New directions in cardiac imaging.

Cardiac imaging is among the most commonly used diagnostic techniques in cardiovascular medicine. Conventional imaging modes (chest roentgenography, echocardiography, radionuclide imaging, and angiography) allow delineation of cardiac morphology, coronary anatomy, ventricular and valvular function, and cardiac shunts, and permit qualitative evaluation of myocardial perfusion. Four new imaging procedures (digital subtraction angiography, rapid acquisition x-ray computed tomography, emission computed tomography, and magnetic resonance imaging) promise to expand diagnostic capabilities by permitting quantitative analysis of myocardial perfusion, evaluation of myocardial metabolism, and characterization of cardiac tissue composition. These techniques differ widely in cost, availability, and in the additional information they offer. Optimal use will be achieved only through carefully controlled comparative clinical trials directed at specific diagnostic questions.