Real-time Cross-sectional Contrast Echocardiography

Abstract

Gramiak and Shah [1] reported in 1968 that rapid injection of indocyanine green produced a cloud of echoes in the blood which is otherwise echofree. They used this method to identify intracardiac structures and to validate echocardiographic patterns. Subsequent studies showed that any solution rapidly injected into the circulation produces echocardiographic contrast [2]. The effect most likely results from the drop in pressure at the catheter tip during injection which allows the gasses dissolved in the blood to escape in the form of miniature bubbles following the Bernoulli principle [3, 4]. Other explanations for the phenomenon include turbulence, temperature differences and fluid acoustic impedance difference. These clouds of echoes can be observed downstream from the injection site on and loose their echo producing quality with a single transit through either the pulmonary or the systemic capillary bed. This means that detection of echoes in both the venous and arterial blood pool after peripheral vein injection of a contrast producing agent is always indicative of abnormal shunting. This principle has been used with M-mode echocardiography to study intracardiac shunts, blood flow patterns and pressure - flow relationships [5–13].