Sonographic tissue texture: influence of transducer focusing pattern

The ultrasonic beam profile pattern is not accurately known for most transducers in clinical use. A simple scan of an easily available phantom permits the clinician to determine the focusing pattern of his own transducer and equipment. Disregarding other operator-controllable parameters such as the time-gain compensation, output, and system sensitivity, the true echo pattern of a tissue is not accurately represented until the distance of the region of narrowest beam focus is reached. The fine speckled echo pattern commonly seen in uniform organs near the transducer is largely artifactual due to interference phenomena in the near field of the acoustic beam. Closest approximation of true texture is not displayed until near the depth at which the narrowest focus occurs. Beyond that depth, broad, coarser patterns can be expected.
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