Week 6 - Range, Displays, Dynamic range, Harmonics, and Contrast Flashcards
In order to create a dot on the image, a pulse of sound must what?
travel to a reflector and return to the transducer
The time it takes to go and return from a reflector is known as what?
Time of Flight
Time of Flight is what?
the round trip of a pulse
The total distance a beam and echo travels is what?
twice the depth of the reflector
What is the speed of US?
1.54 mm/µsec
What MUST you do to accurately calculate the reflector depth?
divide the round-trip distance by 2
How long does it take US to travel 1 cm?
13 µsec
4 cm would take how long to travel?
52 µsec
How can you adjust the amount of time between pulses?
by adjusting the depth
What do PRP and PRF stand for?
pulse repetition period, pulse repetition frequency
What is PRP?
the length of time between pulses
Relation. PRP and depth.
Directly
What is PRF?
the number of pulses sent per sec (Hz)
Relation. PRF and depth.
Inversely
As depth increases, the frequency of pulses __________.
decreases, since they need more time to travel
A low PRF is (GOOD or BAD). Why?
BAD, because something may have been missed by sending fewer pulses which results in less information
A high PRP is (GOOD or BAD). Why?
BAD, because more time between pulses means less information resulting in something being missed
You should use the _________ depth when scanning.
least amount of
You should use the _________ depth when scanning.
least amount of
What are 3 major ways to display US image data?
A mode, B mode, M mode
What does A mode display?
the AMPLITUDE of each echo on a graph
In A mode, the Y axis measures __________ and the X axis measures ___________.
amplitude, depth
What does B mode display?
gray scale imaging
In B mode, the Y axis is the ___________ of the reflector, and the X axis is ______________.
depth, each point the transducer sent a soundwave
What does brightness represent in B mode?
the strength of the echo
What is M mode used to measure and how is it displayed?
M mode measures the motion of a structure (esp. the heart) and it is displayed with wavy and straight lines.
Dynamic range describes what?
the number of grays available for imaging
What changes the dynamic range?
Compression
A __________ dynamic range = many shades of gray and _________ contrast. This is helpful to see differences in _________.
wide, low, plaque
A __________ dynamic range = few shades of gray and _________ contrast. This is helpful to see ____________.
narrow, high, vein compressions
Harmonic images are created from reflections that are __________ the frequency of the probe.
twice
A 2 MHz fundamental frequency would create a Harmonic frequency of __________.
4 MHz
The best use of harmonic imaging is in ___________.
Deeper structures
Strength of the harmonic wave ___________ as sound travels.
increases
Microbubbles are ___________, and they are used to do what?
contrast agents, create stronger reflectors
Microbubbles are used to see ___________ better in small spaces
blood flow
Microbubbles have a _____________ behavior, meaning that they do what?
non-linear, grow and shrink when hit with soundwaves
Low _______ and high _________ will increase harmonics.
frequency, amplitude
The mechanical index estimates the amount of what?
harmonics created
What is a common, short-lived contrast agent?
Agitated Saline
