Echocardiographic Image Acquisition & Doppler

Sound Waves

Mechanical waves that travel in straight lines and are longitudinal, meaning particles move in the same direction as the wave.

Frequency

Measured in Hertz (Hz); the number of cycles per second, where an increase in frequency results in a decrease in period.

Period

The time it takes for one complete cycle of a wave.

Wavelength

The distance required for one complete cycle of a wave, measured in millimeters (mm).

Propagation Speed

The speed at which sound travels in soft tissue, approximately 1540 m/s.

Amplitude/Power/Intensity

Terms used to describe the strength of a sound wave.

Wavelength Formula

Wavelength = Propagation speed ÷ Frequency.

Attenuation

The weakening of sound waves due to reflection, scattering, and absorption.

Attenuation Causes

Includes reflection (echo back), scattering (spread in many directions), and absorption (converted to heat).

Attenuation Coefficient

Calculated as frequency divided by 2, expressed in dB/cm/MHz.

Impedance

The product of density and stiffness; differences in impedance result in reflection of sound waves.

Transducer Function

Converts electricity to sound and vice versa, utilizing the piezoelectric effect.

Basic Parts of Transducer

Comprises a piezoelectric crystal and housing.

Near Zone (Fresnel Zone)

The area where the beam narrows before reaching the focus.

Focus

The narrowest point of the sound beam where the best image quality is achieved.

Far Zone (Fraunhofer Zone)

The area where the sound beam widens after the focus.

Focal Zone

The region around the focus that provides the best resolution.

Axial Resolution

Refers to the ability to distinguish two objects positioned along the front-to-back axis; better than lateral resolution.

Lateral Resolution

Refers to the ability to distinguish two objects positioned side-to-side; best at the focal zone.

Doppler Effect

Utilizes blood cell scattering to analyze motion and is affected by particle size, hematocrit, transducer frequency, and blood compressibility.