Resident Categorical Course Doppler Ultrasound Resident Categorical Course

Laminar Flow also called parabolic flow fluid layers slide over one another central portion of fluid moves at maximum speed flow near vessel wall hardly moves at all friction with wall

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 Quantity of flow is function of Pressure Resistance Heart provides pulsating pressure

Flow and Pressure Low Pressure Low Flow High Pressure High Flow

Resistance to Flow more resistance = lower flow rate resistance affected by fluid’s viscosity vessel length vessel diameter

Resistance to Flow Less Viscosity More Flow More Viscosity Less Flow

Resistance to Flow Shorter Vessel More Flow Longer Vessel Less Flow

Resistance to Flow Larger Diameter More Flow Smaller Diameter Less Flow

Flow Variations Large fluctuation in pressure & flow in arteries with pulse Less fluctuation in pressure & flow in veins pulse variations dampened by arterial system

Normal Vessel Distensible Vessel expands during systole Expands & contracts with pressure changes Changes over cardiac cycle Vessel expands during systole Vessel contracts during diastole

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

Any change in flow rate would mean you’re gaining or losing fluid. Volume Flow Rates constant volume flow rate in all parts of closed system 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 flow resistance 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 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

Doppler Angle Angle between direction of sound and direction of fluid flow q

Flow perpendicular to sound Doppler Sensing Flow vector can be separated into two vectors Only flow parallel to sound sensed by scanner!!! Sensed flow always < actual flow Flow parallel to sound Flow perpendicular to sound

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 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) v

Relationships Positive Doppler shift Negative Doppler shift 2 X fo X v X cosq f D = fe - fo = ------------------------- c Positive Doppler shift reflector moving toward transducer echoed frequency > operating frequency Negative Doppler shift 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 Larger angle Smaller cosine Small 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 Constant 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 2 transducers used one continuously transmits one continuously receives

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 Different Imaging & Doppler pulses short pulses required for imaging Accurate echo timing 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 defines active Doppler region (gate) only sound in gate analyzed

Spectral Display Displays real-time range of frequencies received amplitude of each frequency indicated by brightness display indicates range of frequencies received corresponds to range of speeds of blood cells indicative of type of flow laminar, turbulent

Absolute Speed Measurement Absolute speed measurements must include Doppler angle angle between flow & sound propagation Indicated by operator Accuracy affects flow speed accuracy

Relative 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 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-Flow spectral Display shows detailed frequency data for single location Color Doppler’s color represents complete spectrum at each location in window

"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