final review from canvas file Flashcards
Which is larger macro or micro
macro means bigger
symbol for millions
mega
symbol for millionths
micro
symbol for hundreds
hecto
symbol for hundreths
centi
a frequency of 15,000 hz is
audible sound
if power in a wave is halved the intensity is reduced to
half
if the amplitude of a wave is increased 3 times, the intensity is increased by
9 times
propagations speed is determined by
medium
propagations speed increases as frequency increases or decreases
false
not realated
how many intensities are needed to calculate decibels
two
path length increases what happens to the attenuation
increases
which is lower spatial peak or spatial average intensity
spatial average
in addition to location in a beam, intensities also vary with
time
the most important intensity in soft tissue is
SPTA
duty factor is a unitless number between
0 and 1
intensities may be reported in various ways in respect to
time and space
duty factor for a pulsed ultrasound system is typically
0.2%
beam intensity is the same at different depths and lateral locations
true/false
FALSE
at a particular depth the center of a beam is more intense than the edges
true/false
TRUE
temporal peak is the maximum intensity in
time
3 MHz is how many Hz
3 million
how much bigger is a billion than a million
1000
what are the units of a wavelength
mm
what are the units of frequency
Hz
what are the units of intensity
w/cm^2
what are the units of propagatoin speed
m/s
what are the units of period
us
what is determined by sound source
period
frequency
amplitude
power
intensity
if the intensity is the same while the power is doubled what happens to the beam area
increases
sound beam travels a total of 10cm in 2 sec. What is the speed of sound in this medium
5 cm/sec
what term describes the time from the start of a pulse to the end of the pulse
pulse duration
PRF is the recipricol of
PRP
dB is a mathmatical representatoin with a __________scale
logarithmic
rayleigh scattering is related to
frequency^4
which media has the greatest attentuatoin and slowest speed
Air
what mathmatically describes the physics of refraction
snells law sin (tran)/ sin(inc)= speed 2/speed 1
two PZT crystals are made from the same material. The thicker will have a pulse transducer with
lower frequency and slower speed
when PZT exceeds the curie point the PZT
depolarizes
PZT is also known as
crystal, active element, ceramic
what reduces the ringing in a transducer
backing material
mathmatically the Q factor is the frequency divided by the
bandwidth
imaging transducers are also referred to as
pulsed wave transducer
what type of crystal will produce sound with the lowest freq
thick and slow
the damping material in the transducer improves the systems what resolution
axial
if the electrical excitation volt is 6MHz then the output freq of a CW transducer is
6 MHz
the impedance of a transducer active element is 19Mrayls, and the impedance of the skin is 14Mrayls. What is an acceptable impedance for the matching layer
anything between 14 and 19 Mrayls
which transducer component is a thin barrier of cork or rubber that isolates or uncouples the internal components from the case
acoustic insulator
what is the purpose of the backing material in an imaging transducer
reduce ringing and improve axial resolution
what creates the beam with deepest focus
large diameter and high freq
how are freq and near zone length related
directly, lower freq shorter near zone
what crystal creates the least divergence
large diameter higher freq
what creates the most divergence
small diameter
lower frequency
what determines the freq of sound created by a pulsed transducer
thickness and speed of the PZT
what determines the spread of a sound beam in the far field
diameter of crystal and frequncy
frequency does not change, if the diameter of the new PZT increases what happens to the wavelength
no change
imaging to greater depths requires the listeing time to
increases
when reporting a beams intensity the maximum is referred to as
SPTP
the highest temporal intensity is
temporal peak
units for reporting intensity are
w/cm^2
what is measured where intensity is maximum and averaged over time
SPTA
which intesity is measureed over the entire cross section of the beam and over all time
SATA
what is the same as normal incidence
perpendicular, orthogonal, right angle, 90 degrees
intensity of a sound beam just prior to striking a boundry is referred to as
incident intensity
the portion of a sound beam that contimnues on after striking a boundry is the
transmitted intensity
the percentage of US intensity that is allowed to pass through when the beam reaches a boundry between two media is referred to as
intensity transmission coefficient
a sound beam with an intensity of 50 w/cm^2 strikes a boundry and is totally reflected. What is the intensity reflectoin coefficient
100%
the intensity reflection coefficient of sound is 99.9% . What percentage is transmitted into the body
0.1%
specular reflections arise when the interface is
smooth
what do we know about oblique incidence
nothing
transmission with a bend is
refraction
Snells law describes what physics
refraction
sound waves strike a boundry at normal incidence. The impedances of the two are identical. What percentage of the beam is reflected
0%
must be difference in impedance for reflection to occur
what processes occur as the ultrasound passes through all media
reflection, scattering and absorption
two waves are traveling through a medium and arrive at a location at the same time. What event takes place
interference
the percentage of time that a system is transmitting a pulse is referred to as
duty factor
a 3MHz beam travels though two media. It attentuates 5 dB in A and 6 dB in B.
What is the total attenuation of the beam
11 dB
what is the dominant factor in attenuation
absorption
impedance is a characteristic of
acoustic resistance of sound traveling in media
density x propagation speed
hertz is a unit used to describe what wave characteristic
frequency
a low freq transducer is best at imaging what structures? Deep or shallow
deep
The percentage of the US intensity that is allowed to pass through when the beam reaches a boundary between two media is
intensity transmission coefficient
what is the best estimate for attenuation coefficient of sound traveling in soft tissue
.5 dB/cm/MHz
Attenuation is determined by two factors
path length and freq of sound
With longer distances and higher frequencies you have
higher attenuation
With shorter distances and lower frequencies you have
lower attentuation
Because attenuation means a weakening or a decrease, the dbs must be
negative
Which term best describes redirection of sound in many directions
scattering
Reflections from a smooth reflector are referred to as
specular
When a boundary is rough, reflected sound is disorganized and random, also called
diffuse or backscatter
Rayleigh scattering increases dramatically with increasing frequency, which is the relation
frequency 4
Acoustic Impedance is equal to
density x propagation speed
The time needed for a pulse to travel to and from the transducer and the reflector is called
go return time, time of flight,
A sound wave is created by the transducer, reflects off an object and returns to the transducer in 52, what is the reflector depth and total distance traveled
4 cm depth and 8 cm total travel
The maximum imaging depth during an ultrasound exam is 5 cm. The sonographer adjusts the depth to 10cm.
What happens to pulse repetition frequency
PRF is halved
A sound wave is created by the transducer, reflects off an object, and returns to the transducer. The time of flight is 130 microseconds. What is the maximum PRF
7,700 Hz
A sound wave is created by the transducer, reflects off an object, and returns to the transducer. The go return time is 39 microseconds. What is the total distance traveled
6 cm
Axial resolution deals with structures that are ___________to the sound beam
parallel
As frequency increases, the numerical value of LARRD resolution
lowers
Superior axial resolution is associated with the following
shorter spatial pulse length, shorter pulse duratoin, higher Freq, fewer cycles per pulse, lower numerical values
