Ultrasound Physics Notes

  • Important Terms:

    • Unrelated: Two things not associated (e.g., hair color and shoe size).
    • Related/Proportional: Two associated things, relationship unspecified (e.g., Santa and Christmas).
    • Directly Related/Proportional: One increases, the other increases (e.g., skill vs. practice).
    • Inversely Related/Proportional: One increases, the other decreases (e.g., grades vs. party time).
    • Reciprocal Relationship: Two numbers multiply to one; e.g., 2 and ( \frac{1}{2} ) are reciprocals.

  • Units:

    • All numerical values must have a unit; e.g., length, volume, area, time.
    • To convert between units, follow specified multiplication or division depending on size.

  • Metric System:

    • Prefixes indicate powers of ten: e.g., kilo (10^3), mega (10^6), milli (10^-3).
    • Scientific notation simplifies large/small numbers (base 10).

  • Waves:

    • Mechanical Waves: Require medium (e.g., sound).
    • Non-mechanical Waves: Do not require medium (e.g., electromagnetic waves).
    • Types of mechanical waves: Longitudinal (particle motion parallel to energy) and Transverse (particle motion perpendicular).

  • Acoustic Variables:

    • Pressure, Density, Distance: Define sound waves; sound must oscillate rhythmically.

  • Sound Wave Parameters:

    • Period: Time for one cycle (fixed, determined by source).
    • Frequency: Cycles per second; imaging frequency 2-15 MHz (fixed, determined by source).
    • Wavelength: Distance of one cycle (affected by source and medium).
    • Propagation Speed: Speed of sound in a medium (depends solely on medium).

  • Pulsed Ultrasound:

    • Definitions:
    • Pulse Duration: Time of a pulse (fixed, determined by source).
    • Spatial Pulse Length: Distance occupied by a pulse (depends on source and medium).
    • Pulse Repetition Frequency (PRF): Pulses per second (depends on source).
    • Relationships: PRF and PRP are inversely related; Duty Factor relates to operational time.

  • Wave Interference:

    • Constructive Interference: In-phase waves combine for higher amplitude.
    • Destructive Interference: Out-of-phase waves reduce amplitude.

  • Key Relationships:

    • Parameters determined by source: Period, Frequency, Amplitude, Power, Intensity.
    • Parameters dependent on medium: Propagation Speed, Wavelength.
    • Certain parameters can be adjusted by the sonographer, others cannot.