Doppler Ultrasound Basics and Applications

Imaging through the Lifespan

• Doppler Ultrasound Basics and Applications
  By Jill Clarke

Introduction to Christian Doppler

• Christian Doppler: Austrian physicist, lived from 1803 - 1853.

• First described the Doppler effect in 1842 during a lecture at the Natural Sciences Section of the Royal Bohemian Society.

• His thesis: "Uber das farbige Licht der Doppelsterne" (Concerning the coloured light of the double stars and certain other stars).

The Doppler Effect

• Description: The change in observed frequency of a wave (sound or light) when the source and observer are in relative motion.

• Three Scenarios:

  • When source is stationary, frequency occurs at regular intervals.

  • When source approaches the observer, the frequency increases (more wavefronts hit the observer).

  • When source moves away, frequency decreases (fewer wavefronts hit the observer).

Applications of the Doppler Effect

• Medical Uses:

  • Measurement of speed and direction of blood flow in various parts of the body.

  • Provides physiological data during imaging (as opposed to structural data provided by typical imaging).

  • Can quantify hemodynamic parameters.

Doppler Equation

• Doppler Equation: {f_D}={\frac{2fv{cos}(heta)}{c}} Where:

  • {f_D} = Frequency of the Doppler shift

  • {f} = Emitted frequency

  • { heta} = Angle between the direction of flow and the sound

  • {v} = Velocity of the scatterer

  • {c} = Speed of sound in the medium.

Ultrasound Beam Orientation

• Best imaging practices:

  • For 2D images: The beam should be perpendicular to the structure being viewed.

  • For Doppler signals: The beam should be parallel to the direction of blood flow to maximize the signal.

Colour Doppler Imaging

• Functionality:

  • Color Doppler uses various sample gates to detect Doppler shifts.

  • Color Indicators:

  • Blue: Shift away from the transducer

  • Red: Shift towards the transducer

• Can be modified to show arteries in red and veins in blue.

Doppler Examination Techniques

1. Continuous Wave Doppler:

   • Utilizes two transducers to continuously send and receive signals.

   • Example: Fetal heart monitoring.

2. Pulsed Wave Doppler:

   • Measures blood velocities at designated points by sending pulsed signals.

3. Power Doppler:

   • Displays the strength of Doppler signals rather than direction and velocity.

   • More sensitive, particularly in low flow environments.

Doppler Applications in Medicine

• General: Utilized across most ultrasound exams, including obstetric, pediatric, and cardiac applications.

• Specific Uses:

  • Assess blood vessel patency, detect arterial stenosis, rule out venous thrombosis.

  • Assess blood flow in conditions like deep vein thrombosis (DVT) and chronic venous insufficiency (CVI).

Conclusion

• The Doppler ultrasound technique is essential in modern medical imaging, providing crucial information about blood flow dynamics for diagnosis and treatment planning.