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Image optimisation (artefacts, gains, focus)

Contrast Echocardiography in Practice: Contrast for Enhancing Endocardial Border Visualisation

Non-invasive Imaging: Echocardiography

The GAIN should be INCREASED during contrast-specific imaging for LVO / EBD (as opposed to harmonic non-contrast imaging) because harmonic signals generally are reduced. For myocardial contrast echocardiography (MCE), DECREASE gains so that only speckles are observed as myocardial tissue signals need to be suppressed.

The FOCUS in echocardiography is the point at which the MECHANICAL INDEX is most concentrated – thus, image quality is best during non-contrast scanning at this point. However, this could cause excessive bubble destruction and thus in contrast imaging a balance needs to be struck between imaging quality, contrast agent durability and artefacts.

As with all imaging techniques in cardiology, contrast echocardiography also has ‘pitfalls’ or ARTEFACTS which one must become aware of in order to avoid erroneous diagnosis (or mis-diagnosis!).


 

Attenuation / Shadowing

Problem:

An elevated concentration of microbubbles (increased echogenicity, often seen after a large or overly rapid bolus injection). There are different types of attenuation artefact, as the examples below will illustrate.

Consequence:

Ultrasound completely scattered & absorbed in the near field, such that there is little penetration into deeper parts of the image.

Solution:

If this happens, the best course of action is to wait for washout and for ‘dilution’ of the contrast agent with blood. To prevent ATTENUATION ARTEFACTS, one can use a SLOWER injection of bolus, LOWER DOSE during bolus injection, or use a CONTINUOUS INFUSION instead of bolus injection.

Blooming

This is a power Doppler movie showing examples of both attenuation and blooming artefacts. Intermittently, there is marked shadowing at the base of the LV cavity (bottom of image) due to attenuation. Additionally, the myocardial walls should appear black, but due to blooming, there is the appearance of contrast within the myocardium (which could be mistaken for perfusion).

Problem:

Spread of contrast signals beyond tissue of origin into neighbouring regions.

Consequence:

Cavity signals exceed endocardial borders and may resemble myocardial perfusion.

Solution:

Try a SLOWER injection of bolus, use a CONTINUOUS INFUSION instead of bolus injection or break off ultrasound emission for a few seconds before resuming scanning.

Swirling

Problem:

Excessive bubble destruction in the near field (apex) that may be due to a combination of factors: high MI, high frame rate, insufficient contrast administration or severe LV dysfunction with sluggish flow at the apex.

Consequence:

Often a large apical artefact and incomplete LV contrast opacification and incomplete endocardial border delineation.

Solution:

Decrease the mechanical index, increase contrast dose, move the focus away from the mitral valve towards the apex (apical views).  

Wall motion / thoracic cage artefacts

Problem:

Apparent defects (e.g. in the lateral wall) may occur due to shadowing from ribs or lung tissue or movement of the heart in and out of the scan plane.

Consequence:

Possible misdiagnosis of a perfusion defect (absent contrast) which is in reality an artefact.

Solution:

Adjust transducer position on the chest wall, ask patient to hold breath during image acquisition, in case of large hearts may have to image each wall (e.g. inferior and anterior in apical 2-chamber view) separately.