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Flashcards in Chapter 17 Deck (39):
1

What is harmonic imaging?

the creation of image from sound reflections at twice the freq of the transmitted sound

2

What is the formula for harmonic imaging?

twice the fundamental freq
2x freq

3

What is the freq of sound created by the transducer and transmitted into the body called?

fundamental freq

4

Where do harmonic freq sound waves arise from?

nonlinear behavior

5

What is the fundamental image?

the image created by processing reflections that have the same freq as the transmitted sound

6

What is the harmonic image?

the image created by processing reflections that are twice the fundamental freq

7

What are the two form of harmonics?

tissue harmonics and contrast harmonics

8

Why does harmonic imaging improve poor quality images?

b/c harmonic freq waves undergo less distortion that fundamental sound waves

9

What is linear behavior?

proportional or symmetrical. linear systems respond in an even manner

10

what is nonlinear behavior?

irregular or disproportionate. the system is nonlinear when it behaves unevenly

11

What are the main differences between linear and nonlinear?

linear is symmetrical and nonlinear is asymmetrical

12

When is tissue harmonics created?

when a miniscule amount of energy is converted from the fundamental freq to the harmonic freq. this conversion create tissue harmonics during transmission

13

What creates the nonlinear behavior in tissue harmonics?

sound travels at slightly uneven speeds through soft tissue-faster through compressions and slower through rarefactions

14

What two strong artifacts arise with tissue harmonics?

the beam is very strong
the many different superficial anatomic layers distort the sound beam

15

What does the use of harmonics increase?

signal to noise ratio

16

Do strong or weak sound beams create tissue harmonics?

strong

17

Beams that are most likely to create harmonics are least likely to create ___?

artifacts

18

When is tissue harmonics created?

during transmission and in the tissues

19

What is pulse inversion harmonics?

an imaging technique specifically designed to utilize harmonic reflections, which are distortion free, while eliminating distotred fundamental reflections

20

What is the disadvantage of pulse inversion harmonics?

that two pulses are transmitted down each scan line and twice the number of pulses are required to create each image. frame time is doubles, frame rate is halved and temporal resolution is reduced

21

What is power modulation harmonic imaging?

similar to pulse inversion and its designed to augment harmonic reflections

22

How hoes power modulation work?

the harmonics are extracted by sending one strong pulse and one weak pulse down each scan line

23

Another word for contrast agents?

microbubbles

24

What are contrast agents?

gas bubbles encapsulated in a shell.

25

What five standards do contrast agents need to meet?

safe
metabolically inert
long lasting
strong reflector of US
small enough to pass through capillaries

26

Why were contrast agents designed?

to create strong reflections that actually light up blood chambers, vessels, or other anatomic regions.

27

Why are contrast harmonics created?

b/c microbubbles act in a nonlinear manner when struct by sound waves

28

When are contrast harmonics created?

during reflection as energy is converted from the fundamental freq to the harmonic freq

29

Bubbles ___ to a greater extent than they ____

expand, shrink

30

What is the uneven behavior of contrast harmonics called?

resonance

31

When does the Mechanical index increase?

with lower freq
and stronger sound waves (substantial pressure variation) such as amplitude

32

What is the formula for mechanical index

peak rarefaction pressure/square root of freq

33

__ mechanical index sound beams do not create harmonics b/c the microbubbles expand and contract evenly in a linear fashion

low

34

High mechanical index is considered what?

great than 1.0

35

What happens when the MI is less than 0.1?

no harmonics
backscatter
linear behavior
higher freq sound
low beam strength
bubbles expands very little

36

What happens when the MI is between 0.1-1.0?

some harmonics
resonance
nonlinear behavior
lower freq sound
higher beam strength
bubbles expand moderately

37

What happens when the MI is greater than 1.0?

strongest harmonics
bubble disruption
extreme nonlinear behavior
lowest freq sound
highest beam strength
bubble expands greatly

38

what are the important characteristics of contrast agents when used with harmonic imaging?

the nature of the outer shell
the gas that fills the microbubble

39

Are contrast harmonics stronger or weaker than tissue harmonic?

stronger if they are created by microbubbles