Medical Ultrasound Imaging
Saturday, 27 April 2024
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This coefficient is a quantification of the energy intensity loss of waves (electromagnetic or mechanical) due to attenuation.
In ultrasound imaging it is the relative energy intensity loss per traveled centimeter. The ultrasound attenuation coefficient is measured in units of dB/cm. The attenuation coefficient in soft tissues is nearly proportional to the ultrasound frequency. The attenuation coefficient is doubled when the frequency is doubled. This coefficient (dB/cm) divided by the frequency (MHz) is almost constant in a given tissue.
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blood: 0.2 MHz x dB/cm;
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fatty tissue: 0.6 MHz x dB/cm;
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liver: 0.9 MHz x dB/cm;
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soft tissue: 0.5-1.0 MHz x dB/cm.
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Digital systems use discrete numerical values or non-numeric symbols for input, processing, transmission, storage, or display rather than being composed of variable voltage, acoustic field or electromagnetic field. See also Digital Imaging and Communications in Medicine and Analog to Digital Converter. •
A filter in electronics is a circuit that only passes certain signals. In ultrasound is a filter a device to suppress acoustic or electromagnetic waves of certain frequencies, letting other frequencies pass, e.g. high pass filter, low pass filter. The high pass filter is the wall filter (also called thump filter) used in Doppler devices to eliminate low frequency Doppler shifts caused by clutter. For blood flow measurement, a low pass filter is often used to strip out high frequency noise, leaving only the biological components of interest. Frame averaging is a form of a low pass filter.
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