phyrev ch.8 - Spectral analysis used to interpret...

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Spectral analysis – used to interpret individual velocities in the signal. For pulsed or CW dopper Accurate – Fast Fourier Transform (FFT) - FFT – mathematical algorithm used to derive various frequency shifts that are coming back from return Doppler echo sot hey can be processed and displayed., show all individual velocities in the signal For color flow Doppler – autocorrelation - autocorrelation – used with color Doppler, less accurate, but faster than FFT Both FFT and autocorrelation are digital techniques that are performed by computers. Ch. 18 Artifacts Reverberations – multiple echoes appears on display due to ping ponging between two strong reflectors, - multiple, equally spaced, parallel to the sound beam, deeper and along a straight line. Ring Down or Comet tail – single, solid hyperechoic line, long echo, parallel to sound beam, reverb - ex. gas bubbles, tiny calcifications Shadowing – US beam unable to pass through a structure, has HIGHER THAN USUAL ATTENUATION , absence of true anatomy in region of shadow. Edge Shadow by refraction – refraction at the edge of a circular structure, shadowing by refraction Enhancement hyperechoic , occurs when the medium through which the sound travels has a LOWER ATTENUATION RATE
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phyrev ch.8 - Spectral analysis used to interpret...

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