Sound Propagation and Attenuation

Flashcards covering the key concepts and terminology related to sound propagation, attenuation, reflection, imaging modes, and transducer characteristics.

Sound Propagation

Describes how sound travels through the body and interacts with tissues.

Attenuation

The loss of sound energy as it propagates, caused by absorption, scattering, and reflection.

Absorption

The conversion of ultrasound energy into heat, directly proportional to frequency.

Scattering

The redirection of sound beams in many directions, also directly proportional to frequency.

Rayleigh Scattering

Occurs from structures small relative to the wavelength, such as red blood cells, resulting in equal redirection in all directions.

Acoustic Impedance

The resistance to sound in a medium, measured in Rayls, calculated as Z=ρ×c.

Specular Reflection

Occurs at a smooth surface, resulting in a single organized reflection.

Diffuse Reflection (Backscatter)

Created from an irregular surface, reflects sound in multiple directions and represents most of what returns to the transducer.

Angle of Incidence

The angle at which the sound beam strikes a boundary.

Axial Resolution

The ability to distinguish structures that are parallel to the sound beam's main axis.

Lateral Resolution

The ability to distinguish structures that are side-by-side and perpendicular to the beam.

Linear Transducer

Has a large probe face, used for vascular scanning, with increased near-field image quality.

Sector Phased Array Transducer

Electronically steered, primarily used for cardiac scanning.

Curvilinear Array Transducer

Used for abdominal scanning.

Near Field (Fresnel Zone)

The region from the transducer to the focus where the beam narrows.

Focal Zone

The region where the beam is relatively narrow and produces more accurate images.

A-Mode (Amplitude Modulation)

Creates a one-dimensional image with amplitude spikes representing strong or weak reflections.

B-Mode (Brightness Modulation)

Displays reflections as dots, where brightness indicates the strength of reflection.

M-Mode (Motion-mode)

Depicts motion over time, used to show movement in cardiac structures.

Color Flow Doppler

Displays the direction and velocity of blood flow, indicating flow direction relative to the transducer.

Backing Material (Dampening)

Located behind piezoelectric elements to reduce ringing and improve image quality.

Matching Layers

Layers typically one-quarter of the wavelength thick, present in a transducer.

Active Elements

The size range is from 0.2 mm to 1.0 mm; typically half the wavelength in thickness.