CH 17 - Harmonics and Contrast Agents

Question 1

the creation of an image from sound reflections at twice the frequency of the transmitted sound

Answer 1

harmonic imaging

Question 2

is the fundamental frequency transmitted or received

Answer 2

transmitted

Question 3

twice the transmitted frequency

Answer 3

harmonic frequency

Question 4

harmonic frequency sound waves arise from _____ behavior

Answer 4

nonlinear

Question 5

another name for harmonic frequency

Answer 5

second harmonic frequency

Question 6

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

Answer 6

fundamental image

Question 7

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

Answer 7

harmonic image

Question 8

two forms of harmonics that are important in diagnostic sonography

Answer 8

tissue harmonics

contrast harmonics

Question 9

harmonic imaging is most useful in improving what

Answer 9

image quality

because harmonic frequency waves undergo less distortion than fundamental sound waves

Question 10

linear systems respond in an even manner

Answer 10

linear behavior

Question 11

other words for linear

Answer 11

proportional or symmetrical

Question 12

a system is nonlinear when it behaves unevenly

Answer 12

nonlinear behavior

Question 13

other names for nonlinear

Answer 13

irregular or disproportionate

Question 14

does harmonic frequency sound arise from linear or nonlinear behavior

Answer 14

nonlinear

Question 15

as a sound wave travels into the body, a small amount of energy is converted from the fundamental frequency to the harmonic frequency. this conversion creates _____ during transmission

Answer 15

tissue harmonics

Question 16

why does sound travel slightly at uneven speeds through soft tissue

Answer 16

travels faster as it comprises and slower through rarefactions

Question 17

this variation in speed creates ____ in the biologic media

Answer 17

tissue harmonics

Question 18

the variation in speed alters the shape of the sound beam and a small amount of energy is transferred from ___ frequency to ___ frequency

Answer 18

fundamental to harmonic

Question 19

the strength of the harmonic wave (increases/decreases) as it travels through tissue

Answer 19

increases

Question 20

what is the significance of the gradual development of a harmonic signal?

Answer 20

harmonic signals cannot distort because they do not exist in the superficial depths

Question 21

the use of harmonics (increases/decreases) signal to noise ratio?

Answer 21

increases

Question 22

why do strong artifacts appear within the first few centimeters of tissue during fundamental imaging?

Answer 22

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

Question 23

Is there another form of nonlinear behavior that further minimizes distortion with tissue harmonics?

Answer 23

the relationship between the sound beam strength and harmonic creation is nonlinear

Question 24

what would happen if it were linear?

Answer 24

weak beams would create weak tissue harmonics. medium strength beams would create medium harmonics, and strong beams would create strong harmonics

Question 25

Why do only strong sound beams create harmonic signals?

Answer 25

harmonics are only produced in the sound beams main axis, where the beam is strong

Question 26

beams that are most likely to create harmonics are least likely to create _____

Answer 26

artifacts

Question 27

tissue harmonics are not present as sound leaves the transducer. Where are they created?

Answer 27

in deep tissues during transmission

Question 28

what is the behavior of harmonics?

Answer 28

nonlinear

Question 29

harmonic frequencies are not created at the skins surface. this avoids what?

Answer 29

distortion and reduces noise

Question 30

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

Answer 30

pulse inversion harmonics

Question 31

this type of imaging creates images from the portion of the reflected sound that has the same frequency as the transmitted sound

Answer 31

fundamental imaging

Question 32

type of imaging that creates images only from the harmonic, which is twice the frequency of the transmitted sound

Answer 32

harmonic imaging

Question 33

instead of filters, we now use _________ to separate the harmonics from the fundamental frequencies

Answer 33

pulse inversion harmonics

Question 34

in pulse inversion harmonics, two consecutive ultrasound pulses are transmitted down each scan line. what are these pulses

Answer 34

first is a typical pulse | second is an inverted copy that is out of phase with the first

Question 35

wherever a compression exists in the first pulse, a _______ exists in the second pulse

Answer 35

rarefaction

Question 36

the reflections from these two pulses are combined where

Answer 36

in the receiver

Question 37

since the two waves are linear and one is out of phase, what happens to the waves

Answer 37

they destructively interfere and completely cancel each other out

Question 38

when these waves cancel out, the fundamental portions disappear but what portion stays?

Answer 38

the harmonic portion

Question 39

disadvantage of pulse inversion harmonics

Answer 39

2 pulses are transmitted down each scan line and twice the number of pulses are required to create each image which means the time required to create a Fram e is doubled, the frame rate is halved, and the temporal resolution is reduced

Question 40

does pulse inversion harmonics increase or decrease temporal resolution

Answer 40

decrease

Question 41

What is power modulation in harmonic imaging?

Answer 41

With power modulation, the harmonics are extracted by sending one strong pulse and one weak pulse down each scan line. The fundamental portions of each wave completely cancel each other out and leave only the harmonic portion of the reflection. The harmonics create an image with less distortion, the frame rate is halved, and temporal resolution is decreased

Question 42

gas bubbles that are encapsulated in a shell that are injected or ingested

Answer 42

contrast agents or microbubbles

Question 43

what do contrast agents do

Answer 43

light up blood chambers, vessels, or other anatomic regions for diagnostic purposes

Question 44

5 requirements that contrast agents must meet

Answer 44

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

Question 45

are contrast harmonics created during transmission or reflection

Answer 45

reflection

Question 46

contrast harmonics are created during reflection as energy is converted from ____ frequency to ____ frequency

Answer 46

fundamental to harmonic

Question 47

what nonlinear behavior of a micro bubble creates contrast harmonics?

Answer 47

resonance

Question 48

what is resonance

Answer 48

when bubbles expand and compress when exposed to sound beams

Question 49

when exposed to high pressure, bubbles ____

Answer 49

compress

Question 50

when exposed to low pressures, the bubbles ___

Answer 50

expand

Question 51

bubbles expand (more or less) than they shrink

Answer 51

more

Question 52

because bubbles expand more than they shrink, this uneven, nonlinear change, a small amount of energy is transferred from the ___ frequency to the ___ frequency

Answer 52

fundamental to harmonic

Question 53

what does rarefaction of a sound wave do to a bubble

Answer 53

expands the bubble

Question 54

What is mechanical index?

Answer 54

a calculated number that is related to the likelihood of harmful bio effects from cavitation depends on the frequency of the transmitted sound and the rarefaction pressure of the sound wave effects the amount of contrast harmonics produced

Question 55

Higher MI

Answer 55

``` large pressure variation low frequency strong harmonics nonlinear behavior high beam strength bubble greatly expands ```

Question 56

Lower MI

Answer 56

``` small pressure variation higher frequency low beam strength bubble doesn't expand much linear behavior backscatter no harmonics ```

Question 57

Why are micro bubbles strong scatterers of sound waves?

Answer 57

they resonate (oscillate) when exposed to sound in the 2-4 MHz range

Question 58

Is there another form of nonlinear behavior of a micro bubble that creates contrast harmonics?

Answer 58

yes the relationship between the mechanical index and the harmonic creation is nonlinear (if it was linear, a low MI would create weak harmonics, etc)

Question 59

Why don't low MI sound beams create harmonics?

Answer 59

micro bubbles expand and contract evenly in a linear fashion

Question 60

why do beams with a high MI create harmonics?

Answer 60

the bubbles expand and may burst (extreme nonlinear behavior) which creates strong harmonic reflections

Question 61

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

Answer 61

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

Question 62

How do the strengths of tissue and contrast harmonics compare?

Answer 62

contrast harmonics created by micro bubbles are much stronger than tissue harmonics

Question 63

Summary of contrast harmonics

Answer 63

created during reflection nonlinear behavior related to MI affected by micro bubble's shell and the gas within it

Question 64

tissue harmonics

Answer 64

transmission occurs during sound propagation results from nonlinear behavior of sound beam weak harmonic signal

Question 65

contrast harmonics

Answer 65

reflection occurs when contrast agents are present and when MI greater than 0.1 nonlinear behavior from microbubble strong harmonics