Chapter 1 penny Flashcards
the conversion of sound energy to heat
absorption
the interference pattern caused by scatterers that produces the granular appearances of tissue on a sonographic image
acoustic speckle
changes that occur within a medium as a result of sound traveling through that medium
acoustic variables
the maximum or minimum deviation of an acoustic variable from the average value of that variable; the strength of the reflector
amplitude
a decrease in the amplitude and intensity of the sound beam as sound travels through tissue
attenuation
the rate at which sound is attenuated per unit depth
attenuation coefficient
the ability to accurately identify reflectors that are arranged parallel to the ultrasound beam
axial resolution
scattered sound waves that make their way back to the transducer and produce an image of the display
backscatter
the ratio of the center intensity to the average spatial intensity; also referred to as the SP/SA factor or beam uniformity coefficient
beam uniformity ratio
technology used to create comparable transducer technology to piezoelectric materials
CMUT
an area in the sound wave of high pressure and density
compression
sound that is continuously transmitted
continuous wave
the process of reducing the number of cycles of each pulse in order to improve axial resolution
damping
a unit that establishes a relationship or comparison between two values of power, intensity, or amplitude
decibels
mass per unit volume
density
relationship that implies that if one variable decreases, the other decreases or if one variable increases the other increases
directly related
how far apart objects are; may also be referred to as vibration or displacement
distance
the percentage of time that sound is actually being produced
duty factor
elasticity
stiffness
the number of cycles per second
frequency
the depth at which sound has lost half of its intensity
half-intensity depth
half intensity depth
half value layer thickness
a unit of frequency
hertz
a device used to measure the output intensity of the transducer
hydrophone
the resistance to the propagation of sound through a medium
impedance
Newton’s principle that states that an object at rest stays at rest and an object in motion stays in motion unless acted on by an outside force
inertia
the power of the wave divided by the area over which it is spread; the energy per unit area
intensity
the percentage of sound reflected at an interface
intensity reflection coefficient
the percentage of sound transmitted at an interface
intensity transmission coefficient
the dividing line between two different media
interface
relationship that implies that if one variable decreases, the other one increases, and vice versa
inversely related
waves in which the molecules of the medium vibrate back and forth in the same direction that the waves are traveling
longitudinal waves
any form of matter
medium
reflectors that are smaller than the wavelength of the incident beam
nonspecular reflectors
angle of incidence is 90 degrees to the interface
normal incidence
angle of incidence is less than or greater than 90 degrees to the interface
oblique incidence
a measurable quantity
parameter
the movement of molecules due to propagating sound energy
particle motion
distance to the reflector
path length
the time is takes for one cycle to occur
period
a material that generates electricity when pressure is applied to it, and one that changes shape when electricity is applied to it; also referred to as the element or crystal
piezoelectric materials
the rate at which work is performed or energy is transmitted
power
force per unit area of the concentration of force
pressure
to transmit through a medium
propogate
the speed at which a sound wave travels through a medium
propagation speed
the time during which the sound is actually being transmitted; the “on” time
pulse duration
the number of pulses of sound produced in 1 second
pulse repetition frequency
the time taken for one pulse to occur
pulse repetition period
sound that is sent out in pulses
pulsed wave
an area in the sound wave of low pressure and density
rarefaction
the fixed quantity owed as the sound beam travels through tissue
rate
small scattering reflectors
Rayleigh Scatterers
the echo; the portion of sound that returns from an interface
reflection
the change in the direction of the transmitted sound beam that occurs with oblique incidence angles and dissimilar propagation speeds
refraction
the phenomenon that occers when sound waves are dispersed into different directions because of the small reflector size compared with the incident wavelength
scattering
law used to describe the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media
snell’s law
a traveling variation in pressure
sound
the length of a pulse
spatial pulse length
reflections that occur when the sound impinges upon a large, smooth reflector at a 90 degree angle
specular reflections
the ability of an object to resist compression and relates to the hardness of a medium
stiffness
the total amount of sound in dB that has been attenuated at a given depth
total attenuation
type of wave in which the molecules in a medium vibrate at 90 degree to the direction of travel
transverse waves
sound waves of frequences exceeding the range of human hearing
ultrasound
the length of a single cycle of sound
wavelength
infrasound range
less than 20 Hz
audible sound range
20-20,000 Hz
ultrasound range
20,000 Hz or more
diagnostic ultrasound range
between 2 and 15 MHz (or higher)
pressure units
Pascals or pounds per square inch
density units
kg/cm3
particle motion units
feet, inches, centimeters, or miles
period units
us
frequency units
Hz, kHz, MHz
if frequency increases, period _______
decreases
if frequency decreases, period ________
increases
Formula for period
T = 1 / f
formula for frequency
f = c / ^
if stiffness increases, propagation speed _______
increases
if density increases, propagation speed _______
decreases
formula for propagation speed
c = e / p
wavelength units
mm
if frequency increases, wavelength ______
decreases
if frequency decreases, wavelength _______
increases
formula for wavelength
^ = c / f
amplitude units
Pa
power units
W and mW
intensity units
W/cm2 mW/cm2
______ and ______ are proportional to amplitude squared
power
intensity
power decreases as amplitude _______
decreases
intensity is proportional to
power
formula for intensity
I = Power / Area
formula for impedance
z = pc
pulse repetition frequency units
kHz
if imaging depth increases PRF
decreases
if imaging depth decrease PRF
increases
PRP units
ms
If PRF decreases PRP
increases
If PRF increases PRP
decreases
Pulse duration units
us
formula for pulse duration
PD = nT
Duty factor units
no units
duty factor formula
df = pd / prp
SPL unit
mm
SPL formula
SPL = n^
increasing frequency = ________ attenuation
increasing
increasing path length = _______ attenuation
increasing
formula for total attenuation
TA = f / 2 x L
smooth surface
border is larger than incident wavelength
angle dependenct
specular reflectors
rough surface
border is smaller than incident wavelength
not angle dependent
nonspecular reflectors
Formula for ITC
ITC = 1 - IRC
Formula for IRC
IRC = Ir / Ii = [z2 - z1 / z2 + z1]2
Normal perpendicular incidence
impedance mismatch
percentage or intensity of sound reflected and transmited at an interface
reflection
oblique incidence
propagation speed mismatch
angle of transmitted sound
refraction
snells law formula
sin 0t = sin 0i (c2 / c1)
formula for BUR
BUR = SP/SA
Temporal average formula
TA = PA x DF
list intensities from lowest to highest
SATA, SPTA, SAPA, SPPA, SATP, SPTP
3 primary acoustic variables
pressure, density, particle motion
two parts of a cycle
compression rarefaction
particle motion units
mm
parameters of sound waves
period
frequency
amplitude
power
intensity
propagation speed
wavelength
average speed of sound in soft tissues
1540 m/s or 1.54 mm / us
Propagation speed is influenced by _____ and ______.
density stiffness
if frequency increases, wavelength _____
decreases
the faster the propagation speed, the _____ the wavelength
longer
wavelength formula
^ = c / f
amplitude doubles, power ______
quadruples
amplitude triples, power increases _____
9 times
amplitude halved, power reduced by _____
one-fourth
impedance units
rayls
large impedance = ______ reflection
stronger
more subtle impedance difference = _____ reflection
weaker
impedance the same = _____ reflection
no
Parameters of pulsed wave ultrasound
PRP
PRF
PD
DF
SPL
typical values of PRF
between 1,000 and 10,000 Hz
duty factor formula
DF = PD / PRP
reduces the long “ring” of a vibrating crystal to 2 or 3 cycles per pulse
damping
Spatial pulse length depends on _____ and _____.
wavelength and number of cycles in each pulse
shorter wavelengths result in ____ SPLs
shorter
device that is creating the sound
sound source
tissue through which sound waves are traveling
medium
3 mechanisms of attenuation
absorption reflection scattering
greatest contributor to attenuation
absorption
used when evaluating two intensities, powers, or amplitudes
dBs
if an intensity or power has doubled, it has changed by __ dB
3
if an intensity of power halves, it has changed by __dB
-3
as path length increases, attenuation ____
increases
average rate of attenuation in soft tissue
.7 dB/cm/MHz
In soft tissue the HID is equal to _____
6/f
higher frequency transducers = _____ intensity of scatter
higher
reflection formed when two criteria are met:
normal incidence
two media have different impedances
two types of oblique incidence
obtuse
acute
Intensity of sound reflected at an interface depends on:
intensity of transmitted sound
difference in impedances between two media
the average intensity across the face of the entire beam
spatial average
highest of all temporal intensities
temporal peak
the average of all the intensities during both transmission and the listening period
temporal average
lowest of all temporal intesnsities
TA
measured only during pulse transmission
PA
TA formula
TA = PA x DF
lowest of the intensities
SATA
highest of the intensities
SPTP
The _____ is altered by adjusting the depth control on the machine
PRF
In increase in PRF a _________ in DF
increase
As imaging depth increases prf
decreases
the amount of refraction that occurs at an interface
snells law
pressure is typically expressed in
pascals
the attenuation coefficient in soft tissue is equal to
one-half of the operating frequency
requires an oblique interface and a propagation speed mismatch
refraction
density is typically measured in
kilograms per cm cubed
what is the total amount of attenuation that occurs if a 6 MHz sound beam travels through 4 cm of tissue
12 dB
as imaging depth increases PRP
increases
What are the units of DF?
unitless
density and propagation speed are ____ related
inversely
the inertia of the medium describes its
density
if the angle of incidence is 40 degrees, what is the angle of transmission at the interface if medium 1 has a propagation speed of 1320 m/s and medium 2 has a propagation speed of 1700 m/s?
<40 degrees
In clinical imaging, the wavelength typically mesaures between
0.1 and 0.8 mm
whatr is the change in intensity if the power decreases by half?
intesnity is halved
Damping of the sound beam _____ the SPL
reduces
adding damping to the transducer improves which type of resolution?
axial
what is the change in power if amplitude triples?
it increaes nine times
The portion of the sound beam where teh molecules are farther apart describes an area of
rarefaction
if only the density of a medium is increased, then the
propagation speed will decrease
