Pulse Flashcards
To place an echo on the screen (B mode), the U/S machine needs to know…
- direction of sound entering patient
- propagation speed
- time to reflector
- distance to reflector
What does the U/S machine need to know to adjust echo brightness on the screen?
strength of the reflector
4 characteristics of a pulse?
- short burst of sound energy
- a collection of a number of cycles
- cycles travel together
- each pulse has a beginning, middle, & end
What is pulse repetition frequency (PRF)?
the number of pulses in a second
2 reasons there are limits to PRF
- echoes must return to machine before another pulse is sent out
- depth will increase the time it takes for echo to return
PRF is set by…
source
What is PRF influenced by?
frequency, damping, depth
How can PRF be adjusted by the sonographer?
by adjusting depth
What is pulse repetition period (PRP)?
the time it takes from the start of one pulse to the start of the next pulse
Components of PRP
pulse duration, idle time, period
What is the relationship between PRF & PRP?
inversely related & reciprocals
Frequency sets the ____ of the pulse
period
What is the pulse duration?
time it takes for one pulse to occur – start of one pulse to the start of the end of the pulse
What determines the number of cycles in the pulse?
damping layer
Are the number of cycles in the pulse user adjustable?
no
Does increased damping lead to more or less cycles in the pulse?
less
Idle time is set by the…
depth of an image
Is idle time user adjustable?
yes
What is duty factor?
the percentage of time the machine is on & working
What is the spatial pulse length (SPL)?
the distance a pulse takes up in space
Does SPL affect axial or lateral resolution?
axial
Will a pulse that propagates through muscle have an SPL that is shorter or longer than normal?
longer (faster speeds = longer pulse lengths)
What is pulsed ultrasound?
Collection of cycles that travel together
2 components of ultrasound
- Transmission
- Reception
