Ultrasonic contrast agents consists of bubbles, which absorb acustic energy, when they beginn to oscillate. Acustic energy is reduced, the higher the concentration of the contrast medium and the greater the distance to the transducer. High concentrations of contrast agent not only lead to a blooming – effect, but also to a strong decrease of ultrasonic energy in the nearfield of the transducer. If acustic energy falls below a critical value, bubbles are no longer stimulated to resonance, but represent only weak reflectors. This weak signal is absorbed on the way back to the probe of the intervening bubbles, so that a “shadow” is created.
|There is a blooming artifact in the apex, the apical thrombus can not be clearly delineated. Signals of bubbles in the left atrium do not reach the probe, the atrium remains black and free of contrast.
|After one minute the concentration of bubbles has decreased. The blooming artifact has disappeared. The thrombus can be better defined. The attenuation artifact with the “shadow” in the area of the left atrium is no longer detectable.
Shadowing and blooming often occur together. Countermeasures that reduce the concentration of contrast media, such as waiting, or the waiver of bolus injections of contrast agent reduce the effect of both artifacts.