Abdominal Vessel Doppler Flow Patterns PPT 1-27

Abdominal Vessel Doppler Flow Patterns

• Doppler ultrasound is used to visualize blood flow in abdominal vessels.
• Key aspects of the technique include placing a sample volume "gate" within the vessel and adjusting it to encompass the vessel's diameter without exceeding it.
• The angle of the gate should be 60 degrees or less for accurate measurements.
• Adjusting the angle is done using the angle knob on the control panel.
• Sometimes, the patient may need to hold their breath during the procedure to get clear images of certain vessels.

Abdominal Vascular Pathologies

• Blood flow characteristics can reveal presence/absence of blood flow within certain vessels, the direction of the blood flow, and flow disturbance patterns.
• Doppler ultrasound can be used for tissue characterization through analyzing blood flow patterns and waveforms.
• In certain conditions, blood flow in particular vessels may be reversed (e.g., in portal hypertension, the blood in the portal vein may be hepatofugal instead of hepatopedal)
• Variations in flow, such as turbulent or swirling flow, are often associated with vessel stenosis (narrowing) or an aneurysm (dilation).

Doppler Technique

• The sample volume "gate" is positioned within the target vessel and adjusted to appropriately encompass the vessel without exceeding it.
• The angle of the Doppler gate should not exceed 60 degrees to avoid inaccurate velocity measurements. Angle adjustment is usually done through an angle knob on the control panel.
• Patient respiration may need to be controlled, especially during imaging of particular vessels.

Spectral Waveform Analysis

• The shape of the spectral waveform provides information about the vascular impedance of the organ being assessed. This indicates the amount of pressure/effort required to get blood into the organ.
• Spectral analysis yields the velocity (speed and direction) and turbulence of the blood flow in a vessel.

Abdominal Doppler Techniques

• Doppler is often used to detect the presence/absence, direction, and flow disturbance patterns within blood vessels.
• Doppler can be used in characterizing tissues, examining perfusion patterns.

Presence/Absence of Flow

• Doppler can differentiate between vascular and non-vascular structures.

Direction of Flow

• Doppler allows for the detection of flow reversal. This is frequently used to tell arteries apart from veins.
• Blood flow in a portal vein can be "hepatofugal," flowing away from the liver, or "hepatopedal," flowing toward the liver. Hepatopetal is considered normal.
• Hepato-petal flow is commonly used and observed.

Disturbance of Flow

• Blood flow is often faster where there is a flow disturbance, typically following stenosis.
• Flow disturbance is characterized by swirling or eddy currents in various directions.
• Disturbances can be due to stenosis or aneurysm (dilation) formation.

Tissue Characterization

• Doppler is considered useful for tissue characterization due to the unique perfusion patterns associated with different tissues.

Tissue Characterization - Examples

• Analysis of specific Doppler patterns can aid in confirming specific tissue characteristics, such as hepatocellular carcinoma presence in the liver or the presence of specific patterns characteristic of tumors such as pancreatic tumors.
• Peripancreatic artery pseudoaneurysms display turbulent flow patterns.

Doppler Waveform Analysis

• The shape of the spectral waveform reveals vascular impedance of the target organ and the pressure/effort required for blood supply into the organ.
• Spectral analysis provides details about blood flow velocity and turbulence.

Nonresistive/Low Resistance Waveform

• Characterized by a significant diastolic component.
• The blood vessels in organs that require constant perfusion typically exhibit this type of waveform.
• Examples include the internal carotid artery and hepatic artery.

Resistive/High Resistance Waveform

• Display minimal/absent diastolic flow, potentially including reverse flow during diastole.
• Found in organs that do not require continuous perfusion.
• Examples include the external carotid and brachial arteries.

Quantifying Resistance

• The Resistive Index (RI) is a ratio comparing peak systolic velocity to minimum diastolic velocity.
• An RI less than 0.7 typically indicates normal vascular function.

Spectral Display

• The x-axis of a spectral Doppler graph represents time.
• The y-axis indicates Doppler shift frequency, reflecting velocity.
• The z-axis represents the quantity of blood flow at a given velocity and is displayed via grayscale. The intensity of the grayscale signal is correlated with the amount of blood flow.

Plug Flow/Laminar

• This flow pattern is characterized by a visibly clear "window" in the spectral waveform where the blood cells are traveling at roughly similar velocities. This is considered a smooth, normal flow pattern.
• Opposite to spectral broadening.
• The clear "window" is caused by friction between the blood cells and the vessel walls in stenotic areas.

Spectral broadening

• Stenotic areas are characterized by an increase in velocity, and this acceleration frequently causes a broadening effect in the spectral tracing, which can appear as noise beneath the signal.

Doppler Artifacts - Aliasing

• High-frequency Doppler ultrasound may produce an artifact called aliasing.
• The artifact occurs when the frequency "wraps" around the baseline.
• Aliasing can be corrected by using a lower frequency transducer or continuous wave Doppler.

Abdominal Doppler Techniques (General)

• For optimal results, patients should hold their breath during abdominal Doppler scans.
• The Doppler Sample Volume (gate) should encompass the vessel's width but not exceed it.
• The angle between the Doppler beam and blood flow should be less than 60 degrees to prevent inaccurate velocity calculations.
• The top of the color Doppler map indicates flow towards the transducer, and the bottom indicates flow away from the transducer.