Ultrasound Physics and Principles Flashcards
What is sound?
it is a longitudinal, mechanical wave that require a medium for transmission
longitudinal waves vibrate in which direction?
in the direction they are moving (propagate)
transducer frequency for USG procedures vary because of
structure depth, structure location, and composition of surrounding tissue
frequency
cycles/second
wavelength
(meters/cycle) = (meters/sec) / (cycles/sec)
propagation velocity
(meters/sec) = (meters/cycle) x (cycles/sec)
high frequency transducers are considered
> or equal to 7 MHz
low frequency transducers are considered
1-5 MHz
high frequency vs low frequency
high frequency
- more cycles per second
- higher resolution images
- increased attenuation
- imaging limited to shallow structures
low frequency
- fewer cycles per second
- lower resolution images
- less attenuation
- imaging deeper structures possible
a high frequency transducer is typically used for vascular access because:
a. the sound beam has increased attenuation
b. there are fewer cycles per second
c. it generates a high resolution image
d. imaging deep structures is possible
c. it generates a high resolution image
propagation velocity for soft tissue (average)
1,540 m/s
the less dense the medium, the ____ sound travels
slower
true or false: all frequencies travel at the same speed through the same medium
true
which of the following statements regarding sound is faster?
a. sound requires a medium to propagate
b. hertz = cycles/sec
c. the higher the frequency, the shorter the wavelength
d. sound travels through all tissue at 1540/sec
e. all statements are correct
e. all statements are correct
which zone of the ultrasound beam has the best resolution?
focal zone
which zone has the poorest resolution?
far field/ fraunhofer zone
which zone has decent resolution?
near field/fresnel zone
which technique allows US systems to send and receive echoes?
pulse-echo technique
brightness results from the differences in
acoustic impedance between adjacent tissues
doppler is dependent on the angle of
insonation
which of the following statements regarding doppler ultrasound is incorrect?
a. doppler is nore used to create an image
b. the optimal angle of insonation is 60 degrees
c. either the sender or the receiver must be moving
d. colors depicted with doppler indicate flow, but not direction
e. all of the above are correct
d. colors depicted with doppler indicate flow, but not direction
