Study guide Ch 16/17:quiz 1 Flashcards Preview

Spring: Physics > Study guide Ch 16/17:quiz 1 > Flashcards

Flashcards in Study guide Ch 16/17:quiz 1 Deck (13):
1

What are the five requirements for contrast agents?

Contrast agents must be:

1) safe

2)metabolically inert (metabolized throughout system and then removed)

3)long lasting

4)strong reflector of ultrasound

5)small enough to pass through capillaries

2

If you know the fundamental frequency of a transducer, what is the harmonic frequency?

harmonic frequency is twice the fundamental frequency

3

If you are in harmonic mode, what is the fundamental frequency?

fundamental frequency is 1/2 the harmonic mode

4

What type of behaior creates harmonics?

nonlinear behavior

5

Fewer shades of gray

few choices

black and white(bistable)

narrow dynamic range

high contrast

6

many shades of gray

many choices

gray scale

wide dynamic range

low contrast

7

Tissue harmonics

created during transmission in tissue

occurs as sound propagates in tissue

results from nonlinear behavior of transmitted sound beam

weaker harmonic signal

8

Contrast harmonics

created during reflection off of microbubble

occurs only when contrast agents are present and with MIs > 0.1

results from nonlinear behavior of microbubble

stronger harmonic signal

9

How is Mechanical Index calculated?

MI= peak rarefaction pressure/ square root of frequency

10

Mechanical Index and Harmonics

Low MI:<0.1 

No harmonics

backscatter

linear behavior

higher frequency sound

low beam strength

bubble expands very little

11

Mechanical Index and Harmonics

Higher MI 0.1-1.0

some harmonics

resonance

nonlinear behavior

lower frequency sound

higher beam strength

bubble expands moderately

12

Mechanical Index and Harmonics

Highest MI: >1

strongest harmonics

bubble disruption

extreme nonlinear behavior

lowest beam strength

bubble expands greatly

13

What is pulse inversion?

Pulse inversion utilizes harmonic reflections while eliminating distorted fundamental reflections

Pulse inversion harmonics:

utilizes a wide range of frequencies, positive and negative reflections are combined

Disadvantages:

time required to create a frame is doubled, frame rate is halved, temporal resolution is reduced