Term
| Explain motion of the source when the source moves TOWARDS the receiver. |
|
Definition
| - When the source moves TOWARDS the receiver, HIGHER frequency is heard. |
|
|
Term
| Explain motion of the source when the source moves AWAY from the receiver. |
|
Definition
| - When the source moves AWAY from the receiver, LOWER frequency is heard. |
|
|
Term
| Why does this happen with motion of the source? |
|
Definition
Formula: Wavelength = v/f
So smaller wavelength, means a higher frequency is heard. |
|
|
Term
| Explain motion of the receiver if the receiver is moving away from the source. |
|
Definition
| If the receiver is moving AWAY from the source, then a LOWER frequency is heard. |
|
|
Term
| When the receiver is moving TOWARDS the source , what kind of frequency will be heard? |
|
Definition
| A higher frequency will be heard if the receiver moves TOWARD the source. |
|
|
Term
| What creates a frequency shift? |
|
Definition
| A RELATIVE motion between the source and the listener. |
|
|
Term
| If the source is moving towards... |
|
Definition
| then the wave crests are smaller. |
|
|
Term
| If the source is moving away... |
|
Definition
| then the distance between the wave crests get bigger. |
|
|
Term
| If the receiver is moving towards... |
|
Definition
| then the distance between the crests is the same, but the speed at which the crests approach the receiver is bigger. |
|
|
Term
| If the receiver is moving away... |
|
Definition
| then the distance between the waves won't change, but the speed at which the crests approach the receiver is smaller. |
|
|
Term
| Regardless of the relative motion towards or away, what do you have to consider? |
|
Definition
| - Regardless of the relative motion towards or away, you have to consider motion of the source and receiver SEPARATELY. |
|
|
Term
|
Definition
| - A doppler shift is a change in the frequency of the sound due to a relative motion of the sound source and the receiver. |
|
|
Term
| How does the machine calculate doppler shift? |
|
Definition
| - The machine calculates doppler shift by comparing the sent frequency and the received frequency. |
|
|
Term
| What unit is used for doppler shift in medical ultrasound? |
|
Definition
|
|
Term
| If the blood moves TOWARDS the probe... |
|
Definition
F' > Fo
Doppler shift is POSITIVE. |
|
|
Term
| What is the doppler shift if the blood moves AWAY from the probe? |
|
Definition
F' < Fo
The doppler shift is NEGATIVE. |
|
|
Term
| What is the angle for a zero doppler shift? |
|
Definition
| Zero doppler shift is an angle of 90 degrees. 90 degree angle isn't possible for DOPPLER, but 90 degrees is the best angle for IMAGING. |
|
|
Term
| What is the maximum doppler shift? |
|
Definition
| The maximum doppler shift is an angle of 0 degrees. This isn't possible with vascular though. |
|
|
Term
| What is the optimal doppler shift? |
|
Definition
| The optimal doppler shift is an angle between 45-60 degrees. |
|
|
Term
| The closer the angle to 0 degrees... |
|
Definition
| the more accurate the velocity measurement. |
|
|
Term
| Explain Christian Doppler |
|
Definition
| - He first demonstrated doppler shift in 1842 when he had a musician play a note while on a train. |
|
|
Term
| Explain what Shigeo Satomura did. |
|
Definition
- in 1957 Satomura constructed an ultrasonic doppler to DETECT blood flow in arteries.
- Within a couple years Kaneco who worked with Satomura on the project developed a spectrum analyzer, to LOOK at the display. (Could look but still not do any measurements). |
|
|
Term
| What did D.W. Baker and H.F. Stegall do? |
|
Definition
| - They introduced the first doppler instrument intended to measure the transcutaenous blood flow velocity in man. They used continuous wave doppler with two piezoelectric crystals, with one constantly emitting signals and the other constantly receiving signals. The change in frequency from emission to received was then used to estimate blood flow velocity. |
|
|
Term
|
Definition
| Described the first COMBINED use of B-mode ultrasonography and pulsed doppler velocity DETECTION, introducing the term duplex scanning. Flow velocity was not MEASURED. This was in 1974. |
|
|
Term
| What became available in the late 1970s? |
|
Definition
| Combined real-time B-mode imaging and pulsed doppler velocity MEASUREMENT became available, which today is known as duplex imaging. |
|
|
Term
| What is triplex scanning? |
|
Definition
| The combination of duplex scanning and doppler sonography. |
|
|
Term
| What can blood flow velocity be displayed in? |
|
Definition
- Color
- Doppler Audio
- Spectral Analysis |
|
|
Term
|
Definition
- The calculated velocity represents color from the color map.
- Flow TOWARDS is generally represented in RED.
- Flow AWAY is generally represented in BLUE.
- Operator CAN reverse the color map. (This is why I have to hit doppler invert when I start scanning because the veins are usually in red, and arteries are in blue) |
|
|
Term
| What does a high pitched sound coming from doppler audio indicate? |
|
Definition
| - A large doppler shift, indicating the presence of high velocities. |
|
|
Term
| What does a low pitched sound mean? |
|
Definition
| Means a small doppler shift, and the presence of lower velocities. |
|
|
Term
| What determines FLOW DIRECTION with Doppler audio? |
|
Definition
| - Flow moving towards the transducer comes out of one speaker, and flow moving away from the transducer comes out of the other speaker. |
|
|
Term
| What will you hear from laminar flow with doppler audio? |
|
Definition
| Laminar flow presents smooth, pleasant tone. |
|
|
Term
| What will you hear from turbulent flow with audio doppler? |
|
Definition
| You will hear a high pitched and whisteling or harsh and raspy sound. |
|
|
Term
| What does the audio output remain an indespensable guide for? |
|
Definition
| - For the operator to achieve proper orientation of the ultrasound beam. |
|
|
Term
| What are the limitations of audio doppler? |
|
Definition
- Subjective Interpretation (criteria can vary from tech to tech's opinion)
- lack of a permanent objective record (no set standard for what sound should represent) |
|
|
Term
| Are audio output of doppler and stethoscope the same or even similar? |
|
Definition
| NO, THE AUDIO OUTPUT OF DOPPLER IS NOT THE SAME AS HEARD IN A STETHOSCOPE |
|
|
Term
| Stethoscope Vs. Doppler Audio |
|
Definition
STETHOSCOPE: Transmits pressure waves or vibrations as a result of rapid accelerations and decelerations of blood.
DOPPLER AUDIO: The audio display of the doppler frequency shift created by the red blood cells moving in the path of the ultrasound beam. It does NOT occur in nature. |
|
|
Term
| What is spectral analysis? |
|
Definition
- A graphy of velocity (or delta frequency) vs time.
> Velocity or delta f on y-axis
> Time on x axis |
|
|
Term
| On a spectral analysis, flow velocity towards the transducer... |
|
Definition
| is displayed ABOVE the baseline. |
|
|
Term
| On a spectral analysis, flow velocity away from the transducer... |
|
Definition
| shows BELOW the baseline. |
|
|
Term
T or F
Can a operator invert the spectral analysis, above or below baseline or scale based on direction of flow velocity. |
|
Definition
|
|
Term
| BRIGHTNESS of the pixel... |
|
Definition
| represents AMPLITUDE of the returning echo = AMOUNT OF BLOOD moving at that velocity. |
|
|
Term
| Explain what a spectral analysis looks like when the flow is LAMINAR. |
|
Definition
| - When the flow is laminar the red blood cells are accelerating and decelerating at all the approximate same velocity, a neat envelope of similar velocities are recorded over time. (Clear window) |
|
|
Term
| Explain what a spectral analysis looks like when flow is TURBULENT. |
|
Definition
| - There are many different velocities detected at any one time (wide spectrum of velocities). Display of the velocities that are low, mid, high is called spectral broadening or window filling. |
|
|
Term
| What is another name for spectral broadening? |
|
Definition
|
|
Term
| Explain step 1 in guidelines to using PW doppler |
|
Definition
1. Obtain a long axis view of the vessel
> Never use cross-sectional view, even though there may be color filling and a velocity reading, it is never accurate because the doppler angle is not measured WITH the flow. |
|
|
Term
| Explain step 2 in guidelines to using PW doppler |
|
Definition
- Place cursor in the vessel wall parallel to the vessel flow, and the direction of the flow.
> A controversy exists in our field whether the cursor should be placed parallel to the flow, or to the vessel wall. In a healthy vessel, flow will be parallel to the wall, but with advanced plaque, this could be very different. For our reasons we will stick with staying parallel to the VESSEL WALL. |
|
|
Term
| Explain step 3 in guidelines to using PW doppler |
|
Definition
- Doppler angle should be between 45-60 degrees.
- An angle greater than 60, means the calculated blood flow velocity is greatly overestimated.
- An angle less than 30 degrees means a critical angle between soft tissue and blood may be reached. Imaging and doppler wouldn't be possible.
- An angle of 0 degrees gives the maximum doppler shift, however most vessels run parallel to the skin. |
|
|
Term
| How can you obtain a proper angle? |
|
Definition
| By heel-toe and angle steer function. |
|
|
Term
| Explain step 4 in guidelines to using PW doppler |
|
Definition
- Sample volume (gate size) should be approximately 2/3 the diameter of the vessel
> If it is larger than the gate will pick up the smaller velocities of the vessel wall and cause spectral broadening.
> In a very tight stenosis (small velocity) you need to increase sample volume to detect slow motion.
- In the vein, gate size can take up the whole diameter of the vessels because spectral broadening has no diagnostic value in venous disease. Also blood flow velocity in the center of the vein is not so different from along the walls. |
|
|
Term
| Quick summary of the guidelines to PW doppler. |
|
Definition
1. Get vessel in long axis
2. Place cursor in vessel, parallel to the flow and in the direction of flow.
3. Doppler angle should be between 45-60 degrees.
4. Open sample volume (gate size) to 2/3 of the vessel diameter. |
|
|
