final pt 1 Flashcards
The frequency of a transducer is 25 million Hz (cycles/sec). What’s another way to write it?
25 MHz
2.5 * 107
What do we call a sound that is below the audible range?
infrasound
Which items are determined by the sound source?
period
frequency
amplitude
power
intensity
Which item(s) are determined by both media and sound?
wavelength
Which is only determined by the medium?
propagation speed
What are acoustic variables?
pressure
density
distance
Given choices of freq, which one would have the longest wavelength?
one with lowest freq
If the intensity remains the same, the power is doubled, what will happen to the beam area?
it is doubled
What term describes the start of a pulse to the end of a pulse?
pulse duration
What kind of scale has dB?
logarithmic scale (relative scale that requires two intensities)
For every 3dB, what will the intensity do?
doubles
If initial intensity is less than the final intensity, then a gain in dB will be what?
positive
What is Rayleigh scattering related to?
frequency4
In soft tissue, attenuation coefficient is directly related to what?
frequency
Which media will have the greatest attenuation and which media will have the fastest and slowest speeds?
Greatest
air>bone>muscle>soft tissue>blood>water
With 2 PZT electric crystals made from the same material, the thicker transducer will make a pulse with what?
lower frequency and slower speeds
When PZT exceeds the curie point, what happens to the PZT?
PZT is depolarized
What are the other names for PZT?
piezoelectric, ferroelectric, lead zirconate titanate, crystal, ceramic, active element
Which component of the transducer reduces the ringing of the pulse?
backing material (dampening element)
Which crystals will produce sound with the lowest freq?
thick active element with a low speed
What resolution does damping material improve?
axial resolution
If the freq of the electrical excitation of the voltage in a p__ulsed wave transducer is 6Hz, what is the operating freq of the transducer?
In a pulsed wave transducer, freq is not determined by the electrical signal
The impedance of a transducer’s active is 1,900,000 rayls, and the impedance of skin is 1,400,000 rayls. What would be an acceptable matching layer?
a number between the active element and the skin
Which transducer component has a thin barrier of cork or rubber that isolates or uncouples internal components of the transducer from the case?
acoustic insulator
Which component of a transducer increases the efficiency of sound energy transfer between the active element and the body?
matching layer
How are freq and near zone length related?
directly
Two transducers have the same diameter. The first probe has a 6MHz freq and the second has a 8MHz freq. Which beam will have a more shallow focus?
lower frequency
(6 MHz: smaller diameter, lower freq)
Which probe will create a beam with the least divergence?
larger diameter
higher frequency
Which probe will create a beam with the most divergence?
smaller diameter
lower frequency
What determines the freq of sound created by a pulsed wave transducer?
speed of sound in the PZT
thickness of the PZT
What determines the focal length of a sound beam?
transducer diameter
frequency of sound
Which transducer has the best lateral resolution in the far field?
high freq
(larger diameter crystals)
A sound beam is created by a round PZT crystal with a diameter of 10mm. The focal depth of the sound beam is 8cm. What diameter is the sound beam at a depth of 8cm?
(5mm: the diameter is half at the focal depth of 8)
What are the other names for lateral resolution?
Lateral
Angular
Transverse
Azimuthal
Lateral resolution is what to the beam?
perpendicular (side by side)
Know the characteristics of lateral resolution.
(Determined by width of the sound beam, narrower beams have better resolution, is best at focus where beam is narrowest. Lateral resolution=beam diameter?)
Several different methods are used to describe US beam intensity. These different methods evaluate tissue exposure to sound energy and are important in what kinds of studies?
the study of bioeffects
When reporting a beam’s intensity at the location where it is it’s maximum, it is referred to as what?
spatial peak intensity
What are the units for intensity?
Watts/cm2
What is measured where intensity is maximum and averaged over transit time?
spatial peak, pulse average (SPPA)
What is it called when intensity is maximum and averaged over all time, both transmit and receive?
spatial peak, temporal average (SPTA)
Which intensity is measured over the entire cross-sectional area of the crossbeam and over all time?
spatial average, temporal average (SATA)
Know all the terms that mean the same as normal incidence:
(PORN)
Perpendicular
Orthogonal
Right angle
Ninety degrees (90o)
What is sound beam at the instant before it hits the boundary called?
incident intensity
What is the portion of the incident intensity after striking the boundary continues on called?
transmitted intensity
The half layer thickness depends on which factors?
the medium and the freq of sound
If we have normal incidence, that means that the sound beam strikes the boundary at how many degrees?
90o
Sound waves with an intensity of 50w/cm2, strikes a boundary and totally reflected. What is the intensity reflection coefficient?
100%
Sound wave strikes the same intensity 50w/cm2, totally reflected. What is the reflected intensity?
50w/cm2
If the intensity reflection coefficient of sound is 99.9%, what is transmitted into the body?
0.1%
With normal incidence, reflection depends upon different what?
media with different impedances
What type of incidence do we know nothing about?
oblique
Specular reflections arise when the interface is what?
smooth
Transmission with a bend. What is it?
refraction
If we have oblique incidence and different propagation speeds, what might occur?
(refraction)
What does Snell’s law describe?
the physics of refraction
Sound waves strike a boundary at normal incidence. The impedance of the media are identical. What percentage of the sound wave is refracted?
refraction does not occur with normal incidence
Two sound waves travel through the medium at the same time and arrive at the same time. What event takes place?
interference
Which will create fastest speed of speed?
(thinner PZT
higher freq)
(low density
high stiffness)
3MHz sound beam travels through 2 medium. It attenuates 5dB in A and 6dB in B. What is the total attenuation of the sound beam as it travels through both media?
11dB
Which of the following are considered contributors to attenuation and which is the most important contributor?
reflection, scattering, absorption
absorption=most important
As path length increases, attenuation of US in soft tissue does what?
increases
Attenuation in soft tissue is less than which of the following?
Which attenuates more than soft tissue?
low>high
water>blood, urine, biological fluids>fat>soft tissue>bone>lung>air
muscle, bone, lung, air
Impedance is a characteristic of what?
(reflection?)
Reflection occurs only if the 2 medium at the boundary have different what?
Impedances
Low freq transducers are best at imaging what types of structures?
deep structures
Ability to distinguish two structures lying close together is considered what?
resolution
What is the best way to image the thyroid?
high frequency transducer
What is the best estimate for attenuation coefficient of sound traveling in soft tissue?
0.5 dB/cm/MHz
(1/2 freq, atten coef=freq/2)
Attenuation is determined by what two factors?
path length and freq of sound
Know what contributes to attenuation:
path length and frequency
(more attenuation=longer distances and higher freq
less attenuation=shorter distances and lower freq)
Which term describes the redirection of sound in many directions?
scattering
(omnidirectional-Rayleigh scattering)
When a boundary is rough, the reflected sound is disorganized and random. What is that called?
diffuse reflection (backscatter)
When time of flight is known, what else can be determined?
reflector depth and total distance traveled
When one reflector is twice as deep as another reflector, the time of flight is what for the deeper reflector?
twice as long
The sound wave is created by the transducer, reflects off of an object and returns back to the transducer. 10cm deep, round trip 25sec.
What is the speed of sound in the medium?
The time needed for a pulse to travel from a transducer to the reflector is called what?
time of flight (go return time)
Sound wave is created by transducer. Reflection return is 52microsec. What is the reflector depth?
4cm
Max imaging depth is 4cm, sonographer adjusts depth to 8cm. What happens to PRP?
it is doubled
If the go return time is 39microsec, what is the total distance traveled?
6cm
Axial resolution deals with structures that are what to the sound beam?
parallel
As freq increases, the numerical value of LARRD resolution does what?
the numerical value is lowered
Two different transducers create pulses, both 5MHz. Which will create a better image in regards to axial resolution?
the shorter cycle pulse transducer will create better axial resolution
Conservation of energy
100% of energy is either reflected or transmitted at the boundary
Which one has less biological effects, focused or unfocused?
focused
Hugen’s Principle
disc shaped (v) tiny pieces in hourglass shape
