chapter 19 doppler pt 1 basics

a change in frequency due to the doppler effect

• doppler shift

• demodulation

• doppler frequency

• velocity

• speed

in a normal incidence why does the vessel appear without color(figure A) ?

• angle between direction of flow and direction of sound beam is parallel

• angle between direction of flow and direction of sound beam is perpendicular at 90degrees

• color box is steered

• not enough information

disadvantages of power mode

• • - increased sensitivity to low flow

  • - unaffected by doppler angles

  • - no aliasing

• • - no measurement of velocity of or direction

  • - lower frame rates (creating reduced temporal resolution) susceptible to motion of the transducer, patient or soft tissue

• multiple ultrasound pulses used to accurately determine blood velocities

• • - more time needed to acquire data

  • - reduced frame rate

  • - decreased temporal resolution

what does switching to a lower frequency do ?

• increase nyquist limit

• decrease Doppler shift/frequency

• remains the same

more aliasing is created with ;

• • - faster blood velocity

• higher frequency transducer

• deep gate

• shallow gate

• lower frequency

inaccurate measurement of high velocity signals (aliasing)

• disadvantages of pulsed wave doppler

• advantages of CW doppler

• nondirectional doppler

• disadvantages of CW doppler

• advantages of pulse wave doppler

advantages of pulsed wave doppler

• being able to select the exact location where velocities are measured(range specificity) and can use a sample gate

• measures movement of blood cells presence of shift but cannot distinguish direction

• ability to accurately measure very high velocities

• does not use backing material so it results in undampened transmitted signal, narrow bandwidth, high quality factor, higher sensitivity

• inaccurate measurement of high velocity signals (aliasing)

true or false

• - laminar flow on spectral analysis has a broad spectral window

• false

• true

Answer explanation

false because that is describing turbulent flow not laminar flow

what are disadvantages of CW doppler

• the exact location of the moving blood cells cannot be determined(range ambiguity) and there is lack of TGC

• measures movement of blood cells presence of shift but cannot distinguish direction

• being able to select exact location where velocities are measured(range specificity) and can use a sample gate

• oes not use backing material so it results in undampened transmitted signal, narrow bandwidth, high quality factor, higher sensitivity

• ability to accurately measure very high velocities

what is the cosine for 180°

• -1.0 because it is parallel and away from transducer

• 1 because it is parallel and toward the transducer

• 0.5 because it is one-half of the value

• 0 because it is perpendicular and away from transducer