Ultrasound Focusing: Maximizing the resolution in the area of interest.
©Walter Rasmussen, R.D.C.S.
The phased-array transducers used for echocardiography exams are capable of adjusting the narrowest point in the ultrasound beam anywhere along its length. This is called the focal zone and it is within this 2-4 cm portion of the ultrasound beam that the highest resolution is achieved, resulting in the best quality images.
During the course of an exam, it may be necessary to focus the ultrasound beam at various depths in order to see individual structures with the greatest clarity. For example, in the apical four-chamber view, the best endocardial detail of the left ventricle is obtained when the focus is set at the mid region of the chamber however, if there is a suspected apical thrombus, the focal zone marker should be moved adjacent to the apex. Focus is also an important adjustment for M-Mode and color Doppler.
Ultrasound machines automatically adjust the focal zone when the zoom function is used, when color Doppler is activated, and when the image depth is changed however; upon finishing the use of these features, it is important to make certain that the focal zone is re-positioned to the new area of interest because the machine will not always reset it.
Some new ultrasound machines are able to effectively focus in multiple areas along the ultrasound beam however this can affect other factors such as frame rate since more than one scan or pulse is necessary to build the image.
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