Display of Motion & Doppler Ultrasound Resident Class.

Display of Motion&

Doppler Ultrasound

Display of Motion&

Doppler Ultrasound• Resident Class

George DavidAssociate Professor

News FlashNews Flash

The following slides describe motion or m-modem-mode

ultrasound. M-mode does not use Doppler but does

display motion.

B ModeB Mode• 1-dimensional display of single pulse

Each echo displayed as dot along line

• X-axis is pulse echo time

• Echo intensity portrayed as brightness of spot

• reflector motion seen as motion of spot along line

Pulse Echo Time

B ScanB Scan• 2 dimensional image

• collection of B mode scan lines each pulse produces single line direction of lines indicates direction of sound pulses

• image filled in by scanning (moving) sound beam

Echo Delay Time

• stands for Motion mode

• M mode is moving B mode

• shows variations in brightness over time

M ModeM Mode

Elapsed Time

Each vertical line is one pulse

Echo Delay Time

M ModeM Mode

Elapsed Time


Echo Delay Time

• horizontal axiselapsed time (not time

within a pulse)

• vertical axistime delay between pulse &

echo» indicates distance of

reflector from transducer

M ModeM Mode

Elapsed Time


Echo Delay Time

• reflections for 1 pulse shown on vertical line

• application example» heart studies» useful in quantifying

structure motion


M-Mode (left ventricle)M-Mode (left ventricle)

M-Mode (1st Trimester Fetal Heart)

M-Mode (1st Trimester Fetal Heart)

Cardiac Pulsations


HemodynamicsHemodynamics

• Plug

• Laminar

• Disturbed

• Turbulent

Blood Flow Characterization


Plug FlowPlug Flow

• Type of normal flow

• Constant fluid speed across tube

• Occurs near entrance of flow into tube

Laminar FlowLaminar Flow• also called parabolic flowparabolic flow• fluid layers slide over one

another• occurs further from entrance to

tube• central portion of fluid moves

at maximum speed• flow near vessel wall hardly

moves at all friction with wall

FlowFlow

• Disturbed FlowDisturbed Flow Normal parallel stream lines disturbed primarily forward particles still flow

• Turbulent FlowTurbulent Flow random & chaotic individual particles flow in all directions net flow is forward Often occurs beyond obstruction

such as plaque on vessel wall

Flow, Pressure & ResistanceFlow, Pressure & Resistance• Pressure

pressure difference between ends of tube drives fluid flow

• Resistance more resistance = lower flow rate resistance affected by

» fluid’s viscosity» vessel length» vessel diameter

flow for a given pressure determined by resistance


Flow VariationsFlow Variations

• pressure & flow in arteries fluctuate with pulse

• pressure & flow in veins much more constant pulse variations dampened by arterial system


Normal VesselNormal Vessel

• Distensible Expands & contracts with

» pressure changes

» Changes over cardiac cycle

• Vessel expands during systole

• Vessel contracts during diastole

Flow Rate MeasurementsFlow Rate Measurements• Volume flow rate

Volume of liquid passing a point per unit time

• Example 100 ml / second

Flow Rate MeasurementsFlow Rate Measurements• Linear flow rate

Distance liquid moves past a point per unit time

• Example 10 cm / second

Flow Rate MeasurementsFlow Rate Measurements

Volume Flow Rate = Linear flow rate X Cross Sectional Area

Flow Rate MeasurementsFlow Rate MeasurementsVolume Flow Rate = Linear flow rate X Cross-sectional Area

Same Volume Flow Rate

High VelocitySmall Cross-section Low Velocity

Large Cross-section

Volume Flow RatesVolume Flow Rates• constant volume flow rate in

all parts of closed system

Sure! Any change in flow rate would

mean you’re gaining or losing

fluid.


StenosisStenosis

• narrowing in a vessel• fluid must speed up in stenosis to

maintain constant flow volume no net gain or loss of flow

• turbulent flow common downstream of stenosis


StenosisStenosis

• If narrowing is short in length Little increase in overall resistance to flow Little effect on volume flow rate

• If narrowing is long Resistance to flow increased Volume flow rate decreased



Doppler ShiftDoppler Shift

• difference between received & transmitted frequency

• caused by relative motion between sound source & receiver

• Frequency shift indicative of reflector speed

IN

OUT

Doppler ExamplesDoppler Examples• change in pitch of as object approaches

& leaves observer train Ambulance siren

• moving blood cells motion can be presented as sound or as an image

http://images.google.com/imgres?imgurl=www.users.waitrose.com/~laceyhelen/train.jpg&imgrefurl=http://www.users.waitrose.com/~laceyhelen/cross.htm&h=432&w=390&prev=/images%3Fq%3Dtrain%26start%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26safe%3Doff%26sa%3DN


Doppler AngleDoppler Angle

• angle between sound travel & flow

• 0 degrees flow in direction of sound travel

• 90 degrees flow perpendicular to sound travel

Trig ReviewTrig Review

Side Adjacent(SA)

Side Opposite(SO)

Hypotenuse(H)

Right Angle

H2 = SA2 + SO2


Cosine FunctionCosine Function

Side Adjacent(SA)

Side Opposite(SO)

Hypotenuse(H)

Right Angle

Cosine () = SA / H


Cosine SummaryCosine Summary

Angle(degrees)

Cosine

0 130 .86645 .70760 .590 0

cosine

1

0

Angle0o 90o

Doppler AngleDoppler Angle

Angle between direction of sound and direction of fluid flow

Flow ComponentsFlow Components

Flow vector can be separated into two vectors

Flow parallel to sound

Flow perpendicular to sound

Doppler SensingDoppler SensingOnly flow parallel to sound

sensed by scanner!!!

Flow parallel to

sound

Flow perpendicular to sound

Doppler SensingDoppler Sensing

Sensed flow always < actual flow

Sensed flow

Actual flow

Doppler SensingDoppler Sensing

cos() = SF / AF

Sensed flow(SF)

Actual flow(AF)


Doppler EquationDoppler Equation

• wherefD =Doppler Shift in MHz

fe = echo of reflected frequency (MHz)

fo = operating frequency (MHz)v = reflector speed (m/s) = angle between flow & sound propagationc = speed of sound in soft tissue (m/s)

2 X fo X v X cosf D = fe - fo = ------------------------- c

RelationshipsRelationships

• positive shift when reflector moving toward transducer echoed frequency > operating frequency

• negative shift when reflector moving away from transducer echoed frequency < operating frequency


RelationshipsRelationships

• Doppler angle affects measured Doppler shift


cos

Simplified (?) EquationSimplified (?) Equation

• Solve for reflector velocity

• Insert speed of sound for soft tissue

• Stick in some units


77 X fD (kHz)v (cm/s) = -------------------------- fo (MHz) X cosSimplified:


Doppler RelationshipsDoppler Relationships

• higher reflector speed results in greater Doppler shift

• higher operating frequency results in greater Doppler shift

• larger Doppler angle results in lower Doppler shift

77 X fD (kHz)v (cm/s) = -------------------------- fo (MHz) X cos


Continuous Wave DopplerContinuous Wave Doppler

• Audio presentation only

• No image

• Useful as fetal dose monitor


Continuous Wave DopplerContinuous Wave Doppler

• 2 transducers used one continuously transmits

» voltage frequency = transducer’s operating frequency

• typically 2-10 MHz

one continuously receives

• Reception Area flow detected within overlap of

transmit & receive sound beams

• receives reflected sound waves

• Subtract signals detects frequency shift typical shift ~ 1/1000 th of source frequency

» usually in audible sound range

• Amplify subtracted signal

• Play directly on speaker

Continuous Wave Doppler:Receiver Function

Continuous Wave Doppler:Receiver Function

- =

Pulse Wave vs. Continuous Wave Doppler

Pulse Wave vs. Continuous Wave Doppler

Continuous Wave Pulse Wave

No Image Image

Sound on continuously

Both imaging & Doppler sound pulses generated


Doppler PulsesDoppler Pulses

• short pulses required for imaging minimizes spatial pulse length optimizes axial resolution

• longer pulses required for Doppler analysis reduces bandwidth provide purer transmitted frequency

» important for accurate measurement of frequency differences needed to calculate speed


Color-Flow Display FeaturesColor-Flow Display Features

• Imaged electronically scanned twice imaging scan processes echo intensity Doppler scan calculates Doppler shifts

• Reduced frame rates only 1 pulse required for imaging

» additional pulses required when multiple focuses used

several pulses may be required along a scan line to determine Doppler shift

• operator indicates active Doppler region on display regions are called gatesgates

• only sound in gate analyzed for frequency shift can be isolated based on delay time after pulse

Duplex Doppler GatesDuplex Doppler Gates

Gate


• shows range of frequencies received amplitude of each

frequency indicated by gray shade

• can be displayed real time fast Fourier Transform

(FFT) technique

Spectral DisplaySpectral Display

Elapsed Time

Frequency

frequencyrange


• display indicates range of frequencies

• corresponds to range of speeds of blood cells

• range indicative of type of flow laminar, disturbed, turbulent

Spectral BroadeningSpectral Broadening

Time

Frequency

frequencyrange

Pulse Wave DopplerPulse Wave Doppler• Allows range selectivityrange selectivity

• monitor Doppler shift (frequency difference) at only selected depth(s)

• ability to separate flow from >1 vessel or localize flow within vessel


Absolute Speed MeasurementAbsolute Speed Measurement

• all absolute measurements must include Doppler angleDoppler angle angle between flow & sound

propagationDopplerAngle

Doppler AngleDoppler Angle• Operator manually

indicates Doppler angle on display graphically line up arrow &

vessel

• Angle accuracy affects flow speed accuracy


Relative Speed MeasurementRelative Speed Measurement

• relative measurements can be useful Doppler angle not required

• indications of spectral broadening do not require absolute measurements

• ratio of peak-systolic to end-diastolic relative flows independent of angle

Color DopplerColor Doppler• User defines window superimposed

on gray scale image• For each location in window

scanner determines flow direction mean value Variance

• window size affects frame rate larger window = slower scanning more Doppler pulses required

Spectral vs. Color-FlowSpectral vs. Color-Flow

• spectral Display shows frequency range directly

• Color Doppler’s color represents complete spectrum at each pixel

Elapsed Time

Frequency

frequencyrange

Display of Motion & Doppler Ultrasound Resident Class.

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