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Page: Weaknesses of Ultrasonic Imaging
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* Large body habitus, obese patients limit image quality as the overlying adipose tissue (fat) scatters the sound and greater depth the sound waves need to travel attenuate or weaken the signal on transmission and reflection back to the transducer. A fetus close to the surface will be imaged at a higher resolution than those at greater distance to the skin surface.
* Sonographic devices have trouble penetrating bone. For example, sonography of the brain is very limited.
* Sonography can detect fluid surrounding the lung (pleural effusion) but the high impedance mismatch between the solid tissues and the air filled lungs limits image.
* Sonography performs very poorly when there is a gas between the transducer and the organ of interest, due to the extreme differences in acoustical impedance. For example, overlying gas in the gastrointestinal tract often makes ultrasound scanning of the pancreas difficult, and lung imaging is not possible (apart from demarcating pleural effusions).
* Even in the absence of bone or air, the depth penetration of ultrasound is limited, making it difficult to image structures deep in the body, especially in obese patients.
* The method is operator-dependent. A high level of skill and experience is needed to acquire good-quality images and make accurate diagnoses. For information on education and certification in sonography see ARDMS.
* There is no scout image as there is with CT and MR. Once an image is acquired there is no exact way to tell which part of the body was imaged.
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