Ultrasonography Sound Waves and Properties Notes

Sound in Diagnostic Ultrasonography

  • Sound Pulses and Transducer
    • Sound pulses generated by a transducer travel through biological tissue (media).
    • Reflections from boundaries between structures return to the transducer and are processed into images.

Sound Waves

  • Definition of Waves

    • Waves carry energy from one location to another.
    • Types of waves include: heat, sound, magnetic, and light.

  • Characteristics of Sound

    • Sound is a mechanical wave where particles in the medium vibrate back and forth from a fixed position.
    • Cannot travel through a vacuum; must have a medium for propagation.
    • Sound travels in a straight line and is categorized as a longitudinal wave.

Acoustic Propagation Properties

  • Medium Effects on Sound Waves
    • Biologic Effects: The impact of sound waves on biological tissues as they pass through.

Acoustic Variables

  • Sound waves distinguished by oscillation in three acoustic variables:
    • Pressure: Rhythmic oscillation representing force concentration in an area.
    • Units: Pascals (Pa)
    • Density: Concentration of mass in a volume.
    • Units: kg/cm³
    • Distance: Measure of particle motion.
    • Units: cm, feet, mile
    • If any of these oscillate rhythmically, it indicates a sound wave.

Acoustic Parameters

  • Seven acoustic parameters critical for describing sound waves:
    • Period: Time for one complete wave cycle.
    • Frequency: Number of cycles per second.
    • Amplitude: Height of the wave from rest to peak.
    • Power: Rate of energy transfer in the wave.
    • Intensity: Power per unit area.
    • Wavelength: Distance between two consecutive peaks.
    • Propagation Speed: Speed at which the wave travels through the medium.

Types of Waves

  • Transverse Waves

    • Particles move perpendicular to the wave direction.
    • Example: Shaking a string creates an up-and-down motion while the wave moves horizontally.

  • Longitudinal Waves

    • Particles move in the same direction as the wave travels.
    • Example: In sound waves, particles oscillate back and forth in the direction of the wave.

In-Phase and Out-of-Phase Waves

  • In-Phase Waves

    • Peaks and troughs occur simultaneously at the same locations.
    • Example: Members of a synchronized marching band.

  • Out-of-Phase Waves

    • Peaks and troughs occur at different times and places.
    • They are ‘out of step’.

Interference

  • Occurs when multiple sound beams arrive at the same location at the same time.
  • The individual characteristics of waves combine to form a single wave.
  • Types of Interference:
    • Both in-phase and out-of-phase waves can undergo interference, combining differently based on their phase relationship.