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K thut v thit b siu(Ultrasound diagnostics)
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K thut siu m (Ultrasounddiagnostics)
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OutlineI. Physical properties of ultrasound and acoustic parameters of mediumII. Ultrasonography (Chn on hnh nh bng siu m)
Impulse reflection method
A-mode one-dimensional B-mode two-dimensional M-mode Basic characteristics of US images Interventional sonography Echocontrast agents Harmonic imaging
Principle of 3D imagingIII. Doppler flow measurement
Principle of Doppler effect Principle of blood flow measurement CW Doppler system Systems with pulsed wave PW Doppler Duplex and Triplex methods
Power Doppler method Tissue Doppler Imaging (TDI)
Ultrasonic densitometryIV. Advantages Patient Safety: reducing Ultrasound Doses
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History Ultrasound has been used as a navigational and detection aid by the
bat for millions of years. It was not until the second world war, however,that man started extensive use of ultrasound for the same purpose.With the enormous potential of military research programs, ultrasoundtechnology rapidly developed.
Although ultrasound had already been used in the therapy (cha bnh)and was proposed by S.Y. Sokolov for diagnostic use (mc ch iutr) in 1937, no successful attempt to apply the ultrasound echo-sounder principle to medical diagnosis was made until the early 1950s.
Most of the equipment used at that time were industrial-type ultrasounddevices for detecting flows in metal, but soon ultrasonic devicesgenerally known as ultrasonoscopes specifically intended for medicaldiagnostics were developed. The major advantages of these devicesare the non-invasive and non-ionizing nature of the examination andtheir relatively low cost when compared to X-Ray, MagneticResonance (MR), CT and Isotopic Scanning techniques.
Over the last decade, the diagnostic usefulness of the equipment hasbeen vastly improved, as better instruments were developed and moreclinical experience gained, and in several diagnostic fields, ultrasoundtechnique has shown to be superior to other methods.
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Siemens P10 handheldultrasound machine
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Contrast media sensitivities in imagingonly nuclear imaging has the sensitivity
10-5MRS
10-5MRI
10-9 - 10-12PET
10-9 - 10-12Nuc Med
10-3CT
10-3Sono
Contrast media concentration(mol/kg BW)
Imaging method
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Ultrasound diagnostics
K thut chun on siu m (ultrasound diagnostics) c pht trin u
nhng nm 50 ca th k 20. K thut cho phpthu c cc nh ct lp
(cross-sectional images) ca c th con ngi vi ccthng tin v sinh l
(physiology) v bnh l (pathology).
Nguyn l chung: da trnhin tngphn x (reflection) ca sng siu
m ti c c b mt tip gipm hc (acoustical interfaces)
Mt s ni dung k thut chnh v siu m:
Ultrasonography (A, B and M mode, 3D and 4D imaging)
Doppler flow measurement, including Duplex and Triplex methods
(Duplex, Colour, Triplex, Power)
Tissue Doppler imaging
Ultrasound densitometry
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I. Physical properties (cc tnh cht Vt l) casng siu m
Questions: what is ultrasound and what are the main acousticalproperties of medium ?
Sound is a periodic disturbance (vibrations) that in fluids density,propagates as longitudinal waves (Mechanical vibration or wave).
Ultrasound is sound with a frequency over 20,000 Hz, which isabout the upper limit of human hearing.
Obeys the same physical laws as wave.
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Basic Principles of Sound
Sound is produced by a vibrating body and travels in the form
of a wave.
Sound waves travel through materials by vibrating the
particles that make up
the material.
The pitch ( cao/mc )of the sound is determined
by the frequency of the wave
(vibrations or cyclescompleted in a certain
period of time).
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Sound spectra
Diagnostic
Imaging
0 20 Hz 20 kHz 1 MHz 30 MHz
Infrared Audible NDTSound Sound Cleaning
Sng sium(US) l cc daong c hc (mechanical oscillations)vi tn s > 20 kHz lan truyn trong mt mi t rng n hi (elasticmedium). For medical diagnosis, typically ranging from 1 to 30 MHz.
Trong c ht lng v kh, US lan truyn nh mt sng dc
(longitudinal waves). Trong cht rn, US lan truyn nh mt sngngang (transversal waves).
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In medical US, images representing human organs (b phn c th) areformed by transmitting sound waves into the body and receiving back and
processing the resultant echoes from the tissues.
To accomplish this, medical ultrasound uses a process very similar to anocean-going vessels depth sounding equipment or oceanic surveyequipment. All of these systems make use of sound waves and their
reflections.
Sea
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Several wave modes ofvibration are used in
ultrasonic inspection.
The most common arelongitudinal, shear, and
Rayleigh (surface)
waves
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Ultrasound generation
High frequency ultrasound is generated with a transducer.
The transducer is capable of bothtransmitting and receiving soundenergy.
A piezoelectric element in thetransducer converts electricalenergy into mechanicalvibrations (sound), and viceversa.
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Tng tc ca US vi m (tissue) Phn x (reflection): xy r a vi c c mt phn cch ngnht, nhn, c
kch thc > b rng chm tia (smooth homogeneous interfaces of sizegreater than beam width), VD: cc phn t hu c (organ outlines)
Tn x Rayleigh (Rayleigh scatter): xy r a vi cc kchthc phn hi mnh (small reflector sizes), VD cc t bo mu trongmt mi t rng khngngnht.
Khc x (refraction): xy r a vi cc mi trng khng cht, c (lessdense to denser medium), khc vi nh sng ikhi to r a s bin dng(distortion)
Hp th (absorption) (sng m chuyn thnh nhit - sound to heat) Hin tng tngtheo tn s f, ngc vi t ia X Hp th mnh trong phi (lungs), gim dn trong xng (bone) v cc
m mm (soft tissue), ngc vi t ia X.
Giao thoa (interference): Cc vn hoa (speckles) trn nhUS l do sgiao thoa gia cc sng tn x Rayleigh.
Nhiu x (diffraction)
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Reflection
Medium 1 Medium 2
Transmitted waveIncident wave
Reflected wave
- One of the basic principles of medical ultrasound diagnosis.
- Occurs at areas of acoustic impedance mismatch.
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Refraction
Medium 1
Medium 2
i ncident wave Ref lected wave
Transmitted wave
When a propagating ultrasoundwave encounters a interface at anoblique angle, it is Refracted inthe same way that light is refractedthrough a lens. The portion of the
wave that is not reflectedcontinues into the second medium.It is dependent on the velocities ofthe two medium. If the velocitiesare equal, There would be no
refraction occurred and the beamgoes straight into the secondmedium. For the velocities ofthe different tissues in the human
body are quite close, refraction'scan be ignored.
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Diffraction
DiffractingObject
If an ultrasound beam passes
an obstacle within a distanceof 1 or 2 wavelengths, itsdirection of propagation is
deflected by diffraction asshown in the figure. Thecloser the beam is to the
diffracting object, the greaterthe deflection is.
1 or 2 wavelengths
Deflecting beam
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Scattering
Spherical Scatter-waveOccurs when small particlesabsorb part of the ultrasound
energy and re-radiate it in alldirections as a spherical field.This means that the transducer
can be positioned at any angleto the ultrasound beam and
still receive echoes back.Scattering allows reflectionsfrom objects even smaller than
the wavelength. Manybiological interfaces haveirregular surfaces, tending to
give scatter-like reflection,which is quite useful, as it will
give at least some echoes eventhough the beam is not directlyperpendicular to the reflectinginterface.
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Backscatter
Backscatter or Rayleigh scattering occurs
with structures smaller than the transmittedwavelength. Reflected energy is very low,but contributes to the texture of the image.
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CCCCcccc thngthngthngthng ssss ssssngngngng mmmm ((((acoustic parameters)))) ccccaaaamimimimi trtrtrtrngngngng
Tng tc ca USvi mi t rng phn x, tn xngc (back-scattering), khc
x, suy gim(attenuation: dotnx v hp th)
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Cc thng s sng m
Tc truyn sng (speed) of US cph thuc vo tnh n hi vmt (elasticity and density r) ca mi t rng. K- modulnn(modulus of compression).
- trong nc v m mm c= 1500 - 1600 m.s-1
- in bone c ~ 3600 m.s-1
Ph thuc c nhit (temperature) mi trng
Velocity (c) = Frequency (f) Wavelength ()
[ ]1. = smKc
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S suy gim (attenuation) of US th hin qua vic bin snggim dn trong qu trnh truyn (decrease of wave amplitudealong its trajectory). Suy gim ny ph thuc vo tn s:
Ix = Io e-2ax = .f2
Ix final intensity, Io initial intensity, 2x medium layer thickness
(reflected wave travels to and fro), - linear attenuation
coefficient (increases with frequency).
V: =log10(I0/IX)/2x
nn n v ca l dB/cm.
Ti f = 1 MHz = 1.2 vi c bp (muscle), 0.5 (gan - liver), 0.9 (no- brain), 2.5 (connective tissue - m ni), 8.0 (xng - bone)
Cc thng s sng m
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Attenuation
Attenuation of ultrasound wave occurs when it is propagating
through the medium. Loss of propagating energy will be in the
form of heat absorbed by the tissue, approximately 1 dB/cm/MHz,
or caused by wavefront dispersion (s phn tn) or wavescattering.
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Cc thng s sng m
Attenuation ofAttenuation ofAttenuation ofAttenuation of
ultrasoundultrasoundultrasoundultrasound
When expressing intensity of
ultrasound in decibels, we can
see the amplitudes of echoes(ting vng) to decreaselinearly.
xk
I
Ix
I
Ie
I
Ixxxx ,
00
2
0
log2ln ===
depth[cm]
I or P
[dB]attenuation
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Acoustic impedance (tr khng): product of US speedcand medium density
Z = . c (Pa.s/m)
Z.10-6: muscles 1.7, liver 1.65, brain 1.56, bone 6.1,
water 1.48
Acoustic parameters of medium
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We suppose perpendicular incidence of US on an interface betweentwo media with different Z - a portion of waves will pass through and aportion will be reflected (the larger the difference in Z, the higherreflection).
Acoustic parameters of medium: USreflection and transmission on interfaces
P1 Z 2 - Z 1R = ------- = ---------------
P Z2 + Z1
P2 2 Z 1D = ------- = ---------------
P Z2 + Z1
Z
P P2
1P
Z1 2
Coefficient of reflection R ratio of acoustic pressures (p sut mthanh) of reflected and incident waves
Coefficient of transmission D ratio of acoustic pressures oftransmitted and incident waves
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Near field (Fresnel area) this part of US beam is cylindrical thereare big pressure differences in beam axis
Far field (Fraunhofer area) US beam is divergent (phn k, lchng) pressure distribution is more homogeneous
Increase of frequency of US or smaller probe diameter causeshortening of near field - divergence of far field increases
Acoustic parameters of medium: Near field andfar field (trng gn v xa)
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II. Ultrasonography (Chn on hnh nh bng siu m)
Passive US low intensity waves which cannot cause substantial
changes of medium.
In US diagnostics (ultrasonography = sonography = echography) -
frequencies used are 2 - 40 MHz with (temporal average, spatial peak)
intensity of about 1 kW/m2
Impulse reflection method (phn x xung in): a probe with one
transducer (b chuyn i) which is source (b pht sng US) as well
as detector (u thunhn tnhi u) of US impulses. A portion of emitted
(pht ra) US energy is reflectedon the acoustic interfaces and the
same probe then receives reflected signal. After processing, the signal
is displayed on a screen.
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Transducer
The transducer is the component which, when connected to
the ultrasound equipment, transmits the ultrasound andreceives its reflections or echoes from tissues.
Transducer is one of the most important component of theultrasound system. For more detail information, please referto System Components.
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Transducer is one of the most important component of the ultrasound system.The transducer is the component which, when connected to the ultrasound
equipment, transmits the ultrasound and receives its reflections or echoesfrom tissues.
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Matching Layer
Transducer
Crystal
Tissue
Impedance Matching
TransducerCase
-To transmit as much power as possible from transducer to the tissue.
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Ultrasonography
Impulse reflection method
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Ultrasonography
Impulse reflection method
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Ultrasonography
Impulse reflection method
Main parts of the US apparatus (thitb):
Common to diagnostics and therapy
probe with electroacoustic transducer
(transducers)generator of electric oscillations
(continuous, pulsed)
Special parts of diagnostic apparatus
electronic circuits for processing ofreflected signal
display unit
recording unit
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Ultrasonography
A-mode one-dimensional
Distances between reflecting interfaces and the probe are
shown (cho bit khong cch gia cc mt phn x tipgip)
Reflections from individual interfaces (boundaries of
media with different acoustic impedances) are representedby vertical deflections( lchng lch theophng tr c y) of base line, i.e. the echoes.
- Echo amplitude is proportional to the intensity of reflected
waves (amplitude modulation)
- Distance between echoes shown on the screen is
proportional to real distance between tissue interfaces.Today used mainly in ophthalmology (nhn khoa).
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Ultrasonography
A-mode one-dimensional
IH1
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Slide 48
IH1 olej se ji dvno nepouv, doporuuji opravit na gel filmIvo Hrazdira, 11/15/2008
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A tomogram (phng php chp ri) is depicted basedon the following principle:
- Brightness of points on the screen represents intensityof reflected US waves (brightness modulation).
- Static B-scan: a cross-section (ct ngang) image ofexamined area in the plane given by the beam axis anddirection of manualmovement (di chuyn bng tay) ofthe probe on body surface. The method was used in 50
and 60 of 20th century
Ultrasonography
B-mode two-dimensional
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Ultrasonography
B-mode two-dimensional - static
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Ultrasonography M-mode
One-dimensional static B-scan shows movement of reflecting
tissues. The second dimension is time in this method.
Static probe detects reflectionsfrom moving structures. The bright
pointsmove verticallyon the screen, horizontal shiftingof the record
is given by slow time-base.
Displayed curves represent movementof tissue structures
chest wallchest wallchest wallchest wall
((((llllngngngngngngngngcccc))))
LungsLungsLungsLungs((((phphphphiiii))))
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Ultrasonography
Comparison of A-, B- and M-mode principle
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Repetitive formation (s hnh thnh/sp xp lp li) ofB-mode images of examined area by fast deflection( lch nhanh) of US beam mechanically (in the past)or electronically in real time today.
Electronic probes consist of many piezoelectrictransducers which are gradually activated (s dngtng bc mt).
Ultrasonography
B-mode - dynamic
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Ultrasound probes for dynamic B-mode: electronic and
mechanical (history), sector (hnh qut) and linear (tuyn tnh).
Ultrasonography B-mode - dynamic
Abdominal cavity (khongt rng, l hngtrongbng) isoftenexamined byconvex probe (u d li) a combinationof a sector and linearprobe.
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Modern ultrasonography - digital processing of image
Analogue part detection system
Analogue-digital converters (ADC)
Digital processing of signal possibility ofprogramming (preprocessing, postprocesssing), image storage
(floppy discs, CD, flash cards etc.)
Ultrasonography B-mode - dynamic
MEMORY
MEMORY
MEMORY
MEMORY
samplingsamplingsamplingsampling
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Ultrasonography B-mode - dynamic
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Degree of reflectivity (mc phn x) echogenity( vng). The images of cystic (nang/u nang, liquid-filled)and solid structures are different. According to the intensityof reflection we can distinguish structures:
- hyperechogenic, izoechogenic, hypoechogenic,anechogenic.
Solid structures acoustic shadow (vng ti m)(caused by absorption and reflection of US)
Air bubbles and other strongly reflecting interfacescause repeating reflections (reverberation s di m,comet tail ui sao chi).
Ultrasonography
Basic characteristics of US images
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Acoustic shadow caused byabsorption and reflection of US
by a kidney stone (si thn,see the arrow)
Hyperechogenic area below acyst (nang/u nang) (lowattenuation of US duringpassage through the cystcompared with the surroundingtissues see the arrow)
Ultrasonography
Si thn
Nang thn
IH3
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Limitation! absorption of US increases with frequency ofultrasound = smaller penetration depth
Ultrasonography
Spatial (v khng gian)resolution of US imagingsystem is determined bythe wavelength of theUS. When the objectdimension is smaller thanthis wavelength only
scattering occurs.Hence higher spatialresolution requires higherfrequencies
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Higher frequency ultrasound gives better resolution, but attenuationin the tissue also increases with increased frequency. Therefore, acompromise has to be made between resolution andpenetration depth.
Compromise frequency3-5 MHz penetration in depth of about20 cm
Frequency Low High
Resolution Better
Penetration Better
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IH3 doplnny ipkyIvo Hrazdira, 11/15/2008
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Axial (theo trc) spatial resolution - it is given by the shortestdistance of two distinguishable structures lying in the beam axis
it depends mainly on frequency (at 3.5 MHz about 0.5 mm)
Lateral (bn/ bn) spatial resolution - it is given by the shortestdistance of two distinguishable structures perpendicularly to the
beam axis depends on the beam width Elevation (mt/mt chiu) resolution ability to distinguish two
planes (sections) lying behind or in front of the depicted tomographic(chp ri) plane it depends on frequency and beam geometry
Ultrasonography Spatial Resolution
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The best resolving power (kh nng phn gii caonht) can be found in the narrowest part (phn hpnht) of the US beam profile.
Focusing US beam is converged (hi t) at theexamined structure by means of acoustic lenses (shapesof the layer covering the transducer) or electronically.
The probes can be universal or specially designedfor different purposes with different focuses.
The position of focus can be changed in most sectorprobes.
Ultrasonography Spatial Resolution
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Typical acoustic lens with logarithmic profile
By changing the lens shape, the beam diameter and length of focal zonecan be controlled.
A transducer with an axially symmetric logarithmic acoustic lens will form anarrow axially symmetric weakly diverging US beam. A transducer with acylindrical logarithmic lens will create a "knife-like" ultrasonic beam: narrow
and weakly diverging in one direction but wide and uniform in theperpendicular direction. If the logarithmic surface of the lens is attached to the piezoelement and the
front (radiating) surface is flat the probe can be used as both an immersionand a contact transducer.
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Ultrasonography
Interventional sonography (chn on c can thip)
Interventional sonography is used mainly for guidingpunctures (chch/chch l):
- diagnostic (chn on) thin needle (kim tim)punctures to take tissue samples for histology (tin s cam)
- therapeutic (cha bnh) for aspiration (ht) of a cyst(nang) or an abscess (p-xe) content or an exudate (chtdch), etc.
Puncture can be done by free hand the probe is next tothe puncture site or the puncture needle is guided by aspecial probe attachment.
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UltrasonographyUltrasonographyUltrasonographyUltrasonography
Echocontrast agents (Cc cht tng tng phn)
- increase echogenity ( vng) of streaming blood, gasmicrobubbles(mainly air or volatile
hydrocarbons)
- free- enclosed inbiopolymer
envelope
A SEM micrograph ofencapsulatedechocontrast agent
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UltrasonographyUltrasonographyUltrasonographyUltrasonography
Echocontrast agents - application
Enhanced demarcation (ranh gii) of heart ventricle (tmtht) after application of the echocontrast agent
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An impulse (xung in) with basic frequencyf0 is emitted into the tissue. The receiver,however, does not detect the reflected USwith this same frequency but with the secondharmonic frequency 2f0. Its source is tissue
itself (advantage in patients ). The method isalso used with echocontrast agents sourceof the second harmonic are oscillatingbubbles. Advantageous when displayingblood supply of some lesions (vt thng).
Conventional (left) and
harmonic (right) images of akidney with a stone.
Ultrasonography
Harmonic imaging (to nh iu ha)
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- The probe is linearly shifted, tilted or rotated.The data about reflected signals in individual planes are stored inmemory of a powerful PC which consequently performs mathematicalreconstruction of the image.
- Disadvantages of some 3D imaging systems: relatively long timeneeded for mathematical processing, price.
Ultrasonography
Principle of three-dimensional (3D) imaging
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Four-dimensional (4D) imageThe fourth dimension is time
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III. Doppler flow measurement(o dngchy Doppler)
Hiu ng Doppler:- The Doppler effect: frequency shift of waves formed or reflected ata moving object.
- Application: can be used for detection and measurement of bloodflow, as well as, for detection and measurement of movements ofsome acoustical interfaces inside the body (foetal heart tim thai,blood vessel walls vch mch mu)
Christian. A. Doppler (1803-1853), Austrian physicistand mathematician, formulated his theory in 1842during his stay in Prague.
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perceived (nhn/thu c)frequency corresponds with
source frequency in rest (trngthi ngh)
perceived frequency is higher
when approaching (vt chuynng li gn ngun thu)
perceived frequency is lowerwhen moving away (di chuynra xa)
Doppler flow measurement
Principle of Doppler effect
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When something moves toward you, radiation emited from it has anapparently shorter wavelength, and for away moving, longerwavelength:
= change in wavelength
= wavelength
v= relative velocity (speed)
c= speed of radiation
(in this case, light)
Doppler flow measurement
Principle of Doppler effect
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Application of Doppler effect
in blood flow velocitymeasurement
Moving reflector (backscatterer) = erythrocytes
(erythrocyte)
Doppler flow measurement
Principle of Doppler effect
(hng cu)
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US Doppler blood flow-meters (my o lu lng mu):are based on the difference between the frequency ofultrasound (US) waves emitted by the probe and those
reflected (back-scattered) by moving erythrocytes.
The frequency of reflected waves is (in comparison withthe emitted waves):
- higher in forward blood flow (towards the probe)
- lower in back blood flow (away from the probe)
The difference between the frequencies of emitted andreflected US waves is proportional to blood flow velocity.
Doppler flow measurement
Principle of blood flow measurement
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Doppler flow measurement
General principle of blood flow measurement
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1) Calculation of Doppler frequency change fd2) Calculation of reflector (erythrocytes) velocity v
1) 2)
fv- frequency of emitted US waves
- angle made by axis of emitted US beam and the velocityvector of the reflector
c US speed in the given medium (about 1540 m/s in blood)
c
vff
vd
cos2 = cos2
= v
d
f
cf
v
Doppler flow measurement
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Dependence of velocityoverestimation on theincidence angle (if thedevice is adjusted fora = 0, i.e. cosa = 1)
a - angle made by axis of emitted
US beam and the velocity vector of
the reflector
Doppler flow measurement
Angle alpha
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1) Systems with continuous wave CW. They are used for measurement onsuperficial (trn b mt) blood vessels. High velocities of flow can bemeasured, but without depth resolution. Used only occasionally.
2) Systems with pulsed wave - PW. It is possible to measure blood flow withaccurate depth localisation (v trchnh xc). Measurement of high velocitiesin depths is limited.
Doppler flow measurement
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The probe has only one transducer which acts alternately asemitter and receiver.
The measurement of velocity and direction of blood flow in the
vessel is evaluated in the so-called sampling volume withadjustable size and depth.
The pulse duration defines the size of the sampling volume
(this volume should involve the whole diameter of the examinedblood vessel).
Doppler flow measurement
Systems with pulsed wave - PW
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Aliasing (s mo tn hiu) at high repetition frequencyof pulses the upper part of the spectral curve can appearin negative velocity range
- at velocity above 4m/s aliasing cannot be removed
NyquistNyquistNyquistNyquist limitlimitlimitlimit
Doppler methods
Pulse wave (PW) systems
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DUPLEX method
is a combination
of dynamic B-mode imaging (the morphology ofexamined area with blood vessels is depicted)
and the PW Doppler system (measurement of velocityspectrum of blood flow).
It allows to examine blood flow inside heart or in deep blood
vessels (flow velocity, direction and character)
Doppler methods
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Doppler methods
Scheme: sector imagewith sampling volume
DUPLEX method
Image of carotid (ng mch) withspectral analysis of blood flow velocity
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Doppler methods DUPLEX method
Placement of sampling volume (left) and the record of blood flow
velocity spectrum in stenotic (hp) a. carotis communis(ngmch/tnh mch chung) (right)
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Doppler methods
Colour Doppler imaging (nh Doppler mu)
Principle:- The image consists of black-white and colour part.- The black-white part contains information about reflectivityand structure of tissues.
- The colour part informs about movements in the examinedsection. (The colour is derived from average velocity of flow.)
The apparatus depicts distribution and direction of flowing bloodas a two-dimensional image:
- BART rule blue away, red towards. The flow away from theprobe is coded by blue colour, the flow towards the probe iscoded by red colour. The brightness is proportional to the velocity,
turbulences (s hn lon) are depicted by green patterns.
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Doppler methods
Colour Doppler imaging
Carotid bifurcation(chia/r nhnh ngmch)
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Doppler methods TRIPLEX method
A combination of duplex method (B-mode imaging withPW Doppler) and color flow mapping
Normal finding of blood flow in a. carotis communis(left) andabout 90%-stenosis (hp) of a. carotis interna(right)
IH6
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Doppler methods TRIPLEX method
stenosis
of
a. carotis
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Doppler methodsPOWER DOPPLER method
- the whole energy of the Doppler signal is utilised
- mere (phn/on) detection of blood flow only l ittle dependson the so-called Doppler incidence angle- imaging of even very slow flows (blood perfusion of tissuesand organs)- flow direction is not shown
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Slide 86
IH6 opravena chybn formulaceIvo Hrazdira, 11/19/2008
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Tissue Doppler Imaging (TDI)
Colour coding of information about velocity and direction of
movements of tissues
Velocities 1-10 mm/s
are depicted.
TDI of a. carotis
communisduringsystole (tm thu)
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Ultrasonic densitometry (o ttrng bng siu m)It is based on both the measurement of speed of ultrasound in bone
and the estimation of ultrasound attenuation in bone. In contrast to X-raymethods, ultrasound densitometry also provides information on thestructure of bone and its elastic properties:
The speed of ultrasound depends on the density and elasticity of the
measured medium. The anterior ( pha trc) area of the tibia (xngchy/xng ng chn) and the posterior ( pha sau) area of the
calcaneus (xng gt) are frequently used as places of measurement.The speed of ultrasound is given by the quotient of measured distanceand the transmission time.
Ultrasound attenuation depends on the physical properties of the givenmedium and the frequency of the ultrasound applied. For the frequencyrange 0.1 - 1 MHz the frequency dependence is nearly linear.
Attenuation is currently expressed in dB/MHz/cm.
Clinical importance: diagnostics of osteoporosis (chng long xng)
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Ultrasonic densitometry
Ultrasound measurements usedto assessbone density at the calcaneus
US advantages/disadvantages
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Advantages
By comparison with X-ray, CT, MR and other diagnostic methods,Ultrasound diagnosis, especially for soft tissues and moving organ
like heart and blood flow, has shown great advantages as following:
* Real Time Imaging (except MR)
* Non-invasive (except MR)
* Non-ionizing Radiation (except MR)
* Relatively Low Cost
* Wide Applications
* Mobility
* Flexible Imaging
* Biopsy (sinh thit)
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Limitations
Surface must be accessible to transmit ultrasound.
Skill and training is more extensive than with some other methods.
Normally requires a coupling medium to promote transfer of sound
energy into test specimen.
Materials that are rough, irregular in shape, very small, exceptionally
thin or not homogeneous are difficult to inspect. Cast iron and other coarse grained materials are difficult to inspect
due to low sound transmission and high signal noise.
Linear defects oriented parallel to the sound beam may go
undetected.
Reference standards are required for both equipment calibration,and characterization of flaws.
Patient Safety: reducing UltrasoundDoses
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Prudent use of Ultrasound
US is non-ionising BUT since many bioeffects ofultrasound have not yet been studied fully, prudent
(cn trng) use is recommended
ALARA as low as reasonably achievable (exposure)
In practice prudent = justification (cn chnh) +optimisation (ti u)
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Biological Effects
Possible bioeffects: inactivation of enzymes, altered (bin i) cellmorphology, internal haemorrhage (chy mu/xut huyt trong), freeradical formation
Mechanisms of bioeffects:
Mechanical effects
Displacement and acceleration of biomolecules
Gas bubble cavitation (to l hng) (stable and transient vnhvin v tm thi)
Elevated tissue temperatures (absorption of ultrasound andtherefore increase in temperature high in lungs, less in bone, leastin soft tissue)
All bioeffects are deterministic with a threshold (cavitation) or withoutit (heating).
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Output Power from Transducer
varies from one machine to another
Increases as one moves from real-time imaging tocolour flow Doppler
M-mode output intensity is low but dose to tissue ishigh because beam is stationary
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Risk Indicators
To avoid potentially dangerous exposures, two indices were
introduced: TI and MI. Their values (different for different organs)are often displayed on device screens and should not be
exceeded.
Thermal Index (TI): TI = possible tissue temperature rise if
transducer is kept stationary
TIS: soft tissue path
TIB: bone near focus of beam
TIC: Cranium (near surface bone)
Mechanical Index (MI): measure of possible mechanical bioeffects
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More on the TI and MI
Thermal index device power divided by the power that wouldincreased the temperature by one degree under conditions ofminimum heat loss (without perfusion).
Mechanical index (for assessment of cavitation-conditioned
risk, increased danger when using echocontrast agents):
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Justification
No commercial demos on human subjects
No training on students
No see baby just for fun or excessive screening inobstetrics
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Optimisation of Dose 1
Minimise TI and MI and use appropriate index (TIS, TIB,TIC), care in cases when these underestimate
Check acoustic power outputs on manual
Use high receiver gain when possible as opposed to hightransmit power
Start scan with low transmit power and increasegradually
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Optimisation of Dose 2
Avoid repeat scans and reduce exposure time
Do not hold transducer stationary
Greater care when using contrast agents as these increasethe possibility of cavitation
Exceptional care must be taken in applying pulsed Doppler inobstetrics
Regular quality control of the ultrasound device
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Other applications
Some of the applications for which ultrasonic testing may be
employed include:
Flaw detection (cracks, inclusions, porosity, etc.)
Erosion & corrosion thickness gauging
Assessment of bond integrity in adhesively joined and brazedcomponents
Estimation of void content in composites and plastics
Measurement of case hardening depth in steels
Estimation of grain size in metals
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Thickness Gauging
Ultrasonic thickness gauging isroutinely utilized in thepetrochemical and utilityindustries to determine variousdegrees of corrosion/erosion.
Applications includepiping systems,storage andcontainment facilities,and pressure vessels.
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Flaw Detection De-laminations
Contact, pulse-echo inspection for delaminations on 36rolled beam.
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Flaw Detection in Welds
One of the most widely usedmethods of inspecting
weldments is ultrasonic
inspection.
Full penetration groove welds
lend themselves readily toangle beam shear wave
examination.
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Applications: Equipment
Equipment for ultrasonic testing is very diversified. Proper
selection is important to insure accurate inspection data as
desired for specific applications.
In general, there are three basic components that comprisean ultrasonic test system:
- Instrumentation
- Transducers
- Calibration Standards
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Transducers
Transducers are manufactured in a variety of forms,shapes and sizes for varying applications.
Transducers are categorized in a number of ways whichinclude:
- Contact or immersion
- Single or dual element
- Normal or angle beam
In selecting a transducerfor a given application, itis important to choose thedesired frequency,
bandwidth, size, and in some cases focusingwhich optimizes the inspection capabilities.
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Instrumentation
D-meters or digital thicknessgauge instruments provide theuser with a digital (numeric)readout.
They are designed primarily for
corrosion/erosion inspectionapplications.
Some instruments provide the user with both a digital readout anda display of the signal. A distinct advantage of these units is thatthey allow the user to evaluate the signal to ensure that the digitalmeasurements are of the desired features.
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Flaw detectors are instruments
designed primarily for theinspection of components for
defects.
However, the signal can be
evaluated to obtain other
information such as materialthickness values.
Both analog and digital display.
Offer the user options of gating
horizontal sweep andamplitude threshold.