THE BASICS

Introduction to Ultrasound Physics

  • Presented by Jenna LaCare, an ARDMS certified sonographer.
  • Purpose: To introduce the basics of ultrasound physics.

Transducers

  • Definition: Transducer is any device that converts energy from one form into another.
    • Example: Ultrasound transducers convert electric energy to acoustic energy and vice versa.
  • Functionality:
    • Generates pulses of sound that travel through a medium (e.g., tissue).
    • The acoustic energy reflects off of different anatomical structures, with reflections returning to the transducer where they are processed back into electric energy.
    • The electric signal is then used to create an image displayed on an ultrasound monitor.

Sound Waves

  • Definition: Sound wave, also referred to as an acoustic wave, is a mechanical wave.
    • Sound waves convey energy through the vibration of molecules within a medium.
  • Transmission:
    • Sound cannot travel in a vacuum; it requires a medium.
    • Example: Astronauts cannot hear each other in space due to lack of molecules to convey sound.
  • Molecular Behavior:
    • Molecules vibrate, leading to compression (squeezing together) and rarefaction (stretching apart).
  • Visualization of Sound Wave:
    • Illustrates compression and rarefaction visually represented through vibrating molecules in a medium.

Acoustic Variables and Parameters

  • Acoustic Variable: Used to distinguish sound waves from other wave types.

    1. Pressure:
    • Definition: Concentration of force in an area, measured in pascals (Pa).
    1. Density:
    • Definition: Concentration of mass within a volume, measured in kilograms per cubic centimeter (kg/cm³).
    1. Distance:
    • Definition: Measure of particle motion relative to tissue.

  • Acoustic Parameters: Help describe sound wave properties.

    • Upcoming discussion on seven acoustic parameters related to sound waves and five additional parameters related to pulsed sound.
    • Importance of differentiating questions concerning sound versus pulsed sound parameters for exam purposes.

Longitudinal and Transverse Waves

  • Sound Waves:
    • Type: Longitudinal waves, where molecules in a medium vibrate in the same direction as wave propagation.
    • Diagrammatic Representation: Illustrates how molecules approach and retreat as sound travels.
  • Transverse Waves:
    • Comparison to sound waves: Water waves are an example of transverse waves where movement is perpendicular to the wave propagation direction.
    • Diagram of ocean waves shows peaks and troughs that don't align with wave direction.

Interference

  • Definition: Occurs when two sound waves overlap in a medium, affecting their properties.
  • Transmission Period:
    • A pulse of sound is emitted by the transducer, followed by a listening period where no sound is transmitted to prevent interference between outgoing and incoming waves.
  • Types of Interference:
    1. Constructive Interference:
    • When two waves are in phase, their peaks and troughs align, creating a larger wave with increased amplitude.
    1. Destructive Interference:
    • When waves are out of phase, meaning their peaks and troughs do not align, producing a smaller wave or cancelling each other out.
    • Complete destructive interference occurs when two waves of equal amplitude are perfectly out of phase, eliminating sound reflection.

Amplitude

  • Definition: The height of the wave, related to the pressure exerted by the wave.

Review Questions

  1. Identify whether the depicted wave is longitudinal or transverse based on molecular movement.
  2. Acoustic variable definition inquiries regarding pressure, density, and distance.
  3. Identify in-phase versus out-of-phase waves with regards to their respective peaks and troughs.
  4. Distinguish between acoustic parameters and variables, particularly focusing on the definition of density as a variable.

Conclusion

  • Upcoming modules will delve deeper into the seven parameters that describe a sound wave, essential for understanding ultrasound physics.