of potassium and its analogues,’ it was possible to develop a method for myocardial scintigrams,‘J using salts of cesium-131. This method permitted the demonstration of the left ventricular myocardium through the intact chest wall, without significant contribution to the image from the cardiac blood pool or adjacent non-cardiac tissues. After original developrnent of the technique in dogs, it was extended to humans and the myocardial scintigram has subsequently been shown capable of demonstrating myocardial infarcts,2-g aneurysm of the left ventricle,2j6 cardiomyopathies,7,8 neoplasm in the ventricular wall,‘O and rejection of the transplanted heart.” However, the long biologic half-life of cesium creates difficulties, not only from the standpoint of radiation dose, but also through interference with performance of serial scintigrams. As skeletal muscles retain cesium much longer than cardiac muscle,12,13 the uptake by intercostal muscles interferes with serial myocardial scintigrams during the days that follow injection of a single dose of cesium-131. Moreover, its principal emission, a 29.4 KEV x-ray, poses a considerable problem as a result of its low energy and consequent high absorption in tissues. Therefore, although cesium131 has proved an important radionuclide by permitting the demonstration of the validity of the myocardial scintigram for diagnosis, the general clinical usefulness of the myocardial scintigram would be greatly increased by the availability of a more convenient radioactive compound for this