Instrumentation for contrast echocardiography

A number of new imaging methods have been developed specifically for use with ultrasound contrast agents. These methods rely on the peculiar behavior of microbubbles in an ultrasound field. At low incident acoustic pressures (reflected by the mechanical index, MI) microbubbles emit harmonics. These can be detected using harmonic or pulse inversion imaging. At higher MI, bubbles are disrupted, emitting a strong, nonlinear echo. Harmonic power Doppler methods are able to detect this echo, offering the most sensitive method for the detection of microbubble at the perfusion level. Although the first images of myocardial perfusion were made using this disruption method, it requires intermittent imaging with interframe intervals of up to 6 heart beats. Pulse inversion Doppler imaging is a newer method that is able to detect the nonlinear component of bubble echoes at a very low MI, thereby making possible real-time myocardial perfusion imaging. An understanding of the behavior of bubbles during an imaging examination is an essential prerequisite to its success in clinical practice.