# Harmonics and Contrast Flashcards Preview

## Ultrasound Physics > Harmonics and Contrast > Flashcards

Flashcards in Harmonics and Contrast Deck (35)
1
Q

How are harmonic images created?

A

They are created from sound reflections that are TWICE the frequency of the probe.

For example: 2 MHz pulse is the FUNDAMENTAL frequency of the probe. The HARMONIC frequency would be 4 MHz.

2
Q

Where do harmonic frequency waves arise from?

A

They arise from non-linear behavior of waves as they travel through the tissue.

3
Q

What is another name for harmonic frequency?

A

Second harmonic frequency.

4
Q

How do waves vary from a fundamental frequency to harmonic frequency?

A
• Waves move slightly faster in compression and slightly slower in rarefraction.
• The peak travels faster than the trough.
• So a miniscule amount of energy is transferred from the fundament to harmonic frequency during its travel.
5
Q

When does the strength of the harmonic wave grow?

A

It grows as sound travels in the tissue.

6
Q

What is the best use of harmonic imaging?

A

It is best used in deeper structures.

7
Q

Why might artifacts occur with fundamental frequency?

A

Artifacts occur in the first few cm of tissues due to the strong signal and many superficial layers distorting the beam.

8
Q

Harmonic signals do not even exist in superficial layers which reduces artifacts because?

A

Harmonic signals cannot distort early in the path.

9
Q

What does less distortion lead to?

A

It results in a cleaner image from strong beams in deeper tissue.

10
Q

How is a harmonic image created?

A

It is created using only echoes that are two times the initial frequency.

ie: 2 MHz yeilds 4 MHz harmonic.

11
Q

Why are microbubbles injected into the vascular system?

A

Microbubbles, also known as contrast agents, are injected to create stronger reflectors.

12
Q

What are microbubbles?

A

Gas bubbles encased in a shell.

13
Q

Why do microbubbles create stronger reflections than RBC’s?

A

They are larger than RBC.

14
Q

What are some of the contrast requirements?

A
• Safe
• metabollically inert
• long lasting
• Strong ultrasound reflector.
• Can pass through capillaries.
15
Q

How are contrast harmonics formed?

A

They are formed as sound travels through a tissue.

16
Q

What type of behavior do microbubbles have when they are hit with sound waves?

A

Non-linear behavior.

17
Q

What is the response of microbubbles to high and low pressure variation (compression, rarefraction) of energy in sound waves?

A

Microbubbles grow and shrink in response.

18
Q

When are greater harmonics formed?

A

During reflection.

19
Q

What will happen to a microbubble when it is hit with the high pressure of a sound wave?

A

The bubble will shrink, and pressure in the bubble increases so it wont shrink.

20
Q

What will happen to a microbubble when it is hit with the low pressure of a sound wave?

A

The bubble expands, and pressure in the bubble decreases.

21
Q

What is the term used to describe when bubbles expand more than they shrink?

A

nonlinear.

22
Q

What is resonance?

A

The nonlinear, uneven change in the size of the bubble.

23
Q

What does nonlinear behavior create?

A

Hermonic frequency.

24
Q

What does the mechanical index (MI) estimate?

A

The amount of harmonics created.

25
Q

What does MI equal?

A

MI= peak rarefraction pressure in soundwave

26
Q

If the strength of the wave increases (higher and lower pressure, amplitude), what will happen to the harmonics?

A

Increase.

27
Q

If the frequency goes down, what will happen to the MI and harmonics?

A

Increase.

28
Q

As the MI increases, what will happen to the harmonics?

A

Increase.

29
Q

What does a low frequency and a high amplitude do to harmonics?

A

Will increase harmonics.

30
Q

Low MI (<.1)

A

No harmonics.

31
Q

Moderate MI (0.1-1.0)

A

Small amunt of harmonics

32
Q

High MI (>1.0)

A

High amount of harmonics.

33
Q

Describe shaken saline:

A

Causes bubbles with no shell, so they are short lived.

34
Q

What do flexible shells do?

A

They make it easier for the bubble to get through capillaries.

35
Q

Contrast harmonics are stronger than what?

A

Tissue harmonics.