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44 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Doppler Shift or Doppler Frequeny ? |
-the change or variation, the difference between received & transmitted frequency -Units= Hertz, cycles per second - Typical Values- 20 Hz -20kHz (Created when sound reflects off of red blood cells) -flow toward the transducers ⬆️ frequency -flow away from transducer ⬇️ frequency (Doppler shift produce info. About velocity) |
-greater velocities create greater Doppler shift - (+) = RF ⬆️ than TF - (-) = RF ⬇️ than TF |
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Hint for Doppler Shift ? |
- DS= RF - TF - FD= FR - FE -DS= Doppler shift -RF= receive frequency -TF= transmitted frequency -FE= emitted frequency -FR= reflected frequency -FD=Doppler frequency |
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Demodulation of Doppler ? |
- the process of extracting the Doppler frequency (low) from transducer frequency (high), is performed by a demodulator. |
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Doppler shift is _____ related to RBC speed? |
- directly |
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Doppler Equation? |
- DS = 2 x RS x IF x cos(angle) --------------------------------- PS
-the 2 is double Doppler shift -1st occurs when sound strikes the cell - 2nd results from moving blood cells reflecting the wave bk to the transducer |
-RS = reflector speed -IF = incident frequency -cos= cosine -PS = propagation speed -DS= Doppler shift (in order to accurately determine velocity, the angle between the directions of flow and sound beam must be known) |
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Doppler shift is _____ related to the speed of sound in the medium ? |
-inversely related |
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Speed vs Velocity? |
-Doppler measures velocity, not speed -Speed - magnitude only Velocity - magnitude and direction -v (m) = v x cos (angle); -velocity (measured) = true velocity x cos (angle) |
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Angles and Cosine? |
-Angles. -Cosine -0 degrees. - 1 -60 degrees. - .05 -90degrees - 0 |
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Bidirectional Doppler? |
- Doppler system which distinguishes flow toward and flow away from the transducer by measuring positive and negative Doppler shifts |
- requires stereo headphones, speakers or display represent flow toward the transducer above baseline; flow away from transducer below the baseline |
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Phase quadrature ? |
- a processing used in bidirectional Doppler |
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Continuous Wave Doppler? |
- 2crystals in transducer -1crystal is constantly transmitting -the other is constantly receiving -Able to measure high velocities accurately -higher sensitivity & ease in detecting small Doppler shifts! |
-Disadvantage- echoes arise from entire length of overlap between the transmit & receive beams this is range ambiguity Term 'Range' means 'depth' |
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Pulsed Wave Doppler? |
- 1 Crystal alternates between sending & receiving (performed w/a single crystal) -Advantage- echoes arise only from the area of interrogation, the sample volume or gate. |
-Disadvantage- Aliasing, errors in measuring high velocities **(PW can adjust the receive gate, CW can NOT)*** |
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Aliasing? |
-high velocities appear negative, -Pulse Doppler has PRF too low -DF (Nyquist limit)when aliasing occurs, equals to 1/2 the PRF - Equation: N.Limit (kHz)= PRF/2 -deeper sample volumes, frequ-ency is lower (more aliasing) -high frequency transducer (more likely to see aliasing) |
-eliminating aliasing "improves the ability to measure the maximum velocity w/Doppler (Doppler shifts are less likely to reach the Nyquist limit) |
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5ways to eliminate the unwanted effects of aliasing ? |
1) adjust the scale (⬆️ PRF & Nyquist limit) 2) select a transducer w/a lower frequency (this reduces the Doppler shift for a given velocity) 3) select new view w/a shallower sample volume (this ⬆️ the PRF & Nyquist limit) 4) use CWD (no aliasing w/CW) 5) baseline shift (this is for appearance only |
-adjusting baseline will not eliminate aliasing |
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Horizontal (or X-axis) of a Doppler spectrum is? |
-time ___________________ |
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Vertical axis (or Y- axis) of a Doppler spectrum is? |
-Doppler shift or velocity | | | |
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1.) Small sample volume creates? 2.) Large sample volume creates? |
1.) clean, large window 2.) spectral broadening or fill in |
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Front (Term) |
Know this *on exam* |
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Front (Term) |
- Doppler shift & transducer frequency are directly related -Dopplers are performed w/4 & 8MHz transducer, -8 MHz transducer will yield DS that are twice as large as 4MHz probe . |
-high frequency transducer will create a taller spectrum -transducer frequency is halved, Doppler shift will be halved -*measured velocity stays the same regardless of the transducer* |
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-gray shades are related to: - amplitude of the reflected signal - # RBC creating the reflection |
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Pulsed Doppler (know these points) |
• minimum of 1 Crystal • range resolution • limit on maximum velocity (aliasing) • uses damped,low-Q, wide bandwidth transducer |
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Imaging ( know these points)? |
- normal incidence (90*) -higher frequencies- better resolution -pulsed wave only -at least one Crystal |
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Doppler (know these points)? |
- 0* or 180* incidence (oblique) - lower frequencies- less aliasing - pulsed or continuous wave - one (pulsed) or two (CW) crystals |
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Color Flow Doppler? |
- is pulsed ultrasound technique & is subject to: -range resolution or specificity -aliasing - color identified blood flow velocities and function - also, provides information regarding direction of flow - reports average velocities (mean velocities) |
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Front (Term) |
-Velocity Mode -top = toward transducer -bottom= away from transducer
-Variance Mode -colors vary side-to-side |
- red on top? (Left to Right) - blue on top? (Right to Left ) |
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Life side color flow is? |
- the flow laminar or parabolic, uniform and smooth. Often Normal flow. |
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Right Side flow is? |
- the flow is turbulent or disturbed, random and chaotic (associated w/pathology) (Often Green or Yellow) |
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Color Doppler gain setting has ___ ____ on jet size? |
-greatest effect |
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Doppler Packets? |
-packet- has multiple pulses are called packet, or ensemble length -Advantages - More Pulses -greater accuracy of velocity measurement -sensitivity to low flows is also ⬆️s w/many pulses I. The packet |
-Disadvantage (more pulses) -more time is required to acquire the information - Frame rate and temporal resolution are reduced |
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Packet size must balance between accurate velocity measurements and temporal resolution; this is why Doppler measures? |
-"Mean" velocity (Spectral Doppler (pulsed & CW) measures peak velocity ) - color flow measures mean velocity |
-*this is on EXAM* |
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Color Power Doppler ? |
-Doppler info. Regarding direction and actual velocity is not calculated (Any measured Doppler shift is colorized w/out direction or speed) |
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Advantages and limitations of Color Power Doppler? |
-Advantages ; -⬆️ sensitivity to low flow, venous flow, flow in small vessels -not affected by Doppler angles, unless 90* -no aliasing (we ignore velocity info) |
-Limitations -no measurement of velocity or direction -slower frame rate (reduce temporal resolution) -susceptible to motion of transducer patient or soft tissue (this is flash artifact) |
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Continuous Wave Doppler (know this quick version) |
- identifies highest velocity jets anywhere along the length of the ultrasound beam.Range ambiguity. No aliasing |
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Pulsed Wave Doppler ? (Know this quick version) |
- accurately identifies the location of flow (range resolution). -Has good temporal resolution -aliasing |
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Color Flow Doppler? (Know this quick version) |
-provides 2D flow info directly on anatomic image -size of color jet is most affected by color Doppler gain settings -poorer temporal resolution because of multiple packets -pulsed US subject to range resolution & aliasing |
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Power Mode Doppler? |
- allows the use of color when low velocity or small volumes of blood flow -greatest sensitivity |
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Spectral Analysis ? (Study) (Collection) |
-is performed to extract or identify the individual frequencies making up the complex signal -methods( for pulsed or CW ) -Fast Fourier Transform (FFT) (for color flow doppler)- - autocorrection or correlation function (Both methods are digital techniques performed by computers)
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- it's is used to interpret individual velocities in the signal |
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Bi-directional Doppler uses _____ _____ processing? |
- phase quadrature |
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Difference between FFT and Autocorrelation? |
- autocorrelation is slightly less accurate, but faster, than FFT |
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T or F The higher the emitted frequency, the more likely a pulsed wave signal is to alias ? |
True |
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T or F The shallower the sample volume is, the more likely a signal is to alias? |
False |
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T or F Only pulsed wave Doppler exams have a sample volume? |
True |
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6 basic assumptions of imaging systems? |
1. Sound travels in a straight line 2. Sound travels directly to a reflector and back 3. Sound travels exactly 1,540 meters/second 4. Reflections arise from structures positioned along beams main axis 5. Intensity of reflections is related to the scattering characteristics of the tissue 6. The imaging plane is extremely thin |
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Continuous Wave Doppler (Know these points)? |
-minimum of 2 crystals - range ambiguity - unlimited maximum velocity - uses undamped, hiQ, low bandwidth transducer |
-allows for higher sensitivity to small Doppler shifts |
