Basic Terminology

INTRODUCTION

Discovered by Christian Johann Doppler in 1842.

Color Doppler (CD) is used for detection of blood flow in the vessels.

Doppler shift—Change in frequency of sound waves when there is relative motion between the source and the reflector.

No relative motion of target toward or away from the transducer is detected at an angle of 90 degrees; therefore, no Doppler shift is detected.

$\text{Velocity}=\text{frequency}\times \text{wavelength}$

If an object moves away from the transducer, wavelength increases and frequency decreases (Figure 31.1).

Rayleigh scattering—Occurs when a target is smaller in size than wavelength of incident sound beam. No reflection returns to the transducer. For example, scattering from moving RBCs in color Doppler studies.

Types

Continuous Wave (CW) Doppler

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