After injection of contrast medium the signal difference between the chamber and the myocardium is at its greatest during the early wash in phase of the left ventricle. The capillaries of the ventricular myocardium are not yet filled with contrast bubbles and so not yet stained, while the chamber is already completely stained.
The kinetics during wash in and wash out phase differ between blood pool in the left chamber und the capillaries in the myocardium. When staining of the left ventricle diminishes, the contrast agent concentration in the ventricular myocardium is still high and the myocardium completely stained. The signal difference between the chamber and myocardium is low in this moment. An accurate measurement of volumes and ejection fraction may be impeded.
In this situation of “anti-contrast” a small increase of the mechanical index leads to a decrease of perfusion signal from the myocardium and improves signal difference between ventricle and myocardium. An additional injection of contrast agent can lead to a further improvement of the images.

The video on the left is recorded with a mechanical index of 0.16 during the wash out phase after a bolus injection of contrast medium. There is an unsatisfactory delineation of basal lateral wall segment. In the video on the right the mechanical index is increased to 0.21 without an additional injection of contrast medium. The image quality has improfed significantly. But therefore a slight increase in apical swirling occurs.