Echo Physics

Stephen Devries, MD

Velocity = Frequency(transducer) x Wavelength

Velocity changes with media• increases through muscle (1580 m/sec)• decreases through fat (1450 m/sec)• markedly decreases through air (330 m/sec)

Smaller wavelength Greater resolution

Amplitude is strength of signal (measured in log of decibels)

Power is a function of amplitude

Increase of 6 dB is a doubling of signal amplitude

Ultrasound Transducer

•Pizoelectric crystals, stimulated by AC, generate sound waves•Pizoelectric crystals, deformed by received sound waves, produce current

Increasing Frequency Extends Near Field Resolution

Continuous Wave Doppler

Pulse Doppler

Velocity as a Hemodynamic Measurement

Modified Bernoulli EquationPressure Gradient = 4V2

Several Descriptors of “Gradient”