physics vocab

Frame Rate

Number of images displayed per second.

Temporal Resolution

Ability to accurately display motion.

Axial Resolution

Ability to distinguish structures lying one behind another.

Lateral Resolution

Ability to distinguish structures lying side-by-side.

Elevational Resolution

Ability to distinguish structures in the third dimension of the beam.

Slice Thickness Resolution

Another name for elevational resolution.

Contrast Resolution

Ability to distinguish differences in gray shades.

Frequency

Number of cycles occurring each second.

Period

Time required to complete one cycle.

Wavelength

Distance occupied by one cycle.

Amplitude

Maximum strength of a wave.

Power

Rate at which energy is transferred.

Intensity

Concentration of sound energy in a beam.

Compression

Region of high pressure where molecules are squeezed together.

Rarefaction

Region of low pressure where molecules are spread apart.

Cycle

One compression and one rarefaction.

Pulse

A collection of cycles traveling together.

Pulse Duration (PD)

Time from the start to the end of a pulse.

Pulse Repetition Period (PRP)

Time from the start of one pulse to the start of the next pulse.

Pulse Repetition Frequency (PRF)

Number of pulses transmitted each second.

Duty Factor

Percentage of time the system is transmitting.

Spatial Pulse Length (SPL)

Physical length of a pulse.

Attenuation

Loss of sound energy as it travels through tissue.

Absorption

Conversion of sound energy into heat.

Reflection

Redirection of sound back toward the source.

Scattering

Redirection of sound in many directions.

Transmission

Passage of sound through a boundary.

Acoustic Impedance

Resistance to sound transmission.

Acoustic Variable

A quantity that changes as sound propagates through a medium.

Propagation Speed

Speed at which sound travels through a medium.

Piezoelectric Effect

Conversion between electrical and sound energy.

PZT

Lead zirconate titanate crystal used in transducers.

Operating Frequency

Frequency at which a transducer naturally operates.

Bandwidth

Range of frequencies produced by a transducer.

Matching Layer

Layer that improves sound transmission between crystal and tissue.

Damping Material

Material behind the crystal that shortens pulse length.

Array Transducer

Transducer composed of multiple elements.

Linear Array

Array transducer producing a rectangular image.

Curvilinear Array

Array transducer producing a curved image.

Phased Array

Array transducer that electronically steers the beam.

Beam Steering

Electronic redirection of the sound beam.

Beam Diameter

Width of the ultrasound beam.

Beam Divergence

Spreading of the beam in the far field.

Focal Zone

Narrowest portion of the ultrasound beam.

Focusing

Narrowing of the beam to improve lateral resolution.

Fresnel Zone

Near field of the sound beam.

Fraunhofer Zone

Far field of the sound beam.

Dead Zone

Region directly beneath the transducer that cannot be accurately imaged.

Range Resolution

Ability to determine reflector depth.

Range Ambiguity

Inability to determine correct reflector depth.

Go-Return Time

Time required for sound to travel to a reflector and back.

Specular Reflector

Large smooth reflector.

Rayleigh Scatterer

Reflector much smaller than the wavelength.

Time Gain Compensation (TGC)

Compensation for attenuation with depth.

Dynamic Range

Range of amplitudes processed or displayed.

Compression (Receiver Function)

Reduction of the range of echo amplitudes.

Amplification

Receiver function that increases signal strength.

Compensation

Receiver function that equalizes echo amplitudes.

Demodulation

Receiver function that converts signals into displayable form.

Reject

Receiver function that removes low-level unwanted signals.

Receiver

Portion of the system that processes returning echoes.

System Output

Control that determines transmitted sound energy.

Gray Scale

Range of gray shades displayed.

Persistence

Averaging of multiple frames together.

Line Density

Number of scan lines used to create an image.

Packet Size

Number of pulses used to create one Doppler measurement.

Spatial Compounding

Combining images from multiple angles.

Acoustic Enhancement

Increased brightness behind a weakly attenuating structure.

Shadowing

Signal loss behind a strongly attenuating structure.

Mirror Image Artifact

Duplicate structure displayed deeper than actual location.

Reverberation Artifact

Multiple equally spaced echoes caused by repeated reflections.

Lobe Artifact

Artifact caused by side or grating lobes.

Doppler Shift

Difference between transmitted and received frequency.

Positive Doppler Shift

Frequency increase caused by motion toward the transducer.

Negative Doppler Shift

Frequency decrease caused by motion away from the transducer.

Doppler Angle

Angle between blood flow and ultrasound beam.

Nyquist Limit

Maximum Doppler shift measurable without aliasing.

Aliasing

Incorrect display caused by under-sampling.

Baseline

Reference line representing zero Doppler shift.

Pulsed Wave Doppler

Doppler with range specificity.

Continuous Wave Doppler

Doppler without range specificity.

Color Doppler

Blood flow information displayed in color.

Spectral Doppler

Graphical display of Doppler frequencies over time.

Sample Volume

Location from which Doppler data is collected.

Clutter

Low-frequency unwanted Doppler signals.

Wall Filter

Control that removes low-frequency Doppler signals.

Color Priority

Control determining whether color or grayscale dominates.

Laminar Flow

Orderly blood flow with fastest velocity in the center.

Turbulent Flow

Chaotic blood flow containing many velocities.

Plug Flow

Flow with nearly equal velocities across the vessel.

Spectral Broadening

Filling in of the Doppler spectrum due to multiple velocities.

Reynolds Number

Value used to predict turbulence.

Stenosis

Narrowing of a blood vessel.

Volume Flow Rate

Volume of blood moving through a vessel per unit time.

Mechanical Index (MI)

Indicator of cavitation potential.

ALARA

As Low As Reasonably Achievable.

Binary

Base-2 numbering system using only 0 and 1.

Decimal

Base-10 numbering system.

Normal Incidence

Sound striking a reflector at 90 degrees.

Impedance Mismatch

Difference in acoustic impedance between tissues.