Echo Doppler Basics (9)

Doppler echo includes:
  - Color flow imaging (color): Allows visualization of blood flow direction and pattern.
  - Tissue Doppler Imaging (TDI): Assesses the movement of myocardial tissues.
  - Spectral Doppler:
    - Pulsed Wave (PW): Quantitative assessment from a specific sample volume, ideal for measuring lower velocities.
    - Continuous Wave Doppler (CW): Quantitative assessment from an entire line of scan, used for high-velocity measurements.
    - Tissue Doppler (PW): Similar to PW Doppler but for myocardial assessment.

Doppler is used for:
  - Assessing flow through valves.
  - Evaluating pulmonary venous flow into the left atrium (LA).
  - Monitoring hepatic venous flow.
  - Examining flow through the superior vena cava (SVC) and inferior vena cava (IVC).
  - Aortic flow assessment.
  - Differentiating tissue from blood based on velocity.

Normal velocities (measured in m/sec)
  - Tricuspid Valve (TV): < 1.0
  - Pulmonary Valve (PV): < 1.0
  - Mitral Valve (MV): < 1.3
  - Aortic Valve (AV): < 2.0
Memorization of these approximations is crucial for clinical practice.

Valvular Stenosis:
- A narrowing of the valve resulting in increased flow velocities.
- Occurs during forward (antegrade) flow through a valve.
Valvular Regurgitation:
- Occurs when a valve cannot close properly, leading to leakage and backward flow.
- This happens during the timeframe when the valve should be closed.

Color Doppler:
- Qualitative method offering insights into valve regurgitation or stenosis.
Pulsed Wave Spectral (PW):
- Quantitative method providing spectral signals from a specific sample volume.
Continuous Wave Spectral (CW):
- Quantitative method yielding spectral signals from all depths on the scan line, especially for very high velocities.

Order of images:
  1. 2D/M-mode (+/- zoom): Establish the anatomical structure first.
  2. Color Doppler: Assess for leakages or stenosis.
  3. Spectral Doppler (PW or CW): Quantify normal and abnormal flows.
Image order matters: Good 2D imaging leads to good Doppler assessments.

Flow direction indications:
- Blue: Flow away from the probe (Negative Doppler shift).
- Red: Flow towards the probe (Positive Doppler shift).
Color Doppler Characteristics:
- Color must not be inverted in echo assessments.
- Pulsed wave technique is susceptible to aliasing (ambiguity of direction at high velocities).

Components:
  - Flow direction: Expected patterns flow from atria to ventricles.
  - Flow velocity: Should be consistent with the cardiac cycle.
  - Antegrade flow: Normal forward flow during systole.

Ambiguous Flow Direction:
  - Lowers frame rate.
  - Subject to Nyquist Limit (if flow exceeds limit, will appear ambiguous).
  - Flow > 57 cm/s could be aliased, complicating interpretations.

Sensitivity: Can detect smaller amounts of blood flow (e.g., for PFO).
Region of Interest: Provides both anatomical and hemodynamic information in one image.
Laminar vs Turbulent Flow: Able to differentiate normal laminar flow from turbulent flow.

Aliasing: At high velocities if Nyquist limit is exceeded.
Directional Ambiguity: Flow moving perpendicularly can show multiple colors, complicating interpretations.

Look for Aliasing: Indicates high velocities and possible stenosis or regurgitation.
Know Expectations: Anticipate flow direction and characteristics of normal and abnormal flow.

Color adjustment parameters:
  1. Gain: Adjust until speckle visibility balances over/under-gaining.
  2. Scale: Set according to flow velocities (average: 50-75 cm/s; high: increase, low: decrease).
  3. Box Size: Must balance covering the valve with maintaining frame rate (ideal size is long and lean).
  4. Centering: Always center the subject within the color box, allowing room around it.

Adjustment parameters:
  1. Alignment: Aim for 0 or 180-degree Doppler angles for accuracy.
  2. Baseline: Should be set ¼ - ⅓ from the top or bottom.
  3. Scale: Optimize to display the Doppler signal without aliasing.
  4. Gain: High enough to see the signal and eliminate background noise.
  5. Sweep Speed: Adjust to show at least three beats; higher HR requires increased sweep speed.

When assessing for TR, leave adequate room below the baseline to visualize potential TR. Typical scale set to 240 cm/s where significant TR first appears.

Pulsed Wave (PW):
   - Samples from specific sites for lower velocities.
   - Advantages: Adjust sample volume, velocity mapping.
   - Disadvantages: Limited by speed of sound and aliasing, cannot measure velocities over 2.0-2.5 m/s.
Continuous Wave (CW):
   - Samples entire scan line for high velocities.
   - Advantages: High velocity range measurement.
   - Disadvantages: No range resolution, unclear source location of velocity.

Basic Doppler measurements include:
  - Peak Velocity: Reflects instantaneous pressure gradient; gathered from any valve inflow, regurgitation, or shunts.
  - Velocity Time Integral (VTI): Representation of the distance travelled by blood flow, measured in cm.
  - Instantaneous pressure gradient: Higher pressure gradients yield higher velocities.

“Chin” vs. “Beard”: Obtain the most accurate TR jet velocity measurement by focusing on modal velocity; lessen jet broadening effects with proper settings.