Display of Motion & Doppler Ultrasound Resident Class

Blood Flow Characterization 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 Turbulent 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 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 Low Velocity Large Cross-section Same Volume Flow Rate

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 If narrowing is long 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 90 degrees q angle between sound travel & flow 0 degrees flow in direction of sound travel 90 degrees flow perpendicular to sound travel

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

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

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

Relationships 2 X fo X v X cosq 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 q q

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

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

Doppler Relationships 77 X fD (kHz) 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 No Image 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 pulses required when multiple focuses used 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 range Frequency Elapsed Time

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

"Color Power Angio" of the Circle of Willis 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