Unit 3: The Seven Parameters of Sound

Introduction

• Sound Waves & Characteristics:
  • All sound waves, including ultrasound, have measurable characteristics known as parameters.
  • Important parameters: frequency, period, propagation speed, wavelength, amplitude, power, and intensity.
  • Study Tips: Focus on definitions, units, symbols, formulas, relationships, and sonographer impact.

Section 3.1: Period and Frequency

• Period and Frequency Relationship:

  • Period and frequency are reciprocals (Period × Frequency = 1).
  • Both are defined by the concept of a cycle.

• Period:

  • Definition: Time to complete one cycle.
  • Units: Typically microseconds in ultrasound.
  • Formula: Period (T) = 1 / Frequency (ƒ).
  • Sonographer Impact: Determined by the machine; cannot be changed by the sonographer.

• Frequency:

  • Definition: Number of cycles per second.
  • Units: Hertz (Hz), Kilohertz (kHz), Megahertz (MHz).
  • Typical Range: 2 to 15 MHz in ultrasound.
  • Formulas:
    • Frequency = 1 / Period.
    • Frequency = Speed of Sound / Wavelength.
  • Sonographer Impact: Select appropriate frequency for exam; frequency itself cannot be changed.

• Human Hearing:

  • Audible range: 20 Hz to 20 kHz.
  • Ultrasound: Above 20 kHz.

Section 3.2: Wavelength and Propagation Speed

• Propagation Speed:

  • Definition: Speed that sound travels through a medium; determined only by the medium.
  • Units: Meters per second (m/s), millimeters per microsecond (mm/µs).
  • Average in Soft Tissue: 1540 m/s.

• Wavelength:

  • Definition: Distance a cycle takes up in space.
  • Units: Typically millimeters.
  • Formulas:
    • Wavelength = Speed of Sound / Frequency.
  • Sonographer Impact: Cannot be adjusted; depends on frequency and medium.

Section 3.3: Strength Parameters

• Parameters: Amplitude, Power, Intensity.

• Relationships:

  • All three are directly related; change in one affects the others.
  • Determined by the machine; can be adjusted by the sonographer.
  • Attenuate as they propagate through the body.

• Amplitude:

  • Definition: Difference from average value of acoustic variable to max/min.
  • Units: Pascals (Pa), related to pressure.
  • Formulas:
    • Power ∝ Amplitude².
    • Intensity ∝ Amplitude².

• Power:

  • Definition: Rate of energy transfer.
  • Units: Watts (W), milliwatts (mW).
  • Formulas:
    • Power ∝ Intensity.

• Intensity:

  • Definition: Concentration of energy in the sound beam.
  • Units: Watts per square centimeter (W/cm²).
  • Formulas:
    • Intensity = Power / Area.

Recap

• Period and Frequency: Reciprocals controlled by machine.
• Wavelength and Propagation Speed: Dependent on medium and machine, directly related to speed.
• Strength Parameters: Directly related to one another, adjustable by sonographer, attenuate in the body.
• Key Concepts: Understand reciprocal relationships, conversion of units, and practical applications in ultrasound settings.