Ch.7 Range Equation Flashcards
Ultrasound systems determine reflector depth by measuring a pulses’s what?
time-of-flight with a very accurate stopwatch
Go-Return Time or Time-of-Flight
is the elapsed time from pulse creation to pulse reception
When a reflector is located superficially, the time from pulse creation to reception is ?
Whereas trips to and from the deeper reflectors?
brief
require more time
Time-of-Flight is directly related to?
how deep a sound pulse travels
Greater distances ______ the time-of-flight ; Lesser distances ______ the time-of-flight.
prolong
shorten
what is the average speed of sound in soft tissue that is programmed in ultrasound systems?
1.54 mm/us
State the equation to calculate the depth of a reflector using the go-return time
depth (mm) = 1.54 mm/us x go-return time (us) / 2
When one reflector is twice as deep as another reflector, the pulse’s time-of-flight is ?
twice as long for the deeper reflector
13-Microsecond Rule
for every 13 us of go-return time, the object creating the reflection is 1 cm deeper in the body
The 13-Microsecond rule ALWAYS applies when ?
sound travels thru soft tissue
A pulse travels to the reflector and back to the transducer, the total distance that a pulse travels is?
twice the reflector depth
Time of Flight Reflector depth Total depth
13 us
26 us
Reflector depth Total depth
1cm 2 cm
2cm (13x2=26) 4 cm
Time of Flight Reflector depth Total depth travelled
39 us
52 us
130 us
Reflector depth Total depth
3 cm 6 cm
4 cm 8 cm
10 cm 20 cm
PRP is altered when the system’s maximum imaging depth is adjusted.
When the depth of view is shallow the PRP is ______ .
When the depth of view is deep, the PRP is _______ .
short
long
What is the formula for calculating the PRP when given the imaging depth and 13 us rule?
PRP (us) = imaging depth (cm) x 13 us/cm
When the depth of view is set to 10 cm, the PRP is ?
130 us (10 x 13 = 130 us)
When the depth of view is set to 5 cm , the PRP is?
65 us
(5 x 13 = 65)
What is the relationship between the pulse repetition period and the maximum imaging depth?
directly related
What is the relationship between the pulse repetition frequency and the maximum imaging depth?
inversely related
When the depth of view is shallow, PRF is?
high
When the depth of view is deep, PRF is?
low
What is the formula to calculate PRF using the imaging depth and 77,000 cm/s?
PRF (Hz) = 77,000 cm/s / imaging depth (cm)
When the depth of view is set to 7.7 cm, PRF is ?
10,000 Hz
(77,000 / 7.7 = 10,000)
When the depth of view is set to 15.4 cm, PRF is ?
5,000 Hz
(77,000 / 15.4 = 5000)
