Ultrasound Physics Practice Flashcards

A set of 30 vocabulary flashcards covering ultrasound physics concepts including reflection types, impedance, refraction, and the range equation.

Specular Reflection

A type of reflection that is very angle dependent and occurs with smooth structures; if the transducer angle is altered, echoes scatter in many directions.

Impedance Mismatch

The factor that determines the brightness of echoes, where a large difference causes nearly total reflection.

Internal Tissue

Tissue structures that appear gray and textured in an image because of backscatter due to small reflectors.

Non-specular/Backscatter Reflection

A type of reflection that occurs if the reflectors are smaller than the ultrasound wavelength.

Specular Reflection (Size Condition)

A type of reflection seen clearly if the reflectors are larger than an ultrasound wavelength.

Rayleigh Scattering

Scattering produced by blood cells because they are much smaller than the ultrasound wavelength.

Organ Parenchyma

The tissue texture inside organs that is visualized through non-specular reflections from rough or irregular surfaces.

Acoustic Speckle

Lower-amplitude echoes in all directions formed by many small scatterers within tissue.

Strong Anatomical Echoes

Echoes from large, smooth tissue boundaries used for imaging that are stronger and more consistent than speckle signals.

Acoustic Noise

Signals like speckle that are not considered real anatomical structures and are seen as bright dots on the screen.

Perpendicular Beam Orientation

The alignment that produces the maximum reflected signal from smooth surfaces by reflecting most sound back to the transducer.

Oblique Angle

An angle at which the beam strikes a surface and reflects sound away from the transducer, potentially resulting in refraction.

Acoustic Impedance

The property that determines the proportion of sound reflected versus transmitted at a tissue boundary through mismatching.

Air-Tissue Interface

A boundary with a large impedance mismatch between media that reflects almost all incident ultrasound energy.

Coupling Gel

A substance used to remove air from between the transducer and skin to improve the transmission of sound into the body.

Bone

A material that reflects and absorbs ultrasound energy, often leading to poor visualization of structures located behind it.

Slight Impedance Mismatch

A condition that allows some sound to be reflected back while the rest continues through the boundary.

Acoustically Invisible

A description for a boundary between two tissues with equal acoustic impedance where sound is $100\%$ transmitted.

Refraction

The change in the direction of the transmitted ultrasound beam when crossing media with different propagation speeds at an oblique angle.

Lateral Misregistration

An artifact where a structure is placed in the wrong lateral position because the system assumes sound travels in a straight line while refraction bends it.

Conditions for Refraction

The two simultaneous requirements consisting of an oblique angle of incidence and two tissues with different propagation speeds.

Range Equation

A formula the system uses to determine the distance to a reflector by measuring travel time and using a known propagation speed.

Constant Propagation Speed Assumption

A necessary assumption that allows the ultrasound system to use simple math to calculate distance.

Image Distortion

A result of incorrect assumptions about propagation speed, leading the system to calculate the wrong depth or position.

$13\,\mu s$ per Centimeter Rule

A rule in soft tissue physics stating that it takes $13$ microseconds for ultrasound to travel $1\,cm$ one way.

Reflector Depth Calculation

A process where the system divides the measured travel time by two to account for the pulse traveling to the reflector and back.

Constructive Interference

An interaction of small scatterers that produces stronger echoes within an acoustic speckle pattern.

Destructive Interference

An interaction of small scatterers that produces weaker echoes within an acoustic speckle pattern.

Organ Capsules

Smooth structures that appear as bright linear echoes on an ultrasound image because of equal impedance.

Refraction (Perpendicular Limitation)

A principle stating that refraction cannot occur when the ultrasound beam strikes an interface at exactly $90\,\text{degrees}$.