Week 1 Pulse-Echo Technique

Diagnostic Ultrasound

• Uses the Pulse-echo technique:

  • Transducer sends ultrasound pulses into the body.

  • Pulses interact with tissues/interfaces.

  • Echoes return to the transducer and generate B-mode (grey scale) ultrasound images.

Pulse-echo Principle

• Analogous to Echolocation:

  • Calculate distance between the transducer and tissues/interfaces using the speed of sound.

  • Based on the round-trip time of the echo.

  • 
    \text{Velocity} (\nu) = \frac{d \times 2}{t}

  • Where:

  • d = distance to tissue/interface

  • t = time taken for the echo to return.

Factors Affecting Echolocation

• Key dependencies include:

  • Speed of sound in tissue

  • Time of travel of sound

  • Direction of sound propagation

Scan Lines in Imaging

• Sonographic images consist of scan lines:

  • More scan lines lead to improved image quality.

  • Real-time imaging requires many frames per second for effective visualization.

Types of Imaging Formats

• Basic transducer formats include:

  • Linear array - broad near and far field image; not good for viewing large areas

  • Curved array - larger near field and an even larger far field

  • Sector format - small near field but larger far field

  • 

Modes of Imaging

• B-mode ultrasound

  • Displays 2D images, providing a gray-scale representation of tissue.

• M-mode ultrasound

  • Uses a single beam path, particularly useful for cardiac and fetal imaging.

• 3D imaging

  • Provides volumetric representations of structures.

Doppler Imaging Types

• Doppler Ultrasound is used for measuring the flow of blood:

  • Pulsed Wave (PW) Doppler

  • Types:

    1. PW Spectral Doppler

    2. PW Colour Doppler

    3. PW Power Doppler

  • Continuous Wave (CW) Doppler

  • Used to demonstrate continuous flow information.

PW Colour Doppler

• Color displays provide valuable information:

  • Indicate the direction and velocity of blood flow.

PW Power Doppler (CPD)

• Information is based on the amplitude/strength of blood cell motion:

  • Superimposed over a 2D image.

  • Does not indicate direction of flow but is sensitive to slow flows.

PW Spectral Doppler

• Demonstrates waveforms of different flow types:

  • differentiates between arterial and venous waveforms, indicating flow direction (forward/reverse).

Conclusion

• Enhanced understanding of ultrasound technology and its various applications can significantly improve diagnostic capabilities in clinical practice.

• Special acknowledgment to Dr. Michelle Fenech for contributions to the content.