INTERACTIONS OF ULTRASOUND WITH TISSUE Flashcards by Cee F

Interactions of Ultrasound

Types of Sound

_____
_____
_____

Types of Incidence

_____
_____

Types of Reflection

_____
_____
_____

Types of Interactions

_____
_____
_____
_____ and _____
_____
_____
_____

Echo Ranging

incident
reflected   
transmitted
perpendicular
oblique
specular
diffuse
scattering
reflection
reflectivity
refraction
divergence
diffraction
interference
attenuation
absorption

How well did you know this?

Not at all

Perfectly

TYPES OF INCIDENCE – PERPENDICULAR AND OBLIQUE

Incident sound may intersect a boundary either _____ or _____

perpendicularly

obliquely

How well did you know this?

Not at all

Perfectly

PERPENDICULAR INCIDENCE
A.K.A.: NORMAL INCIDENCE

When a sound beam (incident sound) intersects a smooth surface (the boundary between two tissues), larger than the width of the beam, at 900 (perpendicular), it may be partially _____ towards the sound source.

If reflection occurs, the angle of reflection equals the angle of _____

reflected

incidence

How well did you know this?

Not at all

Perfectly

A sound beam (incident sound) that intersects a smooth surface (the boundary between two tissues), larger than the width of the beam, at LESS THAN 900 (NOT perpendicular) is called:

_____ Incidence

For our purposes always
assume:
there will be \_\_\_\_\_;
                  also,
the angle of Reflection 
            equals 
the angle of \_\_\_\_\_

oblique
reflection
incidence

How well did you know this?

Not at all

Perfectly

To obtain maximum detection of the reflected signal, we must orient the transducer so the generated sound beam will strike an interface _____

perpendicularly

How well did you know this?

Not at all

Perfectly

Types of Reflection

_____
_____
_____

specular
diffuse
scattering

How well did you know this?

Not at all

Perfectly

SPECULAR REFLECTORS

_____ interfaces, _____ than the beam width

Responsible for major organ outlines as seen by US; _____, _____

Produce _____-intensity, unidirectional reflections

Very _____ dependant

smooth
larger
diaphragm
pericardium
high
angle

How well did you know this?

Not at all

Perfectly

DIFFUSE REFLECTION

Large _____-surface interface deflects beam in multiple directions (as opposed to specular = large smooth-surface)

If interface not _____, sound beams strike interface at various angles of incidence yeilding differing angles of reflection

Some categorize as _____ or nonspecular

_____ the echo returning to the transducer

Mirror/steam; concrete/aggregate

rough
flat
scattering
weakens

How well did you know this?

Not at all

Perfectly

SCATTERING

Often referred to as _____ reflection

Occurs because the interfaces are _____ (less than several wavelengths across)

Each interface acts as a separate _____ source and these tiny, punctate interfaces reflect sound in all direction

Responsible for providing the _____ texture of organs in an image

nonspecular
small
sound
internal

How well did you know this?

Not at all

Perfectly

SCATTERING

Nonspecular reflectors are very _____ dependent, which makes them useful in characterizing tissue

Responsible for providing the _____ texture of organs in an image

Scattering by small particles in which the linear dimensions are smaller than the wavelength is called _____ scattering, a classic example, RBCs

Some physicists include _____ reflection (due to the roughened surface) in the category of scattering

frequency
internal
rayleigh
diffuse

How well did you know this?

Not at all

Perfectly

Types of Interactions

_____
_____
_____
_____ and _____
_____
_____
_____

reflection
reflectivity
refraction
divergence
diffraction
interference
attenuation
absorption

How well did you know this?

Not at all

Perfectly

Reflection

Acoustic _____

Impedance _____

_____ Coefficient

_____ Composition

impedance
mismatch
reflection
transmission
interface

How well did you know this?

Not at all

Perfectly

ACOUSTIC IMPEDANCE

The measure of _____ to sound traveling through a medium

Unit = kg/m2/s or simply, the _____

Impedance = _____ (kg/m3) x _____ _____ (m/s)

Z = pc

Determined by the _____

RESISTANCE 
Rayl
Density 
Prop Speed
MEDIUM

How well did you know this?

Not at all

Perfectly

ACOUSTIC IMPEDANCE

Density increase - Impedance _____
Prop. Speed increase - Impedance _____

Impedance is _____ PROPORTIONAL to:
Density and/or Propagation Speed

increase
increase
directly

How well did you know this?

Not at all

Perfectly

IMPEDANCE MISMATCH

In Perpendicular Incidence the amount of sound reflected depends on:

Incident _____
AND
Impedance _____ of the 2 media

Does not apply to _____ incidence!!!!!!!!!!

intensity
Mismatch
oblique

How well did you know this?

Not at all

Perfectly

PIMP OR PRIMP

PIMP
P = _____ Incidence
IMP = _____

PRIMP
P = _____ Incidence
R = _____
IMP = _____

When an incident beam intersects a media boundary Perpendicularly, Reflection will only occur if there is an acoustic IMPedance _____

Perpendicular 
Impedance
Perpendicular 
Reflection
Impedance
mismatch

How well did you know this?

Not at all

Perfectly

IMPEDANCE MISMATCH

No impedance difference - No _____

decrease in impedance difference - _____ in reflection

The difference in acoustic impedance causes some portion of the sound to be reflected at an interface, which allows visualization of _____ structures with US.

reflection
decrease
ST

How well did you know this?

Not at all

Perfectly

DETERMINING THE AMOUNT OF INCIDENT INTENSITY THAT IS REFLECTED and TRANSMITTED

Expressed BY:
_____ -or- _____

Coefficient

Percentage

How well did you know this?

Not at all

Perfectly

DETERMINING THE AMOUNT OF INCIDENT INTENSITY THAT IS REFLECTED and TRANSMITTED

Coefficient

Intensity reflection coefficient IRC
+ Intensity transmission coefficient + ITC
1.0 1.0

Equation

How well did you know this?

Not at all

Perfectly

DETERMINING THE AMOUNT OF INCIDENT INTENSITY THAT IS REFLECTED and TRANSMITTED

Percentage

Percent intensity reflected % IR
+ Percent intensity transmitted + % IT
100 % 100%

Equation

How well did you know this?

Not at all

Perfectly

INTERFACE COMPOSITION

Doesn’t matter of impedance 1 is greater or less than impedance 2; the same percent of reflection/transmission occurs at the interface

_____ differences in impedences yield large magnitudes of reflection

_____ differences in impedences yield small magnitudes of reflection

The _____ of the medium is not as issue!

large
small
thickness

How well did you know this?

Not at all

Perfectly

ECHO-INDUCED SIGNALS

When a device that produces and detects US waves scans a patient, multiple interfaces are encountered

A percent of the beam is _____ and _____ at each interface

A series of echoes is subsequently detected

The relative intensities of the echoes depends on the acoustic impedance mismatch at the interface

–_____ signals if the acoustic impedance mismatch is small (ST to ST)
–_____ signals if the acoustic impedance mismatch is large ( air-ST)
–_____ echoes are produced by diffuse reflection and scattering

reflected
transmitted
small
strong
weaker

How well did you know this?

Not at all

Perfectly

REFLECTIVITY

The fraction of incident intensity that is reflected at an interface back towards the transducer is influenced by many factors.

Factors include:

–Acoustic impedance _____
–_____ of incidence
–_____ of the structure as compared to the, wavelength
–_____ of the structure
–_____ of the surface of the interface

mismatch
angle
size
shape
texture

How well did you know this?

Not at all

Perfectly

REFLECTIVITY

The combination of these factors is described by the term:

Reflectivity

Differences in reflectivity are partially responsible for patient-to-_____ variations encountered

Study These Flashcards

patient

REFRACTION When incident sound intersects a media interface of 900, a percent is reflected back through media 1, and a percent is transmitted into media 2 without a change in _____

direction

REFRACTION When incident sound intersects an interface between two media at an angle _____ (other than 900), the transmitted part MAY be _____ or bent

obliquely | refracted

Refraction and Oblique Incidence If US intersects an interface between two media at an angle other than 900 A portion of the incident sound will be: _____ away from the boundary and _____ through the boundary Assume it; no ands, ifs, buts or impedance matches!!!

reflected | transmitted

Refraction The Transmitted: the angle of transmission MAY _____ the angle of incidence -or- the angle of transmission may be _____ (a change in the direction of sound when crossing a boundary)

equal | refracted

SNELL’S LAW Degree of Refraction is defined by _____ Law Relates the angle of transmission to the relative PROPAGATION _____ of the 2 media NOT based on acoustic impedance mismatch!!!

snell's | speeds

SOS OR ROSS SOS S = _____ O = _____ Incidence S = _____ Law ``` ROSS R = _____ O = _____ Incidence S = _____ S = _____ Law ``` When an incident beam intersects a media boundary at an Refraction will only occur if there is a Oblique angle and a Speed mismatch. The degree of Refraction is defined by _____ Law

``` speed oblique snell's refraction oblique speed snell's snell's ```

SNELL’S LAW sin θi /sin θt = c1 /c2 --- OR --- to solve for what we care about sin θt = (sin θi) c2 /c1

SNELL'S LAW EQUATION

REFRACTION For refraction to occur there MUST be both: _____ incidence AND propagation _____ differences between the media

oblique | speed

- If the velocities of 2 media are the same there will be NO _____!!! If perpendicular incidence occurs there will be NO _____!!!

refraction | refraction

The bending occurs because the portion of the wavefront in the 2nd medium travels at a different _____ from the 1st medium Three scenarios regarding Snell’s Law

velocity

SPEED IN MEDIA 1 IS > (Greater than) MEDIA 2 Then the transmitted (refracted) angle bends _____ the normal -OR- If the speed in media 1 is greater than the speed in media 2, then the angle in media 1 is _____ than the angle in media 2

toward | greater

SPEED IN MEDIA 1 IS < (Less than) MEDIA 2 Then the transmitted (refracted) angle bends _____ from the normal -OR- If the speed in media 1 is less than the speed in media 2, then the angle in media 1 is _____ than the angle in media 2

away | less

Speed in media 1 is < (Less than) media 2 -AND- the angle of incidence is _____ than the CRITICAL ANGLE The refracted angle will travel along the _____ and no energy enters the second medium

greater | interface

The critical angle is different between any two media and is determined by _____ Law _____ artifacts / _____ artifacts

snell's edge refraction

DIVERGENCE and DIFFRACTION _____ causes the US beam to diverge or spread out as it moves further away from the sound source. Rate of divergence increases: 1. As the distance from sound source _____ 2. As the diameter of sound source _____ 3. Frequency of the SS Beam divergence affects the _____ resolution of the beam and the sensitivity of the US system. _____ occurs after a beam passes through a small aperture on the order of one wavelength. The aperture then acts as a small SS and the beam diverges rapidly

``` divergence increases decreases lateral diffraction ```

INTERFERENCE Phase of a Wave Locations along a sine (sinusoidal) wave can be expressed in _____. One complete wavelength is 3600; one half wavelength will be 1800; one quarter wavelength, 900. If two or more waves with the same frequency have the same starting points, they are said to be "in _____”. Whether in or out of phase, superposing these waves will result in the _____ summation of the individual waves.

degrees phase algebraic

This is known as the PRINCIPLE OF _____ -or- _____ PHENOMENA

superposition | interference

CONSTRUCTIVE INTERFERENCE Results from the superposition of two waves of the same _____, exactly in phase. The sum of the waves _____ the amplitude of the resultant waveform.

frequency | increases

DESTRUCTIVE INTERFERENCE Results from the superposition of two waves of the same frequency, that are _____ of phase. The summation of these waves _____ the amplitude of the resultant waveform. The superposition of two waves of the same frequency, that are 1800 out of phase results in waveform of _____

out decreases zero

The addition of two waves with different frequencies results in complex waveforms that are no longer _____. Important in the design of an US transducer because it affects the _____ of the beam. Focusing of the US beam is based on the principle of _____ interference.

sinusiodal uniformity wave

SPECKLE US pulse will simultaneously encounter many scatterers at any point ⇨ generates several echoes at once ⇨ arrive at transducer at same time and may interfere with each other _____ or _____ Results in a displayed “dot” pattern that does not actually represent the scatterers (does not exhibit a one-to-one correspondence to scatters), but an interference pattern called _____. The speckle pattern is _____ dependant Speckle is a form of acoustic _____ in US imaging

``` constructively destructively speckle frequency noise ```

CONTRAST AGENTS 1.0 Liquid suspensions injected into circulation to _____ echogenicity of vessels and perfused tissue in grey-scale US

increase

CONTRAST AGENTS – 1.0 Small enough to pass through capillaries Impedance of suspended particles differs from the impedance of the suspending _____ Microbubble especially _____ echoes Impedance of _____ Bubbles expand and contract producing _____ of the incident sound

medium strong gas harmonics

ATTENUATION The _____ in the intensity (amplitude) of an US beam as it travels through a medium; the _____ of sound as it propagates Encompasses _____, _____, and _____ Generation of echoes from reflection and scattering are crucial to US imaging; contribute little to overall _____ The depth of penetration becomes less as frequency is _____, and the ability to observe deep-lying structures is forfeited Attenuation limits imaging _____ and must be compensated for

``` reduction weakening absorption scattering reflection attenuation increased depth ```

ATTENUATION Absorption The only process whereby sound energy is dissipated in a medium. Absorption (conversion of sound to _____) is normally the dominant contribution to _____ (in ST) Other modes of interactions (_____, _____, scattering, and _____) decrease beam intensity by redirecting its energy Strongly dependent on _____; rate of absorption is directly related, if frequency _____, absorption _____

``` heat attenuation reflection refraction scattering divergence frequency doubles doubles ```

ATTENUATION Attenuation and Decibels _____ are good units for comparing relationships between various measured sound levels and the threshold of human hearing Used for measuring _____, _____ range and _____ Decibels involve _____ Log of a number = number of tens that must be multiplied together to result in that number

``` decibels output dynamic gain logarithms ```

ATTENUATION Attenuation and Decibels Level (dB) = 10 log10 ( I/I0 ) ``` I = intensity at point of interest I0 = original or reference intensity ``` _____ dB of attenuation = decrease to ½ the original intensity _____ dB of attenuation = decrease to ¼ the original intensity _____ dB of attenuation = decrease to 1/10, or 0.1 the original intensity _____ dB of attenuation = decrease to 1/100, or 0.01 the original intensity

3 6 10 20

ATTENUATION Attenuation Units = Decibels = dB for ST: ½ x frequency(MHz) x pathlength (cm) -or- attenuation coefficient x pathlength As frequency 🡹, attenuation _____ As pathlength 🡹 , attenuation _____ As attenuation coefficient 🡹 , attenuation _____

increases increases increases

ATTENUATION SO WHAT’S AN ATTENUATION COEFFICIENT? AC ( dB/cm ) = Attenuation (dB)/Separation between two points (cm) In ST: AC( dB/cm ) = 0.5 X frequency The attenuation per unit _____ of sound travel The attenuation for each _____ of sound travel Numerical values that express how different materials will attenuate an US beam per _____ length Different materials have different _____ coefficients

length cm path attenuation

ATTENUATION In ST: for a 1 MHz transducer, ½ dB of intensity is lost for 1 cm of travel Half-Value Layer (HVL) The amount of material required to reduced the intensity by _____ of its original valve A half-value layer results in a ___-dB reduction in intensity

half | 3

ATTENUATION Attenuation / Intensity Loss _____ frequency sound waves are attenuated more rapidly than low frequency Ability to penetrate tissue is reduced at _____ frequencies Reflectors positioned at increasingly greater depth generate progressively _____ intensity returning echoes

high higher lower

ECHO-RANGING PRINCIPLE In diagnostic US, _____ of the sound beam from interfaces along the US beam path are of primary interest. US wave ⇒ body ⇒ strikes interface ⇒ reflects/transmit

reflections

A system that can generate an US pulse wave and detect the reflected echo after a measured time permits the distance to the interface to be determined. This is called a _____ system, and the design is based on the _____-_____ PRINCIPLE

pulsed | echo - ranging

Echo-Ranging Principle 2 items of info required to properly place echoes on display: _____ from which the echo came (assumed as a straight line from where the transducer is pointed) _____ to the reflector where the echo was produced Distance to the reflector if defined by the _____ Equation

direction distance range

INTERACTIONS OF ULTRASOUND WITH TISSUE Flashcards

(58 cards)