Sound Propagation and Attenuation

These flashcards cover the key terms related to the concepts of sound propagation, attenuation, acoustic impedance, resolution, and transducer characteristics as discussed in the lecture.

Attenuation

The loss of sound energy as it propagates through a medium.

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

A type of scattering that occurs from structures smaller than the wavelength, such as red blood cells.

Acoustic Impedance (Z)

The resistance to sound in a medium, calculated as Z=ρ×c, where ρ is density and c is speed of sound.

Specular reflection

Occurs at smooth surfaces, resulting in a single reflection in an organized manner.

Diffuse reflection (Backscatter)

Reflection from an irregular surface, scattering sound in multiple directions.

Angle of Incidence

The angle at which the sound beam strikes a boundary.

Normal incidence

Occurs at a 90° angle, where reflection depends on impedance mismatch.

Oblique incidence

Occurs at angles not equal to 90°, may result in refraction.

Resolution

The ability to distinguish between two structures that are close together.

Axial Resolution

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

Lateral Resolution

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

Linear transducer

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

Sector phased array transducer

Electronically steered transducer used for cardiac scanning.

Curvilinear array transducer

Used for abdominal scanning, especially when sector phased array is not available.

Focal point

The narrowest point in the sound beam.

Fresnel zone (Near field)

The region from the transducer to the focus where the beam is narrow.

Fraunhofer zone (Far field)

The region from the focus to where the beam diverges and spreads.

A-Mode (Amplitude Modulation)

Creates a one-dimensional image with amplitude represented by spikes.

B-Mode (Brightness Modulation)

Displays reflections as dots, with brightness indicating reflection strength.

M-Mode (Motion-mode)

Displays motion over time, used to depict cardiac structure movements.

Color Flow Doppler

Displays direction and velocity of blood flow, following the BART rule.

Backing material (dampening)

Reduces ringing in a pulse, improving image quality.

Matching layers

Typically two layers that help optimize sound transmission; thickness is one-quarter of the wavelength.

Active elements

Size ranges from 0.2 mm to 1.0 mm and determine the effectiveness of the transducer.