chapter 6-8 Flashcards
Logarithm / Log
represents > # : 10 that are multipled to create the original #
positive decibel
signals > ⬆️ strength or getting larger
when wave intensity doubles what is the relative change is
+3dB
when wave intensity ten fold , what is the relative change is
+10dB
negative decibel
signals > ⬆️ decrease or getting smaller
when wave intensity is reduced to 1/2 , what is the relative change is
-3
when wave intensity is reduced 1/10 , what is the relative change is
-10
attenuation
sound wave weaken as they propagate > medium
Attenuation determined by 2 factor
1.path length
2. frequency : sound
distance / attenuation … related
directly
father sound travels , _____ attenuation , ____ beam becomes
greater
weaker
attenuation / frequency … related
directly
Attenuation is ______ > _______ frequency sound
greater
higher
3 processes contribute to attenuation
- reflection
- scattering
3.absorption
reflection
sound strikes the boundary, portion : wave energy may be redirected or reflected, back to sound sound
Reflection occurs
when dimension : boundary > large
2 forms : reflection
- spectral
2.diffuse
specular reflection
boundary > smooth
sound > reflected in 1 directions in an organized manner
specular reflection occurs
when light wave strikes a mirror
1 limitation : specular reflection
once wave is slightly off-axis, reflection does not return to transducer
diffuse reflection
wave reflects off an irregular surface it radiates in more than one direction
another name for diffuse reflection
backscatter
advantage : diffuse reflection
interface at suboptimal angles to the sound beam can still produce reflections that will return to the transducer
disadvantage: diffuse reflection
signals has lower strength than specular reaction
scattering
redirection : sound > many direction
scattering occurs ..
tissue interface is small
scattering / frequency …. related
directly
ray scattering
structure : dimension > much smaller than beam wavelength
ray scattering / frequency ….. related
directly
absorption occurs
ultrasonic energy > converted into another energy form, ( heat)
Absorption / frequency …. related
directly
attenuation
process > sound energy is extracted from a wave by absorption, scattering, reflection
total attenuation depends >
frequency : sound
distance : beam travels
tissue > sound wave travels
Attenuation coefficient
: decibels : attenuation > occurs when sound travels 1 cm
unit : attenuation coefficient
dB/cm
attenuation coefficient / frequency .. related
directly
1/2 value layer thickness >
distance sound travels > tissue > reduces intensity : sound to 1/2 it original value
1/2 value layer describes
depth : tissue = 3dB : attenuation to intensity
units : 1/2 value layer
cm
units > length
synonyms : 1/2 value layer
Penetration depth
depth : penetration
1/2 boundary layer
1/2 value layer thickness depends >
- medium
2.frequency : sound
reflection
produce as sound moves > 1 medium to another form basic u/s imaging
transmission
u/s ability to image structure located deep > body
acoustic impedance
tissue property > influence the amount : reflection
Impedance
acoustic resistance > sound traveling > medium
how is acoustic impedance calculated
multiplying density : medium by speed at which sound travels > medium
how is impedance calculated
associated w/ medium > which sound travels
reflection : u/S wave depends >
difference > acoustic impedance : 2 media at boundary
units : impedance
rayls
impedance > determined by
medium only
synonyms > acoustic impedance
Characteristic impedance
Incidence
angle at which angle strikes
3 types of angles
- acute
- right
3.obtuse
acute angle
less than 90
right angles
exactly 90
obtuse angles
greater than 90.
Normal incidence
sound beam strikes boundary at exactly 90
synonyms > normal incidence
perpendicular
orthogonal
right angle
90 degree
Oblique incidence occurs
sound beam strikes boundary at any angle other than 90
synonyms oblique
not at right angle
non-perpendicular
reflected intensity
sound beam, after striking boundary returns back from where it came
incidence intensity
sound beam intensity immediately before it strikes boundary
transmitted intensity
incident beam > after striking a boundary continues forward same general direction that it was traveling
intensity reflection coefficient
% : Intensity > bounces back when sound beam strikes boundary b/w 2 media
Intensity transmission. coefficient
% : Intensity > passes in forward direction when beam strikes an interface b/w 2 media
how are IRC & ITC reported ?
%
normal intensity
sound beam strike a tissue boundary at 90 angle
reflection occurs only
if media on either side of boundary have different impedance
transmission w. normal incidence
% : intensity > continues to move forward then beam reaches a boundary b/w 2 media
w/ oblique incidence, reflection occurs
when impedance : 2 media are identical
refraction
change > direction : wave propagation when traveling from 1 medium > another
refraction associated w/ …
& occurs w/
transmission
light wave / sound wave
refraction occurs only if two conditions are satisfied…
- oblique incidence ( not normal)
- differ propagation speed : two media
snells law
quantifies physics : refraction
sine
unitless number w/ value from 0 - 1
how do we identify medium 1 & 2
med 1 - sound currently traveling
med 2 - sound entering
under what conditions will transmission angle = incident angle
oblique incidence
different propagation speed
under what conditions will transmission angle greater than incident angle
when speed : med 2 is greater than speed : med 1
under what conditions will transmission angle less than incident angle
when speed : med 2 less than speed : med 1
go - return time / time : flight
time : flight / how deep sound pulse travels .. related
directly
13 microsecond rule
for every 13 us : go -return time object creating reflection = 1 cm deeper > body
transducer
ultrasound transducer perform 2 functions
transmission
reception
during transmission ….
electrical energy > system , converted > sound
during reception …
reflected sound pulse > converted > electricity
piezoelectric effect
property : certain material to create voltage when mechanically deformed or pressure is applied to them
piezoelectric material changes … when ….
shape
voltage is applied
piezoelectric material coverts >
sound > electricity
synonym PZT
ceramic
active element
crystal
case
Cylindrical tube
electoral shield
thin metallic barrier lignin inside : case
acoustic insulator
thin barrier rubber
prevents vibrations
PZT / active elment
Crystal itself
1/2 wavelength thick
wire
electrical connection b/w PZT / ultrasound system
matching layer
front : PZT at face : transducer
protects active element
backing material
reduces ringing
another name for backing material
damping material
