UltrasoundUltrasound

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Contents

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What is Ultrasound?

Ultra-sound

20 Hz ~ 20 kHz 20 kHz

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What is Ultrasound?

2 ~ 18 MHz7~18 MHz: - 7~18 MHz: (, , )

- 1~6 MHz: (, )( )

: Ultrasonography Sonography : Ultrasonography, Sonography ()

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: (Mechanical wave): (Mechanical wave):

- -

- (t ) (transverse wave)- ()

- ex. , /(longitudinal wave)

- - (), (P)

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Newton-Laplace equation

v: velocity B: bulk modulus (kg/m-sec2); coeffi. of stiffness( g ): density (kg/m3); V: volumeP: pressure

Bulk modulus: measures the substance's i t t if i

P: pressure

resistance to uniform compression

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Air (20oC): 343.2 m/sec Liquid: ~1484 m/sec (~4.3) Iron: 5120 m/sec (~15)( )

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: 1540 m/sec10

: 1540 m/sec

- -

(Reflection) (R f ti ) (Refraction)

(Scattering) (Attenuation)

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!!12

Reflection

(characteristic acoustic impedance) : kg/(m2sec), Raylg ( ), y

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Reflection/Transmission coefficientsReflection/Transmission coefficients

Reflection coefficient

Transmission coefficient Transmission coefficient

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and and

30 dB (PZT)

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decibel (dB)

Power quantities:q

Amplitude quantities:

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decibel (dB)

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!!

=> 18

Refraction

Reflection coefficientIncident Reflection

i r

Transmission coefficientinterface

Z1= 1C1

Transmission coefficientt

C > C

interface Z2= 2C2

Snells LawRefractionC2 > C1

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Scattering

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Sound velocity Sound velocity

v: sound velocityv: sound velocity: wavelengthf: frequency

f: frequency

- V=330 m/sec- f= 2 MHz- = 0.165 mm

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Ultrasound

Frequency (MHz) Period (us) Wavelength (mm)

1 1.00 1.542.25 0.44 0.68

2.50 0.29 0.445.50 0.20 0.31

7.50 0.13 0.21

10.00 0.10 0.15

=1540 m/secQuestion: US , ?

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Ultrasonic scattering in bio-tissues , (scatterers)

100 m (red cell: 5 m)- 100 m (red cell: 5 m)- 5 MHz Ultrasound =?

R l i h iRayleigh scattering23

Ultrasonic scattering in bio-tissues

- Linear summation of all scattering- Coherent interference of scatterers

-

-

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: Speckle

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Speckle noise

(speckle)-

(Multiplicative noise) (Multiplicative noise)

- : ~ 4.34 dB

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Attenuation

:()- ()

- Att ti ffi i t ( ) Attenuation coefficient ()- Attenuation (of intensity) in soft tissue ~ 0.3-0.5 dB/cm-MHz

- ex. What is the maximal depth for a 5 MHz UStransducer with 60dB dynamic range?

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Attenuation

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Attenuation

What is the maximal depth for a 5 MHz UStransducer with 60dB dynamic range?

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Contents

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Pulser

DisplayReceived

Signal Processing

T/R switch

TransducerProcessing switch

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Pulser

TransducerT/R switchswitch

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(probe, transducer)- (piezoelectric) (p )-

Lead zirconate titanates ( PZT)- Lead zirconate-titanates (, PZT) => =>

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Transmitting Receiving

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Resonance in Piezoelectric materials

- Fundamental resonance frequency (f0)

- 0 = v/f0 = 2dT

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Resonance freq enc of transd cerResonance frequency of transducer

Question:Wh t i th thi kWhat is the thickness of the PZT layer in a 10-MHz ultrasound transducer? (sound speed in PZT = 4000 m/sec))

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Matching layer

: Matching layer:g y

- -

-

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Pulser

T/R switch

TransducerReceived

Signal Processing switch

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Processing

Acoustic Impedance () M t i l A ti I d S d l itMaterial Acoustic Impedance

(MRayl)Sound velocity

(m/sec) 1.48 1484 1.65 1550

1.62 1550 6 550 1.34 1450

1.65 1570

1.63 1560

6.0 3360 6.0 3360

17.0 6420

0 0004 343

0.0004 343

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Speed of Sound in Various Tissues15%

p

10%

5%5%

Assumed speed of sound = 1540 m/s

0%

-5%

-10%

DisplayReceived

Signal ProcessingProcessing

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Amplitude (A) mode Brightness (B) modeBrightness (B) mode Motion (M) mode

C l D l Color Doppler:

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A Mode

= - Pulse echo imagingg g

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A mode ultrasound

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A mode ultrasound: brain midline

: brain midline ()

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B Mode

-

=>

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B mode ultrasound

A-mode

B-mode

A-mode

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B mode ultrasound

2D shape and reflectivity of object: Mechanical scanning

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Mechanical scanning

B mode ultrasound

Pulse repetition period (PRP): p p ( )

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B mode ultrasound

Pulse repetition period Range of depth Given matrix size of a B-mode imageg

- frame rate

PRP

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B mode image formation

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B Mode

= 2 x / - 40 cm: ~ 0.5 msec- : ~ 1/24 sec (~ 40 msec)

real time imaging real-time imaging

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Real-Time Imaging

Interactive ()

- : - :

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B mode ultrasound

llbl dd ? Li ? Kid ?: gallbladder? Liver? Kidney?58

B mode ultrasound

: Liver

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B mode ultrasound

Mild plaque & calcification

Intravascular ultrasonic imageIntravascular ultrasonic image60

M Mode

+ -

- : +

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Time-motion ultrasound: mitral valve3 di i d3 cardiac periods

relatively static

moving

relatively static

MV: mitral valve; IVS: interventricular septum;MV: mitral valve; IVS: interventricular septum; LV: left ventricle; LA: left atrium

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M mode ultrasound

www.medical.philips.com63M mode

: Echo display mode

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Color Doppler Ultrasound

- ()-

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Doppler Effect

66: , source

Doppler Ultrasound

- : - :

-

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Doppler Ultrasound

: (/): (/)68

3D ultrasound imaging B-mode

- Not real-time 2D-array transducer

Real time- Real-time-

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- ( bl )- (portable)

- -

- - (, HIFU)

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- bone

( ( ))- gas (lung, pancreas (due to gastrointestinal tract ))- body habitus influence image quality: obese patient- operator-dependent

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: () :

:

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HIFUHIFU

Wh t i HIFU? Hi h I t it F d Ult d What is HIFU? High Intensity Focused Ultrasound

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HIFU transducer (lateral view)

2 cmHIFU transducer

0.5 cm

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MR guided HIFU: g4-spots experiment: porcine muscle

A B

DC

:B=>D=>A=>C

D

US: 40W CW; Heating duration: 45 sec/spot

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Reduction of speckle noise Harmonic imaging Tissue functions Tissue functions Therapy (HIFU) Drug delivery

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