Ch 7 Range Equation
A) What is another name for Go-Return Time?
B) _____ distances prolong the Go-return time; ___ distances shorten the Go-Return time.
Time of flight
greater;lesser
One way that a sonographer can alter the axial resolution achieved during an exam is to adjust the maximum imaging depth.
True of False
False
Depth of view and axial resolution are unrelated. A sonographer cannot adjust imaging depth to change a system's axial resolution.
True or False?
The shorter the pulse duration, the better the picture.
TRUE
SPL=pulse duration×wavelength
A sonographer wants to improve both axial and lateral resolution. Which combination would accomplish this?
A. Increase SPL and increase beam width
B. Increase SPL and decrease beam width
C. Decrease SPL and decrease beam width
D. Decrease SPL and increase beam width
C. Decrease SPL and decrease beam width
If the imaging depth is increased, what happens to the maximum PRF?
A. PRF increases
B. PRF stays the same
C. PRF decreases
D. PRF becomes zero
Answer: C. PRF decreases
Greater depth means the pulse needs more time to travel out and return.
SPL = 1.0 mm. What is the axial resolution?
A. 0.25 mm
B. 0.5 mm
C. 1.0 mm
D. 2.0 mm
Answer: B - 0.5 mm
Axial resolution = SPL/2
When depth of view(DOV) is shallow, PRP is ___.
When depth of view(DOV) is deep, PRP is ___.
short;long
PRP(us) = image depth(cm) x 13 us /cm
Axial Resolution Comparison
Transducer A: 2 cycles/pulse, wavelength = 0.3 mm
Transducer B: 4 cycles/pulse, wavelength = 0.3 mm
Which has better axial resolution?
A. A
B. B
C. Same
D. Cannot determine
Answer: A — Transducer A
The 13 microsecond rule applies when sound travels through soft tissue.
For every ___ us of go-return time. the object creating the reflection is __ cm deeper in the body.
What happens to the total distance?
13 us, 1 cm
total distance will be twice the reflector depth.
Lateral resolution Synonyms
L A T A
What are they?
Lateral
Angular
Transverse
Azimuthal
Axial resolution synonyms :
L A R R D
What are they?
Longitudinal
Axial
Range
Radial
Depth
Lateral Resolution
Two structures are located next to each other and are separated by 1 mm. Which factor is most important in determining whether they can be distinguished?
A. SPL
B. Frequency
C. Beam width
D. PRP
C — Beam width
In soft tissue, sound travels to a reflector and back to the transducer in 39 us. How deep is the reflector?
A. 2cm
B. 6cm
C. 3cm
D. cannot be determined
Answer C. 3cm
Sound travels a round trip depth of 1 cm. Thus, in 39 us, sound travels to and returns from a depth of 3cm.
Axial resolution is determined by _____.
Lateral resolution is determined by ____.
SPL; beam width
A sound wave is created by a transducer, reflects off an object, and returns to the transducer. The go-return time is 26 us. What is the total distance that the pulse traveled?
A. 1cm
B. 2cm
C. 3cm
D. 4cm
D. total distance traveled is twice the depth of the reflector.
How long does it take for sound to make a round trip to and from the skins's surface to a reflector depth of 1cm in soft tissue?
A. 13 µs
B. 150 ms
C. 15 µs
D. 2 seconds
A — 13 µs
One reflector is 5 times deeper than another. The time of flight of sound to the deeper structure is __ the time of flight of the shallower reflector.
A. one fifth as much as
B. equal to
C. less than
D. Five times more than
Answer D. five times more than.
Time of flight and reflector depth are directly related. When a reflector is 5x deeper than another, the pulse's time of flight is also five times greater.
Two reflectors are side-by-side where the ultrasound beam is very wide. What happens?
A. Easily distinguished
B. May appear as one structure
C. Axial resolution improves
D. SPL decreases
Answer: B May appear as one structure
Side-by-side = lateral resolution.
Lateral resolution is poor when the beam is wide.
Wide beam → poor lateral resolution
Narrow beam → good lateral resolution
Which statement about lateral resolution is correct?
A. Determined primarily by SPL
B. Best where the beam is narrowest
C. Best where the beam is widest
D. Independent of beam width
B. Best where the beam is narrowest
Lateral resolution is the ability to distinguish objects that are side-by-side.
A narrow beam can distinguish side-by-side structures better than a wide beam.
The beam is narrowest around the focal zone.
Range Equation
A reflector is located 8 cm beneath the transducer. Assuming a propagation speed of 1.54 mm/µs, approximately how long does it take for the pulse to travel to the reflector and return?
A. 26 µs
B. 52 µs
C. 104 µs
D. 123 µs
Answer: B — 104 µs