Harmonics And Contrast Agents

Question 1

What is the Fundamental Frequency?

Answer 1

Frequency of sound transmitted into the body by the transducer; main frequency of the transducer.

Question 2

What is the Harmonic Frequency?

Answer 2

Twice the fundamental frequency; resonant frequency.

Question 3

What is the Fundamental Image?

Answer 3

Image created by main frequency.

Question 4

What is Harmonic Imaging?

Answer 4

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

Question 5

Define Nonlinear Behavior.

Answer 5

Means irregular or disproportionate, asymmetrical; difference of speed between compression (fast) and rarefaction (slow); creates a ‘spilling’ of energy.

Question 6

Define Linear Behavior.

Answer 6

Means proportional or symmetrical; responds in an even manner.

Question 7

What are Tissue Harmonics?

Answer 7

Resonance of tissue created by the conversion of a miniscule amount of energy from the fundamental frequency to the harmonic frequency as it travels through the body.

Question 8

What are Pulse Inversion Harmonics?

Answer 8

Most commonly used technique that separates fundamental frequency from harmonic frequency by transmitting 2 inverted pulses down each scan line.

Question 9

True or False: Harmonic frequencies undergo more distortion than fundamental frequencies.

Answer 9

False.

Question 10

Fill in the blank: The 1st Harmonic is _______.

Answer 10

Twice the fundamental frequency.

Question 11

What happens to harmonics in superficial layers?

Answer 11

Do not develop in very superficial layers.

Question 12

Where do harmonics develop?

Answer 12

In deeper/intermediate layers.

Question 13

What is an advantage of harmonic imaging?

Answer 13

Increases S/N ratio and is distortion free.

Question 14

What types of artifacts do harmonic frequencies avoid?

Answer 14

Do not create lobe artifacts.

Question 15

What is the significance of the main axis in harmonic imaging?

Answer 15

Arise from main axis, strongest part of the sound beam.

Question 16

What occurs when fundamental signals exhibit linear behavior?

Answer 16

Destructively interfere and completely cancel each other out, leaving only the harmonic portion.

Question 17

What is the effect of harmonic imaging on image quality?

Answer 17

Improves image quality because harmonic frequencies undergo less distortion.

Question 18

What is Power Modulation?

Answer 18

A technique used to augment harmonic reflections while eliminating distorted fundamental reflections.

Question 19

What is the disadvantage of using Power Modulation?

Answer 19

Temporal Resolution is reduced.

Question 20

How does the Power Modulation technique work?

Answer 20

It sends 2 consecutive pulses down each scan line, with the second pulse being 2x the strength of the first.

Question 21

What does the first, weaker pulse in Power Modulation contain?

Answer 21

No harmonics.

Question 22

What happens during reception in Power Modulation?

Answer 22

Reflections from the first pulse are amplified to DOUBLE, cancelling out the fundamental frequency of the second pulse’s reflections.

Question 23

What do microbubbles do in medical imaging?

Answer 23

Create strong reflections that ‘light up’ blood chambers, vessels, or other anatomic regions.

Question 24

What are the requirements for microbubbles?

Answer 24

• Safe
• Metabolically inert (inactive)
• Long lasting
• Strong reflector of ultrasound
• Small enough to pass through capillaries

Question 25

What are microbubbles strong scatterers of?

Answer 25

Sound.

Question 26

Why do microbubbles resonate when exposed to frequencies of 2-4 MHz?

Answer 26

Because they are the same size as RBCs.

Question 27

What are the two characteristics of microbubbles?

Answer 27

* The outer shell should be flexible * The gas molecule that fills the microbubble should be large enough to remain trapped within the bubble.

Question 28

Fill in the blank: Microbubbles are gas bubbles encapsulated in a _______.

Answer 28

[shell].

Question 29

What is the Mechanical Index (MI)?

Answer 29

A number that estimates the amount of contrast harmonics produced; depends on the frequency and peak rarefaction pressure.

Question 30

What are the three classifications of beam strength?

Answer 30

* Weak * Intermediate * Strong

Question 31

What is a summary of tissue harmonics?

Answer 31

Not present as sound leaves the transducer.

Question 32

How are contrast harmonics created?

Answer 32

* Created deeper in the tissues * Created in the tissues during transmission

Question 33

What phenomenon occurs during sound in rarefactions?

Answer 33

Much stronger than tissue harmonics; created during reflection as energy is converted from the fundamental frequency to the harmonic frequency.

Question 34

What nonlinear behavior affects microbubbles when struck by sound waves?

Answer 34

Nonlinear changes in size of microbubbles or resonance: bubbles expand to a greater extent than they shrink.

Question 35

What is the importance of peak rarefaction pressure in relation to contrast harmonics?

Answer 35

It expands the bubble and is most important with regard to contrast harmonics.

Question 36

List the advantages of using contrast harmonics.

Answer 36

* Small pressure variation * Higher frequency * Less bioeffects * Increased spatial resolution * Increased contrast resolution * Reduces artifact

Question 37

What is the relationship between frequency and Mechanical Index?

Answer 37

Inversely related.

Question 38

What is the relationship between peak rarefaction pressure and Mechanical Index?

Answer 38

Directly related.

Question 39

What is the amount of tissue harmonics created primarily influenced by?

Answer 39

Nonlinear behavior in the speed of sound: sound in compressions travels faster than in rarefactions.

Question 40

What are the characteristics of beams that create harmonics?

Answer 40

Primarily created along the beam's main axis; least likely to create artifacts.

Question 41

What is the effect of higher Mechanical Index?

Answer 41

* Large pressure variation * Lower frequency * More bioeffects

Question 42

Fill in the blank: _______ refers to the strength of the beam in ultrasound.

Answer 42

[Beam Strength]

Question 43

What is the Mechanical Index (MI)?

Answer 43

A number that estimates the amount of contrast harmonics produced; depends on the frequency and peak rarefaction pressure.

Question 44

What are the three classifications of beam strength?

Answer 44

* Weak * Intermediate * Strong

Question 45

What is a summary of tissue harmonics?

Answer 45

Not present as sound leaves the transducer.

Question 46

How are contrast harmonics created?

Answer 46

* Created deeper in the tissues * Created in the tissues during transmission

Question 47

What phenomenon occurs during sound in rarefactions?

Answer 47

Much stronger than tissue harmonics; created during reflection as energy is converted from the fundamental frequency to the harmonic frequency.

Question 48

What nonlinear behavior affects microbubbles when struck by sound waves?

Answer 48

Nonlinear changes in size of microbubbles or resonance: bubbles expand to a greater extent than they shrink.

Question 49

What is the importance of peak rarefaction pressure in relation to contrast harmonics?

Answer 49

It expands the bubble and is most important with regard to contrast harmonics.

Question 50

List the advantages of using contrast harmonics.

Answer 50

* Small pressure variation * Higher frequency * Less bioeffects * Increased spatial resolution * Increased contrast resolution * Reduces artifact

Question 51

What is the relationship between frequency and Mechanical Index?

Answer 51

Inversely related.

Question 52

What is the relationship between peak rarefaction pressure and Mechanical Index?

Answer 52

Directly related.

Question 53

What is the amount of tissue harmonics created primarily influenced by?

Answer 53

Nonlinear behavior in the speed of sound: sound in compressions travels faster than in rarefactions.

Question 54

What are the characteristics of beams that create harmonics?

Answer 54

Primarily created along the beam's main axis; least likely to create artifacts.

Question 55

What is the effect of higher Mechanical Index?

Answer 55

* Large pressure variation * Lower frequency * More bioeffects

Question 56

Fill in the blank: _______ refers to the strength of the beam in ultrasound.

Answer 56

[Beam Strength]

Question 57

What is the term for the behavior exhibited by sound at lower frequencies and higher beam strength?

Answer 57

Nonlinear behavior ## Footnote Nonlinear behavior occurs when transmitted sound propagates through tissue.

Question 58

What is the range of Mechanical Index (MI) for higher harmonics?

Answer 58

0.1 to 1.0 ## Footnote Higher harmonics are associated with some resonance and nonlinear behavior.

Question 59

Fill in the blank: The _______ is the strongest type of harmonics created during reflection off of microbubbles.

Answer 59

Contrast Harmonics

Question 60

What happens to bubbles during extreme nonlinear behavior?

Answer 60

Bubbles expand greatly ## Footnote This behavior is observed when contrast agents are present and with MIs greater than 0.1.

Question 61

True or False: Higher MI values indicate weaker harmonic signals.

Answer 61

False

Question 62

What type of sound is created during transmission in tissue?

Answer 62

Tissue Harmonics ## Footnote Tissue harmonics result from the nonlinear behavior of transmitted sound beams.

Question 63

What is the Mechanical Index (MI) threshold for the highest harmonics?

Answer 63

> 1.0

Question 64

Fill in the blank: Lower frequency sound is associated with _______ beam strength.

Answer 64

Lower

Question 65

What is affected by the microbubble's shell and the gas within it?

Answer 65

Stronger harmonic signal

Question 66

What phenomenon occurs when sound propagates in tissue?

Answer 66

Resonance ## Footnote Resonance can occur as sound waves interact with tissues, especially at certain frequencies.

Question 67

What characterizes the behavior of bubbles during transmission?

Answer 67

Bubble expands moderately

Question 68

What is the relationship between beam strength and harmonic signal strength?

Answer 68

Higher beam strength leads to stronger harmonic signals.

Question 69

What type of behavior is characterized by the creation of harmonics during microbubble disruption?

Answer 69

Extreme nonlinear behavior

Question 70

Fill in the blank: The _______ signal is weaker when lower frequency sound is present.

Answer 70

Tharmonic

Question 71

What occurs only when contrast agents are present?

Answer 71

Creation of contrast harmonics