Physical Principles Flashcards
Which of the following factors does NOT affect impedance?
frequency
You are imaging a structure containing two media having the same acoustic impedance. What will occur at the boundary of the two structures?
All of the sound will be transmitted
The unit of impedance
Rayl
An example of a spectacular reflector is
Pericardium
What system control can you adjust to compensate for the effect of sound attenuation in the body?
TGC
The algebraic summation of waves leading to patterns of minima and maxima is called:
Interference
What sound parameter is determined only by the medium?
Propagation speed
Snell’s law describes
The angle of sound transmission at an interface between media having different propagation speeds
During the performance of a sonogram, you would be most likely to encounter refraction in this view:
Curved interface
You may observe sound attenuation by all of the following EXCEPT:
Compression
When you image sound reflected from a large, smooth interface, you are observing results of:
Specular reflection
Normal incidence (perpendicular incidence) occurs when
the sound beam strikes the interface at a 90 degree angle
During a sonographic examination of a large vessel, a 45 degree beam to vessel angle would be called:
Oblique incidence
What occurs when you image a structure with oblique incidence?
The angle of reflection will be oriented away from the transducer resulting in a decreased visualization of the structure
The shadow depicted in an image of a renal stone is primarily a result of the following sound tissue interaction:
Reflection: very little sound is transmitted through the stone to provide reflections from tissue distal to the stone, this results in shadowing distal to the calcification
Which of the following statements regarding the effect of frequency on Rayleigh scattering is TRUE?
Scattering intensity is proportional to frequency raised to the fourth power
An echo from which one of the following sound reflector is most dependent on the angle of incidence?
Specular reflector, the angle of reflection is equal to the angle of incidence
What determines acoustic impedance?
Density and propagation speed of the medium
What system control should you adjust to compensate for sound attenuation with increasing depth?
TGC
Diffuse Reflection
the reflected beam is scattered in various directions
According to snells law the angle of transmission is related to the incident beam angle and:
amount of acoustic impedance mismatch at interface
change in frequency that occurs at an interface
one half the angle of incidence
the relative speeds of sound in the two media
the percentage of diffraction distal to the interface
the relative speeds of sound in the two media
snells law dictates the angle of transmission that will occur at an interface with refraction of the sound beam, Refraction (bending) of the sound beam occurs whenever there is oblique incidence and different propagation speeds between two media
which of the following interactions of sound and tissue decreases the intensity of the transmitted beam?
absorption, reflection, scattering, conversion of sound to heat, all the above
all of the above
all of these interactions will result in decreased intensity of the transmitted beam
The relationship of frequency to absorption
if frequency is doubled absorption is doubled
Directly related to one another
The reduction in the intensity of sound as it propagates through tissue
Attenuation
another term for nonspecular reflection
Scattering occurs when the interface is small, less than several wavelengths across
Frequency and Attenuation are related how?
Directly if one is doubled the other is also doubled
As frequency increases wavelength
decreases improving resolution but decreasing penetration because of increased sound absorption
You are scanning a large mass that is composed primarily of fat. Which of the following are most likely to encounter?
Axial misregistration of objects distal to the mass on the screen due to the slower propagation speed through fat
What two conditions must be present to cause refraction of a sound wave?
Oblique incidence and different media propagation speeds
The transducer you are using transmits wide bandwith pulses whose frequency content is 2-5MHz which of the following describes the reflected echo signals after they have traversed the tissue?
The echo signals will be shifted down in frequency due to the increased attenuation of higher frequencies
When the sound beam is refracted during a sonographic examination, which of the following might you detect on the ultrasound image?
Lateral misregistration
refraction
bending of the sound beam that results in lateral misregistration of structures posterior to the refracted beam
what can you do to enhance the visibility of a specular reflector?
scan with perpendicular incidence
What interaction of ultrasound and tissue is primarily responsible for imaging the internal structure of organs?
scattering
what sound tissue interaction is necessary to form an ultrasound image?
reflection
For soft tissue, one of the factors responsible for determining acoustic impedance is
Density
You are imaging a structure that is highly attenuating. Which imaging effect do you expect to encounter?
Shadowing
What would you change if the image does not show adequate penetration and the far field displays noise instead of tissue?
Decrease transmit frequency
For pulsed ultrasound, which of the following factors determine the frequency of the sound wave?
transmitter frequency
The maximum cyclical change in a quantity is known as
Amplitude
sound propagation in a medium
molecules oscillate back and forth to propagate sound waves but do not move from one end of the medium to another
Molecules oscillate back and forth to propagate sound waves but do not move from one end of the medium to another
What term denotes the time it takes for one cycle to occur
Period
if the number of cycles in a pulse is increased but the wavelength remains the same, whats true?
The pulse duration is increased (the time it takes to complete one pulse, if the number of cycles in the pulse is increased, it will take more time for one pulse to occur)
What is most likely to decrease beam intensity?
increasing beam area
For a given output power the intensity is expected to fall if the beam area is increased
Regions of low pressure and density that are formed during sound propagation are termed
Rarefactions
What property would result in increased propagation speed of sound through a medium
Increased stiffness
attenuation is proportional to
frequency
What frequencies are best to use for scanning a large patient;s abdomen
lower frequencies
Velocity of ultrasound wave in bone
4080 m/s
Wavelength is measured in
Millimeters
Regions of decreased particle density in a sound beam
Rarefaction
ultrasound propagation velocity depends on
density and compressibility
