Physics Quiz Ch 16, 17

Question 1

Sound with a frequency of 5 MHz is created by a transducer. What is the fundamental frequency?

Answer 1

5 MHz. The fundamental frequency is the frequency of sound created by the transducer.

Question 2

Sound with a frequency of 3 MHz is created by a transducer. What is the harmonic frequency?

Answer 2

6 MHz. The harmonic frequency is twice the fundamental frequency.

Question 3

How are harmonics created?

Answer 3

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

*It is useful in improving poor quality images because harmonic frequency waves undergo less distortion than fundamental sound waves.

Question 4

Where are harmonics created?

Answer 4

Harmonics are created in the tissues

Question 5

What type of behavior creates harmonics?

Answer 5

Nonlinear behavior-irregular or disproportionate; behaves unevenly

Question 6

Dynamic range of information, does it increase or decrease as it is processed?

Answer 6

Decreases the more it is processed

Question 7

What does compression do to dynamic range?

Answer 7

Compression reduces the dynamic range of a signal without introducing errors.
Requirements:
-the largest signal remains the largest
-the smallest signal remains the smallest
-the range of signals is reduced

Question 8

Wide dynamic range vs narrow dynamic range

Answer 8

Wide dynamic range:
-more shades
-many choices
-gray scale
-low contrast
Narrow dynamic range:
-fewer shades
-few choices
-black and white (bistable)
high contrast

Question 9

Two forms of harmonics

Answer 9

1. Tissue harmonics

2. Contrast harmonics

Question 10

Where are harmonics mainly located a long the beam?

Answer 10

Harmonics are produced only in the sound beam’s main axis, where the beam is strong. They are not created in the weaker side lobes.

Question 11

The numerical value of the mechanical index, and therefore, harmonic production, increases with..

Answer 11

• Lower frequency
• Stronger sound waves (large pressure variation)

*Mechanical index is directly related to peak rarefactional pressure and inversely related to frequency.

Question 12

Contrast harmonics

Answer 12

• created during reflection off of micro bubbles
• occurs only when contrast agents are present and with MIs greater than 0.1
• results from nonlinear behavior of micro bubbles
• stronger harmonic signal

Question 13

Low MI: less than 0.1

Answer 13

• no harmonics
• backscatter
• linear behavior
• higher frequency sound
• low beam strength
• bubble expands very little

Question 14

Higher MI: 0.1 to 1.0

Answer 14

• some harmonics
• resonance
• nonlinear behavior
• lower frequency sound
• higher beam strength
• bubble expands moderately

Question 15

Highest MI: greater than 1

Answer 15

• strongest harmonics
• bubble disruption
• extreme nonlinear behavior
• lowest frequency sound
• highest beam strength
• bubble expands greatly

Question 16

5 requirements for contrast agents

Answer 16

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

Question 17

Pressure variations

Answer 17

Lower MI:

• small pressure variation
• higher frequency

Higher MI:

• large pressure variation
• lower frequency

Question 18

Pulse inversion harmonics

Answer 18

Is an imaging technique designed to utilize harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections
Two consecutive ultrasound pulses are transmitted down each scan line, one positive and one negative

Question 19

Disadvantage of pulse inversion harmonics

Answer 19

Two pulses are transmitted down each scan line and twice the number of pulse are required to create each image.
The time required to create a frame is doubled, the frame rate is halved, and temporal resolution is reduced.

Question 20

When the bubbles expand, will they expand with a low MI or a high MI?

Answer 20

high MI

Question 21

Tissue harmonics

Answer 21

• created during transmission in tissue
• occurs as sound propagates in tissue
• results from nonlinear behavior of transmitted sound beam
• weaker harmonic signal