In the name of GodIn the name of God

GENERAL PHYSICSGENERAL PHYSICS

PhysicsPhysics

• Physics is a science that study of two Physics is a science that study of two concept : concept :

MatterMatter

EnergyEnergy

MatterMatter

• Matter may be solid, liquid or gasMatter may be solid, liquid or gas

• Examples : Copper, Rubber, Water and Air.Examples : Copper, Rubber, Water and Air.

• Matter is composed of sub-microscopic units called Matter is composed of sub-microscopic units called atoms or molecules. atoms or molecules.

• Matter can be neither created nor destroyed.Matter can be neither created nor destroyed.

EnergyEnergy

• Energy is ability to do work.Energy is ability to do work.

• Energy can be neither created nor Energy can be neither created nor destroyed.destroyed.

ForceForce

• Force produces or tends to produce Force produces or tends to produce movement in a body.movement in a body.

• The unit of force is Newton.The unit of force is Newton.

• A Newton is that force which when A Newton is that force which when applied to a body having a mass of applied to a body having a mass of one Kilogram, gives it an acceleration one Kilogram, gives it an acceleration of one meter per second per second. of one meter per second per second.

WorkWork

• Work is equal to Work is equal to the forcethe force × × the distancethe distance

W = W = fhfh

• The unit of work called joule.The unit of work called joule.

• Joule is the work done when the force of Joule is the work done when the force of one Newton moves to a distance of one one Newton moves to a distance of one meter in the direction of the force. meter in the direction of the force.

Temperature and HeatTemperature and Heat

• Temperature: we may have high or Temperature: we may have high or low temperaturelow temperature

• Heat: we can rise of temperature by Heat: we can rise of temperature by heating a matterheating a matter

• Temperature is commonly measure Temperature is commonly measure by instrument called Thermometer by instrument called Thermometer

The CalorieThe Calorie

• The Calorie is the amount of heat The Calorie is the amount of heat which will raise the temperature of one which will raise the temperature of one gram of water by one degree Celsius.gram of water by one degree Celsius.

Atomic StructureAtomic Structure

• ElementsElements

• CompoundsCompounds

• AtomsAtoms

• MoleculesMolecules

ElementsElements

• Elements: An element is a distinct kind Elements: An element is a distinct kind of matter which cannot be decomposed of matter which cannot be decomposed into two or more simpler kinds of matter.into two or more simpler kinds of matter.

Example: Example: OO and and HH

CompoundCompound

• Compound: A compound is formed Compound: A compound is formed when two or more elements combine when two or more elements combine together chemically to produce a together chemically to produce a more complex kind of matter.more complex kind of matter.

Example: Water is a compound of Example: Water is a compound of oxygen an hydrogen.oxygen an hydrogen.

AtomsAtoms

• Atoms are the smallest particles of an Atoms are the smallest particles of an element that can exist without losing the element that can exist without losing the chemical properties of the element.chemical properties of the element.

• The diameter of an atom is 1/10,000,000,000 The diameter of an atom is 1/10,000,000,000 metermeter

MoleculesMolecules

• Molecules are the smallest particles of a Molecules are the smallest particles of a compound that can exist without losing compound that can exist without losing the chemical properties of the the chemical properties of the compounds. compounds.

Physics of RadiologyPhysics of Radiology

X-raysX-rays

The properties of X-rayThe properties of X-ray• The production of X-rayThe production of X-ray• Interactions of electrons with the Interactions of electrons with the

targettarget• Spectra of X-rays Spectra of X-rays • The quality and intensity of X-raysThe quality and intensity of X-rays• The factors influencing quality and The factors influencing quality and

intensityintensity

The properties of X-rayThe properties of X-ray

• FluorescenceFluorescence• Photographic effectPhotographic effect• PenetrationPenetration• Ionization and ExcitationIonization and Excitation• Chemical changesChemical changes• Biological effectsBiological effects

The properties of X-rayThe properties of X-ray

FluorescenceFluorescence

• X-rays produce fluorescence in some X-rays produce fluorescence in some materials such as Calcium Tungstate, Zinc materials such as Calcium Tungstate, Zinc Cadmium Sulphide and Caesium Iodide.Cadmium Sulphide and Caesium Iodide.

• Afterglow less than 1/100,000,000 secondAfterglow less than 1/100,000,000 second

• It is used in intensifying screen and It is used in intensifying screen and fluoroscopy. fluoroscopy.

Photographic effectPhotographic effect

• X-rays produce a latent image. X-rays produce a latent image. • It is It is utilized in film-badge dosimetry for utilized in film-badge dosimetry for

radiation protection.radiation protection.

• To a small extend in a radiography (5%). To a small extend in a radiography (5%).

PenetrationPenetration

• X-rays penetrate substances that are X-rays penetrate substances that are opaque to visible light.opaque to visible light.

• The amount of absorption depend on:The amount of absorption depend on:

1)Atomic number of the object1)Atomic number of the object

2)Density of the object2)Density of the object

3)Energy of the X-rays 3)Energy of the X-rays

Ionization and ExcitationIonization and Excitation

• X-rays produce ionization and excitation of X-rays produce ionization and excitation of the atoms and molecules of the substances the atoms and molecules of the substances through which they pass. through which they pass.

Chemical changesChemical changes

• X-rays produce chemical changes in X-rays produce chemical changes in substances through which they pass.substances through which they pass.

• One important change is the oxidation One important change is the oxidation of the ferrous sulphate { FeSOof the ferrous sulphate { FeSO4 4 }} in in solution to ferric sulphatesolution to ferric sulphate {{ FeFe22 ( (SOSO44))33 }}

• This is chemical system of dosimetry for This is chemical system of dosimetry for quantity of X radiation absorbed.quantity of X radiation absorbed.

Biological effectsBiological effects

• X-rays produce biological effects in living X-rays produce biological effects in living organism either by :organism either by :

1) Direct action on the cells. 1) Direct action on the cells. 2) Indirect action as a result of chemical changes 2) Indirect action as a result of chemical changes

near the cells. near the cells.• Somatic action ( damage or kill the cells )Somatic action ( damage or kill the cells )• Genetic action ( mutation changes in subsequent Genetic action ( mutation changes in subsequent

generations )generations )• Useful effects : Useful effects : 1) Radiotherapy1) Radiotherapy 2) Sterilization of hospital supplies, such as 2) Sterilization of hospital supplies, such as

syringes and dressing. syringes and dressing.

The properties of X-ray

Diagnostic Diagnostic ImagingImaging

Physics of radiologyPhysics of radiology• IntroductionIntroduction• X-ray departmentX-ray department• X-ray machinesX-ray machines• X-ray unit circuitX-ray unit circuit• X-ray tubeX-ray tube• RectificationRectification• High tension transformerHigh tension transformer• Electromagnetic radiationElectromagnetic radiation• X-ray propertiesX-ray properties• X-ray productionX-ray production• Interaction of X-ray with matterInteraction of X-ray with matter• FocusingFocusing• FiltrationFiltration• X-ray dosimeteryX-ray dosimetery• Radiological protectionRadiological protection• ShieldingShielding

Electromagnetic spectrumElectromagnetic spectrum

X & Gamma rays X & Gamma rays

have got : have got :

Short wave length Short wave length

High energyHigh energy

Wave lengthWave length

Wave length is a distance betweenWave length is a distance between

two equal points two equal points

Physics of RadiologyPhysics of Radiology

The production of X-rayThe production of X-ray

The production of X-rayThe production of X-ray

• Energy loss by electrons : X-rays are Energy loss by electrons : X-rays are produced when electrons give up produced when electrons give up energy by two processes.energy by two processes.

1) The deceleration of a fast-moving 1) The deceleration of a fast-moving electron.electron.

2) The movement of an electron 2) The movement of an electron between two inner shells in an atom. between two inner shells in an atom.

The principles of operation of a X-ray The principles of operation of a X-ray tubetube

• X –ray tube is sometimes called a coolidge X –ray tube is sometimes called a coolidge tube ( inventor ).tube ( inventor ).

• In X-ray tube, electrons are release from a In X-ray tube, electrons are release from a heated filament by thermionic emission.heated filament by thermionic emission.

• The electrons are then accelerated across The electrons are then accelerated across the tube by a high voltage applied the tube by a high voltage applied between the filament and the anode.between the filament and the anode.

• When the electrons reach the anode, they When the electrons reach the anode, they are traveling at a high velocity therefore; are traveling at a high velocity therefore; they have high kinetic energy and this is they have high kinetic energy and this is converted into X-rays and heat. converted into X-rays and heat.

X-ray tubeX-ray tube

The principles of operation of a X-ray The principles of operation of a X-ray tubetube

• The filament, is usually a spiral of The filament, is usually a spiral of Tungsten wire.Tungsten wire.

• It is heated by a low-voltage supply.It is heated by a low-voltage supply.

• Electrons are released from the filament Electrons are released from the filament by thermionic emission.by thermionic emission.

• Tungsten is used because it produces Tungsten is used because it produces appreciable thermionic emission at appreciable thermionic emission at temperatures well below its melting point. temperatures well below its melting point.

The principles of operation of a X-ray The principles of operation of a X-ray tubetube

• A high-voltage supply is connected between A high-voltage supply is connected between filament and target.filament and target.

• Filament acts as the cathode.Filament acts as the cathode.• Target is part of the anode of the tube.Target is part of the anode of the tube.• Target of medical X-ray tubes are usually Target of medical X-ray tubes are usually

made of Tungsten.made of Tungsten.• Tungsten has:Tungsten has: 1) high melting point1) high melting point 2) adequate thermal conductivity 2) adequate thermal conductivity 3) high atomic number (74) which increases 3) high atomic number (74) which increases

the efficiency of X-ray production. the efficiency of X-ray production.

The principles of operation of a X-ray The principles of operation of a X-ray tubetube

• Kinetic energy is gained by the negatively charged Kinetic energy is gained by the negatively charged electrons released from the filament as they are electrons released from the filament as they are accelerated to high velocity by the positive voltage accelerated to high velocity by the positive voltage apply to the target.apply to the target.

• A high vacuum exist in the tube, so no electron A high vacuum exist in the tube, so no electron produces by ionization.produces by ionization.

• A shield or focusing cup, mounted near the A shield or focusing cup, mounted near the filament and it is a part of cathode assembly.filament and it is a part of cathode assembly.

• It has got two acts:It has got two acts: 1) this protects adjacent parts of the tube wall from 1) this protects adjacent parts of the tube wall from

damage by electron bombardment.damage by electron bombardment. 2) this focuses the electrons on to a small area of 2) this focuses the electrons on to a small area of

the target known as the focus or focal area. the target known as the focus or focal area.

X-raysX-rays

The properties of X-rayThe properties of X-rayThe production of X-rayThe production of X-rayInteractions of electrons with the Interactions of electrons with the

targettarget• Spectra of X-rays Spectra of X-rays • The quality and intensity of X-raysThe quality and intensity of X-rays• The factors influencing quality and The factors influencing quality and

intensityintensity

Interactions of electrons with the Interactions of electrons with the targettarget

• The efficiency of X-ray production is less The efficiency of X-ray production is less than 1% in medical X-ray tube.than 1% in medical X-ray tube.

• In a linear accelerator the efficiency is In a linear accelerator the efficiency is about 40% (X-rays are produce at 4 MeV).about 40% (X-rays are produce at 4 MeV).

• X-rays produce in diagnostic radiology X-rays produce in diagnostic radiology unit have got energy between 12.4 KeV unit have got energy between 12.4 KeV and 124 KeV.and 124 KeV.

• Maximum photon energy of the X or Maximum photon energy of the X or gamma rays can be 12.4 MeV.gamma rays can be 12.4 MeV.

Interactions of electrons with the Interactions of electrons with the targettarget

• Four types of interaction are possible Four types of interaction are possible at the target:at the target:

1) Excitation involving an electron in an 1) Excitation involving an electron in an outer shell.outer shell.

2) Ionization by the removal an 2) Ionization by the removal an electron from an outer shell.electron from an outer shell.

3) Ionization by the removal an 3) Ionization by the removal an electron from an inner shell.electron from an inner shell.

4) Bremsstrahlung production. 4) Bremsstrahlung production.

Excitation involving an electron in an outer Excitation involving an electron in an outer shellshell

• The incident electron transfers a The incident electron transfers a small amount of energy ( only a few small amount of energy ( only a few electron volts ) to an electron in an electron volts ) to an electron in an outer shell of an atom in the target.outer shell of an atom in the target.

• It displaces electron to an energy It displaces electron to an energy level farther out.level farther out.

• The electron returns to the vacancy The electron returns to the vacancy in the shell and the energy release as in the shell and the energy release as heat in the target. heat in the target.

ExcitationExcitation

Ionization by the removal an electron from an outer Ionization by the removal an electron from an outer shellshell

• The incident electron transfer sufficient The incident electron transfer sufficient energy to ionize an atom of the target.energy to ionize an atom of the target.

• The displaced electron, known as a The displaced electron, known as a secondary electron may produce secondary electron may produce further ionization or excitation.further ionization or excitation.

• Again only a small amount of energy is Again only a small amount of energy is released and it appears as heat.released and it appears as heat.

Ionization of the outer Ionization of the outer shellshell

Ionization by the removal an electron from an inner Ionization by the removal an electron from an inner shellshell

• The incident electron transfers sufficient energy The incident electron transfers sufficient energy to remove an electron from an inner shell.to remove an electron from an inner shell.

• To do this the electron must have energy equal to To do this the electron must have energy equal to or grater than the binding energy for that shell.or grater than the binding energy for that shell.

• Secondary electron is created.Secondary electron is created.• The vacancy in the inner shell is filled by an The vacancy in the inner shell is filled by an

electron moving inwards from another shell.electron moving inwards from another shell.• It is accompany by the emission of an X-ray It is accompany by the emission of an X-ray

photon of energy equal to the difference between photon of energy equal to the difference between the binding energy of the two shells.the binding energy of the two shells.

• This photon is known as a This photon is known as a Characteristic X-ray Characteristic X-ray photonphoton..

• Its energy depend on the element of which the Its energy depend on the element of which the target is made.target is made.

• The photon energy for Characteristic X-ray for The photon energy for Characteristic X-ray for Tungsten is between 57 to 69 KeV. Tungsten is between 57 to 69 KeV.

Ionization of the inner Ionization of the inner shellshell

Bremsstrahlung productionBremsstrahlung production

• The incident electron passes close to the nucleus The incident electron passes close to the nucleus of an atom in the target.of an atom in the target.

• The electron is negatively charged and the The electron is negatively charged and the attraction of the positive electric charge of the attraction of the positive electric charge of the nucleus makes it decelerate.nucleus makes it decelerate.

• The electron loses energy in the form of an X-ray The electron loses energy in the form of an X-ray photon.photon.

• The energy of the X-ray photon depends on the The energy of the X-ray photon depends on the degree of deceleration.degree of deceleration.

• The photon energy can take any value from zero The photon energy can take any value from zero to a maximum.to a maximum.

• The maximum photon energy occurs when the The maximum photon energy occurs when the electron passes very close to the nucleus and the electron passes very close to the nucleus and the deceleration is so great that the electron comes deceleration is so great that the electron comes to rest.to rest.

• This is known as This is known as Braking radiationBraking radiation and it gives and it gives rise to the continuous spectrum of X-rays.rise to the continuous spectrum of X-rays.

Bremsstrahlung productionBremsstrahlung production

Interaction of X - ray with Interaction of X - ray with mattermatter

Interaction of X ray with Interaction of X ray with mattermatter

• There are 5 process by which X or There are 5 process by which X or gamma ray may absorbed or scattered.gamma ray may absorbed or scattered.

1) Classical or unmodified scattering.1) Classical or unmodified scattering.

2) Photoelectric scattering2) Photoelectric scattering

3) Compton unmodified scattering.3) Compton unmodified scattering.

4) pair production4) pair production

5) Photo – nuclear disintegration5) Photo – nuclear disintegration

Classical or unmodified Classical or unmodified scatteringscattering

Classical or unmodified Classical or unmodified scatteringscattering

• It can occur when an photon with low It can occur when an photon with low energy hits an atoms with high atomic energy hits an atoms with high atomic number.number.

• An incident photon collides with an An incident photon collides with an electron and rebounds without causing it to electron and rebounds without causing it to recoil because electron is tightly rebound.recoil because electron is tightly rebound.

• No kinetic energy is acquired by the No kinetic energy is acquired by the electron because it does not recoil.electron because it does not recoil.

• The photon is scattered without loss of The photon is scattered without loss of energy and with unmodified wavelength.energy and with unmodified wavelength.

Classical or unmodified Classical or unmodified scatteringscattering

• In this process, scattering occurs but In this process, scattering occurs but there is no absorption.there is no absorption.

• The process makes only a small The process makes only a small contribution to the attenuation of a contribution to the attenuation of a beam in radiology.beam in radiology.

• It is also called Thomson scattering. It is also called Thomson scattering.

Classical scatteringClassical scattering

Photoelectric absorptionPhotoelectric absorption

Photoelectric absorptionPhotoelectric absorption

• It can occur when an incident photon has It can occur when an incident photon has energy equal to or greater than binding energy equal to or greater than binding energy of an electron in an atom of the energy of an electron in an atom of the medium .medium .

• The incident photon gives up all its energy .The incident photon gives up all its energy .

• The electron ,known as secondary electron or The electron ,known as secondary electron or photoelectron .photoelectron .

• Photoelectron is ejected with kinetic energy Photoelectron is ejected with kinetic energy equal to the energy of the incident photon equal to the energy of the incident photon minus the binding energy . minus the binding energy .

Photoelectric absorptionPhotoelectric absorption

• The vacancy is then filled by an electron The vacancy is then filled by an electron from outer shell (characteristic from outer shell (characteristic radiation).radiation).

• In this process, no scattering occur.In this process, no scattering occur.

• Attenuation coefficient for photoelectric Attenuation coefficient for photoelectric process is proportional to ZxZxZ.process is proportional to ZxZxZ.

Photoelectric absorptionPhotoelectric absorption

Photoelectric absorptionPhotoelectric absorption

Compton scatteringCompton scattering

Compton scatteringCompton scattering

• It can occur when incident photon has It can occur when incident photon has much energy than the binding energy of much energy than the binding energy of electron in an atom of the medium.electron in an atom of the medium.

• In this process, both scattering and In this process, both scattering and absorption occur.absorption occur.

• The increase of the wavelength of The increase of the wavelength of scattered photon depends on the angle scattered photon depends on the angle through which it is scattered.through which it is scattered.

• Larger the angle, greater the increase of Larger the angle, greater the increase of the wavelength.the wavelength.

Compton scatteringCompton scattering

• Wavelength is greatest, when the angle Wavelength is greatest, when the angle is 180.is 180.

• The increase in wavelength depend only The increase in wavelength depend only on the angle and independent of the on the angle and independent of the medium and of the actual wavelength.medium and of the actual wavelength.

• For example: For example: The increase in the wavelength is The increase in the wavelength is

always 0.0024 nanometer when the always 0.0024 nanometer when the angle is 90 degree.angle is 90 degree.

Compton scatteringCompton scattering

Pair productionPair production

Pair productionPair production

• It can occur when an incident photon has It can occur when an incident photon has energy equal to or greater than 1.02MeV.energy equal to or greater than 1.02MeV.

• At these energies ,a photon can interact with At these energies ,a photon can interact with the field around the nucleus of an atom of the the field around the nucleus of an atom of the medium.medium.

• This results in spontaneous creation of a pair This results in spontaneous creation of a pair of electrons ,one negatively charged of electrons ,one negatively charged (Negatron ) and the other positively charged (Negatron ) and the other positively charged ( positron ).( positron ).

• In this process, mass and energy are In this process, mass and energy are interchangeable ( Einstein law ).interchangeable ( Einstein law ).

Pair productionPair production

Pair productionPair production

• When positron and negatron are When positron and negatron are annihilated secondary annihilation annihilated secondary annihilation radiation produced each having radiation produced each having 0.51MeV traveling at 180 degree to 0.51MeV traveling at 180 degree to each other.each other.

• No scattering occur in this process.No scattering occur in this process.

Photo - nuclear disintegrationPhoto - nuclear disintegration

Photo - nuclear Photo - nuclear disintegrationdisintegration

• It can occur when an incident photon has It can occur when an incident photon has energy enough to disintegrate the energy enough to disintegrate the nucleus of an atom ( to eject proton or nucleus of an atom ( to eject proton or neutron ).neutron ).

• It can occur at the energies range It can occur at the energies range between 20 to 25 MeV between 20 to 25 MeV

PHYSICS OF ULTRASOUNDPHYSICS OF ULTRASOUND

UltrasoundUltrasound

• Ultrasound is > 20000 cycles per second (20 KHz). Ultrasound is > 20000 cycles per second (20 KHz). • Frequencies up to 100 MHz.Frequencies up to 100 MHz.• Medical diagnostic ultrasonography has got frequency 1-20 MHz.Medical diagnostic ultrasonography has got frequency 1-20 MHz.• Dog and cat may perceive ultrasound up to 100 KHz but no disturbance by the Dog and cat may perceive ultrasound up to 100 KHz but no disturbance by the

commonly employed frequencies.commonly employed frequencies.• Sound waves are cyclic alterations of matter in time and space caused by a force Sound waves are cyclic alterations of matter in time and space caused by a force

( in this case mechanical pressure ).( in this case mechanical pressure ).• Sound waves transmitted at velocities characteristic of each medium.Sound waves transmitted at velocities characteristic of each medium.• The particles are alternately compressed and rarefied.The particles are alternately compressed and rarefied.• Wavelength ( Wavelength ( λλ ) consists of the distance between compressed and rarefied ) consists of the distance between compressed and rarefied

particles in one cycle.particles in one cycle.• Wavelengths are inversely proportional to frequency ( Wavelengths are inversely proportional to frequency ( f f ) or cycles per second. ) or cycles per second.• High frequencies have shorter wavelengths and vice versa.High frequencies have shorter wavelengths and vice versa. λλ == c / c / ff or c or c == λλ x x f f • One – ten MHz and a mean velocity of 1540 m/s in soft tissues has a One – ten MHz and a mean velocity of 1540 m/s in soft tissues has a

wavelengths of 1.5 and 0.15 mm.wavelengths of 1.5 and 0.15 mm.• Longitudinal waves have a amplitudes in the transmitting direction.Longitudinal waves have a amplitudes in the transmitting direction.• Transverse waves have a oscillations perpendicular to this direction.Transverse waves have a oscillations perpendicular to this direction.• Medical diagnostic ultrasonography uses only the longitudinal waves. Medical diagnostic ultrasonography uses only the longitudinal waves.

Interaction of ultrasound beams with Interaction of ultrasound beams with tissuetissue

• Sound intensitySound intensity• VelocityVelocity• Acoustic ImpedanceAcoustic Impedance• ReflectionReflection• TransmissionTransmission• RefractionRefraction• ScatteringScattering• AbsorptionAbsorption• Divergence.Divergence.

Sound intensitySound intensity

• Amplitude ( Amplitude ( jj ) : is the maximum ) : is the maximum extension of its oscillation.extension of its oscillation.

• Higher amplitude may be attained by Higher amplitude may be attained by increasing the energy supply.increasing the energy supply.

• High amplitude or high sound intensity High amplitude or high sound intensity is indicative of high sound valium.is indicative of high sound valium.

• In real time ultrasonography the higher In real time ultrasonography the higher the sound intensity the brighter the the sound intensity the brighter the echoes will be on monitor.echoes will be on monitor.

Sound wavesSound waves

Velocity Velocity

• Sound velocity varies in different media.Sound velocity varies in different media.• Sound velocity ( c ) is dependent on the wavelength and Sound velocity ( c ) is dependent on the wavelength and

frequency of sound beams and the density of the media in which frequency of sound beams and the density of the media in which the sound wave transmitted.the sound wave transmitted.

• Stiffness and compressibility of the material probably more Stiffness and compressibility of the material probably more important than density.important than density.

• Examples : Examples : AgAg density is 13.9 times of water., Water density is density is 13.9 times of water., Water density is one., the velocity of sound in the one., the velocity of sound in the AgAg is 1450 and in the water is is 1450 and in the water is 1520 (almost the same) and it is due to stiffness. (stiffness 1520 (almost the same) and it is due to stiffness. (stiffness of the of the AgAg is 13.4 times more than water or compressibility of the is 13.4 times more than water or compressibility of the water is 13.4 times greater than water is 13.4 times greater than AgAg).).

• Sound velocity is varies in the bodies soft tissue between 1520 Sound velocity is varies in the bodies soft tissue between 1520 m/s (water) and 1950 m/s (skin) , the mean value being 1540 m/s (water) and 1950 m/s (skin) , the mean value being 1540 m/s. m/s.

• There is an exception of air filled lung tissue (345 m/s).There is an exception of air filled lung tissue (345 m/s).

Acoustic ImpedanceAcoustic Impedance

• Acoustic impedance ( Acoustic impedance ( ZZ ) ) is tissue is tissue characteristics such as molecule connection characteristics such as molecule connection and elementary substance inertia counteract and elementary substance inertia counteract sound beam transmission.sound beam transmission.

• ZZ = density X velocity = density X velocity

• Examples : Air 0.004 ( g / cm.cm / second X Examples : Air 0.004 ( g / cm.cm / second X 1/100000 )., water 1.54 ., liver 1.65 ., bone 7.8 .1/100000 )., water 1.54 ., liver 1.65 ., bone 7.8 .

Acoustic ImpedanceAcoustic Impedance

ReflectionReflection• Tissues with impedance differences have acoustic interfaces that Tissues with impedance differences have acoustic interfaces that

reflect sound waves with proportional intensity to the degree of reflect sound waves with proportional intensity to the degree of difference in impedances.difference in impedances.

• Sound beams perpendicular to an interface at a 90 degree angle Sound beams perpendicular to an interface at a 90 degree angle ((αα) will be reflected at a 90 degree angle () will be reflected at a 90 degree angle (ββ) to the interface ( ) to the interface ( αα = = ββ = 90 degrees ). = 90 degrees ).

• The sound receiver, scanner or transducer can register these The sound receiver, scanner or transducer can register these echoes.echoes.

• The none reflected sound beams continue transmitting through The none reflected sound beams continue transmitting through the new medium.the new medium.

• Only sound beams perpendicular to an interface will Only sound beams perpendicular to an interface will produce ultrasound images that can be accurately produce ultrasound images that can be accurately assessed for the thickness and echogenicity.assessed for the thickness and echogenicity.

• At an interface with a high acoustic impedance nearly all sound At an interface with a high acoustic impedance nearly all sound intensity is reflected. intensity is reflected.

• Small differences in acoustic impedance will cause the reflected Small differences in acoustic impedance will cause the reflected intensities to be small.intensities to be small.

• Complete reflection caused by interface with gas or mineral.Complete reflection caused by interface with gas or mineral.• Soft tissues show small differences in acoustic impedance.Soft tissues show small differences in acoustic impedance.

ReflectionReflection

ReflectionReflection

• It is true when the reflected echoes are 90 It is true when the reflected echoes are 90 degrees. degrees.

ReflectionReflection

Examples :Examples :

• interface between air and tissues 99.9%.interface between air and tissues 99.9%.

• interface between kidney and fat 0.64%.interface between kidney and fat 0.64%.

• interface between skull and brain 44%.interface between skull and brain 44%.

TransmissionTransmission

• The none reflected sound beams continue The none reflected sound beams continue transmitting through the new medium.transmitting through the new medium.

• Reflected sound beams + Transmitted Reflected sound beams + Transmitted sound beams = 100%.sound beams = 100%.

• The relationship of reflected to The relationship of reflected to transmitted echo amplitude depend on transmitted echo amplitude depend on the impedance difference of two tissues at the impedance difference of two tissues at an interface.an interface.

RefractionRefraction

• When the sound beam angle ( When the sound beam angle ( αα ) is not 90 ) is not 90 degrees some of the reflected sound waves do degrees some of the reflected sound waves do not return directly to the transducer, the result not return directly to the transducer, the result is production of the is production of the ARTIFACTARTIFACT..

• Artifacts is a false position in this case.Artifacts is a false position in this case.• Refraction is due to changes of wavelength in Refraction is due to changes of wavelength in

second medium .second medium .• Changes of the wavelength is due to changes Changes of the wavelength is due to changes

of the velocity.of the velocity.• Frequency doesn’t change.Frequency doesn’t change.• Refraction angle can be measure by Snell’s Refraction angle can be measure by Snell’s

law. law.

Snell’s lowSnell’s low

Angle of incidenceAngle of incidence

Angle of refractionAngle of refraction

Velocity in first mediumVelocity in first medium

Velocity in second mediumVelocity in second medium

RefractionRefraction

Scattering, Absorption & Scattering, Absorption & DivergenceDivergence

• Ultrasound waves encountering small, uneven Ultrasound waves encountering small, uneven and inclined acoustic interface are and inclined acoustic interface are DIFFUSELY DIFFUSELY REFLECTEDREFLECTED also termed also termed SCATTERINGSCATTERING..

• REFLECTION, TRANSSMITION & REFRACTIONREFLECTION, TRANSSMITION & REFRACTION are usually associated with relatively are usually associated with relatively LARGE LARGE OBJECTSOBJECTS, while , while SCATTERINGSCATTERING & & DIVERGECNCE DIVERGECNCE occur with occur with SMALLER STRUCTURESMALLER STRUCTURE..

• Fine tissue structure, e.g. capillaries and cells Fine tissue structure, e.g. capillaries and cells which are smaller than ultrasound wavelength, which are smaller than ultrasound wavelength, show distinct texture in which the separate show distinct texture in which the separate echoes are not represent by an actual dote on the echoes are not represent by an actual dote on the image.image.

Scattering, Absorption & Scattering, Absorption & DivergenceDivergence

• Longitudinal waves travel straight trough a Longitudinal waves travel straight trough a homogeneous medium at a specific velocity.homogeneous medium at a specific velocity.

• At the same time part of the sound waves At the same time part of the sound waves mechanical energy is converted to heat.mechanical energy is converted to heat.

• The decrease in sound energy and intensity The decrease in sound energy and intensity through absorption is dependent upon the through absorption is dependent upon the frequency and the tissue texture ( viscosity frequency and the tissue texture ( viscosity and resilience ) .and resilience ) .

• Increase frequency gives increase attenuation.Increase frequency gives increase attenuation.• High frequencies lead to increase attenuation and High frequencies lead to increase attenuation and

decreased sound wave dept penetration.decreased sound wave dept penetration.• Absorption in soft tissues is relatively minor. Absorption in soft tissues is relatively minor.

Scattering, Absorption & Scattering, Absorption & DivergenceDivergence

• In bones, attenuation becomes squared In bones, attenuation becomes squared with each increase of frequency.with each increase of frequency.

• Absorption in soft tissues is relatively Absorption in soft tissues is relatively minor.minor.

• Bones, calcifications and calculi show Bones, calcifications and calculi show Acoustic ShadowingAcoustic Shadowing. .

Frequency and Frequency and PenetrationPenetration

ScatteringScattering

DivergenceDivergence

Biological Effects Biological Effects CommentsComments• The intensities approved for commercial, 2D The intensities approved for commercial, 2D

ultrasound systems in human medicine are around ultrasound systems in human medicine are around 10 mW / cm.cm .10 mW / cm.cm .

• Duplex ultrasonography, displaying both 2D images Duplex ultrasonography, displaying both 2D images and blood flow, may reach intensities of 60 – 90 and blood flow, may reach intensities of 60 – 90 mW / cm.cm.mW / cm.cm.

• Non-Doppler diagnostic ultrasound may be safely Non-Doppler diagnostic ultrasound may be safely used continuously over a reasonably extended used continuously over a reasonably extended period.period.

• Constant testing for adverse effects is done with any Constant testing for adverse effects is done with any new and improved technique to avoid damage safely new and improved technique to avoid damage safely intensity of over 100 mW / cm.cm should be applied intensity of over 100 mW / cm.cm should be applied for a limited time only.for a limited time only.

• Diagnostic ultrasonography is a safe method when Diagnostic ultrasonography is a safe method when using approved equipment using approved equipment

Biological Effects Biological Effects CommentsComments• High frequencies and high intensities have High frequencies and high intensities have

been shown to cause damage.been shown to cause damage.• Long exposure to ultrasound may lead to tissue Long exposure to ultrasound may lead to tissue

lesions and necrosis, and even to teratogenic lesions and necrosis, and even to teratogenic change chromosomal damage and mutation.change chromosomal damage and mutation.

• Numerous animal experiments and human Numerous animal experiments and human statistics show that adverse side-effects are statistics show that adverse side-effects are not found with diagnostic ultrasound.not found with diagnostic ultrasound.

• No biological effects of ultrasound were noted No biological effects of ultrasound were noted with low MHz frequencies, when intensities less with low MHz frequencies, when intensities less than 100 mW / cm.cm were applied to than 100 mW / cm.cm were applied to mammalian tissue.mammalian tissue.

Biological effects of Biological effects of UltrasoundUltrasound

• Mechanical Effects.Mechanical Effects.

• Thermal Effects.Thermal Effects.

• Chemical Effects.Chemical Effects.

Mechanical EffectsMechanical Effects

• Ultrasound causes mechanical vibration in tissues.Ultrasound causes mechanical vibration in tissues.• The particles are compressed (pressure phase) and then dispersed The particles are compressed (pressure phase) and then dispersed

(suction phase).(suction phase).• Small cavities form in fluids during the suction phase and disappear Small cavities form in fluids during the suction phase and disappear

in the pressure phase.in the pressure phase.• This phenomenon is describe as cavitation in gas-free fluid and This phenomenon is describe as cavitation in gas-free fluid and

psudocavitation in fluid with gas.psudocavitation in fluid with gas.• The amount of cavitation and pesudocavitation depend on the The amount of cavitation and pesudocavitation depend on the

frequency and the intensity (sound energy per areafrequency and the intensity (sound energy per area ( ( ..• High frequency combine with high intensities have great mechanical High frequency combine with high intensities have great mechanical

effects.effects.• There are no confirmed adverse effects or mechanical damage to cell There are no confirmed adverse effects or mechanical damage to cell

membranes or chromosomes by exposure to diagnostic levels of membranes or chromosomes by exposure to diagnostic levels of ultrasound.ultrasound.

• Therapeutic ultrasound which applies higher intensities than Therapeutic ultrasound which applies higher intensities than diagnostic sonography, uses this mechanical forces for generation of diagnostic sonography, uses this mechanical forces for generation of heat or in a more sophisticated application, for destruction of renal heat or in a more sophisticated application, for destruction of renal calculi (Lithotripsy). calculi (Lithotripsy).

Thermal EffectsThermal Effects

• Thermal effects of ultrasound are due to ultrasound Thermal effects of ultrasound are due to ultrasound energy absorption and its transformation into the energy absorption and its transformation into the heat.heat.

• This effect is also depend on frequency and intensity.This effect is also depend on frequency and intensity.• Intensities used in diagnostic Ultrasonography are Intensities used in diagnostic Ultrasonography are

not thought to cause significant thermal effects.not thought to cause significant thermal effects.• Beam characteristicBeam characteristic and the heat reducing effect of and the heat reducing effect of

vasculariztion are thought to contribute to the lack of vasculariztion are thought to contribute to the lack of thermal effects ,provided the vascular system is thermal effects ,provided the vascular system is intact and moves the heat away.intact and moves the heat away.

• Hyperthermia, however, is used in therapeutic Hyperthermia, however, is used in therapeutic Ultrasonography.Ultrasonography.

Chemical EffectsChemical Effects

• The chemical effects of ultrasound are The chemical effects of ultrasound are oxidation, reduction and oxidation, reduction and depolymerization.depolymerization.

• The ability of ultrasound to The ability of ultrasound to depolymerize macromolecules like depolymerize macromolecules like polysaccharides, various proteins or polysaccharides, various proteins or isolated DNA has been demonstrated isolated DNA has been demonstrated experimentally.experimentally.

• These adverse biological effects, These adverse biological effects, however, are not found with diagnostic however, are not found with diagnostic ultrasound.ultrasound.

Mode of DisplayMode of Display

Mode of displayMode of display

• A-Mode ( Pulse-Echo-Mode).A-Mode ( Pulse-Echo-Mode).

• B-Mode.B-Mode.

1) One-Dimensional B-mode.1) One-Dimensional B-mode.

2) Two dimensional B mode.2) Two dimensional B mode.

3) Compound scan3) Compound scan

Real- time Real- time UltrasonographyUltrasonography

• The resulting image is either a:The resulting image is either a:

1) Triangular or Pie-shaped1) Triangular or Pie-shaped

2) Rectangular2) Rectangular

3) Convex3) Convex

• The same classification applies to The same classification applies to transducers.transducers.

Transducers & SonogramsTransducers & Sonograms

Transducers & SonogramsTransducers & Sonograms

•Sector transducer Sector transducer – sector – sector sonogram.sonogram.

•Linear or parallel transducerLinear or parallel transducer –parallel sonogram –parallel sonogram

•Curved – array transducer Curved – array transducer – convex sonogram. – convex sonogram.

Sector transducer Sector Sector transducer Sector sonogramsonogram

Sector transducer – sector Sector transducer – sector sonogramsonogram

• Sector transducers produce a triangular or Sector transducers produce a triangular or pie-shaped image.pie-shaped image.

• The scan line density of the display is The scan line density of the display is higher in the near field, while the lines higher in the near field, while the lines diverge in the far field.diverge in the far field.

• Most commercial sector scanners are Most commercial sector scanners are mechanical.mechanical.

• One to eight crystals are mounted on the One to eight crystals are mounted on the transducer and are either rotated in a transducer and are either rotated in a circular motion or oscillated to-and-fro. circular motion or oscillated to-and-fro.

Sector sonogramSector sonogram

Sector transducer – sector Sector transducer – sector sonogramsonogram

• An angle of 60 -120 can be scanned within An angle of 60 -120 can be scanned within a short time.a short time.

• Echoes from a dept of 10 cm return to Echoes from a dept of 10 cm return to transducer 0.13 ms after being pulsed.transducer 0.13 ms after being pulsed.

• Electronic sector scanners are made of Electronic sector scanners are made of several ceramics, each holding numerous several ceramics, each holding numerous piezoelectric elements.piezoelectric elements.

• Triggering of these crystals must follow at Triggering of these crystals must follow at exact sequence or phases, which is why exact sequence or phases, which is why these electronic transducers are called these electronic transducers are called phased-array scanners. phased-array scanners.

Sector transducer – sector Sector transducer – sector sonogramsonogram

• The crystals in some newer sector The crystals in some newer sector scanner are mounted in an annular scanner are mounted in an annular fashion.fashion.

• This is referred to as an This is referred to as an annular- (phased-) array transducer. annular- (phased-) array transducer.

Linear or parallel transducerLinear or parallel transducer Parallel sonogram Parallel sonogram

Linear or parallel transducerLinear or parallel transducer

• Linear transducers produce rectangular Linear transducers produce rectangular display format.display format.

Linear or parallel transducer Linear or parallel transducer

Parallel sonogramParallel sonogram

Curved – array transducer Curved – array transducer Convex sonogramConvex sonogram

Curved – array transducer Curved – array transducer

• curved – array curved – array transducer are a transducer are a combination of both combination of both sector scanners and sector scanners and linear scanners.linear scanners.

Curved – array transducer Curved – array transducer

Convex sonogramConvex sonogram

Comparison of transducer Comparison of transducer typestypes

CommentComment

• An all-around transducer for both An all-around transducer for both abdominal and cardiac examinations abdominal and cardiac examinations in dogs and cats is a 5 MHz sector in dogs and cats is a 5 MHz sector transducer with near focus.transducer with near focus.