Chapter 7 Flashcards
To position echoes properly on the display, the following two items of information are required:
- The direction from which the echo came (which is assumed to be the direction in which the emitted pulse is launched).
- The distance to the reflector where the echo was produced.
The distance to a reflector is calculated from
the propagation speed and pulse round-trip travel time
Range equation: Distance (mm) =
[speed (mm/μs) x time (μs)]/2
The elapsed time from pulse creation to pulse reception
Time of flight
aka
go return time
Time of flight is directly related to
how deep a sound pulse travels
Ultrasound systems are programmed with
the average speed of sound in soft tissue (1.54 mm/microsecond)
The depth of a reflector can be accurately calculated from the go-return time using the following equation:
depth (mm) = [1.54mm/μsx go-return time (μs)]/2
The 13-microsecond rule always applies when sound travels through
Soft tissue
For every 13 μs of go-return time, the object creating the reflection is
1 cm deeper in the body
Since a pulse travels to the reflector and back, the total distance that a pulse travels is _ the reflector depth.
Twice
When the depth of view is deep, PRP is
Long
When the depth of view is shallow, PRP is
Short
PRP (μs) =
imaging depth (cm) x 13 μs/cm
When the depth of view is shallow, PRF is
High
When the depth of view is deep, PRF is
Low
