Physics Key terms Flashcards
amount of acoustic energy the patient receives
acoustic exposure
as low as reasonably achieveable: used to reduce biological effects in humans and the fetus
ALARA principle
effect of ultrasound waves of living organisms, including their composition, function, growth, origin, development, and distribution
biological effect
interaction of the sound wave with microscopic gas bubbles found in tissues
cavitation
studies of various factors determining the frequency and distribution of diseases in the human community
epidemiology
study of the human body at work
ergonomic
experimentation done in or on living tissue in an artificial environment outside the organism
ex vivo
the technique of performing a given experiment in a test tube or, generally, an a controlled environment outside a living organism
in vitro
experimentation done in or on the living tissue of a whole, living organism as opposed to a partial or dead one.
in vivo
describes the likelihood of cavitation occurring
Mechanical index (MI)
act passed by congress to assure safe and healthful working conditions
Occupational Safety and Health Act (OSHA)
average intensity throughout the pulse duration
Pulse average (PA)
average intensity across the entire sound beam
Spatial average (SA)
peak intensity found across the sound beam
Spatial peak (SP)
average intensity during the pulse repetition period
temporal average (TA)
greatest intensity during the pulse
temporal peak (TP)
relates to the heating of tissue
Thermal index (TI)
relates to the heating of bone
Thermal index for bone (TIB)
relates to the heating of the cranium
Thermal index for cranium (TIC)
relates to the heating in soft tissue
Thermal index for soft tissue (TIS)
injuries that are caused or aggravated by workplace activities including injuries of the muscles, tendons, and joints
Work-Related Musculoskeletal Disorders (WRMSD)
process whereby sound energy is dissipated in a medium, primarily in the form of heat
absorption
having to do with sound
acoustic
resistance of sound as it propagates
acoustic impedance
effects on the sound beam caused by the medium; includes pressure, density, distance (particle motion)
acoustic variables
relating to the strength of the compression wave maximum variation of an acoustic variable
amplitude
amount of space within a specific boundry
area
weakening of sound as it propagates through a medium
attenuation
attenuation occurring with each centimeter that sound travels
attenuation coefficient
range of frequencies found in pulsed ultrasound
bandwidth
distance around the perimeter of an object
circumference
region of high pressure or density in a compression wave
compression
a nonpulsed wave in which cycles repeat indefinitely
continuous wave
one complete variation in pressure or other acoustic variables
cycle
a unit used to compare the ratio of intensities or amplitudes of two sound waves or two points along the wave
decibel
concentration of mass, weight, or matter per unit volume
density
amount of space from one object to another
distance
fraction of time that pulse ultrasound is on
duty factor
CAPABILITY to do work
energy
comparison of range of frequencies (bandwidth) with operating frequency
fractional bandwidth
number of cycles in a wave occurring in 1 second
frequency
original operating frequency
fundamental frequency
thickness of tissue required to reduce the intensity of the sound beam by one-half; also known as depth of penetration, half boundary layer, or penetration depth
half value layer (HVL)
echoes of twice the frequency transmitted into the body that reflect back to the transducer, which improves image quality
harmonic imaging
one cycle per second; unit of frequency
hertz (Hz)
determines how much of an incident sound wave is reflected back from the first medium and how much is transmitted into the second medium
impedance
direction of incident beam with respect to the media boundry
incident angle
initial or starting beam
incident beam
rate at which energy transmits over a specific area
intensity
one thousand cycles per second
Kilohertz (KHz)
wave traveling in a straight line
longitudinal wave
incident ultrasound traveling at an oblique angle to the media boundary
oblique incidence
time to complete one cycle
period
incident ultrasound traveling at an perpendicular angle to the media boundary
perpendicular incidence
concentration of force
pressure
speed at which a wave moves through a medium
propagating speed
a collection of a number of cycles that travel together
pulse
portion of time from the beginning to the end of a pulse; sonography generally uses 2-3 cycles, whereas Doppler uses 5-30 cycles per pulse
pulse duration
number of pulses per second
pulse repetition frequency
time between the beginning of one cycle and the beginning of the next cycle
pulse repetition period
a few pulses of ultrasound followed by a longer pause of no ultrasound. During this “silence”, returning echoes are received and processed
pulse ultrasound
for short pulses, the Q factor is equal to the number of cycles in a pulse; the lower the Q factor, the better the image quality
Quality factor (Q factor)
regions of low pressure or density in a compression wave
rarefraction
occurs when the reflector is much smaller than the wavelength of the sound beam
Rayleigh’s scatter
the beam redirected back to the transducer after striking a media boundary
reflected beam
redirection (return) of a portion of the sound beam back to the transducer
reflection
angle between the reflected sound and a line perpendicular to the media boundary
reflection angle
change in direction of the sound wave after passing from one medium to another
refraction
redirection of sound in several directions on encountering a rough surface; also known as nonspecular reflections
scattering
a traveling variation of acoustic variables
sound
relating to space
spatial
distance over which a pulse occurs
spatial pulse length
multiple echoes received at the same time generating interference in the sound wave, resulting in a grainy appearance of the sonogram
speckle
these comprise the boundaries of organs and reflect sound in only one direction, are angle dependent
specular reflections
resistance of a material to compression
stiffness
relating to time
temporal
the sound beam continuing on to the next media boundary
transmitted beam
amount of occupied space of an object in three dimensions
volume
distance (legth) of one complete cycle
wavelength
the widening of the sound beam in the far field
angle of divergence
size of the transducer element(s)
aperture
nonuniform driving (excitation) of elements in an array to reduce grating lobes
apodization
collection of active elements connected to individual electronic currents in one transducer assembly
array
ability to distinguish two structures along a path parallel to the sound beam
axial resolution
multiple transducer elements with individual wiring and system electronics
channels
occurs when two waves in phase with each other create a new wave with amplitude greater than the original two waves; in phase
constructive interference
curved linear transducer containing multiple piezoelectric elements
convex array
piezoelectric element
crystal
temperature to which a material is raised, while in the presence of a strong electrical field, to yield piezoelectric properties. If the temperature exceeds this point, the PZT properties will be lost
Currie point
Material attached to the rear of the transducer element to reduce the pulse duration
damping
occurs when two waves out of phase with each other create a new wave with amplitude less than the two original waves; out of phase
destructive interference
includes both axial and lateral resolution
detail resolution
deviation in the direction of the sound wave that is not a result of reflection, scattering, or refraction
diffraction
aperture that increases as the focal length increases; minimizes change in the width of the sound beam
dynamic aperture
variable receiving focus that follows the changing position of the pulse as it propagates through tissue the electrical output of the elements can be timed to “listen” in a particular direction and depth
dynamic focusing
piezoelectric component of the transducer assembly
element
detail resolution located perpendicular to the scan plane; it is equal to the section thickness and is the source of the section thickness artifact
elevation resolution
region of the sound beam in which the diameter increases as the distance from the transducer increases
far zone
distance from a focused transducer to the center of the focal zone; distance from a focused transducer to the spatial peak intensity
focal length
concentration of the sound beam into a smaller area
focal point
area or region of the focus
focal zone
far zone
Fraunhofer zone
near zone
Fresnel zone
additional weak beams emitted from a multielement transducer that propagate in directions different from the primary beam
grating lobes
all points on a wave front or at a source are point sources for the production of spherical secondary wavelets
Huygens principle
interference occurring when two waves interact or overlap, resulting in the creation of a new wave
interference phenomenon
ability to distinguish two structures lying perpendicular to the sound path
lateral resolution
a ceramic piezoelectric material
Lead zirconate titanate
material attached to the front face of the transducer element to reduce reflections at the transducer surface
matching layer
region of the beam between the transducer and focal point, which decreases in size as it approaches the focus
near zone
natural frequency of the transducer; it is determined by the propagation speed and thickness of the element in pulse ultrasound and by the electrical frequency in continuous wave
operating frequency
conversion of pressure to electric voltage
piezoelectricity
applying voltage pulses to all elements in the assembly as a group, but with minor time differences.This pulses allow multiple focal zones, beam steering, and beam focusing
phased
operating frequency
resonance frequency
operated by applying voltage pulses to a group of elements in succession
sequenced array
additional weak beams traveling from a single element transducer in directions different from the primary beam
side lobes
dividing each element into small pieces to reduce grating lobes
subdicing
device that converts energy from one form to another
transducer
transducer element, damping, matching layer, and housing, also known as probe, scan head or transducer
transducer assembly
anything not properly indicative of anatomy or motion imaged
artifact
group of bits
binary number
binary digit; smallest amount of computer memory
bit
group of eight bits of computer memory
byte
imaging display where the strength of the electron beam determines the brightness
cathode ray tube (CRT)
an independent signal path consisting of a transducer element, delay, and other electronic components
Channel
storage of the last several real-time frames
cine loop
a series of pulses and gaps allowing multiple focal zones and harmonic frequencies
code excitation
a series of closely spaced reverberation echoes behind a strong reflector
comet tail
the ratio of the largest to the smallest amplitude that the ultrasound system can handle
dynamic range
less in intensity from bending of the sound beam at a curved surface
edge shadowing
the increase in reflection amplitude from structures that lie behind the weakly attenuating structure
enhancement
displayed image of the returning echoes
field of view
a complete scan of the ultrasound beam; individual image composed of multiple scan lines
frame
the number of complete scans (images) displayed per second
frame rate
holding and displaying one frame of the real-time sequence
freeze frame
ratio of amplifier output to input of electric power
gain
secondary sound beams produced by a multielement transducer
grating lobes
number of scans lines per frame; scan-line density
line density
denotes the rows and columns of pixels in a digital image
matrix
storage of echo information
memory
an artifactual gray scale, color flow, or Doppler signal appearing of the opposite side of a strong reflector
mirror image
the path toward and away from a reflector are different
multipath
disturbance that reduces the clarity of the signal
noise
the minimum number of samples required to avoid aliasing; Doppler shift frequency above which aliasing occurs
Nyquist limit
an expanded image display beyond the normal limits of the transducer
panoramic image
picture element; smallest portion of a digital image
pixel
number of picture elements per inch
pixel density
assigning a brightness value to a missing pixel
pixel interpolation
a harmonic imaging technique using two pulses per scan line where the second pulse is an inverse of the first pulse
pulse inversion
the number of voltage pulses sent to the transducer each second
pulse repetition frequency
time form the beginning of one voltage pulse to the start of the next voltage pulse
pulse repetition period
allows access of stored data in an unsystematic order
random-access memory (RAM)
produced when echoes are placed too superficially because a second pulse was emitted before all reflections have returned from the first pulse
range ambiguity
store data cannot be modified
read-only memory (ROM)
two dimensional imaging of the motion of moving structures
real-time imaging
portion of the sound reflected from the boundary of a medium
reflection
change of sound direction on passing from one medium to another
refraction
multiple reflections between a structure and the transducer or within a structure
reverberation
redirection of sound in several directions on encountering a rough surface
scattering
reduction of reflective amplitude from reflectors that lie behind a strongly reflecting or attenuating structure
shadowing
comparison of meaningful information in an image (signal) to the amount of signal disturbance (noise)
signal-to-noise ratio
averaging of frames that view anatomy from different angles
spatial compounding
large, flat, smooth surface
specular
a misrepresentation of the Doppler shift in a negative direction occurring when the pulse repetition frequency is set too low
aliasing
smallest arteries in the circulatory system controlling the needs of organs and tissues
arterioles
pressure reduction in a region of high flow speed
Bernoulli effect
auscultatory sound within an artery produced by turbulent speed
bruit
the smallest of the body’s blood vessels connecting the arterioles to the venules and allowing the interchange of oxygen or carbon dioxide on nutrients to the tissue cells
capillaries
noise in the Doppler signal caused by high-amplitude Doppler shifts
clutter
observed frequency change of the reflected sound resulting from movement relative to the sound source or observer
Doppler effect
frequency shift created between the transmitted frequency and received frequency by an interface moving with velocity at an angle to the sound
Doppler shift
energy difference between two points
energy gradient
to move in a stream, continually changing position and direction
flow
electronic device controlling the transmission or reception of a Doppler signal; size of it is determined by the beam diameter, receiver gate length, and length of the ultrasound pulse
gate
science of physical principles concerned with the study of blood circulation
hemodynamics
the pressure created in a fluid system, such as the circulatory system;
when supine it is 0mm Hg
when upright; above the heart it is negative
below the heart it is positive
hydrostatic pressure
the resistance to acceleration
inertia
the highest frequency in a samples signal represented unambiguously; equal to one half the pulse repetition frequency
Nyquist limit
positioning of multiple pulsed Doppler gates over the area of interest
packet
maximum velocity at any given time
peak velocity
speed is constant across the vessel
plug flow
predicts volume flow in a cylindrical vessel
poiseuille’s equation
difference in pressure required for flow to occur
pressure gradient
predicts the onset of turbulent flow
Reynolds number
difference between the maximum and the minimum Doppler frequency shifts divided by the maximum Doppler frequency shift; also known as Pourcelot index
resistant index
electronic device that controls the region of Doppler flow detection
sample volume
the average velocity is calculated, with the colors placed side to side
variance mode
rate of motion with respect to time
velocity
all measured velocities for each gate are averaged, then the colors are arranged up and down
velocity mode
the smallest veins that receive blood from the capillaries and drain into larger caliber veins
venules
the quantity of blood moving through the vessel per unit of time
volume flow rate
a device that plots the reflection amplitudes received by the transducer
beam profiler
distance closest to the transducer in which imaging cannot be performed
dead zone
testing device that measures acoustic output
hydrophone
the routine, periodic evaluation of data collected of the performance of the ultrasound system and transducers
quality assurance (QA)
tissue equivalent testing device with characteristics that are representative of tissues
phantom
periodic internal cleaning and overall evaluation of the ultrasound system function; generally performed by the system manufacturer
preventive maintenance (PM) service
ability to place echoes in proper position when imaging from different orientations
registration accuracy
measure of how weak a reflection the system can display
system sensitivity
devices without tissue like properties designed to measure some characteristics of the imaging system
test objects
