Angle of Approach

The angle of approach of the needle into the tissue is critical. If the angle of approach is too steep (image below left), the reflected sound does not return to the probe, and consequently no image is seen. Angles less than 45 degrees to the skin are needed to see the needle (image below middle), and the smaller the angle, the better the image.

The image of the scan (below right) shows the concept of keeping the needle within ‘the beam’ in order to keep its image on screen, based on both parallelism and angle of approach.

Learning bite

The angle of approach must be shallow, ideally less than 35 degrees.

Angle too steep Angle close to parallel Keeping the needle within the beam
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