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Exam 1 Study Prep
Advanced Physics
| Question | Answer |
|---|---|
| Which statement best describes the concept of relative motion? | The distance between the source of sound and the observer changes |
| What happens to the Doppler shift frequency if the Doppler angle's cosine INCREASES? | Decreases |
| What happens to the Doppler shift frequency if the Doppler angle's cosine DECREASES? | Increases |
| Earlier Doppler systems displayed the Frequency of the Doppler shift from the moving RBCs. How do modern spectral Doppler scanning systems display the RBCs Velocity? | By rearranging the Doppler shift equation and solving for the velocity component |
| True or False: Initial amplification of the weak Doppler shift signals are under the operator's control | False |
| True or False: Knowing the Doppler angle is a critical component in obtaining accurate velocity measurements in spectral Doppler systems. | True |
| Why is there no detectable Doppler shift at a 90 degree angle of insonation? | The cosine of 90 degrees is zero. |
| What parameter (or component) of blood creates the Doppler shift during cardiovascular applications of Doppler imaging? | Red blood cells |
| What is the function of the Cosine of the Doppler Angle (COS 0) in the Doppler shift equation? | It relates relative motion towards or away from the observer (transducer) |
| Positive Doppler Shift | Sound source moving towards the observer |
| Negative Doppler Shift | Sound source moving away from the observer |
| No Doppler Shift | Sound source and observer moving in the same direction at the same velocity |
| No Doppler Shift | Sound source and observer stationary |
| Why does a Spectral Doppler or a Color Doppler system display a range of frequency shifts instead of just one Doppler shift? | The red blood cells are moving at different velocities and at different Doppler angles |
| Except for vey superficial structures, what is the best optimal Doppler frequency for clinical applications? | Lowest possible frequency |
| What is the purpose of the "2" in the Doppler shift equation? | Accounts for two Doppler shifts (round trip effect) |
| What happens to the Doppler shift frequency if the transmit frequency increases from 2MHz to 4MHz? | Doubles |
| What is the first step a sonographer should take to eliminate aliasing artifacts in a spectral Doppler waveform? | Increase veloctiy scale (PRF) settings |
| Which intricate mathematical process is used to break apart the complex Doppler shift frequency into individual frequencies for eventual display on an image monitor? | Fast Fourier Transform (FFT) |
| What is the function of the wall filter in a Doppler system? | Remove clutter from the Doppler signals |
| What is another commonly used name for the wall filter in a Doppler system? | High pass filter |
| The spectral Doppler window normally indicates undisturbed, laminar blood flow, fill- in of this window MAY indicate what? | Turbulent flow related to pathology |
| Which term refers to the strong signals created by stationary reflectors when they are interrogated by a Doppler beam? | Clutter |
| What happens to a spectral Doppler waveform if the scanning system's PRF falls below the Nyquist Limit? | Aliasing Artifact |
| Although Continuous Wave (CW) Doppler systems do not have depth discrimination capabilities, what is their major advantage when compared to Pulsed Wave (PW) Doppler systems? | Resistance to aliasing artifacts at higher blood flow velocities |
| How is spectral Doppler system able to specify a specific depth for gathering blood flow information? | Electronic range gating |
| If a Doppler waveform is very bright, what does this indicate? | High amplitude |
| How many times per cycle must a Doppler system sample the Doppler shift frequencies in order to prevent the aliasing artifact? | Two |
| What does the "brightness" of the spectral Doppler envelope (spectral waveform) represent? | Amplitude of the Doppler shift frequency |
| What process results in an aliasing artifact in a spectral Doppler waveform? | Sampling the Doppler shift frequencies at a low rate |
| What is one of the major limitations of a Pulsed Wave (PW) Doppler system? | Tendency to aliase at high blood flow velocities |
| What are the visual and aural characteristics of an aliasing artifact in a spectral Doppler waveform? | Spectral waveform wrap-around, audio signals sound reversed |
| What type of flow displays elevated flow velocity, spectral broadening, flow reversal, and fill-in of the spectral window? | Turbulent Flow |
| What velocity flow profile is seen with the spectral window being clearly visible and the spectral envelope being clearly defined during early systole and all of diastole? | Laminar Flow |
| What can happen to the spectral Doppler waveform if the cut-off setting for the wall filter is set too high? | Useful low-frequency Doppler shifts can be removed from the spectral waveform. |
| How much of the Doppler scale should be taken up by the spectral waveform? | 2/3 |
| What determines the amplitude (or strength) of the Doppler shift frequencies? | Number of red blood cells |
| If we see clutter along the baseline of a spectral Doppler, what does this indicate? | The wall filter is set too low |
| If we are losing the low frequency shifts that are real, what does this indicate? | The wall filter is set too high |
| How does optimal sample (range) gate placement differ between arteries and veins? | Since arteries are wider, you use a smaller gate to get right in center best velocities. veins, use larger gates becuase of vessels moving at slow rates.Using a larger size gate would help visualize the flow of the vessel more clearly. |
| If the Doppler angle cursor is misaligned with true flow, applying angle correction will usually? | Underestimate the velocity |
| How does the Fast Fourier Transform (FFT) contribute to Doppler spectral analysis in ultrasound, and why is it essential for separating and interpreting frequency and velocity components of the waveform? | takes individual red blood cell frequencies and puts them into frequency bins. Since vessels have multiple differenct frequencies and velocities, it's not correct to just pick and choose one area and say that applies to the whole vessel. |
| What is the Doppler Effect in sonography? | The Doppler Effect in sonography is the change in frequency caused by the motion of a sound source, receiver, or reflector. |
| What is the relationship between PRF and Doppler frequency shifts? | ? |
| what are some reasons why we would see TRUE spectral broadening on a Doppler waveform? | True spectral broadening is tortuouse vessels...? |
| What are some reasons why we would see a false representation of spectral broadening on a Doppler waveform? | False spectral broadening is too large or too small gates or the wrong angle of correction. |
| Describe the relationship between Doppler shift frequency and the cosine of the Doppler angle. | as the cosine of the Doppler's angle is increasing, Doppler shift frequency is decreasing. the angle we want is 0, but hard to achieve. So we give a limit of 60 degrees. At 0 degrees, cosine of 0 is 1. we increase the angle, cosine decreases. |
| What are the differences in Color Doppler and Power Doppler? | Color Doppler displays mean average velocities, and Power Doppler displays amplitude. |
| For color doppler imaging, what determines the basic colors used to create color flow image? | Color Bar |
| What does the black band in the middle of the color bar represent? | Wall filter setting |
| What does the color on the lower section of the color bar represent? | Flow away from the transducer |
| What is one of the major limitations of color doppler imaging? | Average velocities are displayed |
| What may happen to a color flow image if the color gain is set too low? | False indication of limited or no flow |
| What do the numbers at the upper and lower ends of the color bar represent? | Maximum flow velocities that can be disaplyed without aliasing |
| What is the 90 degree doppler angle with a curvilinear transducer? | Some of the pulses traveling along the scan lines interpret the flow as coming towards the transducer and other pulses interpret the flow as going away from the transducer |
| What does a black area represent in a color Doppler image? | 90 degree Doppler angle, no flow, low frequency shifts rejected by wall filter (all are correct) |
| What is the mathematical process used for Spectral Doppler? | Fast Fourier Transform (FFT) |
| What is the mathematical process used for Color Doppler? | Auto Correlation |
Created by:
marissagirl