Exam 5 Flashcards

Question

What Doppler angle has a cos of (1) What Doppler angle has a cos of (.5) What Doppler angle has a cos of (0) How are cos and Doppler angle related? What is the best angle for 2D gray scale imaging, what is the most accurate angle for Doppler?

Answer 1

What Doppler angle has a cos of (1) 0 What Doppler angle has a cos of (.5) 60 - Half of actual doppler shift What Doppler angle has a cos of (0) 90 no doppler shift can be measure. How are cos and Doppler angle related? Indirectly What is the best angle for 2D gray scale imaging, what is the most accurate angle for Doppler? 60 Or less

Answer 2

Spectral doppler display

Answer 3

Fast Fouier Transform (FFT) How doppler info gets from transducer to graph

Answer 4

Spectral broadening - Spectral window filled in

Answer 5

The presence of a spectral window implies the presence of laminar flow.

Answer 6

How many crystals? 2 crystals – one constantly transmits and one constantly receives reflections from the red blood cells. ADVANTAGE: Accurately measure very HIGH velocities (Aliasing artifact does not occur) , Small probe size, & higher frequencies can be used. No speed limit. DISADVANTAGE: Exact location of the red blood cells cannot be determined. Signals are arising from all blood cells in the region of beam overlap – RANGE AMBIGUITY

Answer 7

How many crystals? 1 Single crystal will transmit and than wait to receive the returning signal ADVANTAGE: Able to select the EXACT location, this is called RANGE RESOLUTION or RANGE SPECIFICITY DISADVANTAGE: Inaccurate measurement of high velocity signals, the high velocity flow in one direction will be incorrectly displayed as traveling in the opposite direction, this is known as ALIASING.

Answer 8

Aliasing is the most common error associated with doppler ultrasound. Aliasing occurs when velocity is above the nyquist limit.

Answer 9

By equation Nyquist limit (Hz)=(PRF(Hz))/2 This equation states that the highest frequency shift that can be measured is equal to one half the pulse repetition frequency.

Answer 10

1. Increase PRF scale setting will Raise the Nyquist limit 2. Lower baseline 3. Depth – move transducer so image is shallow 4. Frequency- lower frequency = smaller doppler shifts are less likely. To exceed Nyquist limit (higher frequency =higher doppler shift thus creating more aliasing) 5. Continues wave transducer – because this has no aliasing

Answer 11

Color Doppler What velocities are displayed by color Doppler? Averae/mean velocity Is color Doppler continuous wave or pulsed wave? Pulsed What are the two types of color maps used to display color Doppler information? Velocity or Variance Mode What is advantage of a larger color packet/ensemble? More accurate velocity measurement What is a disadvantage? Increased sensitivity to low flow

Answer 12

Power Doppler (energy mode or angio mode) Does Power Doppler report velocities or direction? Only identifies the presence of the doppler shift, no speed or direction. The strength (amplitude) of the reflected signal is processed not the direction or speed. Advantages: 1. ) Increased sensitivity to LOW flow 2. ) Unaffected by Doppler angle (unless exactly 90* 3. ) NO aliasing (velocity information ignored) Disadvantages: 1. ) No velocity Measurement 2. ) Lower temporal resolution 3. ) Susceptible to motion artifact (flash artifact)

Answer 13

Doppler Artifacts • Crosstalk o A Spectral doppler form of “mirror image” artifact o Appears as identical doppler spectrum above and below the baseline. why does crosstalk occur? Gain is TOO HIGH -OR- Angle is close to 90* How to fix cross talk; Decrease gain Adjust angle (<90*)