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.


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

    • Where:

    • dd = distance to tissue/interface

    • tt = 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.