Doppler Physics and Instrumentation

sonographic instruments measure:

sonographic instruments calculate:

Doppler shift range

the difference of frequency of the received sound and the frequency of transmitted sound

• combination of 2D gray-scale imaging and Doppler information (color Doppler, power Doppler, spectral Doppler)

• allows for placing sample volume in a specific vessel

presents real-time blood flow or tissue motion information along with gray-scale anatomic imaging

non-Doppler shifted echoes create ___________________

Doppler shifted echoes are detected in the ________________

the signal processor uses a mathematical technique called ______________

determines the mean, variance, and sign of the Doppler shift signal at each location along the scan line

measures dispersion or the spread around the mean

____________ Doppler samples (locations) per scan line

multiple _________________ are involved in all images with autocorrelation because they are required in the autocorrelation process

___________ pulses = 1 scan line with autocorrelation

____________ pulse = 1 scan line with gray-scale

a bigger color box lowers the _______________ because it takes time to generate more scan lines

the color map provides _________________ information

color perceived by viewer

brightness

the amount of hue in a mix with white

upper limit of Doppler shift that can be properly displayed by pulsed-wave

if Doppler shift exceeds ½ the _____________, aliasing occurs

improper color progression—>red to yellow to green to blue

if there is _________________, red and blue will be separated by black

advantages of color Doppler:

color Doppler limitations:

to fix color bleeding:

to fix color noise:

• number of pulses used for each color scan line

• if high—>improved accuracy, improved detection of slow flow, decreased FR

• selects gray-scale echo strength

• lower strength echoes displayed as color

__________ PRF allows for display of slow flow (small fD)

___________ PRF is for fast flow or eliminating aliasing

smoothing/persistence reduces ______________

• threshold below which weak echoes are eliminated

• reduces noise

• rejects frequencies below a threshold

• too low—wall motion appears in color

• too high—slow blood flow signals will be removed

• sudden burst of color beyond region of blood flow

• improper display of color caused by movement of transducer or tissue (cardiac motion, artery pulsatility, respiration, talking, peristalsis)

to reduce flash:

• additional color display at wrong location

• occurs when vessel lies proximal to a highly reflective interface

to reduce mirror image artifact:

presents 2D Doppler information by color encoding the amplitude of the Doppler shifts

in power Doppler, the power of the Doppler shift is determined by the _________________ of the moving scatterers

advantages of power Doppler:

disadvantages of power Doppler:

• presents Doppler shift frequencies in order

• determines their sign

• provides quantitative data for evaluating Doppler shift

• a quadrate phase detector separates forward and reverse Doppler shift voltages

• splits received frequencies into 2 channels (positive shift and negative shift)

• occurs within the signal processor

___________________ is also known as Doppler shift detector

• converts Doppler shift information into a visual spectrum

• breaks down complex signals into individual frequencies which display as vertical lines

• occurs within the signal processor

______________ is also known as the spectrum analyzer

• detects the Doppler shift within the region of overlap between the beams of transmitting and receiving transducer elements

• no depth selectivity

• emits ultrasound pulses and receives echoes using a single element transducer or array

• ability to select information from a particular depth (range gating, sample volume)

• dual element transducer assemblies (one for transmitting and one for receiving)

• not damped

• the region over which Doppler info can be acquired (Doppler sample volume) is the region of overlap between the transmitting and receiving beams

• part of the beam former in CW Doppler instrument

• produces a continuously alternating voltage that drives the transducer element

the signal processor in a CW Doppler instrument includes:

• damped using a single element transducer or array

• pulses are longer than those used in imaging

• line superimposed on the B-mode images that shows the path of the sound beam

• used in both CW and PW

enables depth selectivity and a small Doppler sample volume

PW is a ___________________

with sample volume, width is equal to the _______________ at the sample volume

with sample volume, length is limited by the __________________

a small sample size leads to a ____________ range of fDs

a large sample size leads to a ____________ range of fDs

• vertical thickening of the spectral trace (filling in of spectral window)

• produced by disturbed or turbulent flow

• can also be demonstrated with a large sample size in a vessel with laminar flow

the cosine of the angle and the Doppler angle are ______________ related

the angle should be set parallel with ________________

• amplifies received Doppler signal

• affects both spectral display (brightness) and volume

• should be set high enough to display low flow, but not so high that it produces noise

• adjusts intensity of the transmitted beam

• increased transmitted intensity increases sensitivity

• should be balanced with Doppler gain

• moderate setting is ideal

• aka velocity scale

• adjusts max velocity displayed on spectrum

• low scale for low velocity flow and high scale for high velocity flow to avoid aliasing

__________ sweep speed is good for detailed waveform analysis

_____________ sweep speed is good for inclusion of multiple waveforms, venous response to limb compressions, demonstrate respiratory phasicity

• aka high-pass filter

• removes data below selected frequency

• too low—>may demonstrate artifacts

• too high—>may eliminate low velocity flow

• high-intensity, low-frequency Doppler shifts

• caused by heart, vessel wall, or cardiac valve motion

• a type of mirror-image artifact

• duplication of flow on the opposite side of the baseline

• occurs when the quadrate phase detector is saturated and there is leakage into the opposite direction channel

• important to determine if flow is real or artifact

cross-talk can be eliminated by: