Physical Aspects of Gray Scale Ultrasound
Diagnostic ultrasound is presently being used to image soft tissue within the body. A sound wave is emitted by a high frequency transducer and a portion of that sound wave is reflected back to the transducer when it encounters a change in acoustic impedance. This reflected wave contains several pieces of important information. Specifically, the amplitude of the reflected signal is directly related to the difference in acoustic impedance of the structures on either side of the interface off which the sound wave is reflected. This can give important information regarding the density of the tissue structures since acoustic impedance = density x velocity.
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