Harmonics and Contrast

Question 1

What is the fundamental frequency?

Answer 1

The initial frequency that is created by the transducer and is then transmitted into the body

Question 2

What is the harmonic frequency?

Answer 2

It is twice the fundamental frequency.

Question 3

What is second harmonic?

Answer 3

Synonym for harmonic frequency

Question 4

Do harmonics arise from linear or nonlinear behavior?

Answer 4

Nonlinear

Question 5

What is nonlinear behavior?

Answer 5

Asymmetric behavior that behaves unevenly

When sound moves a little faster in areas of compression and a little slower in areas of rarefaction

Question 6

Where are harmonics created?

Answer 6

Harmonics are created in tissue, not the transducer or receiver

Question 7

How do pulse inversion harmonics affect temporal resolution?

Answer 7

Degrade temporal resolution

- Two pulses are transmitted down the same scan line, halving frame rate and degrading temporal resolution

Question 8

How do pulse inversion harmonics improve spatial resolution?

Answer 8

Improve spatial resolution

- They have better signal to noise ratio and are less likely to create artifacts

Question 9

What are contrast agents made of?

Answer 9

Gas bubbles encapsulated in a shell

Contain fluid that has different acoustic fingerprint than blood or tissue, allowing them to create strong reflections

Question 10

What are the five requirements for contrast agents?

Answer 10

1. Safe
2. Metabolically inert
3. Long-lasting
4. Strong ultrasound reflector
5. Small enough to go through capillaries

Question 11

Describe impedance difference for contrast agents

Answer 11

There is a large difference between the impedance of contrast agents and that of biological tissues.
- This impedance allows the microbubbles to appear brighter when they light up blood chambers, vessels, and other regions

Question 12

How are contrast harmonics created?

Answer 12

They are created during reflection when the energy is converted from fundamental to harmonic
- Stronger harmonics when microbubbles act nonlinear when sound wave strikes

Question 13

What is a mechanical index?

Answer 13

Estimated number of contrast harmonics that are produced

Question 14

How does mechanical index relate to the creation of harmonics?

Answer 14

It is directly related to frequency because a higher mechanical index creates stronger harmonics.