US - Understanding US Physics - 6 Flashcards
STR of attenuation r/t STR of amplitude
inverse
importance of increasing 1-log
by increasing 1-log»_space; 10x more
DECIBEL NOTATION - absolute? measured? calculated?
.relative measurement
. comparison
.ratio
.logarithmic
DECIBELS require…
2 intensities… start & final
positive DECIBELS
final intensities is LARGER than start intensities
INCREASES in intensities
negative DECIBELS
final intensities is SMALLER than start intensities
DECREASES in intensities
+ 3dB
final intensity is DOUBLE start intensity
+ 10dB
final intensity is 10x TIMES start intensity
- 3dB
final intensity is HALF (1/2) start intensity
- 10dB
final intensity is ONE-TENTH (1/10) start intensity
ex: meaning of 6dB change?
** +3dB = 2x
6dB = 2 x (+3dB)
6dB = 2 x (2x)
6dB = 4x
final intensity is [[4x]] start intensity
ex: sound increases by a factor of 100?
want: decibel notation?
** 10x = +10dB
100 = 10 x 10
100 = 2 x (+10dB)
100 = [[[+20dB]]]
def ATTENUATION
= as sound propagates thru medium, sound pulse STR(Power, Amplitude, Intensity) decreases,
.SAME speed
ATTENUATION - 2 factors
. distance
. frequency of sound
ATTENUATION r/t its 2 factors
direct
up ATTENUATION
up DISTANCE
up FREQUENCY
ATTENUATION r/t decibels
ATTENUATION = negative decibels due to decreases in sound pulse STR
ATTENUATION - 3 processes
SAR-Attenuation
.scatter
.absorption
.reflection
def REFLECTION
= when sound waves strike a LARGE BOUNDARY, redirected back to the sound source
REFLECTION - 2 types
specular REFLECTION
diffuse REFLECTION
def SPECULAR REFLECTION
= 1 direction reflected
. smooth boundary
BAD - at off-axis or off angle = no reflection
GOOD - stronger STR reflection than diffuse reflection
def DIFFUSE REFLECTION
aka BACKSCATTER
=multi direction
=irregular surfaces
GOOD - suboptimal angle
BAD - weaker STR reflection than specular reflection
def SCATTERING
= SMALL boundary, sound waves RANDOMLY directed, in MULTI-direction
SCATTERING r/t frequency
direct
example of SCATTERING
lung tissues due to alveoli are filled with AIR
*AIR has HI-attenuation = HI-frequency»_space; HI-scattering
def RAYLEIGH SCATTERING
= organized
=omnidirectional scattering (in all direction)
RAYLEIGH SCATTERING - example
red blood cells
RAYLEIGH SCATTERING equation r/t frequency
RAYLEIGH SCATTERING = frequency (^4) 4th power
REFLECTION - organized, back to transducer
specular REFLECTION
REFLECTION - organized, in all direction
rayleigh REFLECTION
REFLECTION - disorganized, back to transducer
diffuse / backscatter REFLECTION
REFLECTION - disorganized, in all directions
scattering REFLECTION
importance in US r/t attenuation, reflection & scattering
UP f
DOWN pulse
UP accuracy
UP attenuation
DOWN depth
therefore, to UP.accuracy & UP.depth»_space; US goal, to UP.f as much as possible for HI.accuracy without compromising DEPTH
def ABSORPTION
= when US energy is converted into another energy form (heat)
ABSORPTION r/t frequency
direct
ABSORPTION r/t DEPTH, f, attenuation, pulse.L
up ABSORPTION
up frequency»_space; up attenuation
down pulse.L
DOWN depth
ABSORPTION r/t UP.depth….f, attenuation, pulse.L
down ABSORPTION
down frequency»_space; down attenuation
up pulse.L
UP depth
def ATTENUATION COEFFICIENT
= number of decibels of attenuation when sound travels 1cm
= dB/cm
*regardless of sound travel distance
ATTENUATION COEFFICIENT r/t sound travel distance
UNrelated
TOTAL ATTENUATION depends on (3)…
.sound frequency
.beam travel distance
.tissue type
TOTAL ATTENUATION equation
TOTAL ATTENUATION (dB) = ATTENUATION COEFFICIENT (dB/cm) x distance (cm)
ATTENUATION COEFFICIENT - soft tissue value
0.5 dB/cm/MHz
ATTENUATION COEFFICIENT equation
ATTENUATION COEFFICIENT (dB/cm) = f (MHz) / 2
ATTENUATION COEFFICIENT r/t frequency
direct
arrange ATTENUATION MEDIUM from hi»low
hi»low
AIR
BONE & LUNG
MUSCLE
SOFT TISSUE
FAT
FLUIDS, BLOOD, URINE
WATER
ATTENUATION r/t AIR & its f
air ATTENUATION 100%
f > 1MHz
ATTENUATION r/t LUNG, type reflection
LUNG ATTENUATION more than SOFT TISSUES
hi SCATTERING reflection due to air in lung tissue
ATTENUATION r/t WATER, its f
water ATTENUATION less than SOFT TISSUES
hi HI f ~10MHz
ATTENUATION r/t muscles
depends if sound travels along or across fibers
def HALF-VALUE LAYER THICKNESS
aka PENETRATION DEPTH
aka HALF BOUNDARY LAYER
=distance sound travels in tissue that reduces half original intensity of sound
HALF-VALUE LAYER THICKNESS - US range
0.25 - 1cm
HALF-VALUE LAYER THICKNESS depends on (2)
medium
sound frequency
thin HALF-VALUE LAYER THICKNESS & its medium (3)
HI f
HI attenuation
lung, bone, air
thick HALF-VALUE LAYER THICKNESS & its medium (3)
LOW f
LOW attenuation
fat, fluid, water
def IMPEDANCE
= acoustic impedance
= characteristic impedance
**CALCULATED!!!!!, not measured
IMPEDANCE equation
IMPEDANCE (rayls, Z) = DENSITY (kg/m^3) x propagation speed (m/s)
IMPEDANCE - range
1.25 - 1.75 Mrayls
IMPEDANCE - determined by
medium
def INCIDENCE
the angle at which the waves strike the boundary determines the behavior of the pulse
oblique angle
any angles NOT 90 degrees
acute angle
LESS than 90 degrees
right angle
90 degrees
obtuse angle
MORE than 90 degrees
def normal incidence
= the incident sound beam strikes the boundary at exactly 90 degrees
aka PORN
.Perpendicular
.Orthogonal
.Right angle
.Ninety degrees
def oblique incidence
= when the incident sound beam strikes the boundary at angle NOT 90 degrees
what occurs at the boundary between 2 media?
CONSERVATION OF ENERGY, 100%
INCIDENT intensity equation
INCIDENT intensity (W/cm^2) = REFLECTED intensity + TRANSMITTED intensity
def INTENSITY REFLECTION COEFFICIENT (IRC)
IRC = percentage of reflected intensity
IRC value for soft tissue
equal, less than 1%
IRC r/t soft-hard tissues
up IRC b/t SOFT-HARD tissues
def INTENSITY TRANSMISSION COEFFICIENT (ITC)
= percentage of transmission intensity
ITC value for soft tissues
equal, more than 99%
ITC r/t soft-hard tissues
down ITC b/t SOFT-HARD tissues
IRC & ITC equation r/t energy conservation
100% = IRC + ITC
units INTENSITIES vs COEFFICIENT
intensity (W/cm^2)
coefficient (%)
def REFLECTION w/ NORMAL incident
= when incident strikes at 90*
b/t media with DIFF IMPEDANCE
what happens to REFLECTION w/ NORMAL incident with SAME IMPEDANCE?
SAME impedance
no REFLECTION w/ NORMAL incident
REFLECTION w/ NORMAL incident r/t DIFF in IMPEDANCE
direct
INTENSITY REFLECTION COEFFICIENT equation
IRC (%) = [Z2 - Z1 / Z2 +Z1]^2 x {100}
def INTENSITY TRANSMISSION COEFFICIENT (ITC)
= percentage intensity that continues to move forward at boundary b/t 3 media
100% ITC
b/t 2 media with SAME IMPEDANCE
INTENSITY TRANSMISSION COEFFICIENT (ITC) equation
INTENSITY TRANSMISSION COEFFICIENT (ITC) {%} = transmitted intensity (W/cm^2) / incident intensity (W/cm^2) X {100}
INTENSITY TRANSMISSION COEFFICIENT (ITC) equation r/t energy conservation
ITC (%) = 1 - IRC (%)
100% = ITC + IRC
def REFLECTION & TRANSMISSION w/ OBLIQUE INCIDENCE
its not YOU, it’s ME kinda COMPLICATION
REFLECTION & TRANSMISSION w/ OBLIQUE INCIDENCE - 2 physical principles
. conservation of energy
. reflection angle = incident angle
explain CONSERVATION OF ENERGY r/t OBLIQUE INCIDENCE -
100% = reflected coefficient + transmission coefficient
incident intensity (W/cm^2) = reflecte intensity + transmitted intensity
explain REFLECTION ANGLE = INCIDENT ANGLE r/t OBLIQUE INCIDENCE
draw **note CH6
.in oblique incidence, the sound beam does not reflected directly back to the transducer
.with the IMAGINARY LINE locates PERPENDICULAR to the boundary, the INCIDENT angle = REFLECTED angle
example of REFLECTION ANGLE = INCIDENT ANGLE r/t OBLIQUE INCIDENCE
car rear view mirror
def REFRACTION
draw *note CH6
= transmission with a bend
= change in direction of wave propagation after it crosses the boundary
REFRACTION - needs 2 conditions
. oblique incidence
. diff propagation speed b/t 2 media
low REFRACTION r/t speed, b/t media
low REFRACTION
~similar speed
soft-fat
muscle-blood
soft-fluid
hi REFRACTION r/t speed, b/t media
hi REFRACTION
DIFF speed
bone-soft
SNELL’s LAW
=physics attempt to explain refraction
SNELL’s LAW equation
sin{transmission angle} / sin{incident angle} = [propagation speed 2] / [propagation speed 1]
def SINE
draw *note CH6
= angle adjacent to the side
draw NO REFRACTION r/t angle and speed
NO refraction
same angle degree
same speed
draw YES REFRACTION r/t angle and speed (large vs small)
YES refraction with LARGE diff
.incident < transmission angle
.speed 1 < speed 2
YES refraction. with SMALL diff
.incident > transmission angle
.speed 1 > speed 2
