Chapter 17

Question 1

Two of the most significant somewhat recent advancements in diagnostic ultrasound:

Answer 1

1. Tissue Harmonic Imaging
2. Contrast Harmonic Imaging

Question 2

Fundamental Imaging

Answer 2

created by processing reflections that have the same ƒ as the transmitted sound

Question 3

Harmonic Imaging

Answer 3

created by processing only those reflections that are twice the transmitted ƒ

Question 4

the second harmonic

Answer 4

the harmonic ƒ is twice the fundamental ƒ

Question 5

Linear behavior is proportional or symmetrical

Answer 5

As x increases, y increases to a proportional degree
The system responds evenly

Question 6

Nonlinear behavior is nonsymmetrical or disproportionate

Answer 6

There is no consistent relationship between x and y
The system behaves unevenly

Question 7

Tissue Harmonics

Answer 7

Specifically sound travels at slightly uneven speeds through soft tissue; faster through compressions and slower through rarefactions

Question 8

Advantages to tissue harmonics

Answer 8

-Higher frequency reflections are displayed improving resolution;
-Stronger reflection return increasing signal to noise
-Harmonic signals don’t exist initially and escape the distortion caused by superficial layers of tissue
-Only strong beams generate a harmonic signal so we can be confident that reflections came from main beam, not grating lobes

Question 9

Pulse Inversion Harmonics

Answer 9

-A typical pulse is followed by an inverted copy of the pulse
-Both pulses are combined in the receiver; destructive interference removes the fundamental frequency leaving the harmonic signal

Question 10

Power Modulation is another technique to capture the harmonic signal

Answer 10

Two pulses sent down each scan line
First pulse is weaker
Second pulse is 2x the first (stronger generating harmonics)

Question 11

Contrast Agents

Answer 11

UEAs – Ultrasound Enhancement Agents

Question 12

UEAs

Answer 12

are gas bubbles entrapped in a shell

Question 13

UEAs are:

Answer 13

-Safe
-Metabolically inert
-Long lasting
-Strong reflectors of US
-Small enough to pass through capillaries

Question 14

Contrast Behavior

Answer 14

-When hit by a sound beam the microbubbles grow and shrink in relation to the pressure in the sound beam
-During high pressure the bubble shrinks, during low pressure the bubble expands

Question 15

“Resonance”

Answer 15

-If hit with a sufficiently strong beam, the microbubbles behave nonlinearly
-Specifically, the bubble expands to a greater degree than it shrinks (high pressure limits the degree of contraction)

Question 16

Low MI beams (less than .1)

Answer 16

will not create harmonics because the bubbles expand and contract in a linear fashion

Question 17

Intermediate MI beams (.1-1)

Answer 17

-create harmonics as the bubbles expand moderately more than they contract
-Most practical for clinical use
-Settings used for left heart opacification are on the low end of this range

Question 18

High MI beams (> 1)

Answer 18

-create strongest harmonic signals as the bubbles expand greatly more than they contract
-Some bubbles expand to the point of disruption
-Disrupts too many bubbles for effective use

Question 19

Shells

Answer 19

-trap the gas and ꜛ the life of the contrast
-are flexible and change shape (less prone to fracture)
-They ensure that the gas molecules cannot permeate the shell (remain trapped)