What acoustic parameters can be adjusted by the sonographer?
amplitude, power, intensity
What acoustic parameter is determined by both the sound source and the medium?
wavelength
What acoustic parameter is determined by the medium only?
propagation speed
T/F A wave with a frequency of 15,000 MHz is ultrasonic?
true
T/F If amplitude is increased to 3 times it's original value, intensity is increased 6-fold.
false 9-fold
T/F If power is halved intensity is reduced by 1/4.
false it's halved
T/F propagation speed increases as frequency increases.
False
Medium 1 has a density of 9 and a stiffness of 6.
Medium 2 has a density of 8 and a stiffness of 6.
Which medium will be slower?
Medium 1
If the power in a beam is 1 watt and the area is 5 cm^2, what is the beam's intensity?
.2 W/cm^2
If intensity remains the same while the power is doubled, what has happened to the beam area?
doubled
A sound beam travels a total of 10 cm in 2 seconds. What is the speed of sound?
5 cm/sec
T/F Propagation speed increases as frequency increases.
false
T/F Propagation speed increases as frequency decreases.
False
T/F Propagation speed does not change as frequency increases.
True
What is the wavelength of 3 MHz sound in soft tissue?
.51 mm
The effects of sound waves on tissue in the body are called ______.
bioeffects
The effects of tissue on sound waves are called ______.
Acoustic propagation properties
The effects of a medium on an ultrasound wave are called ________.
acoustic propagation properties
T/F Continuous wave sound can create diagnostic images.
false pulse sound
What is pulsed sound?
a collection of cycles that travel together
2 components of pulsed sound
transmit, talking, "on" time
receive, listening, "off" time
Def. the actual time from the start of a pulse to the end of that pulse
Pulse duration
What is pulse duration measured in?
seconds, µs, ms, etc...
What are the typical values of pulse duration?
.3µs to 2µs
What are the formulas for pulse duration?
pulse duration (µs) = # of cycles x period (µs)
pulse duration (µs) = # of cyles / frequency (MHz)
What are the 2 characteristics of long duration pulses?
many cycles in the pulse
individual cycles with long periods
What are the 2 characteristics of short duration pulses?
few cycles in the pulse
individual cycles with short periods
Which type of pulse duration is desirable for imaging?
shorter duration pulses improve image accuracy
Def. the distance from the start to the end of a pulse
Spatial Pulse Length
What is spatial pulse length measured in?
mm, inches, etc...
What are the typical values for spatial pulse length?
.1 to 1 mm
What is the formula for spatial pulse length?
spatial pulse length (mm) = # of cycles x wavelength (mm)
What are 2 characteristics of long pulse length?
many cycles in the pulse
cycles with longer wavelengths
What are the 2 characteristics of short pulse length?
fewer cycles in the pulse
cycles with shorter wavelengths
Which type of spatial pulse length is more desirable?
shorter pulses create more accurate images
Def. the time from the start of one pulse to the start of the next pulse
Pulse Repetition Period
What is pulse repetition period measured in?
units of time, ms
What are the typical values for pulse repetition period?
100µs to 1 ms
Pulse repetition period is controlled by what?
Sound source specifically imaging depth
Def. the maximum distance into the body that an ultrasound system is imaging
Depth of View
What are the 2 components of pulse repetition period?
transmit time
receive time
What is transmit time also known as?
pulse duration
What happens to the depth of view when the listening time and pulse repetition period lengthen?
deeper imaging
What happens to the depth of view when the listening time and pulse repetition period shorten?
shallower imaging
Def. the number of pulses that an ultrasound system transmits into the body each second
Pulse Repetition Frequency
What is pulse repetition frequency measured in?
hertz
What are the typical values of pulse repetition frequency?
1000 to 10000 hertz
How is pulse repetition frequency and depth of view related?
inversely
What are the relationships between pulse repetition frequency and pulse repetition period?
inversely related and reciprocals
What is the easiest formula to remember PRF and PRP?
PRF x PRP = 1
T/F Two waves can have identical pulse repetition frequencies , even if their pulse repetition periods are different.
False
T/F Two waves can have identical PRFs, even if their periods are different.
True
T/F PRF and PRP are determined only by the imaging depth.
True
Def. the percentage or fraction of time that the system is transmitting a pulse
Duty Factor
What is unit for duty factor?
none. it's a percentage therefore dimensionless
What are the typical values for Duty Factor?
.2% to .5%
What is the relationship between depth of view and duty factor?
inversely related
What is the formula for duty factor?
duty factor (%) = (pulse duration / PRP) x 100
What are the factors that determine shallow imaging?
less listening
shorter PRP
higher PRF
higher duty factor
What are the factors that determine deeper imaging?
more listening
longer PRP
lower PRF
lower duty factor
Def. refers to the intensity of the beam at different locations or distances
Spatial Intensity
Def. the maximum intensity
peak intensity
Def. the mathematical middle intensity
Average Intensity
Def. refers to the intensity at all time, transmit and receive
Temporal Intensity
Def. refers to the intensity at the transmit time
Pulsed intensity
Def. the beams intensity at the location where it is maximum
spatial peak intensity
Def. the beams intensity across the entire cross-sectional area
spatial average intensity
Def. the beams intensity at the instant in time of its maximum value
temporal peak
Def. the average intensity during the most intense half-cycle
I max
Def. the average intensity during the pulse duration
pulse average intensity
Def. averaging the intensity during the entire PRP (includes both the transmit and recieve times)
temporal average intensity
T/F Intensities may be reported in various ways with respect to time and space.
True
The different measurements of intensities are important in the study of ________.
bioeffects
______ intensity is the most relevant intensity with respect to tissue heating.
SPTA
What units are all intensities are measured in?
watts/cm^2
What intensity if the highest and which is the lowest?
SPTP is the highest
SATA is the lowest
Def. describes the spread of a beam in space
beam uniformity coefficient or SP/SA factor
Def. describes the relationship of beam intensities with time
duty factor
Continuous wave ultrasound. The pulse average and temporal average intensities are the ______.
Same
T/F For continuous wave ultrasounds, SPTA = SPPA and SATA = SAPA.
True
T/F When pulsed and continuous waves have the same SPTP, the continous wave will have the higher intensity.
True
T/F When pulsed and continuous waves have the same SATP intensities, the continuous wave will have the higher SPTA intensity.
True
Rank the types of intensities from largest to smallest.
SPTP > Im > SPPA > SPTA > SATA
Def. the weakening of sound as it travels in the body
attenuation
Def. strengthening of the ultrasound signal
amplifying
Def. the unit that quantifies the strength of sound beams as they are created by tranducers and travel through the body
Decibels
Def. Decibels that are increasing in strength or getting larger.
Positive Decibels
Def. decibels that are decreasing in strength or getting smaller
negative decibels
The 3 decibel rule.
a change of 3 decibel is equal to doubling or having the intensity of the ultrasound beam
The 10 decibel rule.
a change of 10 decibels it equal to 10-fold or one-tenth of the intensity of the ultrasound beam
A reduction in the intensity of a sound beam to one-half of its original value is _____dB.
-3 dB
A reduction in the intensity of a sound beam to one-quarter of its original value is ______ dB.
-6 dB
-10 dB means that the intensity is reduced to ______ of its original value.
one-tenth
dB is a mathematical representation with a ______ scale.
logarithmic and relative
T/F We need one intensity to calculate dB.
False
A wave's intensity is 2mW/cm^2. There is a change of +9 dB. What is the final intensity?
16 mW/cm^2
2 factors determine attenuation
path length
frequency of sound
3 processes contribute to attenuation
reflection
scattering
absorption
Def. when the wave's energy strikes a boundary and is redirected back toward the sound source
Reflection
2 types of reflection
specular and diffuse
Def. type of reflection when sound is reflected back by a smooth boundary and in only one direction
Specular reflection
Def. type of reflection when sound is reflected back by and irregular surface and radiates in more than one direction
Diffuse reflection
Def. random redirection of sound in many directions that occurs when the tissue interface is smaller or equal to the wavelength of the sound beam
Scattering
Def. a special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength and the sound wave is redirected equally in all directions
Rayleigh Scattering
Def. occurs when ultrasonic energy is converted into another energy form, such as heat
absorption
Def. the number of decibels of attenuation that occurs when sound travels one cm
Attenuation coefficient
What is the attenuation coefficient measured in?
dB/cm
What is the formula for total attenuation?
total attenuation (dB) = atten coefficient (dB/cm) x distance (cm)
What is the formula for attenuation coefficient in soft tissue?
atten. coef. (dB/cm) = frequency (MHz) / 2
Def. the distance that sound travels in a tissue that reduces the intensity of sound to one-half its original value
half-value layer thickness
What are typical values for half-value layer thickness?
.25 - 1 cm
What are synomyns for half-value layer?
penetration depth, depth of penetration, half-boundary layer
2 factors that determine half-value layer thickness
the medium
the frequency of sound
Def. the acoustic resistance to sound traveling in a medium
impedance
What is the formula for impedance?
impedance (rayls) = density (kg/m^3) x prop. speed (m/s)
