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The go-return time (also known as the "time of flight" ) is the time taken between the transmission of a pulse and the reception of the echo. It is the time it takes sound to travel from the transducer down to an interface and the echo to return to the transducer.
All diagnostic ultrasound machines use the go-return time to calculate the distance to each interface using the range equation (See the range equation)
The go-return time in soft tissue is approximately 13 microseconds per centimeter. You should know this value.
This means that in soft tissue the sound travels to a depth of 1 cm and back in 13 us.
You should definitely know the adjacent go-return times:
For those who are interested, here is the derivation of the 13 us/cm go-return time in soft tissue:
We use the range equation to solve for time for a distance of 1 cm
d = (v x t)/2
1 cm = (1.54 mm/us x t)/2
t = (2 x 1 cm)/1.54 mm/us
t= (2 x 10 mm)/15.4 mm/us (Note: 1 cm = 10 mm)
t = 20 mm/1.54 mm/us
t = 12.987 us
Thus, the go-return time per centimeter is approximately 13 microseconds
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