Pulsed ultrasound Flashcards
What is a pulsed ultrasound?
When the crystal cannot transmit and receive simultaneously. Therefore, in pulsed systems the transducer must pause or “listen” after transmitting
In pulsed ultrasound, what does a master synchronizer do?
The master synchronizer sends an electronic signal to pulser
In pulsed ultrasound, the pulse is generated two ways, what are they?
- The electrical output from a generator is gated to apply a rapidly alternating voltage to the crystal
- A charged capacitor is discharged through the crystal which is stimulated to vibrated at a resonance frequency
How does a pulsed ultrasound differ from a continuous ultrasound
In a continuous wave ultrasound the crystal never stops vibrating
What are the pulsed ultrasound parameters?
- Pulse duration
- Spatial pulse length
- Pulse repetition frequency
- Pulse repetition period
- Duty factor
What does PD (pulse duration) mean?
The time it takes for a pulse to occur
What is the PD formula?
PD = (T)(Cycles in a pulse)
Does PD include dead time?
No
What is the unit of measure for PD?
Microseconds or uS
What is spatial pulse length?
Simply the length of a pulse
What is the formula for SPL (spatial pulse length)?
SPL= (lambda)(cycles in a pulse)
Or
SPL = (wavelength)(cycles in a pulse)
What is the typical units of SPL?
mm
If we increase frequency what will happen to wavelength and SPL
Wavelength would decrease which would decrease SPL
If we decrease the number of cycles in a pulse what happens to SPL?
It decreases the SPL
What does decreasing the SPL do?
Increases our image resolution
What is Pulse repetition frequency PRF?
Number of pulses emitted in one second
What are common units for ultrasound in PRF?
Hz or kHz
When doing PRF calculations what is recommended we do for units?
Get units into meters and meters per second
What is Pulse repetition period (PRP)?
The time from the beginning of one pulse to the beginning of the next
What is the measurement of PRP?
Units are in seconds or microseconds
What is the formula for PRP?
PRP = D/C
What is the relationship between PRF and PRP?
Regardless of their names they are still frequency and period, therefore they are reciprocals of one another
PRF = 1/ PRP
What is Duty factor (DF)?
The fraction of time that a pulsed ultrasound is on and is expressed in percentage
What is the duty factor of a continuous wave?
100%
A higher PRF or PD increases what? And why?
Increase the DF because there is less “listening” time between the pulses
What is the DF formula?
DF = (PD/PRP)(100)
What is density?
The mass of an medium per unit volume or the concentration of matter
If all other factors remain constant, an increase in density will do what?
Impede the rate sound travels
What does compressibility indicate?
The fractional decrease in volume when pressure is applied to material. (How squishy is it)
What happens when we compress the material?
We slow the velocity
Dense materials typically have low compressibility, what does this do to sound?
Increased sound velocity
What is bulk modulus?
The reciprocal of compressibility or the negative ratio of stress and strain. “Stiffness”
As bulk modulus increases what happens?
Compressibility decreases and velocity increases
What is elasticity?
The ability of an object to return to its original shape and volume after force is no longer caring on it
How does ultrasound waves cause elastic deformation?
By separation and compression of molecules
If only density of a medium increases what happens?
The velocity of sound in that medium decreases
If the compressibility of a medium increases what happens to it’s stiffness?
The stiffness is decreasing
If the stiffness is decreasing then what happens?
The velocity of sound in that medium will decrease as well
What does temperature do to sound?
The hotter it is the faster sound will travel
