Characteristics of Sound/Acoustic wave
How Sound Travels -sound ONLY travels in straight line, moving back & forth, right & left
-sound transported vibrate parallel to direction the sound wave moves
-sound ONLY travels thru medium, NOT thru vacuum
-sound waves attenuate /weaken as travel in body static
CanNOT have a sw w/o parameters
Medium -substance that wave propagate (transmit / spread) thru
-substance or matrial that carrieswave
Sound-Wave Type -sound is mechanical, longitudinal, pressure wave
(All waves carry energy from 1 location to another, many types of waves ex:light, heat, sound, magnetic)
Mechanical Sound is Mechanical wave b/c particles in medium move
Longitudinal particles of medium move in direction parallel to direction of energy transport.
-composed of compressions & rarefactions
As energy transported from left to right, individual coils of medm will be displacd leftwards & rightwards
Transvers waves move in perpendicular direction-900 angle
-composed of crests & troughs
As energy transported from left to right, individual coils of medium will be displaced upwards & downwards
1 complete Sound -sound cycle consists of 1 compression & 1 rarefaction
Cycle
-sound oscillates-moves to & fro, fluctuates thru medium by compressions & rarefactions
particle velocity largest btwn compressed & rarefactions areas & 0 in center of rarefactns & comprssd areas
Compressions/high -particles squeezed together, MAX density ↑ pressure & ↑ density
pressure region
Rarefactions
-particles stretched apart ↓ pressure & ↓ density, minimum density in long wave
Crest of wave
Trough of wave
Infrasound
Audible
Ultra
point on medium that exhibits max amount of positive or upward displacement from rest position
point on medium that exhibits maximum amount of negative or downward displacement from rest positn
-infra < less 20Hz
btwn 20Hz-20,000 Hz
> 20,000 Hz
Pulse
Wave
consonant
single disturbance moving through a medium from one location to another location.
repeating & periodic disturbance that moves through a medium from one location- source- to another is
referred to as a wave.
-transports energy, X matter
- For wave to be transmitted through a medium, the individual particles of medium must be able to interact
so can exert a push and/or pull on each other; this is mechanism by which disturbances are transmitted
through a medium.
Direct to Pressure
Density
Squeeze
Inverse to Pressure
Density
Squeeze
1
In-Phased Waves Constructive Interfrnc
wen wave peaks (max values) & troughs(minimum values) occur simultaneously at same location
- result in formation of single pair of IN phase wave of ↑ greater amplitude
-combination called constructive interference: resulting wave larger than either of its components
Direct to Amplitude
Frequencies
consonant
Out of Phase
-wen peaks & troughs occur at different locations & X simultaneous
Inverse to Amplitude
-Destructive Interfrnc -result in formation of single pair of OUT phase wave w/ ↓ lesser amplitde than at least one of components Frequencies
Interference
-this combination is destructive interfnce -resultant wave smaller than one of its components
- when 2 out of phase waves of equal amplutde, complete destructive interference may occur
-OUT of phase angle: 0 = 900
> 1 sound beam can travel in medium
-multiple beams may arrive at same location same time
-these waves lose their own characteristics & combine to form a single wave
-In phase & Out of phase undergo interference but combine differently
-wen frequencies of waves differ, both constructive & destructive interference occur
Sound waves interacts w/ each other. Waves may be in phase or out of phase.
In-Phase Waves
Out of Phase Waves
1. Waves stacked
1. Waves overlapped- opposite each other 1800
2. Matching peaks & troughs throughout
2. Have identical amplitudes- can completely cancel each other out
3. In-phase waves meet, undergo Constructive interference-1 big wave 3. Out of phase waves meet, undergo Destructive interference = ↓ wave
2
Determind by
Acoustic Parameters /
describes features of sw:
Sound source/ Medium/
Propagation Properties
-what does medium do to soundwave?
US systm /
Tissue
Factors of Sound transmit/spread -effects of medium on sound wave
Trnsdcr
limits boundaries
-Biological effects-sw effects on body
1. Period
Only
2. Frequency
Only
3. Pro. Speed *Speed ONLY changes wen sw transmit from 1 mdm to anothr
Only
4. Wavelngth
Both
Both
5.
Amplitude
3 factors Bigness
*Rate which Amplitde ↓decrease as sound prpgts thru body
Initial*
Parameters of SW
depends on charctrscs of BOTH-source & medm
-All US system only knows 13 micro sec
6. Power
*Rate which Power ↓decrease as sound propgts thru body
Initial*
depends on charctrstcs of BOTH- source & medm.
-All US system only knows 13 micro sec
7. Intensity
*Rate which Intensity changes as sound propgts thru body
Initial*
depends on charactrstcs of BOTH- source & medm.
-All US system only knows 13 micro sec
-CanNOT have parameters w/o a sound wave
-if 3 variants-pressure, density, or distance acoustic variables have oscillations, then wave IS sound wave.
BUT if something, other than pressure, density, or distance has rhythmic oscillations, then wave X sound wave
Acoustic Variables
1. Pressure
2.
Density
3. Distance / Vibration / Displacemnt
Def
-sw identified by oscillations in acoustic variables
-Concentration of force within an area
-Peak - peak amplitude- fluctuations
Concentration of mass per unit volume
Units
Pascal
kg/cm³
Adjustable by Sonographer?
No
No
No*
No
YES-ctrl on US system allows sono
to alter initial Amplitude of wave
YES-ctrl on US system allows sono
to alter initial Power of wave
YES-ctrl on US system allows sono
to alter initial Intensity of wave
Relation
Direct to-Compression: ↑ pressure/density
-Rarefaction: ↓ pressure/density
Direct to-Compression: ↑ pressure/density
-Rarefaction: ↓ pressure/density
-Measurement of particle motion
-mm, cm, feet
-distance of molecule travls in back & forth directn -any unit distance
Difference btwn Wavelength, Frequncy, & Period
Unit
Relationship btwn Wvlgnth & Frquncy
1. Wavelength refers to length/distance of a single cycle –
unit of distnce If wave remains in same medium,
2. Period refers to time that it takes to complete a single cycle units of time
wvlngth & freqncy INVERSLY related
3. Frequency refers to # of cycles per second
units of hertz
3
Period
-Time takes for 1 complete cycle to occur
-time from start of one cycle to start of next cycle
T
-cycle determind by: 1 compresson & 1 rarefacton
-determind by sound source; created by machine
- # cycles per sec - # of events occur in spcific time
Frquency /
-determined by sound source
1. Main F/
-pitch of sound-sensation of frqncy
2. Resononant F -high pitch-high freqncy sw
3. Natural F /
-low pitch-low freqncu sw
-US: 2MHz - 15MHz
4. Center F
µs
1. Period = __ 1____
-1 millionth of a sec
Frequency
-time unit-hour,day 2. Frqncy x Period (t µs) = 1
-.06-.05 µsec US
-Hz,
1. Frquncy = Prop. speed-c
Wavlngth
- per second
Propagtion
Speed
-mm/µs
𝐌⋅
1. Speed
=Frqncy x Wvlnth Direct to -Stiffness
𝐂
-m/s
-Amplitude
Hz
meters
-500 – 4,000 m/s
2. C= elastisity_
Depnding on tissue
density
Inverse to Density
Speed/Rate wich soundwave trvels thru medium
-meters per sec or any distance divided by time
-dep. on 2 properties of medium:
C
1.Stiffness, elastic, hardness of mdm &
2. Density- mass of medium
- dtrmnd by medium, X adjustable
-ALL sound, regardls of frqncy travel at same speed thru
medm(5 Mhz & 10 MHz trvl same speed thru same mdm
-sound travels fastest thru ↑stiff, ↓ density objects
Speed
-sound travls slowest -fastest in medm: Air/gasses
Liquids
Solids
Stiffness/
Ability of object to resist compression
Bulk Modulus -greatst effect on speed-stiff ↑, > speed than densty
-elasticity & compressibility OPP of stiffness
_1
_
Second
2. Frquncy
= ___1____
Period (t µs)
3. Frqncy x Period (t µs)= 1
-weight of object
-stiffness greater ↑, > effect on speed than density
-bone is stiff but NOT dense
Wavelength -Distance/Length of a single cycle
-mm
-distnce from crest to crest, trough to trough or
-any unit of length
Speed = Frqncy x Wvlnth
(Hz)
(meters)
-Distance from beg - end of 1 cycle
Wavelength Trvl Slowst to fastest in a Medum:

Lung 500 m/s
for

Fat
-Trndcr

Soft tissue 1,540 m/s

Liver
-Soft tissue

Blood

Muscle

Tendon
Bone 3,500 m/s
Acoustic Propagation Properties
-Inverse to -Wavelngth
-Reciprocal to Period -T
Direct to Stiffness
Inverse to Density
Wvlngth mm= Prop. Speed mm/µs Direct to Prop.speed- C
Frequency MHz
Inverse to Frequncy
1540 m/s soft tissue Soft tissue:
1.54 µsec 1 Mhz trd Wavlngth (mm) = 1.54 mm/ µs
Frequency (MHz)
.77 µsec 2 Mhz trd
.1 -.8 mm typcl value
Direct to -Prop. speed C
-Gain Amp
Direct to Speed
Inverse to - Elasticity
- Compressibility
-Density
Inverse to -Speed
-Stiffness
Density
btwn any 2 corresponding points on adjcnt waves
-Reciprocal to Frquency
Travels slowest to fastest:
-Lung 500 m/s
-Fat
-Soft tissue 1,540 m/s
-Liver
-Blood
-Muscle
4
-Tendon
- Bone 3,500 m/s
4
Amplitude -Bigness of a wave
-difference btwn: Max and Average or undisturbed value or
A
-diff btwn minimum & average value
-determin initialy by sond source & thn Medum
-Adjustable
-Ampl ↓ decreased as propagates thru body,that’s why 1st dtrmnd
by sound, then by medium as travls thru
Any of acous. variable:
-Pascal,
-kg/cm³
-cm, inch
Direct to Prop. Speed C
- 1- 3 million pascals
distance from rest to crest or from rest to trough.
-Diff Amp -Ampl measure frm middle/undisturbed value to max/min value
-Peak-Peak to peak: diff btwn max & min values of an acoustic variable
Peak
-Its twice the value of the amplitude
Power Rate work performed
-rate of Energy transmitted
P
-“bigness of wave how much work performd
Intnsity Power of wave ÷ area which spread
-Energy per unit area
- Intensity of Beam, 2 factors:
I
1. Space
2. Time
-Intnsity changes as sound propogates thru bodydepends on both sound wave & medium
mW/Watts
4 - 90mW
Power ~ (amplitude) ²
A 2x, P ↑ 4x,A 3x, P ↑9x
↓A halved,↓ P quarter
mW/cm², W/cm² 1. Intnsity = Power (Watts)
W/cm²
Beam Area(cm²)
US:
2. Intnsity = Power (Watts)
.01 - 100 mW/cm² W/cm²
Area (cm²)
or 300
Direct to Intensity
Amplitude2 NOT 1:1
Direct to Power
Amplitude ²
Inverse to Beam Area
-2 factors Beam Intensity:
1. Space
2. Time
5 Parameters describe Pulsed Sound
Pulsed Ultrasound
Continuous US
Detrmnd by Snd/Medm. Adjstbl? -produce small bursts/pulses of acoustic energy to create anatomical image - can NOT create images
1.Pulse Duration
S
x
-Pulsed US is collection of cycles that travel together
b/c

2.Pulse Rep. Period s
-pulse MUST have a beg. & end
-NO breaks in btwn pulses
-although a pulse has indiv. cycles, the entire pulse moves tgthr as single unit -NO OFF time
3.Pulse Rep. Frequncy S & Img Depth 
-TRAIN has indiv. cars but travel as single entity

4.Duty Factor
s
5.Spatial Pulse Length S & M
x
-2 components of Pulsed US:
1. Transit/ talking/ “ON” time
2. Receive/ listening/ “OFF” time
-Pulse: group of cycles sent together
5
Pulse
-Single transmit “ON” time
Duration -Time it takes for 1 pulse to occur
-2 determining factors:
1. how many cycles in pulse
PD
2. T- period of each cycle
-detrmined by sound, X adjustable
- ↓ Short PD better quality
-µsec
-all units of time
1.PD = # cycles in pulse x Period µs
(µs)
Direct to- SPL, # cycles in pulse
- Period
2. PD (µs) = _# cycles in a pulse
Inverse to Frequency
-Value .3 - 2.0 µs
-Grayscale 2-3 cycls
-Doppler 5-30 cycls
Frequency (MHz)
↑longer PD
↑lots of cycles
↑ long periods
↓ frequency
↓shorter PD
↓Few cycles
↓Short period
↑high freqncy
PR Frqncy -how many # pulses US system transmits in 1 sec -Hz,
1. PRF = PRP (sec) x PRF (Hz) = 1
-Reciprocal to PRP
-determined
by
1.
sound
&
-pulses
per
second
PRF
2. PRF= __ 1____
-Inverse to Imaging depth
2. depth of view
PRP
-US: 1–10 kHz /
↑ Deeper area↓ lower PRF
-Adjustbl: sono by changing depth of view
1,000 -10,000 Hz 3. PRF (Hz) = 77,000 cm/s____
-Unrelated PRF to Freqncy
-we r only interested in # of pulses, NOT # cycles pulses per second
Imaging depth (cm)
1.
PR Period -Time from start 1 pulse to start of nxt pulse
-ms (millisec)
Direct to Imaging Depth
PRP
(
µs
)
=
Imaging
Depth
(
cm
)
x
13
µs/cm
-determnd by 2: 1. sound source &
PRP
- all units of time
Reciprcl to PRF
2. imaging depth
2.
-Adjustbl: sono by changing depth of view
Unrelated PRP to Period (time)
US: 100 µs - 1 ms
- 2 factors PRP which includes both:
PRP(µs or ms)= _ 1____
milli
Depth of View:
1. Transmit/talk/ON time aka Pulse Duration micro
PRF (Hz or,
2. Receiving/listen/OFF time- sono change
max distnce into body that US
pulses per secnd)
-PRP is 100 -1,000 times LONGER than PD
system can image
Duty
-% of time sound produced/system on
Factor/Cycle -CW : 1.0 or 100 %, MAX value b/c always trnsmt
-PW always < 100% systm off longer than ON
DF
-PW .1 % Doppler: .5 % - 5 %
- 0 % MIN value, trnsdcr silent
-detrmnd by Sound
-Adjustbl: sono by changing depth of view-as ↑incrs Img Depth, transmt time/PD stay constant
while listng time prolongd.
-Result: ↓ DF ↑ incrs w/ shallower imging
Unitless 1.
Inverse to -Depth of View
DF(%)= Pulse Duratin (µs) x 100
-PRP
PRP (µs or ms)
- ↑Incr DF ↓shallower Img depth
2.
DF (%)= PD (µs) x PRF x 100
-↑Inc Img Depth
2 Results
↑longer listn time
↓ DF
x time alter Trnsmt/PD ↑inc shalower Imag
6
Spatial Pulse
Length
Length of pulse from beg to end
SPL
Spatial Peak
SP
Spatial Average
SA
SP Intensity
SA Intensity
Beam Uniformity Ratio /
Beam Unfrmty Coefft /
SP Factor
1.
-mm
SPL (mm) = # cycles x Wavelength (mm)
-All units of distance
Direct to -Wavelength
-Damping
2.
-Axial Res/Pic Qualty
SPL(mm)= # cycles x Propgn speed (C mm/µs)
Inverse to Freqncy
Frquncy (f Hz)
-Max value where beam measure
-Measured at center
-Average of all intensities across sound beam where measured
-Incl. gr8er intensity in center & weaker intensity at edges
Measured at center of beam
-Average Intensity across face of entire beam
-Intensity is 0 wen trdcr waiting for pulse to come back b/c sound
produced only during transmissn
Ratio of center Intensity to
average spatial intensity
US: SP/SA factor > 1
BUR= Spatial Peak
Spatial Average
Temporal Peak
TP
-Max intensity within pulse as it passes
-intensity measured at highest intensity / Peak of pulse
- Highest of all temporal intensities
Pulse Average
-Average of all values within a single pulse
-incl larger values at beginning and smaller at end
PA
-averaged only during: 1. PD
2. Beam Transmission
Temporal Average
-Intensity averaged over PRP- transmission & listen
PW: TA= PA x DF
TA, I, I (TA), I (ta)
-depict when beam measured
CW: TA = PA b/c X
-incl time wen value is 0, during gaps transmit/receive
-listening times relevant for 3 Intnsities:
Formula I avg prp
1. TA averaged over PRP
2. PA Intensity averaged over PD
3. TP Intensity X averaged over time
Hydrophone/Microprobe -device, needle, broad disk
-both measure output Intensity, PRP, PD & Period trns path’s beam
Damping
measure output Intensity, PRP, PD &
Period T trans path’s beam
Other Parameters:
Frequency, Wvlngth, SPL, PRF & DF
Vibrations of crystal dampened by special backing material
7
Rules of Intensity
1. Intensities MAY report in various ways ex: SPTA or SPTP
2. Diff measurmnts important b/c of bioeffects-measured best w/ SPTA
3. SPTP has highest value
4. SATA lowest average
4. Beam Uniformity Coeff/Ratio (BUC/BUR) aka SP/SA factorUnitless w/ value greater BUR = Spatial Peak
By using equation SP divided by SA it gives us info how beam is
than 1
Spatial Average
5. Duty Factor describes the relationship of beam Intensities w/ time
6. CW U.S. NO diff. btwn Temporl or Pulse Averages b/c beam always ON
- TA & PA same
7. PW U.S. IS diff btwn Temporal & Pulse Averages in wave
Therefore, PA = TA & combine w/ spatial consdratins
8. wen PW & CW have same SPTP Intnsies, CW ↑ higher SPTA Intnsty
9. wen PW & CW have same SATP, CW has ↑ higher SATA Intnsty
PW always less than CW b/c listening gap in PW ↓reduces Intnsty
CW always operating, ↑ increasing Temporl Avrge
10. Temporal Considerations: TP, Tmax, PA, TA
11. Spatial Considerations: SP & SA
Order of Intensities PW:
1. SPTP- highest value
2. SPPA
3. SPTA- most relevant in heating & bioeffects
4. SATA
Intensity
Spatial Intensty
Temporal Intnsty 4 types:
1. Temporal Peak
2. Temporal Max
3. Tmprl Pulse Avrge
4. Tempral Average
SPTA = SPPA &
SATA = SAPA
SPTA = SPPA &
SATA = SAPA
-CW always ↑TA
-PW always ↓< CW
CW:
Beam always on, PA & TA
SPTA=SPPA &
SATA=SAPA
Define 1. Watts over cm2
2. Power divided by area
Refers to distance or space
Refers to all time-transmit & receive
Strongest
W/cm2 , mW/cm2 I= P
A
Direct to Power
Inverse to Area
Combining Spatial & Temporal Forces
1.SPTP- strongest
2.SATP
3.SPPA
4.SAPA
5.SPTA -most concerned w/ bioeffects
6.SATA - weakest
Weakest
8
Decibel Notation standard measurement tool to report relative changes for amplifction or attenution
Decibels
Change
↑ or ↓ Intensity
- dB describes relationship btwn various measured sound levels
Decibel
nd
-creates a ratio (ratio from initial number & the 2 number)
+ 3 dB Doubles
Mult 2nd power G2
-based on logarithms
Mult 4th power G4
+ 6 dB Quadruple
-Logs represent the number of 10s that r multiplied to create the original number
+ 10 dB Ten times
Mult 10th power G10
-require 2 Intnsities:
1. initial
stronger
2. change
- 3 dB
½ Halved
50% ↓reduct Intnsity
-also known as Amplification
-Positive dB /
- ↑ 1. increasing or
- 6 dB
¼
75% ↓ reduct Intnsity
Amplification
2. strengthening
-10 dB 1/10
90% ↓reduct Intnsity
-Negative dB / also known as Attenuation
as strong
Attenuation - ↓ 1. decreasing or
2. weakening
-sound waves ↓ weaken as propagate in a medium.
-this ↓ decrease in Intensity, Power, & Amplitude is called Attnuation
Attenuation -Weaking of Amp & Int as sound passes thru tissue
dB Coeff. x Depth x Frequency
Direct to 1. Distance/Path Length
-dB quantify attenuation
Attn in Soft tissue w/ trnsdcr msmnt
2. Frequency
-dB Intensifies bfr & after attenuation occur
3. Reflection
- Attenuation occurs w/ each cm sound wave travels
4. Scattering
-Attenutation has 2 determining factors:
1. path length - distance sound beam travels
5. Absorption
2. frequency
* Attntion greater in higher Frqncy b/c
↑ longer sound travels
↑frqncy X penetrate too much
1. ↑ greater the attenuation
-affects Attnution:
2. ↓ weaker the beam/Attnuation
Distance, frquency, reflction, scattering, & absorption
-3 main contributors to attnuation:
-↑higher the Frqncy, ↑quiker to Attnute*
1. Reflection- 2 forms
1a. specular reflection
- ↓lower the Frqncy the ↓less Attnuation
1b. diffuse reflection/backscattering
2. Scattering
3. Absorption
in other -use water-based gel b/c Attentn rate in liquids very ↓low
-if probe on skin w/o gel, tiny pockets of air wud Attnuate
Media
the entire imge and can NOT c anything
9
is number of dB of Attnution that occur wen sound travels 1 cm
-once AC established, stays constant for duration travl thru tissue
-AC rate at which sound is attenuated ↓ per depth
-X change w/ Depth
-Attention Coeff. = one half of frequency in soft tissue
Total
TA (dB) =AC (dB/cm) x distance (cm)
Attenuation
Total amount of sound in dB that attenuated at given depth
Half Intnsity Depth/ -another way to look at Attntion definition:
-How far sound beam needs to travel bfr it was half as strong as it was
HID
-HID describes depth which sound lost half or -3dB of its Intensity
-also described as depth of tissue that results in 3dB of Attnutation
Half Valve
-in 1st quarter to 1 cm, sound beam is already half as strong as it was
Layer Thickness
-HID has 2 dependent factors: 1. medium
2. frequncy
Half Boundary Layer - HID thin for tissue
HID thick for tissue
1. ↑Attenuates a lot
1. ↓ Attenuates a little
Depth of Penetratin/
2.
↑
Frequncies
2.
↓ Frequencies
Penetration Depth
Attenuation
Coefficient
dB/cm
dB
Attn Co. = Frquncy Mhz
dB/cm
2
-US: .7dB soft tissue
TA= Path length x Attn Co
dB
cm
Direct to Frequncy
Distnc-cm
dB /cm
1.
HID(cm) =
3 dB
Attentn Co. (dB/cm)
US: .25 -1 cm
Value
2. Soft tissue
HID =
6
cm
Frequncy
Inverse to Attentn
Freqncy
HID thin for tissue
1. ↑Attents a lot
2. ↑ Frequncies
HID thick for tissue
1. ↓ Attents a little
2. ↓ Frequencies
Attenuation
1. Reflection
As sound strikes boundary, some energy can redirect/reflect back to trnsdcr
-Reflction ↓ weakens part of sound wave that continues forward
- b/c happens wen dimension of boundary is ↑ larger than wavelength, 2-3 wvlngth
-in medium, reflectors referred to as specular/ non-specular
2 forms of reflction 1. specular reflection and
2. diffuse reflection/backscattering
-Specular Rflc - wen sound reflected from large, smooth boundary and returns directly to trnsdcr at 900
-1 direction, in organized manner bck to trnsdcr
-if wave slightly off axis, reflction does NOT return to trnsdcr, will NOT reflect at an angle
-creates very strong signal, reflects back hyperechoic in images
-NOT common
-Diffuse Rflc / -wen sw reflects off irregular surface, travels + 1 directions in disorganized manner back to trnsdcr
-Advntg: Interfaces at suboptimal angles to beam CAN still produce reflctions that’ll return to trnsdcr
-Disadvntg: -Backscattered signals have lower strength compared to specular
Backscatter
-Creates weaker signals that shows greys on images
Random redirection of sound in MANY directions
Direct to Freqncy
-sound scatters wen tissue interface is very small = to or less than the wvlngth
↑ higher the freqncy ,↑ more scatter
extremely
small
reflectors
-Rayleigh
Direct to Frequncy4
scattering -occurs wen structure dimension much ↓ smaller than beam’s wavelength
-redirects the sound wave equally in all directions, in organized manner
-interaction of US and RBC result in Rayleigh scattering
-strongest cause of Attenuation in soft tissue
3. Absorption
Direct to Frequncy
-occurs wen US energy is converted into another form of energy ex: heat
↑ higher the freqncy ,↑ more absorption
-source of bioeffects
-wen sound interacts w/ tissue in body, tissue absorbs the sound and converts into heat
10
-very dense objects absorb the energy
-bone absorbs lots of energy-that’s why intense shadowing behind bony structures
2. Scattering
-composed of black & white
-higher level contrast
-narrow dynamic range
-multiple level of grays
Gray scale
↑ high dynmic range =↓ Less contrast,↑ better resol
-lower levels of contrast
↓low dynmic range= ↑More contrast, ↓worse resol
-wider dynamic range
Display Controls -Contrast & brightness are 2 adjustable controls on video monitor
-Bistable- High contrast
Scan Converters -Gray scale imag made possible w/ scan converts-specificly analog scan converts
-SC first store (write) info & later display(read) it
Analog Numbrs -real world numbers
-infinite variations, continuous range of values ex. 134.29377 or 132.99023
Digital Numbrs -finite
-discrete values ex: 123 or 124
Bistable
Analog Scan Convertr
-1st type of SC
-made gray scale imaging possible
-spatial reso. excellent-image quality
Limitations 1. images fade
2. image flicker
3. instability
4. deteroration
Advtgs
Digital Scan Converter
- digitizing: uses computer tech to convert images into numbers
-images stored on comp as series of 1’s & 0’s
- 2 parts: 1. pixel
2. bit
1. Uniformity
2. Stability
3. Durability
4. Speed
5. Accuracy
11
Digital Scan
Converter
-picture elemnt
1. Pixel
-smallest building block of a digital pic
-an entire pixel is a single shade of gray
Number of pixels per inch
Pixel
-Higher
pixel density-smaller pixels, so more pixels required
Density
-spatial reso.↑ improvs w/higher pixl densty & creates image w/ greater detail
-Low pixel density-large pixels so less pixels required
-spatial reso ↓degrades, causing less detailed image
-smallest
amount of computer memory
Higher pixel density-smaller pixels, so more pixels required
2. Bit
-a bit is bistable, having value of either 0 or 1
-spatial reso.↑ improves w/higher pixl densty & creates image
-w/ ↑increasing bits assigned to pixel, the ↑ more shades of gray will appear
w/ greater detail
-images w/ ↑many shades of gray will have ↑better contrast reso.
-Low pixel density-large pixels so less pixels required
-spatial reso ↓degrades, causing less detailed image
group
of
8
bits
which
is
256
shades
of
grey
w/
↑increasing
bits assigned to pixel, the ↑more shades of
Byte
- word consist of 16 bits or two bytes
gray will appear
-imags w/ ↑many shades of gray will have ↑better contrast
reso.
-binary
#
is
a
group
of
bitsa
series
of
0’s
or
1’s
Binary
-digital or computer based numbers are binary
Digit
Flow
Velocity
Volume flow rate
Units of volume divided by time
Distance divided by time
Liters/min
Cm/s
12
13
14
Attenuation
Weak of Amp & Int as sound pass thru tissue dB
- dB quantify/measures Attenuation
-↑Intnsifes bfr &after Atten happn
-Conversion sound to heat
-source of bioeffects
-main cause to attenua in sft tsue
Attenuation Coefficient Rate which sound attented per unit Depth
-X change w/ Depth
- 3 dB half
- 6 dB quadruple
- 10 dB 90 %/one tenth
- Coeff. x Depth x Frequency
Absorption
Total
Attenuation
Totl amount sound-dB- attend given depth
- 2 factors to Determine Total Att:
1- Rate & 2- Path Lngth-dstnc to rflctr
- Direct to 1. distance sound beam travels
2.Trnsdcr frequency
Intensities & ratio of 2 Powers
-dB dscrbe rlnship btwn diff measurd sound levls
Direct to Frequency
-↑F trnsd X penetrate as well ↓Frequncy trnsd
dB/cm - Att Co (dB/cm) = Frequency
2
dB
-US: .7 dB soft tissue
Totl Attn=Path Lngth x Att Co
dB
cm
dB/cm
Direct to Path Length (distance to reflector)
Half Intnsity Depth/ HID Depth whch sound lost ½ / -3 dB of itsIntnsy
Half Value Layer Thickns
Attenuation Coefficient
-Rate at which sound is attenuated ↓ per depth
dB/cm AC = Frequency (Mhz)
Direct to Frquency
-Attention Coeff. = one half, 1/2 frqncy in soft tissue
2
Total Attenuation
Total amount of sound, in dB, attenuted at given depth dB
TA=Path lngth(cm) x Atten Co (dB/cm)
Half Intensity Depth HID
-Attenuation occurs w/ each cm sound wave travels
cm
Soft tissue: HID is = 6
Inverse to Frquncy
Half Layer Thickness Attenu
-term describ depth which sound lost half/3dB of Intnsity
f
Attn in Sft Tissu w/ Trsd Measurmt - .7 dB/cm/MHz (some say btwn .5 - 1.0 dB/cm/MHz
HID = 6/f
Reflection
Interface
Reflectors
Specular Reflection
Non-Specular Rflctr
Sw hits a boundary & reflected back in certain direction
Dividing line betwn 2 media
In medium referred to- specular or non-specular
Sound impinges upon large, smooth reflctr at 90⁰ angle
Boundary
Back scatter
1. Size < wavelngth of Incidnt beam eg:tissue parnchyma Scatter allows Imagng prnchyma ↑frq trdcr, ↑Int scatter that’s y size reducd
2. X angle dependent
3. Scatter sound in many different directions
Back Scatter
Some of the ↑ makes it back to transducer
Inty backsctter way ↓than In specular rflctrs
Acoustic SpeckleWen sound strikes # of scatters, scatter waves interactInterference pattrn
construct & destruct, & send results back to trnsdcr
Rayleigh Scatters -Extremely small reflectors ex: RBC
Direct to Frequency
-Scatter sound equally in all directions-omnidirectional
Speckle Reduction Manufactur activatd algorithms to smooth out appearnce of speckle & create smoother appearing image
15
Scattering
ONLY wen sw hits small,rough surfcs or heterogns cell tissu Disorganized & chaotic
Scatterers
Rough boundaries or cells which cause scattering
Specular Reflectors
Non- Specular Reflectors
1. Sound impinges upon large, smooth reflector at 90⁰ angle
2. Large Specular reflector-size of reflector > than wavelength
Eg: diaphragm, capsules of organs, & wall of aorta
Border larger than incident of wavelength
3. Angle dependent (Highly dependent)
-Best 2D images come from striking images perpendicular to interface
4. if at oblique angle, x return to transducer
1. Sound impinges upon rough surface
2. Size < wavelength of incident of beam
Eg: tissue parenchyma
Border smaller than incident of wavelength
3. Not angle dependent; scatter sound in many different directions
-Scatter permits imaging parenchyma
Impednce Resistance to Propagation of sound thru a medium
Z
- 2 Factors: Density & Stiffness
Rayls Impdnce Z Rayls = Density(Kg²/m³) x Prop speed (m/s) Direct to Density-P
Prop Speed C
- US: 1,630,000 Rayls avg for soft tissue
Reflction Made w/ 2 factors:
1. Normal incdnce/orthogonal/perpndclr/R angle/90⁰
2. Two media have different impedances
Normal - X change Impedance = X change Reflection = All sound
Incidence transmt thru tissu same direct trvld & rflctd back to source
Oblique -Sound strikes interface at non-perpendicular angle
Incidence -2 types Oblique angles: Acute <90⁰ & Obtuse > 90⁰
-Angle of Reflection=Angle of Incidence
* Only if (C) Prop Speed Identical
Direct to Prop Speed C
Angle of Reflection = Angle of Incidence
-Sound reflctd X return to trnsdcr & X pic on display
Intensity
-Intensity of sound reflected at interface 1. ITC= 1 – IRC
Direct to: Impedance
2
Transmission 2 Factors:
Reflection
2. ITC=Transmtted Intnsty (W/cm ) x 100
2
1. Intensity of transmitted sound
Coefficient
(%) Incident Intensity (W/cm )
* -↑Impdance mismatch, ↑Strong Reflction
2. Diffrnce in impedances btwn 2 medias 3. ITC % = -It x 100
-ITC(% of sound trnsmtd at interface)= 1- IRC (% rflctd @
I
-%
of
sound
transmtd
at
interface
Interfce)
i
ITC
-fraction of Ii transmttd in 2nd medium
Intensity
Reflection
Coefficient
IRC
It
Ir
Ii
Transmitted Intensity
Intensity Reflected
Incident Intensity
100 % Ii
Transmission Dependent on 2:
Angle
1. Incident Angle
2. Media Propagation Speeds- C
4. 100 % = ITC + IRC
1. IRC= Z 2 – Z 1 ² x 100
Z2 + Z 1
2. IRC = Reflected Intensity (mW/cm2)
Incident Intensity (mW/cm2)
3. 100 % = IRC + ITC
*How much sound was trnsmted at intrfce?
-ITC (% of sound trnsmtd at interfce)=1 - IRC (% rflctd @
Interfce)
-IRC + ITC must = 100 %
Ii =Rflctd Intnsity + Transmitted Intnsty
100 % Ii =IRC % + ITC %
-If prop speed thru 2nd medm >1st medm, then
Transmissn Angle > Incidnt
16 Angle
nd
st
-Vice Versa: C thru 2 medm < 1 medm, then
Transmission Angle < Incident Angle
Refraction
Snell’s Law
Ot
Oi
-Redirection of transmtd sound beam
-change direction of sound wen crosses boundary
- causes lateral position artifact
-2 requiremnts: 1- Oblique incidence
2- diff. prop. speed on either side of boundary
-ONLY wen prop speed x match p.s. of 2nd medum
-so Angle of Transmssn < Angle of Incdnce
-If prop speed of 2nd medium > 1st medium
Angle of Transmssn > Angle of Incidence
Angle of Transmssn at Interface based on:
1. Angle of Incidence
2. Prop. speed of the 2 media
-ONLY when C 1 x match C of 2nd medm
-Angle of Transmssn < Angle of Incidence
-C of 2nd medium > 1st medium
Angle of Transmssn > Angle of Incidence
1) Sine(Transmsn angle)=speed of mdm 2
Sine(Incident angle) =speed of mdm 1
2) sinOt = sinOi x C2
C1
Angle of Reflection
Angle of Incidence
Reflection vs. Refraction
Reflection
Refraction
1. Normal / Perpendicular Incidence
1. Oblique Incidence
2. Impedance Mismatch
2. Propagation Speed-C Mismatch
3. % or Intensity of Sound reflected & transmitted at an interface 3. Angle of transmitted sound
Resonating Frquncy/ - > 1 piozo elements attached to wire transducer
Center Operating
Frequency
RF in PW
Depth / Range
Ambiguity
- Applying electricity to element causes it to resonate- expand & contract
-Frequency & Rate at which material resonates depends on 2:
1. Thickness of piezoelectric element
2. prop. speed-c of element itself
-Thickness of elemnt primary determinant of RF of transdcr
-resonating elements produces a pressure wave
-wave consist of alternatng waves of ↑ & ↓ pressure –compress & rarefacts
-US- RF 2-15 MHz
-unique US piozo. Elements: send & receive us but X at same time.
Machine must time how long takes pulse reach rflctr to disply anatm on monitr
Trnsdcr sends pulse bfr receiving last one, unable to recognize where echo
originated & X display received echo correctly on monitor
-Sono X change resonating freqny of piozo. Elemnt
PW-Operating frequency = prop speed C
Direct to Thickness of element of RF of trnsdcr
Thicker element ↓ lower frequency
Thinner element ↑higher frequency
17
2 methods send out scan lines to form real images using real time& sweeping us beam thru tissue repeatedly and rapidly
Mechanical Scanning
Via mechanical transdcs
Electronical Scanning
Electronical trnsdcrs- used tdy
Mechanical Transducer -adv. was inexpensive
-obsolete
-broke easily
-fixed frequency & focus, otherwise needed to change entire scan head
- > 1 PZT connected to motor/fixed elemnt connected to motor
- > 1 PZT steered elemnt to produce scan lines to make image
- produced sector image pattern
-pioz. elemnt & motor inside protective housing
-oil used as coupling medium to prevent air btwn housing & focus beam
-beam-change shape of elemnt or use of lens
-performed w/ arrays
Electronic Scanning
-system can selectively excite elements as needed to shape & steer beam
Multiple active elements: Elements in straight or curved lines & produce various shaped images.
Arrays
1. Sequencing
2. Phasing
-straight line of rectangular elements shape image
Linear Sequenced/
1. cerbrovasculr
-elemnts
arrangd
in
line,
nxt
to
each
other,
but
fired
in
small
groups
in
sequence
by
voltage
pulses
Sequential/ Linear
2. peripheral arterial
-voltage pulses to groups of elements in succession
Array
3. peripheral venous
-each elemnt is 1 wavelength wide
-↑ high resolution imaging
-NOT need beam steering to produce rectangle image
-however, beam steering CAN be electronically steered for Doppler or Vector
-electronically focused
-similar to linear except:
Convex Sequenced/
1. Abdominal
pulses travel out in diff. directions from diff. points across curved surface
2. Deeper structure scanning
Curved/ Curvilinear/
-curved line of elements
Curved Sequential Array -fired in groups
-uses phased focusing
-parallelogram shaped display
Vector Array
-phasing could be applied to each elemnt group in linear array to:
1. Steer pulses in various directions
2. Initiate pulses at various starting points across the way
-Vector trnsdcrs ARE sector trnsdcrs in which scan lines X have common point of origin
18
Phased Array
Phasing
Beam
Steering
-Small footprint
- referred to face of trnsdcr
-permits steering & focusing us beam
-shape of face of trnsdcr X resemble shape of image.
-2 shapes- either trnsdcr makes sector pie shape image or vector flat top trapezoid image
-Sector: - all scan lines originate from common point of origin
- electronic steering needed for every scan line
-phasing is changing the timing of shocking of elements to shape & steer beam
-phased focusing for trnsdcr provides song. ability to control depth of focal zone in scan plane
-order in which elements shocked determines beam steering & focusing
-Order in which elements shocked 2 determining factors:
1. Beam steering
2. Focusing
-by adjusting timing of excitation of indiv. PZT crystals, wavefront of US energy can be directed
-Fundamental feature of 2D
-Phasing applied to arrays to steer beam by sending out several pulses from each group w/ diff phasing
Variable Aperture
-NOT all elements of Phased array used to generate all pulses
-Smaller groups used for Short, Focal lengths
-Larger groups used for FOCI- located at ↑ depths
-to maintain same beam width at focus, for ↑ focal lengths, ↑ aperture must too
Electronic Focusing -Phased array can also focus beam
-Greater curvature places focus closer to trnsdcr
-Lesser curvature moves focus deeper
Used for:
1. Neonatal
2. Cardiac
3. Transcranial
4. Abdominal
5. some Endocavity trnsdcrs
Direct to: -Beam steering
-Focusing
Direct to Focal length
Direct to
- > curvature -focus closer to trnsdcr
- < “
- focus moves deeper
Dynamic
Aperture
-w/ Array trnsdcr, as focus continues to change during echo receptin,
aperture ↑ to maintain constant focal width
Virtual Beam
Focusing
-uses 3 types of beams to
Yield images that r in focus throughout:
Inverse to1. weak or
↓section thickness ↑elevatnl, laterl & axial reso.
2. non-focused
3. computed reception “beams”
-↑enhancs reception focus so echo of image precisely locatd retrospectvly(on reflectn)
VBF
Direct to: Array trnsdcr-Focus continus change during echo reception
- ↑ aperture to maintain constant focal width
Direct to enhancmnt reception focus
19
Near/ Fresnel Zone/
Near Field
Near Zone Length
NZL
Far/ Fraunhofer/
Zone
Far Field
Focusing
-Region of trnsdcr face to focal point
-“ extending from trnsdcr to minimum beam width
- ↓ beam width ↑ distance from trnsdcr
-Determined by 2:
1. Size &
of elements or groups of elemnts
2. Operating frequency
-Effect on NZL:
1. actual diameter of elemnt
2. frequency of trnsdcr
-Focusing ONLY in Near Zone
-after length of focal point reached, beam begins to diverge & spread
-Region distal to focal point
-“ beyond a distance of 1 NZL
-↑ beam width ↑ distance from trsndcr
-Spreading of beam & Far Zone Detrimental to lateral reso.-Divergnce
Beam Width
-↑ Resoltn
-NEAR Zone ONLY
-Sound may be focused by:
1. curved trnsdcr elements
2. using a lens
3. phased arrays
-Limits 3:
1. wavelength,
2. aperture, (size of source)
3. focal length
-↓ in NEAR Zone & FOCAL Zone WIDENs in Far Zone
Focal Length
-Dstnce from trnsdcr to center of focal region
Inverse to ↓ beam width ↑ distance from trnsdcr
Direct to -Frequency
-Aperture(↑ size of elemnt)
Direct to -beam width
- distance from trsndcr
Direct to Reso.
-NEAR Zone ONLY
Inverse to 1. wavelength
2. Aperture (size of source)
3. Focal length
↓ - NEAR Zone
- FOCAL Zone
WIDENs Far Zone
20
Spatial
Resolution
-ability of a system to distinguish btwn closely spaced objects
-“Spatial”- space
-Spatial reso. -relates to quality of detail of the image
-divid. in 4:
1. Axial
2. Lateral
3. Elevational
4. Contrast
relates to Instrument
5. Temporal
1. Axial
-Longtdnl/Axial/Radial/Range/Depth
Resolution -minimum distance 2 reflectors
-parallel to beam
LARRD
-appear on screen as 2 dots
-minimum reflectr separation required along direction sound travls
to produce separate echoes
-SPL determines system’s axial reso.
-Shorter pulse length better axial resol. for system
-system ↓ length of pulse by 2:
1. ↓ # cycles per pulse or
2. ↓ wavelength
- ↓ # of cycles per pulse by ↑ damping material
-↓ wavelength by ↑ frequency
-↑ frequency does 2:
1. shortens pulse &
2. Improvs axial resol.- that’s why
↑higher Frqncy trnsdcr have better axial resol.
than ↓ low frqncy trnsdcrs
--Axial reso.= one half (1/2) SPL
- Smaller numerical value, the better AXIAL reso
(.2 mm better than .4mm axial reso)
-if provided SPL, need to ÷ by 2 to get axial reso.
-most trnsdcrs have Better axial reso. than lateral reso
1.
Axial Reso. (mm) = SPL (mm)
2
2.
Axial Reso (mm) = # Cycles x Wavelength
2
3.
Axial Reso (mm) = # Cycles x Prop speed (C)
2f
4. Soft tissue
Axial Reso (mm) = 0.77 x # Cycles in Pulse
Frequency (MHz)
Direct to
1. SPL
2. wavlngth
3. # cycles
4. # cycls in pulse
5. Prop. speed -C
6. Soft tissue .77
Inverse to
1. Frequency
21
Spatial Resolution
2. Lateral Resolution -Lateral/Angular/Trvs/Azinuthal
-Minimum reflctr separation direction
LATA
-direction Perpendicular to beam direction
-produces 2 separate echoes
-best when numerical value smaller (.2mm better than .4 mm)
-Latrl reso. =
1. beam width &
2. reflectors
that perpendicular to it
-Diameter of Beam determind by 2: (both)
1. Frequency
2. Aperture (diameter of elemnt itself)
-Beam takes shape of Hourglass
-as beam leaves trnsdcr & travels into patint,
diameter of beam varies w/ distance
-Beam begins to narrow immediately wen leaving trnsdcr
-Focal point- narrowest point
-Focal zone placed at or below area of interest to obtain best LATA
-Best LATA- at Focal zone
-Poor ” -occurs wen reflectr appears wider than should be
-Detrimental to LATA: (b/c Narrow beam width desired to improve LATA)
1. Divergence- spreading of beam &
2. Far Zone
Near Focal Zone
-as beam propagates, diameter changes so LATA varies w/ depth
-Effect on NFZ & on amount of divergence in far field:
1. Both- Aperture-actual diameter of elemnt &
2. Frequency of trnsdcr
-if trnsdcr and freqncy X change, but ↑larger aperture utilized ↑Longer NZL w/ ↓ less divergence in far field
-same relat. for Identical aperture size but diff frequency
For given aperture, ↓ lower Frqncy , ↓ shorter NZL w/ ↑ divergnce in far field
↑ Frqncy, ↑Longer NZL w/ ↓ less divergence in far field
Natural Focal Zone
-unfocused trnsdcr have NFZ
-unfocused single elemnt characteristics of trnsdcr
Unfocused trnsdcr
-at face of trnsdcr, beam of diameter = elemnt of diamtr
-distnce of one Near zone length,
beam diameter = 0ne ½ diameter of elemt
-at distance of 2 Near zone lengths, beam diamter = elemnt diametr
Direct to beam Width
Reflectors
Focal Zone
Inverse to Divergence
Far zone
Direct to Aperture
Frequncy
22
Spatial Resolution
3. Elevational Resolution -Slice & Section Thickness Plane/ Elevational Plane means 3rd dimension of beam
-Section thickness/elevational reso. considered 3rd elemnt of detail reso.
-2 Contributions to section thickness artifact: 1. Thinner the section, ↓less neg effect on son image
2. ↓ reduced w/ acoustic lens
-sono. image is 2D representation of 3D objects
-image on US monitor:
-Flat, but US beam has thickness
-Compressed version of any object w/in US beam
-Thinnest plane must be optimizd for most diagn.
-Thinnest plane achieved by focusing-Focusing
is Fixed
Mechanical trnsdcr
-X change regardless of depth
-Focused w/ lens in slice thickness plane
Electronic trnsdcr -Trsndcr w/ latest tech
-Electronically focused
-Elevational plane referred to as 1.5D trnsdcr
-Automatically change slice thickness wen focal zone changed by operator
4. Temporal/Time -represents time by frame rate
-Hz
Resolution
-TF = time to make a frame
-Frames per
1. # of images (frames) per sec
sec
Influenced by:
2. 4 things Influenced by: 1a. depth of image
2b. width of image
3c. # of focal zones
4d. use of Color Doppler
- 2 factors Focal Zone created by: 1. phasing &
Focal Zone
2. 1 FZ per line
created by
-if > 1 FZ desired, xtra pulse per scan line
- For each focal zone required,
4 things Tempral Reso/Frame Rate affected by:
1. Depth/PRF
2. # of scan lines per frame
Temporal Reso/
Frame Rate affectd 3. line density
4. # of focal zones
by:
- 3 things Pulse required for: 1- each focus on
2- each scan line
3- in each frame
Pulse required for: -2 effcts Longer takes frame to be displayed, the
1. ↓ Lower frame rate
2. Worse resolution
-↑ Depth, pulse travl longer in body
Takes longer to send out new pulse
1.
Tf x Fr = 1
Direct to PRF
2.
Inverse to Density
Maxim
77,000
Frame = Pentratn X Lines per frame X # focus
Rate
3.
VPS × TR
23
US Image Quality Depends on:
1. FOV-field of view
Parameters
2. N- # of scan lines per page
3. LD-line density-spacing btwn lines
- ↑ LD, Worse the Temp. reso.
4. Penetrating depth
5. Frame rate image
-preserving Frame rate involves tradeoffs:
-Changing a/t w/ above parameters will affect Frame Rate Unless s/t else changed to counter effect
-ex: if ↓ depth, ↑ Frqncy
-ex: if ↑ depth, to preserve Frqncy, either ↑ or ↓: 1. line density
2. field of view
Trnsdcr
Care & Maintence
-place in proper holder
-X dangle over machine
-hanging trnsdcr puts undue stress on cord & may damage wires inside
-Dropout-wen cord/probe damaged, may appear on screen as dropout-vertical gray line
Bioeffects
-heat created as US travels:
I= P
↑ perfusion to tissue bed &the Faster heat the heat will dissipate,
A
↓ potential damage from Temp. Intensity
-Power: initial amount of power in beam divided by area of beam
-Intensity: amount of power in beam divided by area of beam
-ALARA: As Low As Reasonably Achievable
-use lowest power for shortest amount of time
-Thermal
-Production of heat
-Cavitation
-Creation of bubbles
-Mechanical Index (MI) -likelihood of mechanical bioeffects occurring
-Thermal Index (TI)
-likelihood of injury due to heat
-used to assess thermal bioeffects: 1. Spatial Peak &
2. Temp. avergr Intensity SATA
Invasive Trnsdcr
-enter body via bv, esophagus, vagina, rectum
Direct to -Freqncy
-allows ↑ higher Freqncy
-Resolution
- ↑Improves resolution
24
Grating Lobes
-addtnl ↓ weaker beams resulting from multi elemnt array trnsdcr
-Apodization-can ↓ by driving elemnts in group non-uniformly
-Subdicing of each elemnt into group of small crystals weakens grating lobes
-Duplicate structures lateral to true ones
-Normally X produce displayed echoes
Artifacts
-4 occurs in sono. as apparent structurs either that: 1. Not real
2. Missing
3. Misplaced
4. Incorrect Brightness, Shape, or Size
Assumptions
-Sound travels in straight line
of
-Echoes originate only from objects located on beam axis
US System
-Amplitude of returning echoes related directly to
Reflecting/Scattering properties of distant objects
-Distance to Reflecting/Scattering objects is proportional to round trip travel time
Slice Thickness
-is 3rd dimension
-Beam width perpendicular to scan plane
-Resolve by using Tissue harmonic imaging
-Speckle -Granular appearance of image
-Result of interference of echoes from distribution of scatters in tissue
-Echoes can combine constructively or destructvly
Reverberation
-Equally spaced reflections of
↓ diminishing amplitude w/
↑ imaging depth
-Multiple reflections occur b/c > 2 strong reflectors are encountered in sound path
- form of reverberation common around pleura & diaphragm
Mirror Image
-Duplication of structure on opposite side of strong reflector
-Duplication of vessel or Doppler shift on opposite side of strong reflector
-Mirror vessel will demonstrate color/spectral flow
Speed Error
-Occurs wen speed of sound in soft tissue faster/slower than assumed 1.54 mm/µs
-Slower speeds place echoes deeper
-Faster speeds place echoes closer to trnsdcr
25
Shadowing
Enhancement
Aliasing
Nyquist Limit
Flash Artifact
-Weakening of echoes
1. distal to strongly attenuting or rflcting structure
2. from edges of refracting structre
Strengthing of echoes distal to weakly attenuating structure
-↑ brightness behind ↓weakly attenuating structure
-under sampling of Doppler shift in Pulsed Doppler system
-appearance of Doppler info: spectrol/color on wrong side of baseline
-Equal to one half PRF
-minimum # samples required to avoid aliasing
-sudden burst of color Doppler
-caused by motion of tissue/trnsdcr
-demonstrates extension of color beyond region of blood flow
NL= PRF
2
Range -all echoes X received bfr next pulse emitted
Ambiguity -places structure much closer to surface than shud be
-pulse emitted bfr all echoes from previous pulse received
-Result will be multiple sample volumes
Range
-Distance from trnsdcr to echo generating structure
-US: Range 2-20 MHz, 50 MHz Opthaml, Derma, & Intramuscular
-Position properly: 1. Direction echo came from
2. Distnce to rflctr/scatterer where echo prodced
-Distance = ½ prop. speed(C) X pulse round trip (T)
1.(mm) (mm/µs)
(µs)
Range
(mm)
(mm/µs)
(µs)
Depth = 1.54 X go-return time
Equation
2
-Distance(d) = distance from sound source to reflector- 1 way
2
.(µs)
(cm)
-Prop. speed(c) = prop speed of sound in soft tissue
PRP = Image Depth X 13 µs/cm
-Pulse round trip(t) =total trip time from sound source to rflctr & back
-takes 13 s for sound to travel to depth of 1 cm & return
3.PRF = 77,000 cm/s
-Sft tissue: Round trip time is 13 µs/cm-13 microsec for each cm of depth=.77 t (Hz) Imaging Depth (cm)
↑ F ↑ Reso. ↓ max image
depth
26
Resonating Frequency/
Center Operating
Frequency
RF in PW
Depth/Range
Ambiguity
- > 1 piozo elements attached to wire transducer
-Sono X change resonating frequency of piozo. Elemnt
- Applying electricity to element causes it to resonateexpand & contract
-Frequency & Rate at which material resonates depends on 2:
1. Thickness of piezoelectric element
2. prop. speed-c of element itself
-Thickness of elemnt primary determinant of RF of transdcr
-resonating elements produces a pressure wave
-wave consists of alternating waves of ↑ & ↓ pressure –
compressions & rarefactions
-US- RF 2-15 MHz
-unique US piozo. Elements: send & receive us but X at same time.
Machine must time how long takes pulse reach reflector to display
anatom on monitor
Transducer sends pulse bfr receiving last one, unable to recognize
where echo originated & X display received echo correctly on monitor
PW
-Operating frequency = prop speed C
Direct to Thickness of element of RF of transdcr
Thicker element ↓ lower frequency
Thinner element ↑higher frequency
Operating Freqency of Operating F = prop. speed C of elem.,
Trnsducer for PW
÷ by Thickness of elemnt, mult. by 2
PZT
Matching layer
Used to step ↓ Impednce from element to patient skin
Hydrophone/
Microprobe
Damping
Fo =
C in PZT (mm/ µs)
(MHz) 2 x PZT Thickness(mm)
PZT = ½ wavelength
Matching Layer = ¼ wavelength
Direct to Thickness of PZT
Prop speed- C of PZT
-device, needle, broad disk
measure output Intensity, PRP, PD & Period T trns path’s beam
-both measure output Intensity, PRP, PD & Period T trns path’s beam Other Parameters: Frequency, Wavlngth, SPL, PRF & DF
Vibrations of crystal dampened by special backing material
Transducer
Huygens Principal
-Surface of transdcr made up of many tiny point sources of sound
-each tiny point on trnsdcr produces a wavelet
-all wavelets undergo constructive or destructive interference
-end result is propogating sw whose direction of travel is Perpendicular to wavefront-line tangential to all wavelets
Waves r result of interference of many wavelets produced at face of transdcr
Compound Wave
Resonating Frequency
Changed by Sonographer
x
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Transdcr & electrcty -US trnsdcr converts electric energy into us energy & vice versa
-electrical connection to us machine via wire
-modern scan heads > 100 indivdl trandcr elements;each supplied w/ electrical energy via wire
-wire also transmits received echo amplitude info to machine for processing
-Flexible sheath connector- at this point-wire connects to trsnd
-Imp of Flex. Sheath connector: allows flexibility of cord & prevent damage to wire where conncts to transdcr
Diagnostic US
- use electricity to generate image
-US machine produces 10 - 500 V to driveTransducer
pioze. elements
Assembly
-if
crack
in
trsnsdcr
housing,
risk
for
electric
shock
for
sono./patient
Transducer Part
Purpose
Formula
-trnsdcr insulated-protect images from outside electrical interference/shock
Backing Material
Shortens pulse length by ↓ # cycles in pulse
Crystal
Material that produces diagnostic US
- PZT
Composed of piezoelectric material- most common lead zirconate titanate PZT = ½ wavelength
- Transmission
Converts electrical energy→ acoustic energy
- Reception
Converts acoustic energy →electrical energy
Matching Layer
Used to step ↓ Impedance from element to patient skin
Matching Layer = ¼ wavelength
Wire
Used to transfer electrical signals to & from transdcr
↑ Impedance ↑ stronger Reflection
Matching Layer -located btwn pioz. elemnt & patient skin
-referred to as single layer, but has 5 layers
- step ↓ Impedance from element to patient skin
-impednce from pioz. very different than human skin
-if X matching layer: 80% reflected back
20% trnsmttd to patient
Coupling Medium/ - Additional layer by sonographer
- 2 specially gel formatted for: 1. remove air btwn trsndcr & patient
Gel
2. Impdnce value to enhance trnsdcr sound
Backing Material/
-back of trnsdcr behind elemnt
-↑ Damping ↓ shorter pulse
Backing/ Damping
-aim is get best axial resolution to get optimal diagn. Image
↑ wider bandwidth
-Fx: provide damping-piozlmnt shortens length of pulse by ↓ # of cycles in pulse -Inverse to pulse length
-made of epoxyresin loaded w/ tungsten
-Direct to bandwidth
Backing Material for PW
Advantages
Side Effects-X disadvnt.- 2-3 cycles good to improve image quality
1. Short pulses best for PW, so a/t that will ↓ pulse length SPL 1. ↓ sensitivity (ability to detect echoes)
2. Improves axial resolution
2. produces wide range frequencies
3. ↓ # of cycles in a pulse to 2-3 cycles per pulse.
3. bandwidth in beam (result of wide range frequencies) ↑ bandwidth
4. less pure, ↓ quality factor
Summary of Effects of Damping on PW
↑ Damping = ↓ SPL = ↑ Bandwidth = ↓ Q Factor = Better Axial Resolution
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Quality/Q Factor -Quantitate purity of beam
-q in Q factor is quality but NOT referring to resolution
Referring to purity of beam
-operating frequency of trnsdcr ÷ by bandwidth
- “How near to actual operating frequency is bandwidth”
PW
-low Q factors b/c need damping to make pulse short
CW
-high Q factors
-narrow bandwidth-result of x backing material
Quality factor = operating main frequency
Bandwidth
-Direct to Frequency
-Inverse to Bandwidth
Bandwidth relationships btwn pulse duration, length and BW
↑ pulse length bandwidth bcms narrower = ↓ resolution
To Improve resolution, use SPL
Real Time/ Automatic -Modern US, instant viewing internal structures
Scanning
-real-time, transdcr sends out scan lines across defined planes
-images produces wen us beam swept across that plane
Frame
-All scan lines form image called frame in rapid sequential format wen placed nxt to each other
-Complete scan of us beam is frame
Sound Beam
-Width of pulse travels away from trasndcr
-Transdcr produces sound beam w/ a width that varies according to trnsdcr face
-Width in scan plane NOT same as width perpendicular to scan plane
-Width perpendicular to scan plane determines extent of section thickness artifact
-Intensity NOT uniform thru beam
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