doppler principle

8/13/2019 Doppler Principle

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Doppler Principles

Rachel Lin

GI-US-CAS


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Optimization of ColorBy

Angela Spink


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What is Sensitivity?

Errrrrmmmm.


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PhilipsGlobal Training and Education 4

Sensitivity

Defined as the sampling rate per scanline

Also called Ensemble length

High sensitivity provides better color fill

and edge detection in small vessels

However, frame rate decreases


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Sensitivity

Temporal resolution

Spatial resolution

Uniformity


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Sensitivity Relationships

Temporal resolution

Spatial resolution


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Temporal Resolution

Frame rate determined by number of lines per frame

Number of lines per frame determined by ensemble length

Compromise between accurate color estimation and

frame rate


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Spatial resolution

Axial Defined by sampling time interval

Compromise with velocity estimate accuracy

Lateral

Defined by beam width and line density

Spatial filtering diminishes random color variations

Pixels only coded if neighboring pixels were previously

coded


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TRADE OFFs

SPATIAL RESOLUTION TEMPORAL RESOLUTION

Decrease PRF

Increase Color Sensitivity

Increase Color Line density

Decrease Frame Rate

Decrease Frame Rate

Decrease Frame Rate


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Methods to Increase Sensitivity

Reduce the field depth

Decrease color filter

Decrease PRF

Increase color gain

Increase color line density

Increase system power Use higher frequency transducer


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Methods to Increase Frame Rate

Reduced Doppler frequency

Increase PRF

Decrease color Box size

Change transducer position to minimize depth

Decrease sensitivity

Decrease persistence


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Initial Adjustments

Select appropriate probe for application

Frame rate and sensitivity is a compromise

Need to consider lower frequency if scanning at depth

Sector probe better penetration than curvilinear

Select appropriate TSI

Sensitivities are set for fast/slow flow and depth


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Initial Adjustments

Optimize the color box

Narrow the sector width to improve frame rate

Steer box to obtain optimal Doppler angle

Straight angle can improve sensitivity at depth, e.g vertebral artery


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Color Doppler ImagingSteer


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Adjustment of main Settings

COLOR GAIN

Set as high as possible without displaying random speckle

If set too low: under-estimation of large flow disturbances

Level of gain will vary when other parameters are changed


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Adjustment of main Settings

VELOCITY RANGE

Scale or PRF controls range of velocities displayed

Low velocity range will delineate stenotic jets

Increasing range changes point at which aliasing occurs PRF can be reduced below a diagnostic level causing loss of sensitivity and slow frame

rates


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Adjustment of main settings

ALIASING occurs

the color wraps to the opposite color

this aids in placement of sample volume


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Color Doppler ImagingEcho Write Priority


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Color Power AngioCPA


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Color Power AngioDirectional CPA (DCPA)


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Color Power AngioDCPA Mode


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Chris Sanchez, Boulder CO, USA


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Optimizing the Doppler

Phillip Medical SystemRachael Lin


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Basic Doppler Principles


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What is the Doppler Effect?

Based on work by Austrian

physicist Johann Christian

Doppler


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What is the Doppler Effect?

Apparent change in received frequency due to

relative motionbetween a sound source and

sound receiver

Source moving TOWARD receiver = frequency

Source moving AWAY from receiver = frequency


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Still Sound Source


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Still Sound Source

Both hear same frequencycarrier frequency


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Moving Sound Source


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TheDopplerEffect

Decreased Frequency

Source moving AWAY


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TheDopplerEffect

Increased Frequency

Source moving TOWARDS


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The Doppler Equation

TheDoppler shift (frequency) is equal totwice the velocity of the moving object,multiplied bycosof the angle at which it ismoving relative to the observer, divided by

the speed of the carrier wave (light/sound,etc)

Doppler Shift = 2 v f cosC


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Doppler Equation

The velocity of the moving object can be

calculated from the Doppler frequency!

But remember that cos This is whyangle correctionis so important!

cos 60= 0.5


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Spectral DopplerAngle Correct

Angle Correction


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Spectral DopplerSteer

Steer


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Spectral DopplerSteer


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Spectral DopplerScreen Information


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Spectral DopplerSample Volume Size


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Doppler Display

The spectral waveform represents the audible signal and provides

information about

thedirectionof the flow

how fast the flow is traveling (velocity)

thequalityof the flow (normal vs. abnormal)


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The Direction of Flow

Flow coming TOWARD the scanhead is represented above the baseline

Flow traveling AWAY from the scanhead is represented below the

baseline

Zero

Baseline


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< 90 towards

the transducer

= positive flow


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Cos 90 = 0

=no Doppler shift


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< 90 degrees away

from the transducer= negative flow


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Spectral DopplerFlow Direction

Flow towards the

transducer

Flow away from thetransducer


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Velocity of Flow

Measuring the spectral trace provides information about velocity of flow

Freq/Velocity

Time


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Velocity of Flow

Faster Flow Slower Flow

cm/s cm/s


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What if the velocity is too high to display?

This effect is called ALIASING

The Doppler sample rate (PRF) is not adequate for high frequency

shifts


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What if the velocity is too high to display?

The peaks are cut off and displayed below baseline from the bottom up


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Quality of Flow

Other more complex measurements of the trace provide values such as

Resistive Index (RI)

Pulsatility Index (PI)

Systolic/Diastolic Ratio (S/D ratio)

Acceleration and Deceleration Times


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Spectral Analysis

Each of these measurements has a normal range of values for specific

clinical applications

The amount of disease present is based on these calculated values

Also, the ENVELOPE or WINDOW provides information about the

quality of flow


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Spectral Analysis

Low Resistance Waveform


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Spectral Analysis

High Resistance Waveform


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Spectral DopplerHigh Q


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Clinical Uses of Doppler

Vascular

Carotid Artery Stenosis

Peripheral Artery and Vein Disease (legs & arms)

TCD (Transcranial Doppler)

Cardiology Valve Disease

Cardiac function


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Abdominal

Renal Artery Stenosis

Portal Vein Flow

Tumor Flow (RI, PI, etc.) to evaluate benign vs. malignant


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Small Parts (thyroid, testicle, breast, prostate)

Tumor Flow (RI, PI, etc.) to evaluate benign

vs. malignant

OB/Gyn

Ovarian Cancer Screening

Placental, Circle of Willis, Umbilical Cord

for fetal growth disorders

Fetal Heart Abnormalities


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What defines a good Doppler display?

Minimal background noise

Clean window/envelope in normal flow states

Clear audible signal

Accurate display of velocities


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Clinical Challenges with Doppler

Obtaining the appropriate Doppler angle

Doppler in deep vessels/large patients

Displaying high PRFs found in abnormal flow states without aliasing

(PW Doppler)


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Phili Gl b l T i i d Ed ti

doppler principle

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