pulsed sound Flashcards
Continuous wave has
Extremely _____ axial resolution
and you are ______ to determine depth
it Contains ____ crystals,
it’s main components are: (3)
poor
Unable
2, 1 to send and 1 to receive
frequency, period, wavelength
pulsed US has 6 components:
it allows us to know the _____ from
which a reflection is received which is determined by the _______ equation. which is:
Range Equation (depth), PRF PRP, Pulse Duration, SPL, DF
depth
range
Depth (mm) = C(mm/us) x Time (us) / 2
It take ____ us to image to a depth of 10mm (1 cm) in soft tissue.
to image 20mm (2 cm) would take ____ us, etc…
What is the depth of a reflector in soft tissue
if the round-trip-travel time is 13us?
What is the depth of a reflector in soft tissue
if the round-trip-travel time is 26us?
13
26
Pulses of US are produced by pulses of electrical
voltages hitting the transducer crystals
Diagnostic imaging creates pulses of _____ cycles each
and then the transducer _______ to for the reflections
1-3 , listens
what is the pulse repitition rate or frequency?
Like the “rhythm” of our sound (frequency is like pitch)
Hertz – Hz = 1 pulse/second
1 kHz = 1,000 pulses/second
what is it Determined by ?
Number of pulses per seconds
source
The higher the PRF, the _____ the resolution. why?
The PRF must _____ with increasing depth. why?
you should always use the _______ frequency possible for adequate _____________.
better, More lines per frame
decrease. Takes longer for pulse to go down and back
Inversely (indirectly) proportional
highest, penetration (depth)
________ is the Time required for one pulse to occur or Interval time from the beginning of one pulse to the beginning of the next.
it measures ___ and ___ time
it is teh ____ of prf? making it ____ while prf increases.
what is its relationship to depth?
what is it determined by?
prp
On and off time
measured in seconds (ms)
Reciprocal of pulse repetition frequency 1/PRF
PRP decreases as PRF increases – inversely proportional, indirectly proportional
PRP is directly proportional to depth
source
What is the PRP if the PRF is 10 Hz?
What is the PRP if the PRF is 20 kHz?
What is the maximum PRP when imaging 10 mm deep?
What is the round trip travel time for 10 cm om image?
You just calculated the minimum PRP for this
imaging situation. So what is the maximum PRF?
same as RTT which is 13us/10mm. *13us
130us (x10 to go from mm to cm)
(prp = 1 / prf) 77 kHz
_______ is the Interval time from the beginning to the end of a pulse. Time it takes for one pulse to occur.
it tells you ______ time only and is Measured in______
what is its formula?
pulse duration (pd)
“On”, seconds (us)
PD us = n x T(us)
N = number of cycles in the pulse
T = period of the US being used
PD is determined by ____, both ____ and _______
Average __ cycles per pulse
Increase period _______ PD
Average PD is ._____ us
source, frequency, number of cycles
1-3
increase
0.5 – 3
What is the pulse duration if the period is .25us and there are 3 cycles per pulse?
What is the pulse duration of a 3 MHz transducer with 3 cycles per pulse?
pd = n x t
- 75us
- 5 us
_____ is the Fraction (or percent) of time pulsed sound is on. it is Unitless (or x 100 for %)
what is its formula?
what is it Determined by ?
duty factor DF = PD (us)/PRP (us) source *DF of 1 is continuous wave US DF of PW is always <1
What is the duty factor if the pulse duration is
.0001 ms and the PRP is 1 ms?
What is the duty factor if the pulse duration is
.1 us and the PRF is 1 kHz?
0.001
?
____ is the Length of space over which one pulse occurs. Distance of one pulse.. “On” only. Measured in mm
what is its formula?
________ SPL improves axial resolution
spatial pulse length
SPL (mm) = n x wavelength (mm)
Decreasing
