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Physics Module 4
Physics
| Term | Definition |
|---|---|
| Doppler principle | The frequency and wavelength of transmitted sound are altered when the source of sound is moving |
| Doppler effect | is an apparent change in frequency because of a change in wavelength caused by motion of a wave source relative to an observer |
| Rouleau/RBC Aggregation | constructive interference of wavelets reflected from multiple RBCs stuck together produces a stronger detectable signal |
| Continuous wave doppler | simplest technology for detection of flow with ultrasound, sound is emitted from a transmitting crystal 100% of the time |
| Pulsed wave doppler | uses a single crystal to transmit ultrasound pulses and receive the returning echoes |
| aliasing | the ambiguous plotting of velocities which are too high and wrap around the display spectrum |
| high PRF doppler | method used to measure higher Doppler shifts with less aliasing, multiple gates are used |
| spectral analysis | shows visual Doppler information |
| Fast Fourier Transform (FFT) | Identifies the frequency shifts present in the complex waveform |
| PW Transmitter | applies to the transducer using a well defined frequency |
| transducer | crystal generates ultrasound pulses which are transmitted through the flow area. Returning echo pulses are received by the same crystal which generates RF signals |
| receiver | signals are amplified and sent to the demodulator |
| Quadrature detection | tells the machine the direction of the Doppler shift |
| mixer | where the Doppler shift is extracted from transmitted and reflected frequencies. Performs the equation Δf = fr - fₒ |
| Doppler shift detector | detects every extracted Δf |
| wall filter | electric filter that allows frequencies to be processed above a set level and eliminates frequencies below the indicated level. Also called Reject or Threshold |
| direction knobs | allows sonographer to change the angle of interrogation and invert the Doppler display |
| laminar flow | Stable flow that occurs in fairly straight unobstructed vessels or through unobstructed cardiac valves |
| plug flow | occurs when all blood cells travel at the same velocity |
| parabolic laminar flow | has a bullet shape |
| stenosis | narrowing in the lumen of a vessel |
| modal velocity | corresponds to the brightest display point at the peak of the individual Doppler spectrum |
| mean velocity (Vmean) | mathematical average of the various velocities within the individual Doppler spectral trace |
| maximal velocity (Vmax) | the highest velocity found within the individual Doppler spectrum or phase of the cardiac cycle (peak velocity) |
| Velocity Time Integral (VTI) | distance measurement (in cm) obtained by tracing the individual Doppler spectrum |
| Nyquist Limit | Upper limit to the Doppler shift in frequency that can be measured and processed by a PW Doppler system without error |
Created by:
ginaliane
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