PHYSICS FINAL

Frame Rate

Number of images displayed per second.

Temporal Resolution

Ability to accurately display motion.

Axial Resolution

Ability to distinguish structures along the beam path.

Lateral Resolution

Ability to distinguish structures side-by-side.

Elevational Resolution

Ability to distinguish structures in the third dimension.

Slice Thickness Resolution

Another name for elevational resolution.

Attenuation

Loss of sound energy as it travels through tissue.

Reflection

Redirection of sound back toward the source.

Scattering

Redirection of sound in many directions.

Absorption

Conversion of sound energy into heat.

Acoustic Impedance

Resistance to sound transmission.

Frequency

Number of cycles per second.

Period

Time required for one cycle.

Wavelength

Distance occupied by one cycle.

Amplitude

Maximum strength of a wave.

Intensity

Concentration of sound energy in a beam.

Compression

Region of high pressure.

Rarefaction

Region of low pressure.

Pulse

A collection of cycles traveling together.

Pulse Duration

Time from start to end of a pulse.

Pulse Repetition Frequency

Number of pulses transmitted per second.

Pulse Repetition Period

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

Duty Factor

Percentage of time the system is transmitting.

Spatial Pulse Length

Physical length of a pulse.

Bandwidth

Range of frequencies produced by a transducer.

Piezoelectric Effect

Conversion between electrical and sound energy.

PZT

Lead zirconate titanate.

Matching Layer

Layer that improves transmission between crystal and tissue.

Damping Material

Material behind the crystal that shortens pulse length.

Dynamic Range

Range of amplitudes processed or displayed.

Compression Receiver Function

Reduces the range of echo amplitudes.

Amplification

Increases signal strength.

Compensation

Equalizes echo amplitudes.

Demodulation

Converts signals into displayable information.

Reject

Removes low-level unwanted signals.

Array Transducer

Transducer composed of multiple elements.

Phased Array

Steers the beam electronically.

Beam Steering

Electronic redirection of the beam.

Focal Zone

Narrowest portion of the beam.

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.

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.

Acoustic Enhancement

Increased brightness behind a weakly attenuating structure.

Mirror Image Artifact

Duplicate structure displayed deeper than actual location.

Reverberation Artifact

Multiple equally spaced echoes.

Lobe Artifact

Artifact caused by side or grating lobes.

Spatial Compounding

Combines images from multiple angles.

ALARA

As Low As Reasonably Achievable.

Nyquist Limit

Maximum Doppler shift measurable without aliasing.

Aliasing

Incorrect display caused by under-sampling.

Doppler Shift

Difference between transmitted and received frequencies.

Positive Doppler Shift

Flow toward the transducer.

Negative Doppler Shift

Flow away from the transducer.

Pulsed Wave Doppler

Provides range specificity.

Continuous Wave Doppler

Measures high velocities without aliasing.

Sample Volume

Location from which Doppler data is collected.

Packet Size

Number of pulses used for one Doppler measurement.

Persistence

Averaging of multiple frames together.

Line Density

Number of scan lines used to create an image.

Laminar Flow

Orderly flow with highest velocity in the center.

Turbulent Flow

Chaotic flow with many different velocities.

Plug Flow

Flow with nearly equal velocities across the vessel.

Reynolds Number

Predicts likelihood of turbulence.

Stenosis

Narrowing of a vessel.

Volume Flow Rate

Volume of blood moving through a vessel per unit time.

Baseline

Reference line representing zero Doppler shift.

Clutter

Low-frequency unwanted Doppler signals.

Mechanical Index

Indicator of cavitation potential.

Contrast Resolution

Ability to distinguish differences in gray shades.

Gray Scale

Range of gray shades displayed.

Normal Incidence

Sound striking a reflector at 90 degrees.

Doppler Angle

Angle between beam and blood flow.

Binary

Base-2 numbering system.

Rayl

Unit of acoustic impedance.

What happens to attenuation when frequency increases?

Increases.

What happens to penetration when frequency increases?

Decreases.

What happens to wavelength when frequency increases?

Decreases.

What happens to axial resolution when frequency increases?

Improves.

What happens to SPL when damping increases?

Decreases.

What happens to bandwidth when damping increases?

Increases.

What happens to sensitivity when damping increases?

Decreases.

What happens to frame rate when imaging depth increases?

Decreases.

What happens to frame rate when line density increases?

Decreases.

What happens to frame rate when packet size increases?

Decreases.

What happens to frame rate during duplex imaging?

Decreases.

What happens to temporal resolution when frame rate increases?

Improves.

What happens to temporal resolution when persistence increases?

Decreases.

What happens to lateral resolution when focusing increases?

Improves.

What happens to beam width when focusing increases?

Decreases.

What happens to PRF when imaging depth increases?

Decreases.

What happens to imaging depth when PRF increases?

Decreases.

What happens to Doppler shift when velocity increases?

Increases.

What happens to Doppler shift when frequency increases?

Increases.

What happens to Doppler shift when Doppler angle increases toward 90°?

Decreases.

What happens to velocity when vessel area increases?

Decreases.

What happens to velocity when vessel area decreases?

Increases.

What happens to pressure in a stenosis?

Decreases.