Ch. 5-7 Test Flashcards
Key parameter for bioeffects. It is the concentration of the power in a beam
intensity
What is the maximum value called
peak
What is the mean or average value called
average
Refers to distance or space
Spatial
Refers to all time (transmit and receive)
temporal
Refers only to the time the pulse exists (transmit only)
pulsed
All intensities have units of
w/cm squared
The largest intensity is
SPTP
The smallest intensity is
SATA
The intensity which is most important for thermal bioeffects is
SPTA
Intensities may be reported in various ways with respect to
time and space
As sound travels in the body it _______ or _______
weakens or attenuates
After a sound wave is received by the transducer and ________ into _______ and returned to the ultrasound system, it is _________ or ________
converted, electricity, strengthened, amplified
Decibels are a ______ scale.
logarithm
The _____ of any number represents the number of “10s” that are multiplied together to create the original number
log
What is the log of 100
2
What is the log of 10000
4
How many intensities are required to use decibels
two
Decibels are a ratio of the _________ to the _______
measured level, starting level
The ______ level is ______ by the starting level
measured, divided
What are the units of relative amplitude
dB
Positive decibels report signals that are ______ in strength or getting larger
increasing
Negative decibels report signals that are ______ in strength or getting smaller
decreasing
What dB means two times bigger or double
+3dB
What dB means ten times bigger or ten fold
+10dB
What dB means one half
-3dB
What dB means one tenth
-10dB
6dB means the final is _____ times bigger than the original
4
20 dB means the final is ______ times bigger than the original
100
-20dB means the final has fallen to ______ the original value
1/00
-6dB means the final has fallen to ________ the original value
1/4
A signal’s power increases from 1 to 100 watts. How is this expressed in decibels
20dB (10 x 10= 100)
The power of a system is at 100% and this is 0dB. What is the change in decibels when the system’s power is at 50%
-3dB
The power of a system is at 100% and this is 0dB. The system is adjusted to -6dB. What is the system’s power at this setting
25%
The decrease in intensity, power and amplitude of a sound wave as it travels
attenuation
The further a sound wave travels, the more
attenuation occurs
Attenuation of sound in soft tissue depends upon the wave’s _____ and the ______ the wave travels
frequency, distance
In soft tissue, ____ frequency results in less attenuation resulting in deeper imaging
lower
Distance and attenuation are
directly related
Frequency and attenuation are
directly related
list the 3 components of attenuation
reflection, absorption and scattering
The primary component of attenuation and occurs when the sound energy is converted into heat energy
absorption
What has extremely high attenuation than soft tissue
air
____ and ____ have more attenuation than soft tissue
bone, air
What has much, much less attenuation than soft tissue
water
Higher attenuation occurs with ____ because it absorbs and reflects
air
Higher attenuation occurs with _____ because of scattering and absorption
lung
Occurs when propagating sound energy strikes a boundary between two media and some returns to the transducer
reflection
Occurs when the boundary is smooth and sound is reflected in only one direction in an organized manner
specular
Occurs when the irregularities in the structure’s surface are much smaller than the wavelength
rayleigh scattering
Reflections that move out equally in all directions
omnidirectional/rayleigh
Occurs when the boundary has irregularities about the same size as the sound’s wave length
diffuse reflection or backscattering
When a boundary is ______, reflected sound is disorganized and random
irregular
Backscatter is also called
diffuse reflection
Random redirection of sound in many directions
scattering
Rayleigh scattering when the tissue interface is _______ or _______ than the wavelength of the incident sound beam
organized, much smaller
Lung tissue scatters sound because the alveoli are filled with
air
Rayleigh scattering=
frequency^4
Number of decibels of attenuation that occurs when sound travels one centimeter
attenuation coefficient
The units for attenuation coefficient are
dB, cm (dB/cm)
The value of the _____ DOES NOT CHANGE as path length changes
attenuation coefficient
In soft tissue, the attenuation coefficient is
0.5 dB/cm/MHz
Attenuation is extremely high in
air, lung and bone
Attenuation is extremely low in
fat, water and biological fluids
Gel is used to remove ______ from the path of ultrasound
air
Acoustic resistance to sound traveling in a medium
impedance
Impedance=
density x prop speed
The units for impedance are
rayls
Rayls are represented by
z
Normal incidence means that the incident sound beam strikes the boundary at
90 degrees
What are the other names for normal incidence
perpendicular, orthogonal, right angle, 90 degrees
Oblique incidence occurs when the incident sound beam strikes the boundary at any angle
other than 90 degrees
Sound wave’s intensity immediately before it strikes a boundary
incident intensity
Intensity of the portion of the incident sound beam that, after striking a boundary, returns back in the direction from which it came
reflection intensity
Intensity of the portion of the incident beam that, after striking a boundary, continues forward in the same general direction that it was traveling
transmission intensity
There is __________ of ______ at a boundary, which means the incident intensity equals reflected + transmitted intensities
conservation of energy
Incident intensity=
reflected intensity + transmitted intensity
Percentage of the intensity that bounces back when a sound beam strikes the boundary between two media
Intensity reflection coefficient (IRC)
Percentage of the intensity that passes in the forward direction when the beam strikes an interface between two media
Intensity transmitted coefficient (ITC)
IRC + ITC=
100% (incident intensity)
Intensities are reported with units of
w/cm squared
Intensity coefficients are reported with
percentages
In soft tissue, ______ of the incident US energy is reflected at a soft-tissue boundary between different biologic media
less than 1%
How much is reflected at an air-tissue interface
> 99%
How much is reflected at a bone-tissue interface
greater %
If the intensity reflection coefficient of sound is 99.9% at an air tissue interface, what percent of sound is transmitted into the body
0.1%
A sound beam with the intensity of 45 w/cm squared strikes a boundary and 70% is transmitted, how much is reflected
30%
Reflection with _______ occurs only if the two media at the boundary have different acoustic impedances
normal incidence
Whatever is not transmitted must be
reflected
Reflection and transmission with ________ MAY OR MAY NOT occur
oblique incidence
With oblique incidence, reflection angle equals
incidence angle
Refraction is ______ with a bend
transmission
Change in direction as sound transmits from one medium to another at an oblique angle
refraction
Refraction requires two conditions to be met
oblique incidence, 2 different media prop speeds
Refraction cannot occur with
normal incidence, 2 media with same speed
Describes the physics of refraction
snell’s law
Sound wave strikes a boundary at normal incidence. The impedance of the two media are identical. What percentage of the sound wave is refracted
0%
The impedance of medium 1 is 8 rayls and the prop speed is 1450 m/sec. The impedance of medium 2 is 6 rayls and the prop speed is 1.855 km/s. A sound beam strikes a boundary between the media and is both partially transmitted and reflected. The angle of the incident sound beam is 30 degrees. What is the angle of reflection
30 degrees (angle of incidence=angle of reflection)
The elapsed time from pulse creation to the pulse reception is called the
go-return time or time-of-flight
The time-of-flight is directly related to
how deep a sound wave travels
In soft tissue, every _____ of go-return time means the reflector is 1 cm deeper in the body
13 microseconds
When a reflector is 3cm deep, a pulse’s time-of-flight is
39 miscroseconds
A sound pulse is produced by a transducer and travels in a patient. It travels from the transducer to the kidney, reflects off of it and returns to the transducer in 130 microseconds. How deep is the kidney
10cm
A sound pulse emitted from a transducer travels in a patient, reflects off of the pancreas and returns to the transducer is 52 microseconds. How deep is the pancreas? What is the total distance that the pulse traveled?
4cm, 8cm
