Derivation of 13 us/cm

Here's a 5 minute video explaining the derivation of the 13 us/cm value for the go-return time in soft tissue.

The derivation of this handy shortcut is as follows:

d = (v t) / 2                                        range equation

t = (2 d) / v                                        solve for go-return time

t = (2 x 10 mm) / v                             solve for depth of 1 cm (10mm)

t = (20 mm) / 1.54 mm/us                   solve for depth of 1 cm using speed of sound in soft tissue (1.54 mm/us)

t = 12.987 us

Go-return time to I cm in soft tissue is approximately 13 us.

That's it.  Using the range equation to solve for go-return time we can see that the approximate go-return time to 1 cm depth is 13 us.

Since go-return time is directly proportional to depth, we can use this shortcut to estimate the depth of any reflector in soft tissue.

13 us/cm is the go-return time for any reflector in soft tissue.  Know this value for the Registry.