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Fetal Echocardiography and Ultrasound Physics - Flashcards

  • Direct and inverse relationships

    • Direct proportion: two items increase together
    • Inverse proportion: one item increases as the other decreases
    • Reciprocal relationship: product equals one (e.g., 2 × 1/2 = 1)

  • Unit systems and prefixes (context for numbers)

    • Length: m, cm, mm; Time: s, ms, μs; Mass: kg
    • Common prefixes (symbol, meaning):
    • kilo (k, 10^3), mega (M, 10^6), giga (G, 10^9), tera (T, 10^12), peta (P, 10^15)
    • hecto (h, 10^2), deka (da, 10^1)
    • deci (d, 10^-1), centi (C, 10^-2), milli (m, 10^-3), micro (μ, 10^-6), nano (n, 10^-9)
    • 12 inches = 1 foot is a unit conversion example; total picture does not change with unit choice

  • Acoustic fundamentals: acoustic variables vs acoustic parameters

    • Acoustic variables (instantaneous properties):
    • Pressure (units: Pa)
    • Density (units: kg/cm^3 or similar)
    • Distance/particle motion (units: cm, m, ft)
    • Acoustic parameters (measurable wave features):
    • Period (T), Frequency (f), Amplitude, Power, Intensity, Speed, Wavelength
    • Key distinction: variables describe the wave at an instant; parameters describe wave characteristics over time

  • Core relationships (formulas)

    • Frequency and period
    • f = rac{1}{T}, T = rac{1}{f}
    • Speed, wavelength, and frequency
    • v = f \, \lambda
    • \lambda = \frac{v}{f}
    • In soft tissue: v \approx 1.54\ \mathrm{mm/\mu s} = 1540\ \mathrm{m/s}
    • Wavelength in tissue
    • \lambda = \frac{v}{f} = \frac{1540\ \mathrm{m/s}}{f(\text{Hz})} (or \lambda(\mathrm{mm}) = \dfrac{1.54}{f(\mathrm{MHz})})
    • Spatial parameters
    • Spatial Pulse Length (SPL): length of a pulse in space
    • SPL = (number of cycles in pulse) × (wavelength)
    • SPL units: mm
    • SPL influences axial resolution: shorter SPL -> better axial resolution
    • Pulsed-wave basics
    • Pulse Duration (PD): time the pulse is