2nd sound in medici2 جدي

8/2/2019 2nd sound in medici2

1/70

Sound in MedicineChapter 12

Introduction

Definitions

Physics of ear and hearing

General properties of a Sound

Reflection and transmission of sound waves

Inverse square relationship

Speed of Sound Characteristic of sound waves

The body as a drum (Percussion in Medicine)

Stethoscope

Ultrasound Pictures of the Body Diagram of the outer, middle and inner ear

Blood velocity determination by ultrasound Production of speech (phonation)

The Acoustic Buzzer.

References:1- Medical Physics textbook by Cameron

2- Physics in Biology and Medicine, Third Edition by Paul Davidovits

3- Physics of the Human Body, by Irving P. Herman


2/70

Introduction

Sense of hearing involves: (1) Mechanical system to stimulate the hair cells in th

cochlea (real hearing organ); (2) Sensors that produce the action potentials in

the auditory nerves and (3) The auditory cortex, the part of brain that decodes

and interprets the signals from the auditory nerves. Deafness or hearing loss

results if any of these parts malfunction. Ear is designed to convert very weak

waves in air into electrical pulses in the auditory nerve. Ear is divided into three

areas: outer, middle and inner ear. Physics of sound waves is called acoustics,

because speaking is creating sound and hearing is detecting sound. Acoustics is

in gases, liquids, and solids. A scientistwaves, mechanicalsoundthe study of

who works in the field of acoustics is an acoustician. The medical specialists

concerned with the function, diseases of the ear and hearing are called

Otologist.

is a periodic disturbance that travels in space, It is periodic in time, which meansWave

that at any given position the disturbance is periodic with time t.


3/70

These applications range from the use of the stethoscope (study heart valve

motion) to the use of the modern ultrasonic techniques.

Sound is a mechanical disturbance that propagates as a longitudinal wave

through solid, liquid or gas. The molecules of the conducting liquid move

back and forth producing bands of compression and rarefaction. Each

repetition of this back and forth motion is called cycle, and eachcycle

produce a new wave. The length of the wave is the distance between two

bands of compression and rarefaction.

:There are two types of waves

1) Longitudinal are the waves in which the particles of the medium oscillate

(change in pressure) in the same direction of the wave propagation.

2) Transverse are the waves in which the particles of the medium oscillate

in a direction perpendicular to the direction of the wave propagation.


4/70

Longitudinal Waves

The animation below shows a one-dimensional longitudinal plane wave

propagating down a tube. The particles simply oscillate back and forth about theirindividual equilibrium positions. The wave is seen as the motion of the compressed

region (it is a pressure wave), which moves from left to right.

Transverse Waves

The animation below shows a one-dimensional transverse plane wave propagating

from left to right. The particles simply oscillate up and down about their individual

equilibrium positions as the wave passes by. If you pluck a string, the wave propagates

along the string, but the actual disturbance of the string is perpendicular to it.

L R

Direction of the wave propagation


5/70

These pressure and density variations are in phase with each other, meaning that theyboth increase (compression) or decrease (rarefaction) from the ambient values together.

disturb air around andis generated by a vibrating object. The vibrationswaveA soundcause local increases and decreases in pressure relative to atmospheric pressure, whichcause alternating compressions (regions of crowding) and rarefactions (regions of

scarcity) in the particles of the medium.

compression rarefaction

Sound wave is travelling in this direction

Vibratingobject


6/70

Compression and rarefaction can be described by density changes and by

displacement of the atoms and molecules from their equilibrium positions.

Sound is really tiny fluctuations of air pressure thats why it is considered

as a pressure wave. The audible range of hearing in young people iswithin 20 to 20000 Hz (20 KHz). However, relatively few people can hear

over this entire range. Older people often lose the ability to hear the

frequencies above 10 KHz.

=Compression =Rarefaction

Figure shows the pressure relative to atmospheric pressure versus distance. P is the maximumpressure varied from atmospheric, -P is the minimum pressure and is the wavelength of thesound wave

(Air pressure)

(x)

) (

crest

trough

Maximum

Minimum

Normal

Amplitude


7/70

Sound pollution or noise of undesirable levels is a growing problem in modern

society. Federal regulations now limit the permissible noise levels caused by

cars and trucks on the highways.

Typical limits of noise are 70 decibels (dB) for areas adjacent to highways and

55 (dB) for inside work areas. Noises (unwanted sounds) which are about 175

(dB) can kill.

[Decibel (dB) is the common unit of sound pressure or intensity].Safety organizations recommend that exposure to sound levels above 85 dB

SPL are considered harmful, those above the pain threshold of sound pressure

level (SPL) are unsafe, and those above 150 dB SPL cause physical damage to

the human body.

The sensitivity of the ear is remarkable due to the mechanical construction of

the ear, which amplifies the sound pressure. At the threshold of hearing, in the

range of 2000-3000 Hz, the ear can detect a sound intensity of 1016 W/cm2.


8/70

The frequency range above 20 (KHz) is called ultrasound. Ultrasound is a

form of energy transmitted in beams and can be used to scan different

organs of the body successfully in a number of specialties. It is used by

obstetricians to examine the unborn child. It often gives more information

than x-ray, and it is less hazardous for the fetus.

Infrasoundrefers to sound frequencies below the normal hearing range or less

than 20 (Hz). It is produced by natural phenomena like earthquake waves

and atmospheric pressure changes. It can also be produced mechanically.

Frequencies of about 10 (Hz) cannot be heard but, they can cause

headaches and physiological disturbances.


9/70

Sound is a form of energy produced and trasmitted by vibrating matter, it travels

outward from the source with definite velocity. Sound waves travels more

quickly through solid than liquids or gases since, solid atoms are hooked up by

springs (bonds).

Loudness, pitch, andqualityare some of the terms we use to describe the

sounds we hear.

Tuning fork

Sound (change in pressure) waves


10/70

Definitions:

(L): Energy passing through the unit area during the secondLoudness-1

[Watt/m2]. Loudness is determined by the amount of pressure produced by a

wave, it is measured in Bell, dB orphon. [Decibels measure the ratio of a given

intensity (I) to the threshold of hearing intensity (Io)]. Loudness of sound wave

depends on the pressure.

L = log (I/Io) = 2 log (P/Po) Bell = 2 log (P/Po) x 10 dB = 20 log (P/Po) dB

(P & Po are two compressions and 1 bel = 10 dB)I is referenced to Io = 10

12 W/m2; Io is a sound intensity that is barely audible at 3,000 Hz

Bel Is the scale of sound waves that has been developed for comparing

the intensities of two sound waves and to measure the intensity level of

the sound waves. = Pitch


11/70

[cycles/second = cps]. It isNumber of cycles per second:Frequency (f)-2

measured in Hertz (Hz= s-1). Frequency is determined by how often the

compressions and rarefactions take place. It determines the pitch of a

sound. The sensation of pitch is related to the frequency of the sound.

Pitch increases with frequency.

where/f1, and period is equal toTime duration of one wave cycle:Period-3

f is expressed in cycles/sec, hence the unit of period is second.

Is a measure of how fast an object is rotating:)Angular frequency (-4

perradiansis measured in/dt. It= df2) =((spinning) around its axis

) since radians are unitless.1with units (s,second2f=

( is the angle of rotationon the circular axis)


12/70

5-

Is the tissue thickness need to decrease the:value thickness (HVT)-Half-6

incident intensity (Io) of sound wave into half its value = Io/2

. s)] = Rayls2v [Kg/(m=nce (Z)aAcoustic Imped-7

Acoustic impedance is a fundamental property of matter, is the density of the

medium (Kg/m3). The concept of impedance is more generally used to assess

the characteristics of a medium that opposes energy flow in a system. the

reciprocal of the impedance Z, is called the admittance(Y): Y = 1/Z = 1/v,

which describes the ease of ener flow.

, , can be measured between any two points withsine waveof aWavelength

zero, such as between crests, or troughs, or correspondingphasethe same

.crossings Wavelength is decreased in a medium with higher refractive index.

crest

trough

Zero crossings


13/70

soundof a sound wave is most commonly characterized by itsAmplitude-8

pressure. In a normal working environment, a very wide range ofpressure

usingscalelogarithmiccan occur. Sound pressure is measured on a

times the logarithm20. The sound pressure level (SPL) is defined asdecibel

referenceof the ratio of the pressure to some reference pressure. The

.threshold of hearingis called thesound pressure

Example:

Find the value of angular frequency () of a sound wave whose frequency

is 850 Hz (s-1). Knowing that = 22/7 = 3.14

Answer:

2 x 3.14 x 850 = 5338 (s-1)= = 2f


14/70

Physics of ear and hearing

1-

Outer ear: Protects inner ear and amplifies sound. It consists of (1)pinna (externalauricle) it aids slightly in funnelling sound waves into the canal, (2) external auditorycanal(critical part of outer ear which is closed on one side by the eardrum and (3)eardrum (thickness of tympanic membrane 0.1 mm). Eardrum couples the vibrations inthe air to the small bones in the middle ear. Therefore, incoming acoustic waves ofcertain frequency can resonate. The regular route of receiving sound from the outer earto the inner ear is called air-conduction.

(Tympanic cavity), the hollow space of the middle ear

Naso-

middle ear communicate with the cochlea via a flexible membrane (the oval window)


15/70

2- Middle ear: Is an air- filled (hollow) cavity that contains a linkage of three bones

called ossicles which connect the eardrum to the inner ear. These bones are full adult

size before birth. Ossicles act as a lever, they amplify the pressure of the sound waves

at the entrance to the inner ear and play an important role in matching the impedance of

the sound waves at the eardrum to the liquid-filled chambers of the inner ear. Andossicles are arranged to efficiently transmit vibrations from the eardrum to the inner ear.

x

oval, and external to theeardrumMiddle ear is the portion of the ear internal to the

. The hollow space of the middle ear has also been called thecochleaof thewindow

.cavum tympani, ortympanic cavity


16/70

allowing,connects the middle ear to the upper part of the throatustachian tubeE

pressure to equalize between the middle ear and throat. The movement of air

through the Eustachian tube is aided by swallowing. The primary function of the

middle ear is to efficiently transfer acoustic energy from compression waves in air

.cochleamembrane waves within the-to fluid

Middle ear contains three tiny bones are named after the objects they resemble:

Ossicles directly coupleStirrup).(stapesandAnvil)(incus(Hammer),malleus

of the cochlea.oval windowsound energy from the eardrum to the

Middle ear improves the transmission of sound from the outer ear to the inner ear.

The outer and middle ear are collectively called the conductive system, which

conducts the sound to the inner ear.


17/70

3- Inner ear: It consists of cochlea and three semicircular canals which are allfilled with fluid.Inner ear is hidden with the hard bone of the skull. Consists ofasmall spiral-shaped, fluid- filled structure called cochlea (real hearing organ).

The vibration transmitted to the stapes (stirrup) is transmitted to the fluid in thecochlea by being in contact with a flexible membrane (the oval window)Chemical transmitters are released in the inner ear which cause impulses inauditory nerve. This transmitter excites nerve cells that are connected to thebrain.

If the animal moves to a high-altitude environment, or dives into the water, there

will be apressure difference between the middle ear and the outside

environment. This pressure will cause a risk of bursting or otherwise damaging

Eustachianthe tympanum if it is not relieved. This is one of the functions of the

. The Eustachian tubes are normally pinched off at the nose end, to preventtubes

, but Eustachian tubes may be opened by lowering anmucusbeing clogged with

or chewing helps relieve the pressure feltyawningprotruding the jaw; this is whyin the ears when on board of an aircraft.


18/70

1) Pinna acts as collecting device that funnels the sound waves into the ear canal.

2) Ear canal increases the intensity of the sound by reducing the area.

tympanic membrane (eardrum) to vibrate (thickness~0.5 mm)3) Sound causes the

)the three small bones(ossicles4) This vibrates the

of the cochleaoval window5) Which in turn strike the

6) Cochlea has nerve cells that detect sound to convert it into electrical impulses for

processing by the brain.

(eardrum)

(external flap)


19/70

:Cochlea

Inside the cochlea there is fluid and tiny hairs (cilia). When a sound wave

is made, cilia makes vibrations. These vibrations reach the fluid in the

cochlea and press on the cilia. Higher sounds cause the fluid to press on

more hairs than lower sounds.

Brain receives this message and knows what kind of sound is being made.

In older people the hair in the cochlea are gradually lost when ones gets

older thats why they can hear sounds of frequencies up to 10000-12000

Hz while, young people can hear sounds ranging from 20-20000 Hz.


20/70

We can use a loudspeaker vibrating back and forth in air at a frequency f

to demonstrate the behavior of sound. Sound spread outward as a

longitudinal wave, that is a wave in which the pressure changes occur in

the same direction the wave travels.

General properties of a Sound

Sound wave to be produced needs:

1-An original source of the wave, some vibrating object capable ofdisturbing the first particle of the medium.

2-A medium which carries the disturbance from one location to another.


21/70

Nature of a Sound Wave

LR

Vibrating object Disturbance transmitted through the medium

Velocity of propagation


22/70


23/70

Sinusoidal sound wave produced by a vibrating tuning fork

This figure shows a pure tone, which propagates through air, the pressure variations due

to the compressions and rarefactions are sinusoidal in form. The total pressure in the

path of a sinusoidal sound wave is: P = Pa + Po sin 2ft

Where, Pa is the ambient air pressure, Po is the maximum pressure change due to the

sound wave, and f is the frequencyof the sound in Hertz.

Tuning fork

Compression

Rarefaction

Pressure

= Ambient


24/70

Sound frequencySound frequencyThe speed (velocity) of sound wave in conducting media (v) is independent of frequency,

and it depends on the material through which the sound will propagates. In air at

temperature 20C, the speed of sound is about 3.3 104 (cm/sec), and in water it is

about 1.4 105 (cm/sec) [i.e., the speed of sound in water is larger than in air]. The

relationship between the velocity (v) of sound propagation in (m/sec), wavelength () in

meter and the frequency of vibration (f) of the sound wave in (Hz) is given by this

equation: v = f (m/sec)

The frequency of a wave (f) = v/ (Hz) refers to how often the particles of the medium

vibrate when a wave passes through them.


25/70

Example: For a sound wave with a frequency of 1000 (Hz), the velocity of

sound wave v= 344 (m/sec). Calculate the value of wavelength.

=v/ff hence,v=Answer:

= 344/1000= 0.344 (m)

Frequency in cycles per second is expressed in (Hz). It can be expressed as:

f = 1/TWhere f = frequency (s-1 = Hz), T = time for completing one wave cycle = Period

Octave

Octave is the interval between two points where the frequency at the second

point is twice the frequency of the first (Doubling the frequency).

The ear responds to an enormous range of intensities. At frequency of3000 Hz, the

lowest intensity that the human ear can detect is about 1016 (W/cm2). The loudest

tolerable sound has an intensity of about 104 (W/cm2). These two extremes of the

intensity range are called the threshold of hearingand the threshold of pain, respectively.

Sound intensities above the threshold of pain may cause permanent damage to the

eardrum and the ossicles.


26/70

Pressure

Pressure

Period [Time duration of one wave cycle]

Period

Low Frequency = Low Pitch = Large wavelengtAmplitude = ~Loudness

High Frequency = High Pitch= Small wavelengt

) (High pitch = Tension

Low pitch = Less tension

x

x

Atmospheric (normal)pressure

The height (amplitude) corresponds to loudness and the wavelength to frequency

-P

+P

0


27/70

The intensity (I) of a sound wave or loudness is the energy carried by the wave per unit

area and per unit time (in units of J/m2.s or W/m2). Sound intensity is determined by

the length of oscillation of the particles conducting the waves, the greater the

amplitude of oscillation, the more intense the sound is [i.e., energy passing through

1(m2/s)]. Many sound intensity measurements are made relative to a standard

].oI/I10log10[hence, Intensity (in dB) =ointensity Ithreshold of hearing

[I= Po2/2v] =

Po is the maximum pressure change due to the sound wave, is the density ofthe medium, and vis the speed of sound propagation.

I = (v)A2(2f)2 = ZA22 =Z(A)2

The intensity can also be expressed as I= Po2/2Z = Po

2/2v (Watt/m2) [I Po2]

Where, is the density of the medium (Kg/m3); v is the velocity of sound (m/sec); fis the

frequency in Hz; is the angular frequency=2f (s-1) and z is the impedance.

Note: Intensity level for sound barely perceptible, human with good ears (reference

sound) is 10-12 (W/m2) while, intensity level is 0 in dB SPL

(dB)


28/70

Because of the nonlinear response of the ear and the large range of intensitiesinvolved in the process of hearing, it is convenient to express sound intensity on

a logarithmic scale. On this scale, the sound intensity is measured relative to a

reference level of 1016 W/cm2 (which is approximately the lowest audible sound

intensity at frequency of 3000 Hz). The logarithmic intensity is measured in

units of decibel (dB) and is defined as:

Logarithmic intensity = 10 log10 Sound intensity in (W/cm2)

1016 (W/cm2)

: Find the logarithmic intensity of a sound wave with an intensity ofExample

1012 (W/cm2).

(dB)40=4x10=41010log10=16-10/12-1010log10Logarithmic intensity =:Answer

A is maximum displacement amplitude of the atoms or molecules from the equilibrium

position; Z = v [Kg/(m2.s)] and Po is the maximum change in pressure [Po= (A)].

I Po2 i.e., sound intensity is directly proportional to Po

2.


29/70

What is the maximum displacement (A) in air corresponding to:Example

the intensity 1 (W/m2). Knowing that the frequency = 1 (KHz) and theacoustic impedance is 430 [Kg/(m2.s)]

Solution:

Intensity (I) =1 (W/m2), f =1(KHz) =103 (Hz) and Z = 430 [Kg/(m2.s)]

Intensity (I) = Z(A)2 = Z(A2f)2

1= 430 (A x 2 x 3.14 x 103)2 = 215 (A x 6280)2 = 215 (39438400 A2)

A2 =1/(8.47925 x 109) = 1.179349 x10-10

A =1.08597 x 10-5 (m) 1.1 x10-5 (m)


30/70

Sound can be classified according to its frequency into 3 categories:

1- Infrasound (Frequency less than 20 Hz)

2- Audible sound (Frequency 20 Hz to 20000 Hz)

3- Ultrasound (Frequency more than 20000 Hz )

The (softest) faintest audible sound which the(TOH):Threshold of hearing

typical human ear can detect has an intensity of 10-12 [Watt/m2]. Sound level

are generally referenced to a standard threshold ofdecibelsmeasurements in

hearingor in terms of2Watt/cm16-10=2Watt/m12-10=o: Isound intensity

).2(Dyne/cm4-10x2)=2(Newton/m5-10x2=o: Psound pressure

Classification of sound frequencies

dB SPL.120and that the threshold of pain is about2o/P2= Pothat the I/INote


31/70

This value has wide acceptance as a nominal standard threshold. It represents

a pressure change of less than one billionth (1/1010 =10-10) of standard

of humansensitivity. This is indicative of the incredibleatmospheric pressure

(Hz) is1000of hearing atactual average thresholdhearing. The

2.5 x 10-12

(Watts/m2

) or about 4 (dB), but zero decibels is a convenient

reference. Threshold of hearing varies with frequency.

A special unit called Bell = 10 decibel (dB) has been developed for comparing

the intensities of two sound waves (I/Io).

Sound intensity level (SIL) = log10(I/Io) Bell

(SIL) = 10 log10 (I/Io) dB [Bell=10 dB]


32/70

Normal background noise is 50-60 dB SPL (sound pressure level). Normal

conversation is 60-70 dB SPL.

)2(W/m12-10=o) and I2(W/m8-10: If I =ExampleSound intensity level (SIL) = log10(10

-8/10-12) = log10104 = 4 (Bell)

Since I P2 then the sound pressure level (SPI) can be expressed as follow:

Intensity (in dB SPL) SPI = 10 log10(P/Po)2 = 20 log10 (P/Po) dB

;Example

For an incident ultrasound beam of intensity (Io) of 1 (W/cm2) is reflected with

an intensity 0.1 (mW/cm2). Express the sound intensity level (SIL) in dB.

1(W/cm2), I = 0.1 (mW/cm2) = 0.1 x 10-3 = 0.0001 (W/cm2)=IoSIL= 10 log10 I/IoSIL = 10 log10 0.0001/1 = 10 x - 4 = - 40 (dB)


33/70

Example:

If the sound intensity level (SIL) = 20 dB and the referencesound intensity (Io) = 10

12 (W/m2). Calculate the value of I?

Answer:

SIL= 20 (dB), I = ? Io = 10-12 (W/m2)

SIL = 10 log10 I/Io20 =10 log10 I/10

-12

20/10 = 2 = log10 I/10-12

log-1 (2) = I/10-12

100 = I/10-12

I =100 x 10-12 = 10-10 (W/m2)


34/70

Sound intensity and the Decibel Scale

Sound waves requires energy for pushing the atoms of amedium through a distance, and therefore exert power.

Energy in joule is carried by sound waves (E) as Kinetic energy

and Potential energy.When potential energy equals zero, then the total energy

(E) = Kinetic energy (K.E.) = mv2 (Joule)

Total energy = Potential energy + Kinetic energy:Note


35/70

Reflection and transmission of sound waves at the eardrum

When a sound wave hits the eardrum, part of the wave is reflected (R) and part

is transmitted into the body (T). The fraction of incident energy that is reflected(R) is given by: R = [(Z2 - Z1)/(Z2 + Z!)]2. To optimize the hearing sensitivity

reflection should be minimizedand transmission maximized. The ratio of thereflected pressure amplitude (R) to the incident pressure amplitudeAo dependson the acoustic impedances of the two media, Z1 and Z2:

R/Ao

= (Z2

- Z1)/(Z

1+ Z

2)

The ratio of the transmitted pressure amplitude (T) to the

incident amplitude (Ao) is

T/Ao= 2Z2/(Z1+ Z2)

The ratio of the reflected (R) and transmitted (T) intensities are:

(R2/2Z1)/(Ao2/2Z1) = (R/Ao)

2

(T2/2Z2)/Ao2/2Z1) = Z1/Z2 (T/Ao)

2

(Ao)

)(R

(T)

Density

Speed

Acoustic Impedance

Frequency

Wavelength


36/70

Example

Calculate the ratios of the pressure amplitudes and the intensities of the

reflected and transmitted sound waves from air to muscle. Knowing that

Z1 = 430 (Kg.m-2.s-1) and Z2=1.64 x 10

6 (Kg.m-2.s-1).

Solution

(R/Ao) =(Z2 - Z1)/(Z1+ Z2) = [(1.64 x 106) 430]/[(1.64 x 106) + 430] = 0.9995(T/Ao) = 2Z2/(Z1+ Z2) = [2 x 1.64 x 10

6]/[(1.64 x 106) + 430] = 1.9995

The ratio of the reflected and transmitted intensities are:

(R/Ao)2 = (0.9995)2 = 0.9990

Z1/ Z2 (T/Ao)2 = [430/(1.64 x 106)] . (1.9995)2 = 0.0010


37/70

Inverse square relationship

Inverse square law is applied for sound waves: It is found that the intensity of sound

waves (I) decreases as the wave diverge or spread out the source [ I 1/r2] where, r is the

distance between source and the measuring point.

Source ofsound waves

r (m)

A,B & C aredifferent

measuring points

away from sourceof sound

(m)

(dB)


38/70

Speed of Sound

The wavelength, frequency and speed of a wave are interrelated by this equation:

Speed (v) = distance/time = f = =K is the elastic modulus describing the stiffness of the material and is the mass density.

Example:If the frequency of sound wave in muscle =1(MHz) and its speed is 400 (m/s).Calculate the wavelength of this sound wave.

Answer f = 1 (MHz) = 1 x 106 (Hz), v = 400 (m/s) = v/f

= 400/106

= 400 x 10-6

= 4 x10

-4

(m)

Sound waves move at a speed vs that is determined by the properties of the medium. The)2) medium through which the sound travels, (1depends on the (speed of sound

m/s in air (at343) is aboutv) the air pressure. The speed of sound (3and (temperature

20C) [which is 15 times slower than that in steel as for steel vs = 5,960 m/s]. Soundspeed in water is 1482 m/s. Sound travels at 1540 (m/s) everywhere in body.

vsolids > vliquids > vgases

So, low-frequency waves have long wavelengths, while high frequency waves haveshort wavelengths as frequency (f) is inversely proportional to wavelength ().

hence, f = v/[ = v/f (m)]


39/70

Characteristic of sound wavesThe geometric laws involving the reflection and refraction are the same as for light.Thismeans that 1 (incident angle) = (reflected angle) and the angle of refracted soundwave 2 is, in general a function of the properties of the two media. 2 is determined

by the velocities of sound in the two media v1 and v2 from the equation of Snells law:sin 1/v1 = sin 2/v2When sound waves with amplitude Ao (at x=0) pass

through tissues, the transmitted waves will have less

amplitude (A).There is some loss of

energy due to frictional forces. Absorption ofenergy in tissue causes a reduction in the

amplitude (A) of sound wave. X in (cm) is the

thickness of the medium. Through which the waves

are transmitted. A is related to Ao by the

exponential equation:

Illustration of reflection and refractionA = Ao ex

Knowing that (cm-1) is absorption coefficient

for medium. Xh is the half value thickness.

A

X (cm)

Ao

Ao/2

xh

Normal line perpendicular on theinterface found between two

media

0

Interface


40/70

Since intensity (I) is directly proportional to A2 [I A2] then if I is the intensity at depth x

in the absorber and Io is the intensity of incident beam at x = zero.

Then ln I/Io= -2xThen I/Io = e-2xI = Ioe-2x

The attenuation of sound intensity will be calculated using: ln Io/I = 2x

The half value thickness (HVT) is defined as The tissue thickness required to

decrease the intensity of the incident sound waves (Io at x = 0) to its half value (Io/2).

Sound intensity decreases with the distance according to the inverse square law

Absorption increases as the frequency of the sound waves increases. And:Note

intensity decrease more rapidly than the amplitude with depth.

Example:

If a sound wave of incident intensity 65 (dB) and attenuated intensity 40 (dB) after

passing through a medium of thickness 3 (cm). Calculate the value of absorption

coefficient.

)1-(cm0809.0=4855.0=6=625.1ln6)=40/65x and ln (2/I =oln I:Answer

AoA

x


41/70

The sensation of hearing is produced by the response of the nerves in the ear

to pressure variations in the sound wave. The nerves in the ear are not the

only ones that respond to pressure, as most of the skin contains nerves that

are pressure-sensitive. However, the ear is much more sensitive to pressure

variations than any other part of the body. Sensory cells convert sound to

nerve impulses are located in the liquid-filled inner ear.

The main purpose of the outer and middle ears is to conduct the sound into

the inner ear. When sound waves produce vibrations in the eardrum, the

vibrations are transmitted by the ossicles to the oval window, which in turn

sets up pressure variations in the fluid of the inner ear. The ossicles are

connected to the walls of the middle ear by muscles that also act as a volume

control. If the sound is excessively loud, these muscles as well as the muscles

around the eardrum stiffen and reduce the transmission of sound to the inner

ear.

Hearing and the Ear


42/70

The process of hearing cannot be fully explained by the mechanical

construction of the ear. The brain itself plays an important role in our

perception of sound. For example, the brain can effectively filter out ambient

noise and allow us to separate meaningful sounds from a relatively loud

background din. (This feature of the brain permits us to have a private

conversation in the midst of a loud party). The brain can also completely

suppress sounds that appear to be meaningless. Thus, we may lose

awareness of a sound even though it still produces vibrations in our ear. The

exact mechanism of interaction between the brain and the sensory organs is

not yet fully understood. The most familiar clinical use of sound is in the

analysis of body sounds with a stethoscope

Th b d d (P i i M di i )


43/70

The body as a drum (Percussion in Medicine)Percussion (tapping) on the human body is used as a means of diagnosis since the

18th century with ear directly on the chest. When chests of patients are striking in

various places different sounds are produced. These sounds are related to specified

disease. Stethoscope is a simple hearing aid that permits a physician or nurse to

listen to sounds made inside the patients body, primarily in the heart and lungs. The

act of listening to these sounds using a stethoscope is called mediate auscultationor

usually just auscultation. The main parts of a modern stethoscope are: (1) Bell, which iseither open or closed by a thin diaphragm, (2) Tubing and earpiece as shown in the

following figure. A closed bell is merely a bell with a diaphragm of high resonant

frequency, that tunes out low-frequency sounds.

Factors affecting the best hearing through the stethoscope:- Placing the earpieces in the ear let the eardrum act as the closed end of the systembesides, eardrum is very sensitive to pressure changes.

- To have high pressure change the volume of air inside the stethoscope must be small(volume of the bell, length and diameter of the tube must be small).

- If the volume of the tube is small friction loss will be high.


44/70

[20-200]Hz [200-2000]Hz


45/70

Open bellis an impedance matcher between the skin and the air, itaccumulates sounds from the contacted area. Skin under the open bell

behaves like a diaphragm that has a natural resonant frequency

fresat which it

most effectively transmits sounds. fres depends on (1) the bell diameter (d) and

(2) tension of the diaphragm under which the skin is stretched (T).

fres (1/2d) (T/)

[where, is the area density (Kg/m2)].

Factors controlling the resonant frequency fres are:1-The tighter the skin is pulled the higher fres.2-The larger the bell diameter, the lower the skins fresThus it is possible to enhance the sound range by changing the bell diameterand varying the pressure of the bell (skin tension) against the skin.

Closed bell has a diaphragm of known resonant frequency fres that can becontrolled. The closed bell is used for listening to lung sounds, which are ofhigher frequency than heart sounds.

[Resonant = return of echo]


46/70

Hearing TestsThe basic principle of hearing aids is simple. A microphone converts sound to anelectrical signal. The electrical signal is amplified and converted back into sound using aspeaker-type device. The net result is an amplification of the sound that enters the ear.

A hearing (audiometric) test is part of an ear examination that evaluates a person'sability to hear by measuring the ability of sound to reach the brain.

) the1you have by measuring (hearing lossHearing tests help determine what kind ofability to hear sounds that reach the inner ear through the ear canal (air-conductedsounds) and (2) sounds transmitted through the skull (bone-conducted sounds).Most hearing tests ask you to respond to a series of tones or words, but there are

some hearing tests that do not require a response.An audiometer hearing test is usually administered to a person sitting in a soundproofbooth (small room) wearing a set of headphones which is connected to an audiometer(generates pure tones over a wide range of pitch).


47/70

The audiometer produces tones at specific frequencies and set volume

levels to each ear independently. The audiologist or licensed hearing aid

. People havingaudiogram, on andecibelsspecialist plots the loudness, in

their hearing tested will convey that they have heard the tone by either

raising a hand or pressing a button. As the test progresses, the audiologist,

plots points on a graph where the frequency in Hertz is on the x-axis and

the loudness (hearing level in dB) on the y-axis.

Once each frequency of hearing ability is tested and plotted, the points are

that may be present.hearing lossjoined by a line to identify the degree of

dB.20ofsound pressureNormal hearing at any frequency is a

H i t t h t h i h i l


48/70

Hearing test chart showing hearing loss

The audiogram is a physical representation of your hearing capabilities that showsthe range of pitches or frequencies that youre able to hear with each ear, and atwhat intensity level youre able to hear them. Frequency is measured in Hertz, whichwe feel as pitch. Intensity is measured in decibels, and is perceived as loudness.

l d i


49/70

Ultrasound Imaging

based diagnostic-ultrasound) is anultrasonography(Diagnostic sonography

technique used for visualizing subcutaneous body structures includingimaging , joints, vessels and internal organs for possible pathology ormuscles,tendonsis commonly used during pregnancy. AnObstetric sonography.lesions

ultrasound technician moves the transducer unit over the abdomen of apregnant woman while adjusting the brightness of the image on the monitor.The frequencies used in diagnostic ultrasound are between 2 and18 (MHz).

Monitor

Transducer(hand held

probe)


50/70

Sonography is effective for imaging soft tissues of the body. Superficial structure

brain are imaged atneonataland thebreast,testes,tendons,musclessuch as

MHz), which provides better axial and lateral18-7(frequencya higher

. Deeper structures such as liver and kidney are imaged at a lowerresolution

frequency (1- 6 MHz) with lower axial and lateral resolution but greater

penetration.

Ultrasound is used to help physicians:Ultrasound Pictures of the Bodydiagnosing a variety of conditions and to assess organ damage following

illness. Basically an ultrasound source sends a beam of pulses of 1-5 MHz

(106 Hz) sound into the body. The time required for sound pulses to be

reflected gives information on the distances to the various structures or organs

in the path of the ultrasound beam. Ultrasound is a mechanical, longitudinal

wave with a frequency exceeding the upper limit of human hearing (20 KHz).

Medical ultrasoundis within the range of2-16 (MHz).


51/70

Ultrasound is produced by passing an alternating voltage (AC) electrical current

through piezoelectrical crystal [naturally occurring (quartz)] which causes it to

expand and contract to generate ultrasound [i.e. voltage generated when

certain materials are deformed by pressure].

?What is piezoelectricity

When certain types of crystals are mechanically deformed, the charges in them

are displaced; as a result, they develop voltages along the surface. This

phenomenon is called thepiezoelectric effect.

C


52/70

:AC causes

- Alternating dimensional changes

- Alternating pressure changes

Then pressure propagates as sound wave

A device that converts electrical energy into mechanical energy or vice versa is called

transducer. Ultrasound transducer is used to convert electrical signal into ultrasound

wave which can be transmitted through the tissues. Waves reflected back from thetissue and incident on the crystal will be converted by the crystal to electrical charge.

The most important component is a thin piezoelectric crystal located near the face of the

transducer. Each transducer has a natural resonant frequency (fres) of vibration.

Ultrasound imaging is also called ultrasound scanning orsonographywhich involvesexposing part of the body to high frequency sound waves in order to produce pictures

of the inside of the body. To obtain diagnostic information about the depth of structures in

the body, we send pulses of ultrasound into the body by placing the vibrating crystal in

close contact with the skin, using water or jelly paste in order to eliminate air.


53/70

This gives a good coupling at the skin and greatly increases the transmission ofthe ultrasound into the body and measure the time required to receive thereflected sound (echoes) from the various surfaces. This procedure is called theA

scan method of ultrasound diagnosis. Pulses for A scan are typically a fewmicroseconds long, and they are usually emitted at 400-1000 pulses/sec. Thefrequency of the ultrasound waves increase with decreasing the thickness of thecrystal (i.e. The thinnerthe crystal the higherthe frequency at which it willoscillate). Ultrasound image is an electronic representation of data generatedfrom returning echoes and displayed on TV monitor, such image can provide

valuable information regarding the size, location, displacement or velocity of agiven structure without the necessity of surgery or using harmful radiation.

The sonographic scanner must determine three things from each received echo:1- How long it took the echo to be received since the sound was transmitted.

2- From this the focal length for the phased array is deduced, enabling a sharpimage of that echo at that depth.3- How strong the echo was. It could be noted that sound wave is not a click, buta pulse with a specific carrier frequency. Moving objects change thisfrequency on reflection.

Many of the applications of ultrasound in medicine are based on the principles


54/70

Echoencephalography(EEG)measures potentials along the surface of the scalp. EEGsignal is a complex irregular wave containing several frequencies and amplitudes. It isused to detect brain tumors using A scan. Where pulses are sent into a thin region of theskull slightly above the ear and echoes from different structures within the head aredisplayed on an oscilloscope. The usual procedure is to compare the echoes from theleft side of the head to those from the right side and to look for a shift in the midline

structure . A tumor on one side of the brain tends to shift the midline toward the otherside.

object

Many of the applications of ultrasound in medicine are based on the principlesofsonar. In sonar a sound wave pulse is incident through any medium and isreflected from an object; from the time (t) required to receive the echo and theknown velocity (v) of sound, the distance (d) between the source of sound

waves and the object can be determined by: d = vtThe amount of the reflected beam from the tissue depends on: (1) Differencebetween the acoustic impedance between two mediums. (2) The angle ofincidence between the ultrasound beam and the reflecting surface, when angleincreases the reflection will decrease.

of sound

Medium

(d)


55/70

onescans in ophthalmology can be divided into two areas:AApplications of

is concerned with obtaining information for use in the diagnosis of eye

involve measuring the distances in the eye. For manyseconddiseases; the

clinical purposesA scan have been largely replaced by the Bscans

(Brightness Mode). The B scan method is a series of gray shade dots

which is used to obtain two-dimensionalviews of parts of the body. Dot

position ideally indicates source of echo.

that theexceptscan are the same as for the A scanBThe principles of

transducer is moving. Each echo produces a dot on the oscilloscope at a

position corresponding to the location of the reflecting surface. B scansprovide information about the internal structure of the body. They have been

used in diagnostic studies of the eye, liver, breast, heart and fetus. B scan

can detect pregnancy as early as the 5th week. In many cases scans can

provide more information than x-rays and they present less risk.


56/70

Ultrasound Display

B-scan (Brightness Mode) Image

series of gray shade dots (echoes).

For each dot, scanner must

calculate: Position & Gray shade

Loud echo = bright dotSoft echo = dim dot

1-A-mode (A-scan, 1D)

2- B-mode (Gray scale, 2D, moving transducers)

3- M-mode (motion in the body) e.g., heart valves


57/70

In B scan all the echoes are displayed on the CRT (cathode ray

tube) were the same brightness. Operator could exclude

echoes of low magnitude by setting an electronic control this is

called leading-edge display,

The improved gray-scale displayelectronically changes the

brightness on the CRT so that the large echoes appear brighter

than weak ones. The success of the gray-scale display has led

to the development of color display that shows a greater range

of echoes.


58/70

Ultrasound to measure motion

Two methods are used to obtain information about motion in the body with

ultrasound; the M (motion) scan, which is used to study motion such as that of

the heart valves, and the Doppler technique, which is used to measure the

blood flow.

M-scan combines certain features ofA scan and the B scan. The transducer is

held stationary as in A scan and the echoes appear as dots as in the B scan.

M-scans are used to obtain diagnostic information about the heart. By putting

the probe it is possible to obtain information about the behavior of a particular

valve or section of the heart.


59/70

The speed of a sound wave in air depends upon the properties of the air,namely the temperature and thepressure

Pressure of air (like any gas) will effect the mass density of the air and thetemperature will effect the strength of the particle interactions.

At normal atmospheric pressure, the temperature dependence of thespeed of a sound wave through air is approximated by the following

equation: v = 331 (m/s) + (0.6 m/s/C) x T

At a temperature of 20C

v = 331 m/s + (0.6 m/s/C) x 20

v = 331 m/s + 12 m/s

v = 343 m/s

The Speed of Sound

T= temperature in C


60/70

Physics of ear and hearingSense of hearing involves:

1- The mechanical system that stimulates the tiny hair cells in the inner ear (Cochlea).

2- The sensors that produce the action potential in the auditory nerves.

3- The auditory cortex (part of the brain) that interprets (explain) the signals coming fromthe auditory nerves.

If any of these parts malfunction hear loss (deafness) will be obtained.

:There are two common causes of reduced hearing: In which sound waves do not reach the inner ear which isConduction hearing loss-A

due to something wrong in the outer and middle ear such as a plug of wax which blockthe eardrum. Or a fluid in the middle ear or a solidification of the small bones in themiddle ear. If conduction hearing loss is not curable a hearing aid can be used totransmit the sound through the bones of the skull into the inner ear.

: In which sound waves reaches the inner ear but not nerve signalsNerve hearing loss-Bare sent to the brain and this may be due to nerve damage. An electronic hearing aidconsists of a microphone to detect sound, an amplifier to increase the sound energy anda loudspeaker to deliver the sound waves with high energy into the ear.

There are four steps in the hearing process within the ear:


61/70

e e a e ou steps e ea g p ocess e ea(1) The sound wave enters the outer ear through the pinna into ear canal (Acoustic filter)(2) The movement of the tympanic membrane is transferred by conduction through theossicles to the oval window of the cochlea (Mechanical transformer).(3) The movement of the oval window generates a compressional (sound) wave in the

fluid of the cochlea.upon which the primary auditory receptorsbasilar membraneThis wave moves the)4(

(the hair cells) are located, and the electrical signals generated by the hair cells are sentmechanoelectricalto the brain. This conversion of sound into electrical signals is called

.transduction

Properties of Sound


62/70

Properties of SoundWhen a wave enters one medium from another, part of the wave is reflected atthe interface, and part of it enters the medium.

of sound waves off of surfaces canlike)-or (mirror(bouncing back):Reflection

lead to one of two phenomena-an echo orreverberation:Incident angle (i)= Reflected angle (r)

When a wave encounters an obstacle , it spreads into the:Diffractionregion behind the obstacle. This phenomenon is called diffraction. The amountof diffraction depends on the wavelength: The longer the wavelength, the

greater is the spreading of the wave. Diffraction involves a change in directionof waves as they pass arounda barrier in their path.Refraction: of waves involves a change in their direction as they pass from onemedium to another. The degree of refraction depends on the properties of the twmedia and the angle of incidence (i).

- Using specialized techniques called ultrasoundimaging, it is possible to form visible images ofultrasonic reflections and absorptions.The frequency of sound detected by an observerdepends on the relative motion between the sourceof sound and the observer. This phenomenon is

called the Doppler effect.

1st medium

2nd medium

Normal line

Interface

Doppler Effect


63/70

Doppler EffectDopplereffect is a phenomenon observed whenever the source of sound waves ismovingwith respect to a stationary (not moving) observer. It can be used to measurethe speed of moving objects or fluids within the body, such as blood. It can be shown

that if the observer is stationary and the source of waves is in motion, the frequencyof the sound f ' detectedby the observer is given by: f ' = f v

v vswhere fis the frequency in the absence of motion, v is the speed of sound, and vs isthe speed of the source.

(Sound source approaching

stationary listener standing in front of it)

(Sound source moving

away from stationary

listener standing behind it)

Change in frequency is called Doppler shift


64/70

RBCs moving toward sound waves

RBCs moving away from the sound waves

Source ofsound waves

Doppler shift

The shiftingof the acoustic frequency when the ultrasound

reflects from a moving target (the Doppler effect) is the

basis for measuring blood flow direction, turbulence, and

speed (Doppler ultrasonography).

A moving sound source compress (push together) the

sound waves in front of the object in the motion direction.

Motion direction


65/70

Laminar and Turbulent flow of blood

Blood velocity determination by ultrasound

If the velocity of a blood exceeds a specific critical value, the flow becomes

turbulent. Through most of the circulatory system, the blood flow is laminar. Only in

the aorta (the main artery arising out of the left ventricle of the heart), the flow

occasionally become turbulent.

Blood velocity determination


66/70

Blood velocity determination

V cos is the velocity of blood in the same direction of the velocity of incident sound

waves. And c is the velocity of the sound wave that are transmitted from transducer

through skin and tissue to red blood cells (RBCs) in an artery and fo is frequency of

continuous incident sound wave

Moving RBCs inside anartery from the left to right

side

Artery


67/70

Echolocation by bats

Bats and porpoises (kind of fish) use sonar principle for navigating and finding food. Blind humansuse the same principle when they listen to echoes from the tap of a cane to help avoid largeobjects.

Echolocation by dolphin

[Echoes of sound tell size, shape anddistance of prey

Sound returning

Prey

Prey

Dolphin

f ( )


68/70

Human speech is made by air from the lungs as it passes through the

trachea, larynx (which houses the vocal folds or cords), andpharynx

(throat),through the mouth and nasal cavities, and then out of the

mouth and nose [The vocal folds (or vocal cords) are folds of ligament

extending on either side of the larynx, with the space in between them

called the glottis]. The structure above the larynx is called the vocal tract.

Adjusting the vocal tract to produce speech sounds is called articulation.

The basic elements of speech are classified as: (1) phonemes (the basic

sounds), (2) phonetic features (how the sounds are made), and (3) the

thearePhonemes.sounds)theofnatureacoustic(thesignalacoustic

shortest segments of speech, Each phoneme is produced by distinctive

movements of the vocal tract, which are the phonetic features of speech.

=Phonetic

Production of speech (phonation)

=Distinctive

The Acoustic Buzzer


69/70

During speaking, air rushing through vocal folds in the larynx from the

trachea to the pharynx causes the vocal folds to vibrate, which in turn

leads to a modulation of the air flowing into the trachea. Initially the foldsare apart and the pressure in the trachea and pharynx are equal to each

other, and to the atmospheric pressure. Because of the separation

between folds, the pressure is the same before and after the folds, even

with air flowing from the lungs. Muscle contractions cause the folds tomove to the midline of the tube (as shown in figure). Because of this

constricted air flow, the pressure before the glottis [sub glottis pressure

(Psub glottis)] exceeds the oral pressure (Poral). This pressure difference

forces the folds to separate rapidly, leading to a rapid burst of air. Thisproduces an overpressure above the glottis and an acoustic shockwave

that moves up the vocal tract. The folds then reboundback to their initial

positions because of their elastic recoil properties and the pressure

gradient.

The Acoustic Buzzer

i d d th l i fhS h i ti i th t d f h


70/70

is produced, the analysis ofspeechSpeech communication is the study of how

speech signals and the properties of speech transmission, storage, recognition and

enhancement. Normal speech sounds are produced by modulating an outward flow

of air. Sound modulation are produced by changing volume of resonating cavities.

For most sounds the lung furnish the stream of air, which flows through the vocal

folds [located within the larynx or Adams apple inside the trachea or windpipe], and

several vocal cavities and exits from the body through the mouth and to a slight

degree through the nostrils. Speech sounds produced in this way are called voiced

sounds [5 vowels: a, e, I, o & u] which rely on changing resonator volume only. Some

sounds are produced in the oral portion of the vocal tract without the use of vocal

folds and these are called unvoiced sounds which, require supporting movement of

tongue and/or lips [s, f, th] and are called frictive sounds. These sounds involve air

flow through constructions or past edges formed by the tongue, teeth, lips and palate

(roof of the mouth). Sounds which rely on build-up and sudden release of pressure in

the oral cavities are called explosive sounds (p, t, k, q). There is a combination of the

2nd sound in medici2 جدي

Documents