Ch. 1-4 Physics Test Flashcards
Concentrations of energy in a sound beam
intensity
Intensity units are
watts/squared
Intensity is determined by the
sound source
Relationship between intensity and power
directly proportional
If the amplitude is doubled, the intensity is increased by a factor of
4
If the amplitude is halved, the intensity is reduced by a factor of
1/4
Length or distance of a single cycle
wavelength
Wavelength units
length
Wavelength determined by
both medium and sound source
Wavelength equation
wavelength (mm)= (1.54mm/microsec)/(MHz)
In soft tissue, sound with a frequency of 1 MHz has a wavelength of
1.54mm
rate that sound travels through a medium
propagation speed
Propagation speed is also called
speed or velocity
Speed units
distance over time (m/sec)
Speed determined by
medium
General Rule: ____
gases, liquids, solids
Put the following in order from fastest to slowest: fat, lung, air, soft tissue, bone, tendon
bone, tendon, soft tissue, fat, lung, air
Related to weight
Density
Related to change in shape
stiffness
When stiffness increases, speed
increases
When stiffness decreases, speed
decreases
When density increases, speed
decreases
When density decreases, speed
increases
In-phase waves interfere
constructive waves
Out-of phase waves interfere
deconstructive waves
A wave with a frequency of 15,000 MHz is ultrasonic. T/F
true
If the power of a wave is halved, the intensity is reduced to one-fourth its original value. T/F
false
The sonographer adjusts the output of the ultrasound system by increasing the amplitude by a factor of 3. What happens to the intensity
increased by a factor of 9
Collection of cycles that travel together
pulse
five parameters of pulsed ultrasound are
pulse duration, spatial pulse length, pulse repetition period, pulse repetition frequency, duty factor
time from the start of a pulse to the end of that SAME pulse
pulse duration
pulse duration is the
units of time that the pulse is ON
pulse duration is determined by the
sound source
time from the start of one pulse to the start of the NEXT pulse
pulse repetition period
PRP includes one
pulse duration time and one listening time
PRP is determined by the
sound source
As imaging depth increases, PRP
increases
As imaging depth decreases, PRP
decreases
number of pulses that occur in one second
pulse repetition frequency
PRF units
hertz
PRF determined by the
sound source
As imaging depth increases, PRF
decreases
As imaging depth decreases, PRF
increases
percentage or fraction of time that the system’s probe is transmitting sound waves
duty factor
If the duty factor is 100% or 1.0, the the system is
ON (cw)
If the duty factor is 0%, then the machine is
off
CW sound can be used to make anatomical images. T/F
False
length or distance that a pulse occupies in space
Spatial pulse length
The distance from the start to the end of one pulse is
SPL
SPL units
distance and length
SPL determined by
both medium and sound source
determines axial resolution
SPL
SPL equation
SPL= # cycles x wavelength (mm)
By adjusting imaging depth, the operator changes the
duty factor, PRF, PRP
What two are characteristics of the pulse itself and are inherent in the design of the transducer system
pulse duration, SPL
A 5MHz probe uses a cw with a prop speed of 1.8km/sec. The probe then uses pulsed wave with a duty factor of 0.5. What is the new prop speed
1.8km/sec
How many hertz is 5MHz
5,000,000 hertz
How much bigger is a billion than a million
1000 (10^3)
If you have to divide an exponential number you will
subtract exponents
If you have to multiply an exponential number you will
add the exponents
Macro means
large
Micro means
small
Sound is comprised of
compressions and rarefactions
Compressions are regions of ____ pressure and density
increased
Rarefactions are regions of _____ pressure and density
decreased
The 3 acoustic variables are
pressure, density and distance
Time required to compete a single cycle
period
period units
time
period determined by
sound source
number of certain events that occur in a particular time duration
frequency
frequency units
hertz
frequency determined by
sound source
Can period be adjusted
no
Can frequency be adjusted
no
Period and frequency are
reciprocals, inversely related
As frequency increases, period
decreases
As frequency decreases, period
increases
> 20,000Hz
ultrasound
between 20Hz and 20,000Hz
audible sound
<20Hz
infrasound
Describes the strength of a sound beam
amplitude, power, intensity
difference between the average value and the max value of an acoustic cariable
amplitude
amplitude units are
pressure, density, distance
amplitude is determined by the
sound source
amplitude ____ as it travels through the body
decreases
rate that work is performed, or the rate of energy transfer
power
power units
watts
power is determined by the
sound source
power is proportional to the wave’s amplitude
squared