Display of Motion Doppler Ultrasound Resident Class Hemodynamics

Display of Motion & Doppler Ultrasound �Resident Class

Hemodynamics Blood Flow Characterization �Plug �Laminar �Disturbed �Turbulent

Plug Flow �Type of normal flow �Constant fluid speed across tube �Occurs near entrance of flow into tube

Laminar Flow �also called parabolic 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

Flow �Disturbed Flow �Normal parallel stream lines disturbed �primarily forward particles still flow �Turbulent 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 & 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 Variations �pressure & flow in arteries fluctuate with pulse �pressure & flow in veins much more constant �pulse variations dampened by arterial system

Flow Rate Measurements �Volume flow rate �Volume of liquid passing a point per unit time �Example � 100 ml / second

Flow Rate Measurements �Linear flow rate �Distance liquid moves past a point per unit time �Example � 10 cm / second

Flow Rate Measurements Volume Flow Rate = Linear flow rate X Cross Sectional Area

Flow Rate Measurements Volume Flow Rate = Linear flow rate X Cross-sectional Area High Velocity Small Cross-section Same Volume Flow Rate Low Velocity Large Cross-section

Volume 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.

Stenosis �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

Stenosis �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 Shift �difference between received & transmitted frequency �caused by relative motion between sound source & receiver �Frequency shift indicative of reflector speed IN OUT

Doppler 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

Doppler Angle �angle between sound travel & flow � 0 degrees � flow in direction of sound travel � 90 degrees � flow perpendicular to sound travel

Flow Components �Flow vector can be separated into two vectors Flow parallel to sound Flow perpendicular to sound

Doppler Sensing �Only flow parallel to sound sensed by scanner!!! Flow parallel to sound Flow perpendicular to sound

Doppler Sensing �Sensed flow always < actual flow Actual flow Sensed flow

Doppler Sensing �cos( ) = SF / AF Actual flow (AF) Sensed flow (SF)

Doppler Equation 2 X fo X v X cos f D = fe - fo = ------------c �where f. D =Doppler Shift in MHz fe = echo of reflected frequency (MHz) fo = operating frequency (MHz) v = reflector speed (m/s) = angle between flow & sound propagation c = speed of sound in soft tissue (m/s)

Relationships 2 X fo X v X cos f D = fe - fo = ------------c �positive shift when reflector moving toward transducer �echoed frequency > operating frequency �negative shift when reflector moving away from transducer �echoed frequency < operating frequency

Relationships 2 X fo X v X cos f D = fe - fo = ------------c �Doppler angle affects measured Doppler shift cos

Simplified (? ) Equation 2 X fo X v X cos f D = fe - fo = ------------c 77 X f. D (k. Hz) v (cm/s) = -------------Simplified: fo (MHz) X cos �Solve for reflector velocity �Insert speed of sound for soft tissue �Stick in some units

Doppler Relationships 77 X f. D (k. Hz) v (cm/s) = -------------fo (MHz) X cos �higher reflector speed results in greater Doppler shift �higher operating frequency results in greater Doppler shift �larger Doppler angle results in lower Doppler shift

Continuous Wave Doppler �Audio presentation only �No image �Useful as fetal dose monitor

Continuous 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

Continuous Wave Doppler: Receiver Function �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 - =

Pulse Wave vs. Continuous Wave Doppler Continuous Wave Pulse Wave No Image Sound on continuously Both imaging & Doppler sound pulses generated

Doppler 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 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 used pulses required when multiple focuses �several pulses may be required along a scan line to determine Doppler shift

Duplex Doppler Gates �operator indicates active Doppler region on display �regions are called gates �only sound in gate analyzed for frequency shift �can be isolated based on delay time after pulse Gate

Spectral Display �shows range of frequencies received �amplitude of each frequency indicated by gray shade �can be displayed real time �fast Fourier Transform (FFT) technique Frequency frequency range Elapsed Time

Spectral Broadening �display indicates range of frequencies �corresponds to range of speeds of blood cells �range indicative of type of flow Frequency frequency range � laminar, disturbed, turbulent Time

Pulse Wave Doppler �Allows range selectivity �monitor Doppler shift (frequency difference) at only selected depth(s) �ability to separate flow from >1 vessel or localize flow within vessel

Spectral vs. Color-Flow �spectral Display shows frequency range directly �Color Doppler’s color represents complete spectrum at each pixel Frequency frequency range Elapsed Time

Power Doppler �AKA �Energy Doppler �Amplitude Doppler �Doppler angiography �Magnitude of color flow output displayed rather than Doppler frequency signal �flow direction or different velocities not displayed "Color Power Angio" of the Circle of Willis