Pulsed Ultrasound Flashcards
Describe pulsed ultrasound
- a master synchronizer sends and electronic signal to a pulse
- the transducer must pause (listen) after transmitting
- the crystal can not transmit and receive at the same time
In pulsed ultrasound the pulse can be generated in two ways describe these ways.
1- electrical output from generator is gated to apply rapidly alternating voltage to crystal
2- charged capacitor is discharged through crystal which is stimulates to vibrate at resonance frequency (not common)
What are the 5 wave parameters of pulsed sound
Pulse duration Spatial pulse length Pulse repetition frequency Pulse repetition period Duty factor
The time it takes for one pulse to occur is called?
Pulse duration (PD)
What is the formula for PD?
PD = T times cycles in a pulse
What does the pulse duration NOT include and what are the units it is measured in?
PD does not include the dead time
Usually measured in microsecond (us)
If frequency was increased what would happen to the pulse?
The pulse would decrease, go down (it would get shorter)
The length of the pulse is called ?
SPL
What is the formula for SPL? And what is it usually measured in?
SPL = wavelength times cycles in a pulse
Typically measured in millimeters (mm)
Cycles in a pulse is also known as ?
Ring down
If frequency is increased what happens to the spatial pulse length?
Increasing frequency will decrease the wavelength which will result in the SPL being decreased as well
If frequency (wavelength) decreases the SPL, what else will decrease the SPL?
Decreasing the ring down (number of cycles in a pulse ) will also decrease the SPL
Decreasing the SPL does what to our image on the screen?
Improves the image resolution
The number of pulses emitted in one second is called what?
Pulse repetition frequency (PRF)
Ultrasound probes typically emit how many pulses per second?
Few thousand pulses per second
What affects pulse repetition frequency?
Depth!!
If depth is decreased, what will happen to the PRF?
The PRF will be increased.
Half the distance, now the sound is being reflected back quicker so it can send out another wave sooner
What is the time from the beginning of one pulse to the beginning of the next called?
Pulse repetition period (PRP)
PRP is another way of expressing the —— calculated in the range equation.
Time (there and back)
D D
PRP = —— T = ——
C C
What is the relationship between PRF and PRP
Reciprocals
1 1 C D
PRF = —— PRP = —— PRF = —— PRP = ——
PRP PRF D C
What is the fraction of time that a pulsed ultrasound if on, expressed as a percentage?
Duty factor (DF)
Continous wave is on what percent of the time?
100%
A higher PD and PRF does what to the DF?
This increases the DF because there is less “listening” time,
pulse length goes up
What is the equation for DF as a percentage?
PD
DF = ——— times 100
PRP
Sound velocity is dependent on the medium it travels through. What two characteristics of the medium determine the velocity?
Density
Compressability
The mass of a medium per unit volume….concentration of matter is called ?
Density
If ONLY density increases (all other factors are constant) what will happen to the velocity?
The velocity will decrease.
More mass requires more energy for particle motion
What has a greater transfer of energy, something more stiff or something less stiff?
More stiff!!
Think of people putting hands against one another and having floppy arms versus locked arms
Indicating the fractional decrease in volume when pressure is applied to the material is known as?
Compressibility
The more dense the material (less compressible) results in a decreased or increased sound velocity?
Increased
The easier it is to compress a material the higher or slower the velocity ?
Slower
The reciprocal of compressibility is known as ?
Bulk modulus (stiffness)
If bulk modulus (stiffness) is increased, what happens to compressibility and velocity?
Bulk modulus increases
Compressibility decreases
Velocity increases
The ability of an object to return to its original shape and volume after a force is no longer acting on it is referred to as?
Elasticity
Does ultrasound cause elastic deformations by separation and compression or molecules?
Yes it sure does
What is the dominant factor, stiffness or density?
Stiffness baby
If only the density increases then the velocity in that medium
Decreases
If compressibility increases then stiffness is
Decreasing
If stiffness increases then the velocity
Increases
Does Temperature effect the speed of sound?
Yes
If temperature increases the velocity of sound will
Increases as well
How is a pulsed system different then a continous wave system ?
Pulsed - one crystal to send THAN listen
Continous - two crystals, send and listen at same time
How does pulse repetition frequency relate to the operating frequency of the probe?
NOT RELATED jokes on ya
Is pulsed ultrasound or continous wave ultrasound capable of obtaining an image.
Pulsed
