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Physics I > INTERACTIONS OF ULTRASOUND WITH TISSUE > Flashcards

INTERACTIONS OF ULTRASOUND WITH TISSUE Flashcards

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1
Q

Interactions of Ultrasound

Types of Sound

  • _____
  • _____
  • _____

Types of Incidence

  • _____
  • _____

Types of Reflection

  • _____
  • _____
  • _____

Types of Interactions

  • _____
  • _____
  • _____
  • _____ and _____
  • _____
  • _____
  • _____

Echo Ranging

A 
incident
reflected   
transmitted
perpendicular
oblique
specular
diffuse
scattering
reflection
reflectivity
refraction
divergence
diffraction
interference
attenuation
absorption
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2
Q

TYPES OF INCIDENCE – PERPENDICULAR AND OBLIQUE

Incident sound may intersect a boundary either _____ or _____

A

perpendicularly

obliquely

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3
Q

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 _____

A

reflected

incidence

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4
Q

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 \_\_\_\_\_
A

oblique
reflection
incidence

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5
Q

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

A

perpendicularly

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6
Q

Types of Reflection

  • _____
  • _____
  • _____
A

specular
diffuse
scattering

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7
Q

SPECULAR REFLECTORS

_____ interfaces, _____ than the beam width

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

Produce _____-intensity, unidirectional reflections

Very _____ dependant

A 
smooth
larger
diaphragm
pericardium
high
angle
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8
Q

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

A

rough
flat
scattering
weakens

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9
Q

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

A

nonspecular
small
sound
internal

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10
Q

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

A

frequency
internal
rayleigh
diffuse

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11
Q

Types of Interactions

  • _____
  • _____
  • _____
  • _____ and _____
  • _____
  • _____
  • _____
A 
reflection
reflectivity
refraction
divergence
diffraction
interference
attenuation
absorption
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12
Q

Reflection

Acoustic _____

Impedance _____

_____ Coefficient

_____ Coefficient

_____ Composition

A 
impedance
mismatch
reflection
transmission
interface
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13
Q

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 _____

A 
RESISTANCE 
Rayl
Density 
Prop Speed
MEDIUM
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14
Q

ACOUSTIC IMPEDANCE

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

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

A

increase
increase
directly

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15
Q

IMPEDANCE MISMATCH

In Perpendicular Incidence the amount of sound reflected depends on:

Incident _____
AND
Impedance _____ of the 2 media

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

A

intensity
Mismatch
oblique

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16
Q

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 _____

A 
Perpendicular 
Impedance
Perpendicular 
Reflection
Impedance
mismatch
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17
Q

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.

A

reflection
decrease
ST

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18
Q

DETERMINING THE AMOUNT OF INCIDENT INTENSITY THAT IS REFLECTED and TRANSMITTED

Expressed BY:
_____ -or- _____

A

Coefficient

Percentage

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19
Q

DETERMINING THE AMOUNT OF INCIDENT INTENSITY THAT IS REFLECTED and TRANSMITTED

Coefficient

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

A

Equation

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20
Q

DETERMINING THE AMOUNT OF INCIDENT INTENSITY THAT IS REFLECTED and TRANSMITTED

Percentage

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

A

Equation

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21
Q

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!

A

large
small
thickness

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22
Q

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
A 
reflected
transmitted
small
strong
weaker
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23
Q

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
A 
mismatch
angle
size
shape
texture
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24
Q

REFLECTIVITY

The combination of these factors is described by the term:

Reflectivity

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

A

patient

25
Q

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 _____

A

direction

26
Q

REFRACTION

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

MAY be

_____ or bent

A

obliquely

refracted

27
Q

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!!!

A

reflected

transmitted

28
Q

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)

A

equal

refracted

29
Q

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!!!

A

snell’s

speeds

30
Q

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

A 
speed
oblique
snell's
refraction
oblique
speed
snell's
snell's
31
Q

SNELL’S LAW

sin θi /sin θt = c1 /c2

— OR —
to solve for what we care about

sin θt = (sin θi) c2 /c1

A

SNELL’S LAW EQUATION

32
Q

REFRACTION

For refraction to occur there MUST be both:

_____ incidence

AND

propagation _____ differences
between the media

A

oblique

speed

33
Q
  • If the velocities of 2 media are the same there will be

NO _____!!!

If perpendicular incidence occurs there will be

NO _____!!!

A

refraction

refraction

34
Q

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

A

velocity

35
Q

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

A

toward

greater

36
Q

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

A

away

less

37
Q

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

A

greater

interface

38
Q

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

_____ artifacts / _____ artifacts

A

snell’s
edge
refraction

39
Q

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

A 
divergence
increases
decreases
lateral
diffraction
40
Q

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.

A

degrees
phase
algebraic

41
Q

This is known as the

PRINCIPLE OF _____
-or-
_____ PHENOMENA

A

superposition

interference

42
Q

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.

A

frequency

increases

43
Q

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 _____

A

out
decreases
zero

44
Q

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.

A

sinusiodal
uniformity
wave

45
Q

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

A 
constructively
destructively
speckle
frequency
noise
46
Q

CONTRAST AGENTS 1.0

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

A

increase

47
Q

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

A

medium
strong
gas
harmonics

48
Q

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

A 
reduction
weakening
absorption
scattering
reflection
attenuation
increased
depth
49
Q

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 _____

A 
heat
attenuation
reflection
refraction
scattering
divergence
frequency
doubles
doubles
50
Q

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

A 
decibels
output
dynamic
gain
logarithms
51
Q

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

A

3
6
10
20

52
Q

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 _____

A

increases
increases
increases

53
Q

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

A

length
cm
path
attenuation

54
Q

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

A

half

3

55
Q

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

A

high
higher
lower

56
Q

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

A

reflections

57
Q

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

A

pulsed

echo - ranging

58
Q

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

A

direction
distance
range

Physics I (8 decks)

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