ultrasound physics ch. 17

Harmonic imaging created by

reflections at twice transmitted F

fundamental F

transducer F

fundamental image

image created by fundamental F
-created by processing refections that have the same frequency as the transmitted sound

harmonic F

twice fundamental F or second harmonic F

harmonic image

image created by processing reflections that are 2X the fundamental F

harmonic imaging is most useful in improving poor quality images because

harmonic F waves undergo less distortion than fundamental sound waves

with harmonic imaging ___________ Is reduced, improving poor images

distortion

sound is a _________ wave

pressure

as sound travels through tissue shape is _____________, pressure peak travels __________ than valleys

deformed, faster

the deeper sound travels

the more deformation occurs

The deeper it travels, the more deformation occurs which causes

vibrations of the patients own tissues called harmonics

fundamental F goes at 2MHz
harmonic F returns at

double the fundamental F (4MHz)

fundamental F is filtered out of the

received F

Harmonic F sound waves arise from

non linear behavior

change in the output ____________ proportional to the change of the input

is not

in tissue harmonics, energy is converted from F frequency to

harmonic F during transmission

sound travels ___________ through compressions and ____________ through rarefactions

fast; slower
-an uneven speed

tissue harmonics non linear behavior causes change in

sound wave shape

strength of harmonic wave increases as

sound travels through tissue

no tissue harmonics at ________ depths

superficial

uneven speed as sound travels __________

deeper

harmonic signal strength builds as

wave travels deeper into tissue

harmonic signals not created superficially. develop __________ in tissue and do not distort

deep

tissue harmonics and beam strength have what relationship

non linear

weak beams don't create

harmonics

moderately strong beams create

only a tiny amount of harmonics

strong beams create

significant harmonics

harmonics are produced

along main axis where beam is produced

side lobes or grating lobes produce no

harmonics

beams most likely to create harmonics are less likely to create

artifacts

tissue harmonics created during ____________ of sound

transmission

tissue harmonics produced by __________ not TRX

patient

tissue harmonics is possible due to

non linear behavior in the speed of sound

Pulse inversion harmonics

technique that separated distorted fundamental F from harmonic F in the receiver

pulse inversion harmonics: 2 pulses per scan line

-typical pulse and "inverted" pulse, out of phase with the 1st
-fundamental signals cancel, harmonic signal remains

power modulation harmonic imaging

technique to increase harmonic signal and eliminate distorted fundamental signals

power modulation harmonic imaging has _________ pulses per scan line, one with _________ power

2, extra

power modulation harmonic imaging is doubled during

reception

power modulation harmonic imaging process

"extracts" the harmonic signal

Pulse inversion harmonics & Power Modulation advantage

less distortion

Pulse inversion harmonics & Power Modulation disadvantage

-lower frame rate and temporal resolution
(doubles the pulses)

Contrast Agents/ Microbubbles helpful in

cardiac wall motion studies

Contrast agents enhance

image quality

Contrast has a high degree of

echogenicity

Contrast agents must meet certain requirements

-Safe
-Metabolically inert
-Long lasting
-Strong reflector
-Small in size (pass through capillaries)

contrast agents administered

orally, IV

when US strikes a macro bubble

some reflected F is converted to harmonic F

contrast harmonics result from

non linear behavior of micro bubbles and sound

Bubbles oscillate shrink during

high pressure point in sound wave

Bubbles oscillate expand during

low pressure point in the sound wave

Bubbles under low and high pressure. Under low P, a ___________ signal is produced.

harmonic

Contrast harmonics created during ___________ of sound.

reflection

Micro-bubbles the size of RBC resonate from sound in the _______ MHz range.

2-4

the amount of contrast harmonics produced is estimated by

Mechanical index

relationship between harmonic production and mechanical index

direct

Mechanic index depends upon

F of transmitted wave and P of the wave

High mechanical index=

high P; low F
-non linear behavior
-expansion > compression

low mechanical index=

low P; high F
-linear behavior
-no harmonics

Very high mechanical index

nice reflections

Shell of Microbubble

flexible, non permeable

Gas

large molecules stay put longer

octafluoropropane

Important Contrast Agent Characteristics

-shell of microbubble
-gas

contrast harmonics Created by

non-linear behavior of microbubble.

contrast harmonics influenced by

shell and gas of a contrast agent

Tissue harmonics created during _________________ by non-linear behavior speed of sound.

transmission

tissue harmonics more likely to be created along

beams main axis

linear behavior means

proportional or symmetrical

nonlinear behavior means

Irregular or disproportionate. Behaves unevenly.

as sound waves travels in the body, a small amount of energy is converted from fundamental F to harmonic F. this conversion creates _______________ during transmission

tissue harmonics

a sound wave is a series of

compressions and rarefactions

variation in speed of sound waves alters

the shape of sound beam

during fundamental imaging significant amounts of artifact Aries within

the first few cm of tissue

strong artifacts that arise in the first few cm appear for two reasons

-beam is very strong
-many different superficial anatomic layers distort the sound beam

use of harmonics increases

signal to noise ratio

distortion that degrades the fundamental image does not appear in the

harmonic image

when sound beams are distorted, a small portion of the sound energy is directed away from the beam's main axis in the form of

side/grating lobes

are tissue harmonics present has sound leaves the transducer

No

tissue harmonics are created in the tissues during ___________

transmission

how much harmonic frequency does the beam contain at the skins surface

none

imaging technique that is utilized for harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections

pulse inversion harmonics

Low MI (less than .1)

-no harmonics
-backscatter
-linear behavior
-higher F sound
-lower beam strength
-bubble expands little

higher MI (.1 to 1)

-some harmonics
-resonance
-nonlinear
-lower F sound
-higher beam strength
-bubble expands moderately

highest MI (greater than 1)

-strongest harmonics
-bubble disruption
-extreme nonlinear
-lowest F sound
-highest beam strength
-bubble expands greatly

contrast harmonics (4)

-created during reflections of microbubble
-occurs only w/contrast agents and MIs greater than .1
-results from nonlinear behavior of micro bubble
-stronger harmonic signal

tissue harmonics (4)

-created during transmission
-occurs as sound propagates
-results from non liner behavior of transmitted sound beam
-weaker harmonic signal