IntroAndUltraSound

BMEG 4330 : Tele-medicine & Mobile Healthcare

Introduction to Sound and Light

Waves

11

BMEG 4330: Sound & Light Waves in Medicine Prepared by E. MacPherson

Sound Waves

12 http://www.sciencedirect.com/science/article/pii/S0378595512002778

160 kHz =

0.16 MHz Ultrasound frequencies

used in imaging are

typically 1-10 MHz

http://www.sciencedirect.com/science/article/pii/S0378595512002778

BMEG 4330: Sound & Light Waves in Medicine Prof E MacPherson

Uses of sound waves in medicine

• Ultrasound imaging

– imaging of internal organs

– Image guided surgery

– Monitoring fetal development

– Blood flow (Doppler)

• Ultrasound therapy

– High-Intensity Focused Ultrasound (HIFU)

• precise high-intensity focused sonic energy applied to locally

heat and destroy diseased or damaged tissue through

ablation.

13

http://www.telegraph.co.uk/health/healthnews/9206425/New-treatment-for-

prostate-cancer-gives-perfect-results-for-nine-in-ten-men-research.html

http://www.telegraph.co.uk/health/healthnews/9206425/New-treatment-for-prostate-cancer-gives-perfect-results-for-nine-in-ten-men-research.html




























Uses of sound waves cont’d

• Lithotripsy

– physical destruction of hardened masses like

kidney stones or gallstones.

• Teeth cleaning

• Physiotherapy

– Increases blood flow

– Reduces swelling

– Massages muscles, tendons, ligaments and

softens scar tissue 14

http://www.youtube.com/watch?v=BoZo08WSbsQ

http://www.youtube.com/watch?v=BoZo08WSbsQ


15

Light Waves


Uses of Light waves in medicine

• X ray imaging

• Nuclear imaging (PET, SPECT)

• Optical imaging

• Terahertz imaging (in research)

• Photodynamic Therapy

• Laser surgery

16

http://lipas.uwasa.fi/~TAU/memos/AUTOaiv

o/Bslides.php?Mode=Printer

http://www.youtube.com/watch?v=GuT_XXyFPUI

http://lipas.uwasa.fi/~TAU/memos/AUTOaivo/Bslides.php?Mode=Printer

http://lipas.uwasa.fi/~TAU/memos/AUTOaivo/Bslides.php?Mode=Printer

http://www.youtube.com/watch?v=GuT_XXyFPUI


Schedule

17

Week

Mon 12:30-13:15

Wed 15:30-17:15

1 7 9 Sept Introduction

2 14 16 Sept Ultrasound-wave equation

3 21 23 Sept Ultrasound-transmitivity and reflectivity

4 28 30 Sept Ultrasound instrumentation

5 5 7 Oct Ultrasound therapeutics and revision

6 12 14 Oct Midterm test

7 19 21 Oct THz introduction

8 26 28 Oct terahertz imaging

9 2 4 Nov terahertz spectroscopy, project briefing

10 9 11 Nov U/S Demo

11 16 18 Nov THz lab tour, Laser treatments and surgery

12 23 25 Nov Photo dynamic therapy

13 30 2 Nov/Dec Revision lecture

14 1 3 Dec Project presentations

BMEG 4330 : Tele-medicine & Mobile Healthcare

Ultrasound Imaging

• Ultrasound wave theory

• Imaging techniques and examples

http://www.nlm.nih.gov/medlineplus/ency/imagepages/18056.htm

http://www.nlm.nih.gov/medlineplus/ency/imagepages/18056.htm


• Ultrasound waves are pressure waves

• Ultrasound imaging does not usually use higher frequencies than 10 MHz.

• Ultrasound has a wavelength of about 1.5 mm.

• Higher frequency ultrasound waves can form sharper images

• But higher frequency images are fainter

– Because higher frequency energy is absorbed more strongly

Pressure waves

Periodic motion causes pressure waves. In the

diagram a piston is attached to one end of a

spring. When the piston is shoved forward it

compresses one part of the spring. The

compression continues to travel through the

spring. As the piston moves back and forth, it

creates more compressions that travel down

the spring. The more quickly the piston moves

back and forth, the closer one compression is

to the next one.

http://www.physics247.com/physics-tutorial/ultrasound-physics.shtml

http://www.youtube.com/watch?v=711bZ_pLusQ

What you probably know so far …






http://www.youtube.com/watch?v=711bZ_pLusQ


The speed of Ultrasound

• The speed of ultrasound does not depend on its frequency – Speed depends on the material

• Ultrasound travels faster in dense materials and slower in compressible materials. – sound travels at around 1500 m/s in soft tissue, 3400 m/s in bone, and

330 m/s in air .

• Ultrasound is reflected at the boundaries between different materials. – Ultrasound reflects very well wherever soft tissue meets air, or soft

tissue meets bone, or where bone meets air.

• Frequency is unchanged as sound travels through various tissues. – This means that in tissues where sound travels more slowly, the

wavelength decreases. Traffic jam due to road works analogy.



Ultrasound Generation

http://science.howstuffworks.com/ultrasound2.htm

http://hopelifescan.com/physicsp2.htm

http://science.howstuffworks.com/ultrasound2.htm

http://hopelifescan.com/physicsp2.htm


Piezoelectric effect

http://www.pixelandlight.com/portfolio/animation.html

Converts mechanical

energy into electrical

energy and vice-versa

By applying pressure or mechanical stress on certain

natural non-symmetrical crystals an electric charge is

produced in direct proportion to the pressure.

If the same crystal is subjected to an electric field, the

crystals expand or contract in direct proportion to

the electric field. http://www.everythingcarwash.com/customkraft.html

http://www.youtube.com/watch?v=OG6kI65PAaw

http://www.pixelandlight.com/portfolio/animation.html

http://www.everythingcarwash.com/customkraft.html

http://www.youtube.com/watch?v=OG6kI65PAaw


Probe design • The shape of the probe determines its

field of view

• The frequency determines the depth of

penetration and resolution of the image.

• Transducer probes may contain one or

more crystal elements – in multiple-element probes, each crystal has its own circuit.

• Beam steering – Requires multiple-element probes

– important for cardiac ultrasound.

• Impedance matching – transducer face has a rubber coating. In addition, a water-

based gel is placed between the probe and the patient's

skin.

• Echoes – The sound wave is partially reflected from the interface

between different tissues and returns to the transducer. This

returns an echo. Sound that is scattered by very small

structures also produces echoes.

http://www.olympus-ims.com/en/ndt-tutorials/transducers/pa-

beam/steering/

http://www.olympus-ims.com/en/ndt-tutorials/transducers/pa-beam/steering/








Image formation • Receiving the echoes

– The return sound wave vibrates the transducer's elements and turns that

vibration into electrical pulses that are sent from the probe to ultrasound scanner

where they are processed and transformed into a digital image.

• Forming the image

– The ultrasound scanner must determine three things from each received

echo:

• The direction of the echo.

• How strong the echo was

– white for a strong echo, black for a weak echo, and varying shades of grey for

everything in between

• How long it took the echo to be received from when the sound was

transmitted.

– Used to calculate depth information

• From this information, the ultrasound scanner can locate which pixel

in the image to light up and to what intensity.


Echography

• Using ultrasound echoes to image blood

flow and the heart

25 http://www.genesis.net.au

http://www.genesis.net.au/~ajs/projects/medical_physics/ultrasound/index.html


Principles of Doppler Echocardiography

• Doppler effect – reminder??!

26


Doppler shift from blood cells • For any given transmitted ultrasound frequency, the

returned frequency will be:

– higher after encountering red blood cells moving toward the

transducer = POSITIVE Doppler shift; and

– lower after encountering red cells moving away from the

transducer = NEGATIVE Doppler Shift

27

Doppler Shift = Frequency received by transducer – Frequency transmitted by transducer


Advantages of Ultrasound • Safe

– Ultrasound imaging does not use ionizing radiation, non-invasive (no needles or

injections) and is usually painless.

– Ultrasound causes no health problems and may be repeated as often as is

necessary.

– Ultrasound is the preferred imaging modality for the diagnosis and monitoring of

pregnant women and their unborn infants.

• Good for soft tissue imaging

– gives a clear picture of that do not show up well on x-ray images.

• Real-time imaging

– a good tool for guiding minimally invasive procedures such as needle biopsies and

needle aspiration of fluid in joints or elsewhere.

• Widely available, easy-to-use and less expensive than other imaging

methods.


Quantitative vs Qualitative

• In previous BME courses ultrasound

imaging was mostly discussed qualitatively

– The only calculations we made were for

Doppler echoe-ography

• In BMEG 4330 we will be more

quantitative

– we will look at the equations used to model

ultrasound wave propagation

29


The wave equation

• Acoustic waves are pressure waves

– They propagate through matter via the compression

and expansion of the material

– Generated by compressing a small volume of material

and then releasing it

– The elastic properties cause the material to expand

beyond its equilibrium point and this causes

neighboring volumes to compress and thus the wave

propagates

30


Sound is a longitudinal wave

• Movement of particles is along the same direction as the direction of

wave propagation

• http://www.youtube.com/watch?v=4iIE1Rm__-E

31

http://www.youtube.com/watch?v=4iIE1Rm__-E





Wave parameters

32


Dependent variables

• Acoustic waves also depend on space

(position x,y,z) and time (t)

• Eg. A sudden bang – dies away quickly

and can only be heard within a certain

distance from the source.

33


Acoustic pressure

• The compression and expansion of small

volumes causes a local change in the

material’s pressure

• An acoustic wave can be described by a

spatially dependent and time varying

pressure function p(x,y,z,t) – called

acoustic pressure

34


Acoustic pressure, p

• For longitudinal waves: p = zv

– z is characteristic impedance z = ρc

– v is particle speed

• Particle speed ≠ speed of sound

– v ≠ c

35


Table of acoustic properties

36


The 3D Wave equation

37


Plane waves

38


General solution for plane waves

39

Forward wave Backward wave


Example

40


Spherical waves

41

http://www.youtube.com/watch?v=Z43AfidDbQs

http://www.youtube.com/watch?v=Z43AfidDbQs


General solution for spherical waves

42

Outward

travelling

wave

Inward travelling

wave

Does not exist in practice


Example

43


Acoustic Energy and Intensity

• Acoustic waves carry energy

– Kinetic Energy (from particles in motion)

– Potential Energy (from particles poised for

motion)

• For a wave we use energy density in

energy per unit volume

– KE density = ½ ρv2

– PE density = ½ κp2

– Total acoustic energy density = KE+PE 44


Acoustic intensity

• Captures the idea of a change in energy

that moves with the wave

• I = pv = p2/z (as v=p/z)

• Analogy to circuits – can you see it?!

45


Reflection and refraction at plane

interfaces

46

Material 1 Material 2

Normal line

θi

θt θr


Example

• A plane ultrasound wave is incident at 45o

on an interface between the fat and liver of

a patient.

– What is the angle of reflection?

– What is the angle of transmission?

cfat = 1450m/s, cliver= 1570m/s

47


Total internal reflection

48


Transmission and reflection

coefficients at plane interfaces

49


Derivation of the previous

coefficients • Uses the fact that velocity must be

continuous at the interface

• And pressure is continuous

50


Worked Example(s)

51


Attenuation

52


Phenomenological solution

53


Nepers

54


Frequency dependence of

absorption coefficient

55


Coefficient a for different tissues

56


Combining factors to calculate

reflection properties

Resulting reflected

amplitude is a product

of the reflection

coefficient and the

attenuation loss


Worked example

58


Resolution

59


Frequency vs penetration and

resolution

• Higher frequency

– Shorter wavelength

– More attenuation

– Less penetration

– Better axial and lateral

resolution

60

• Lower frequency

– Longer wavelength

– less attenuation

– greater penetration

– Lower axial and lateral

resolution


Ultrasound instrumentation

• How to control the frequency of ultrasound

generated

• How the ultrasound beam is focused

• How to steer the ultrasound beam

61


Instrumentation • Most medical ultrasound systems use

the same transducer for generation and

receiving of ultrasound

– “pulse-echo” mode

• The transducer is coupled to the body

using an acoustic gel

– The wave can then propagate to the

body to then be reflected off surfaces

and scatterers – part of this signal is

returned to the transducer

• The transducer converts the acoustic

wave sensed at its face into an electrical

signal

– This can be stored, amplified and

displayed


The transducer

• Uses piezoelectric crystals to

generate and receive U/S

• eg. Lead zirconate titanate (PZT)

• The crystals can be manufactured

in any shape

– Most commonly rectangular or

circular

63


Crystal properties

• Transmitting constant, d, is the strain

produced by a unit electric field:

– units m/V

• Receiving constant, g, is the potential

produced by a unit stress:

– units Vm/N or V/(N/m)

64

Material d m/V g V/(N/m)

PZT 300x10-12 2.5x10-2

Quartz 2.3x10-12 5.8x10-2

PVDF (PolyVinylidene

Fluoride)

15x10-12 14x10-2


Resonance

• Transducer crystals are resonant

– http://www.youtube.com/watch?v=10lWpHyN0Ok

• The resonant frequency fT depends on:

– The thickness of the crystal, dT

– The speed of sound in the crystal, cT

• fT =

• Hint. What is the effective wavelength for

constructive interference? 65

http://www.youtube.com/watch?v=10lWpHyN0Ok


Question

• What thickness of PZT crystal is needed to

make a transducer working at 10 MHz?

cT=8000m/s for PZT.

66


Ultrasound transducer and output

A large voltage is applied to the crystal for a short

duration to excite (shock) the crystal into

resonance.


Ultrasound Imaging modes • A (amplitude)- Mode

– Generates a one dimensional waveform (a point measurement so

not strictly an image). Can obtain detailed information about rapid or

subtle motion, eg of a heart valve

• B (brightness)-Mode

– Cross-sectional (2D) anatomical imaging (a line scan)

• C (computed) -Mode

– 3D constructed image – an array of B-Mode line scans

• M-Mode

– A succession of A-mode signals, brightness modulated and

displayed in time

• Doppler

– Uses the property of frequency or phase shift caused by moving

objects to generate images colour-coded by their motion


69


70


71

• http://www.slideshare.net/vaseemali/ultrasound-instrumentation-physics

– Good for:

– Equipment usage

– Time gain dispersion

http://www.slideshare.net/vaseemali/ultrasound-instrumentation-physics






Summary Video

• http://www.youtube.com/watch?v=aYq9QSEBcCc

– Good summary of u/s settings but quite slow!

72

http://www.youtube.com/watch?v=aYq9QSEBcCc


Beam pattern formation and focusing

• The spatial distribution

of the acoustic intensity

is called the field

pattern

• Simple field model

gives beamwidth, w(z):

– w(z)=D, in the near field

– w(z)=λz/D in the far field

• This approximation

ignores the “waist” in

the Fresnel region.

73

Near Field Far Field


Focusing • Most transducers are focused

to some extent

– By making the transducer crystal

in a curved shape

– By applying a lens to a flat

crystal

– By electronic focusing of crystals

arranged in arrays • http://www.olympus-ims.com/en/ultrasonics/intro-to-pa/

• A narrower beam gives better

spatial resolution • http://www.olympus-ims.com/en/ndt-tutorials/transducers/focusing/

74

http://www.olympus-ims.com/en/ultrasonics/intro-to-pa/







http://www.olympus-ims.com/en/ndt-tutorials/transducers/focusing/






Mechanical scanning

• For imaging the ultrasound beam must be steered

(scanned, swept)

• This is done mechanically or electronically

75

Mechanical designs –

a) Uses a rocking motion – travels

in one direction then the other

b) Always goes in the same

direction, but switches in a new

transducer element

Note the field of view is always pie-

shaped.


Electronic scanning • Transducers with multiple elements can be

electronically scanned to sweep the field of view.

• Each element is rectangular and is focused in

the longer dimension using a lens

• Two main arrangements:

– Linear array probe

– Phased array sector scanners

• Nice summary here: http://www.bercli.net/documentation/article_principles.htm

http://www.bercli.net/documentation/article_principles.htm


Phased array sector scanners

77

These next few slides

contain figures from the

course text book… we will go

through the details on the

board – bring paper!


Transmitting pulses


Beam steering

79










Question

80

A linear transducer array is operating in water (c=1484m/s). Adjacent

transducers are separated by d=0.8mm. A focal point at z=5cm on the

z axis is desired. If the outermost transducers fire at t=0, when does

the central transducer element fire?


Receiving pulses


Time gain compensation

• TGC

– increasing amplification of echoes from

increasing tissue depths. Used in ultrasound

to correct for increased attenuation of sound

with tissue depth.

• http://www.youtube.com/watch?v=t_721Q

wF9V8

82

http://www.youtube.com/watch?v=t_721QwF9V8



TGC

83 http://www.youtube.com/watch?v=t_721QwF9V8



Summary video

• Good overall summary video of how US

works

• http://www.youtube.com/watch?v=t_721QwF9V8

84



Therapeutic Ultrasound

• Tissue stimulation

• Fat reduction

• HIFU and MRI guided HIFU

85


Physiological effects of Ultrasound • Thermal effects of ultrasound

– increased blood flow, reduction in muscle spasm, increased

extensibility of collagen fibres and a pro‐inflammatory response.

– It is estimated that thermal effects occur with elevation of tissue

temperature to 40–45°C for at least 5 min

– Excessive thermal effects, seen in particular with higher

ultrasound intensities, may damage the tissue

86

http://www.youtube.com/watc

h?v=fmFUwe7AqBQ

http://www.youtube.com/watch?v=fmFUwe7AqBQ

http://www.youtube.com/watch?v=fmFUwe7AqBQ


Ultrasound therapy for babies

• Ultrasound helps the neck muscle to heal

87

http://kidshealth.org/parent/medical/bones/torticollis.html


Non‐thermal effects of ultrasound

• Cavitation and acoustic microstreaming,

– more important in the treatment of soft tissue lesions than thermal

effects

• Cavitation occurs when gas‐filled bubbles expand and compress

because of ultrasonically induced pressure changes in tissue fluids,

with a resulting increase in flow in the surrounding fluid

– Stable (regular) cavitation

• beneficial to injured tissue, sustained at lower intensities

– unstable (transient) cavitation

• causes tissue damage, sustained at higher intensities

• Acoustic microstreaming, is the unidirectional movement of fluids

along cell membranes,

• occurs as a result of the mechanical pressure changes within the ultrasound field.

• Microstreaming may alter cell membrane structure, function and permeability, which has

been suggested to stimulate tissue repair

88


Cavitation example

• http://www.youtube.com/watch?v=iceEuakmdNo

89

http://www.youtube.com/watch?v=iceEuakmdNo


Applications • Drug delivery

– Delivering chemotherapy to brain cancer cells and various drugs to other tissues

is called acoustic targeted drug delivery (ATDD). These procedures generally

use high frequency ultrasound (1-10 MHz) and a range of intensities (0-20

watts/cm2).

– The acoustic energy is focused on the tissue of interest to agitate its matrix and

make it more permeable for therapeutic drugs. (ATDD).

– High intensities can disrupt the blood-brain barrier for drug delivery

• Cleaning teeth in dental hygiene.

• Low intensity pulsed ultrasound is used for therapeutic tooth and

bone regeneration.

• Focused ultrasound sources may be used for cataract treatment by

phacoemulsification.

90


Applications cont’d • Ultrasound-assisted lipectomy. Liposuction can also be assisted by

ultrasound.

• Focused high-energy ultrasound pulses can be used in a process

known as lithotripsy to break calculi such as

– kidney stones, gallstones, tumours, fibroids

• Alternatively, ultrasound may be used for its thermal effects to

relieve pain and muscle spasm to increase tissue extensibility

– Use in combination with stretching exercises to achieve optimal tissue length

– Once the tissue has been heated to an adequate level (considered to be 40–

45°C), the opportunity to stretch the tissues lasts for up to 10 min before the

tissue cools 91

http://www.youtube.com/watch?

v=544oDmiWq-E

http://www.youtube.com/watch?v=544oDmiWq-E





Hi Intensity Focused Ultrasound (HIFU) • In this procedure, generally

lower frequencies than

medical diagnostic

ultrasound are used (250–

2000 kHz), but significantly

higher time-averaged

intensities.

• The treatment is often guided

by magnetic resonance

imaging (MRI)—this is called

''Magnetic resonance-guided

focused ultrasound''

(MRgFUS).

• Analogy to light 92

http://www.internationalhifu.com/what-is-hifu/how-it-

works.html

http://www.youtube.com/watch?v=XFw7U7V1Hok

http://www.youtube.com/watch?v=jrje73EyKag

http://www.internationalhifu.com/what-is-hifu/how-it-works.html














Wave focusing geometry for HIFU

93

http://bjr.birjournals.org/content/76/909/590.full

http://bjr.birjournals.org/content/76/909/590.full


MRI guided HIFU • ultrasound waves are focused into

a small area of between 4–16mm,

– produces heat and energy, which kills

the tumor cells.

• MRI guiding

– localizes the area for ablation as well

as monitors the temperature.

• Advantages over other treatments

– no surgery, no radiation, no scar, no

anesthesia, quicker recovery, more

precise image guided treatment and

less traumatic.

94

http://www.youtube.com/watch?v=3FOy6YaTMPY

http://www.youtube.com/watch?v=3FOy6YaTMPY


HIFU for prostate cancer

• HIFU treats prostate cancer. It is a therapy that destroys tissue with rapid

heat elevation, which essentially "cooks" the tissue. Ultrasound energy, or

sound waves, is focused at a specific location and at that "focal point" the

temperature raises to 90 degrees Celsius in a matter of seconds.

95

http://www.youtube.com/

watch?v=EkDquVhW-rk

Uses Ultrasound only during the procedure

http://www.youtube.com/watch?v=EkDquVhW-rk





Summary

• Ultrasound can be used at different

frequencies and powers for therapeutic

purposes

• Thermal and non thermal effects can

change tissue properties to benefit the

patient

• HIFU can be used for tumour ablation and

can be guided by MRI or ultrasound

96

IntroAndUltraSound

Documents

macpherson ultrasound

sound light waves

light waves bmeg

macpherson sound waves

ultrasound frequencies

ultrasound instrumentation

ultrasound therapeutics

ultrasoundwave equation