Doppler Instruments and Hemodynamics

Comprehensive practice questions covering Doppler instrumentation types, flow characteristics, aliasing, spectral analysis, and waveforms associated with stenosis and collateral circulation.

What are the four types of Doppler instruments provided in a single duplex ultrasound machine?

Color Doppler, Power Doppler, Continuous wave Doppler, and Pulse wave Doppler.

What type of Doppler information is shown by Color Doppler instruments?

Mean velocities shown as color maps on a color bar and in the vessels.

In velocity mode Color Doppler, what does the black color in the middle of the color bar represent?

The baseline, which indicates no Doppler shift.

According to the transcript, what do red and blue usually represent in Color Doppler flow direction?

Red indicates flow toward the transducer; blue indicates flow away from the transducer.

What are the limitations of Color Doppler?

It is angle dependant, subject to aliasing, and provides limited velocity information (only mean velocities).

What are alternate names for Power Doppler instruments?

Color Doppler Energy, Color Power Angio, or Ultrasound Angio.

What is the primary advantage of Power Doppler over Color Doppler?

Higher sensitivity to slow flow or velocity (e.g., venous system or tissue perfusion) with no aliasing or angle dependency.

How many crystals are used by a Continuous Wave (CW) Doppler transducer?

Two separate crystals: one for transmission of impulses and one for receiving.

What is the primary disadvantage of Continuous Wave Doppler?

Range ambiguity, which is confusion about signals where vessels overlap.

What technique is used by both PW and CW Doppler for spectral analysis?

Fast Fourier Transformation (FFT).

In a spectral display, what is represented on the vertical and horizontal axes?

Velocities are on the vertical (Y) axis and time is on the horizontal (X) axis.

Describe the appearance of laminar flow in a spectral display.

Narrow spectral tracing with a clear spectral window (the black area under the trace).

What is the definition of the Nyquist Limit (NL)?

The upper limit of Doppler shift that can be detected properly by Pulsed Wave Doppler, equal to half of the Pulse Repetition Frequency ($NL = \frac{1}{2} \text{PRF}$).

List six methods to correct aliasing in Pulsed Wave Doppler.

1. Increase PRF (increase scale). 2. Move baseline to zero. 3. Change to a low frequency transducer. 4. Change window for a shallow sample volume. 5. Use a higher Doppler angle. 6. Use continuous wave Doppler.

What two factors determine the systolic and diastolic components of the cardiac cycle?

The systolic component depends on myocardial force of contraction (stroke volume), and the diastolic component depends on peripheral resistance.

What are examples of low resistant (low pulsatility) vascular beds?

Internal Carotid Artery (ICA), Vertebral, Renal, and Celiac artery branches.

What is the hallmark of a high resistant (high pulsatility) triphasic waveform?

The presence of reverse flow in early diastole.

What changes occur in the prestenotic zone spectral waveform proximal to a significant stenosis?

Increased pulsatility/resistance and decreased velocity throughout the cardiac cycle.

Which Doppler parameter is the first to increase in the stenotic zone and is a good marker for up to 50% stenosis?

Peak Systolic Velocity (PSV).

Which parameter is a good marker for severe stenosis (e.g., 50% to 70% diameter reduction)?

End Diastolic Velocity (EDV).

What are the characteristics of a damped spectrum in the post stenotic zone, also known as TardusParvus?

Slow systolic acceleration (Tardus), rounded PSV with low velocity (Parvus), and continuous diastolic flow.

How does the External Carotid Artery (ECA) react as a collateral vessel to an ipsilateral ICA stenosis?

The ECA shows a low resistant spectrum with relatively higher velocity than normal.

What happens to the vertebral artery when there is a Subclavian artery obstruction proximal to the origin of the vertebral artery?

It shows a high resistant spectrum, higher velocity than normal, and reversed flow direction to supply blood to the arm.