# In the name of God. GENERAL PHYSICS Physics Physics is a science that study of two concept : Physics is a science that study of two concept : Matter.

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In the name of God

GENERAL PHYSICS

Physics Physics is a science that study of two concept : Physics is a science that study of two concept : Matter Matter Energy Energy

Matter Matter may be solid, liquid or gas Matter 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 atoms or molecules. Matter is composed of sub-microscopic units called atoms or molecules. Matter can be neither created nor destroyed. Matter can be neither created nor destroyed.

Energy Energy is ability to do work. Energy is ability to do work. Energy can be neither created nor destroyed. Energy can be neither created nor destroyed.

Force Force produces or tends to produce movement in a body. Force produces or tends to produce movement in a body. The unit of force is Newton. The unit of force is Newton. A Newton is that force which when applied to a body having a mass of one Kilogram, gives it an acceleration of one meter per second per second. A Newton is that force which when applied to a body having a mass of one Kilogram, gives it an acceleration of one meter per second per second.

Work Work is equal to the force × the distance Work is equal to the force × the distance W = fh W = fh The unit of work called joule. The unit of work called joule. Joule is the work done when the force of one Newton moves to a distance of one meter in the direction of the force. Joule is the work done when the force of one Newton moves to a distance of one meter in the direction of the force.

Temperature and Heat Temperature: we may have high or low temperature Temperature: we may have high or low temperature Heat: we can rise of temperature by heating a matter Heat: we can rise of temperature by heating a matter Temperature is commonly measure by instrument called Thermometer Temperature is commonly measure by instrument called Thermometer

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

Atomic Structure Elements Elements Compounds Compounds Atoms Atoms Molecules Molecules

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

Compound Compound: A compound is formed when two or more elements combine together chemically to produce a more complex kind of matter. Compound: A compound is formed when two or more elements combine together chemically to produce a more complex kind of matter. Example: Water is a compound of oxygen an hydrogen. Example: Water is a compound of oxygen an hydrogen.

Atoms Atoms are the smallest particles of an element that can exist without losing the chemical properties of the element. Atoms are the smallest particles of an element that can exist without losing the chemical properties of the element. The diameter of an atom is 1/10,000,000,000 meter The diameter of an atom is 1/10,000,000,000 meter

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

X-rays  The properties of X-ray The production of X-ray The production of X-ray Interactions of electrons with the target Interactions of electrons with the target Spectra of X-rays Spectra of X-rays The quality and intensity of X-rays The quality and intensity of X-rays The factors influencing quality and intensity The factors influencing quality and intensity

The properties of X-ray Fluorescence Fluorescence Photographic effect Photographic effect Penetration Penetration Ionization and Excitation Ionization and Excitation Chemical changes Chemical changes Biological effects Biological effects

The properties of X-ray

Fluorescence X-rays produce fluorescence in some materials such as Calcium Tungstate, Zinc Cadmium Sulphide and Caesium Iodide. X-rays produce fluorescence in some materials such as Calcium Tungstate, Zinc Cadmium Sulphide and Caesium Iodide. Afterglow less than 1/100,000,000 second Afterglow less than 1/100,000,000 second It is used in intensifying screen and fluoroscopy. It is used in intensifying screen and fluoroscopy.

Photographic effect X-rays produce a latent image. X-rays produce a latent image. It is utilized in film-badge dosimetry for radiation protection. It is utilized in film-badge dosimetry for radiation protection. To a small extend in a radiography (5%). To a small extend in a radiography (5%).

Penetration X-rays penetrate substances that are opaque to visible light. X-rays penetrate substances that are opaque to visible light. The amount of absorption depend on: The amount of absorption depend on: 1)Atomic number of the object 1)Atomic number of the object 2)Density of the object 2)Density of the object 3)Energy of the X-rays 3)Energy of the X-rays

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

Chemical changes X-rays produce chemical changes in substances through which they pass. X-rays produce chemical changes in substances through which they pass. One important change is the oxidation of the ferrous sulphate { FeSO 4 } in solution to ferric sulphate { Fe 2 ( SO 4 ) 3 } One important change is the oxidation of the ferrous sulphate { FeSO 4 } in solution to ferric sulphate { Fe 2 ( SO 4 ) 3 } This is chemical system of dosimetry for quantity of X radiation absorbed. This is chemical system of dosimetry for quantity of X radiation absorbed.

Biological effects X-rays produce biological effects in living organism either by : X-rays produce biological effects in living organism either by : 1) Direct action on the cells. 1) Direct action on the cells. 2) Indirect action as a result of chemical changes near the cells. 2) Indirect action as a result of chemical changes near the cells. Somatic action ( damage or kill the cells ) Somatic action ( damage or kill the cells ) Genetic action ( mutation changes in subsequent generations ) Genetic action ( mutation changes in subsequent generations ) Useful effects : Useful effects : 1) Radiotherapy 1) Radiotherapy 2) Sterilization of hospital supplies, such as syringes and dressing. 2) Sterilization of hospital supplies, such as syringes and dressing. The properties of X-ray

Diagnostic Imaging

Physics of radiology Introduction Introduction X-ray department X-ray department X-ray machines X-ray machines X-ray unit circuit X-ray unit circuit X-ray tube X-ray tube Rectification Rectification High tension transformer High tension transformer Electromagnetic radiation Electromagnetic radiation X-ray properties X-ray properties X-ray production X-ray production Interaction of X-ray with matter Interaction of X-ray with matter Focusing Focusing Filtration Filtration X-ray dosimetery X-ray dosimetery Radiological protection Radiological protection Shielding Shielding

Electromagnetic spectrum X & Gamma rays have got : Short wave length Short wave length High energy High energy

Wave length Wave length is a distance between two equal points two equal points

The production of X-ray

Energy loss by electrons : X-rays are produced when electrons give up energy by two processes. Energy loss by electrons : X-rays are produced when electrons give up energy by two processes. 1) The deceleration of a fast-moving electron. 1) The deceleration of a fast-moving electron. 2) The movement of an electron between two inner shells in an atom. 2) The movement of an electron between two inner shells in an atom.

The principles of operation of a X-ray tube X –ray tube is sometimes called a coolidge tube ( inventor ). X –ray tube is sometimes called a coolidge tube ( inventor ). In X-ray tube, electrons are release from a heated filament by thermionic emission. In X-ray tube, electrons are release from a heated filament by thermionic emission. The electrons are then accelerated across the tube by a high voltage applied between the filament and the anode. The electrons are then accelerated across the tube by a high voltage applied between the filament and the anode. When the electrons reach the anode, they are traveling at a high velocity therefore; they have high kinetic energy and this is converted into X-rays and heat. When the electrons reach the anode, they are traveling at a high velocity therefore; they have high kinetic energy and this is converted into X-rays and heat.

X-ray tube

The principles of operation of a X-ray tube The filament, is usually a spiral of Tungsten wire. The filament, is usually a spiral of Tungsten wire. It is heated by a low-voltage supply. It is heated by a low-voltage supply. Electrons are released from the filament by thermionic emission. Electrons are released from the filament by thermionic emission. Tungsten is used because it produces appreciable thermionic emission at temperatures well below its melting point. Tungsten is used because it produces appreciable thermionic emission at temperatures well below its melting point.

The principles of operation of a X-ray tube A high-voltage supply is connected between filament and target. A high-voltage supply is connected between 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 made of Tungsten. Target of medical X-ray tubes are usually made of Tungsten. Tungsten has: Tungsten has: 1) high melting point 1) high melting point 2) adequate thermal conductivity 2) adequate thermal conductivity 3) high atomic number (74) which increases the efficiency of X-ray production. 3) high atomic number (74) which increases the efficiency of X-ray production.

The principles of operation of a X-ray tube Kinetic energy is gained by the negatively charged electrons released from the filament as they are accelerated to high velocity by the positive voltage apply to the target. Kinetic energy is gained by the negatively charged electrons released from the filament as they are accelerated to high velocity by the positive voltage apply to the target. A high vacuum exist in the tube, so no electron produces by ionization. A high vacuum exist in the tube, so no electron produces by ionization. A shield or focusing cup, mounted near the filament and it is a part of cathode assembly. A shield or focusing cup, mounted near the 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 damage by electron bombardment. 1) this protects adjacent parts of the tube wall from damage by electron bombardment. 2) this focuses the electrons on to a small area of the target known as the focus or focal area. 2) this focuses the electrons on to a small area of the target known as the focus or focal area.

X-rays The properties of X-ray The properties of X-ray The production of X-ray The production of X-ray  Interactions of electrons with the target Spectra of X-rays Spectra of X-rays The quality and intensity of X-rays The quality and intensity of X-rays The factors influencing quality and intensity The factors influencing quality and intensity

Interactions of electrons with the target The efficiency of X-ray production is less than 1% in medical X-ray tube. The efficiency of X-ray production is less than 1% in medical X-ray tube. In a linear accelerator the efficiency is about 40% (X-rays are produce at 4 MeV). In a linear accelerator the efficiency is about 40% (X-rays are produce at 4 MeV). X-rays produce in diagnostic radiology unit have got energy between 12.4 KeV and 124 KeV. X-rays produce in diagnostic radiology unit have got energy between 12.4 KeV and 124 KeV. Maximum photon energy of the X or gamma rays can be 12.4 MeV. Maximum photon energy of the X or gamma rays can be 12.4 MeV.

Interactions of electrons with the target Four types of interaction are possible at the target: Four types of interaction are possible at the target: 1) Excitation involving an electron in an outer shell. 1) Excitation involving an electron in an outer shell. 2) Ionization by the removal an electron from an outer shell. 2) Ionization by the removal an electron from an outer shell. 3) Ionization by the removal an electron from an inner shell. 3) Ionization by the removal an electron from an inner shell. 4) Bremsstrahlung production. 4) Bremsstrahlung production.

Excitation involving an electron in an outer shell The incident electron transfers a small amount of energy ( only a few electron volts ) to an electron in an outer shell of an atom in the target. The incident electron transfers a small amount of energy ( only a few electron volts ) to an electron in an outer shell of an atom in the target. It displaces electron to an energy level farther out. It displaces electron to an energy level farther out. The electron returns to the vacancy in the shell and the energy release as heat in the target. The electron returns to the vacancy in the shell and the energy release as heat in the target.

Excitation

Ionization by the removal an electron from an outer shell The incident electron transfer sufficient energy to ionize an atom of the target. The incident electron transfer sufficient energy to ionize an atom of the target. The displaced electron, known as a secondary electron may produce further ionization or excitation. The displaced electron, known as a secondary electron may produce further ionization or excitation. Again only a small amount of energy is released and it appears as heat. Again only a small amount of energy is released and it appears as heat.

Ionization of the outer shell

Ionization by the removal an electron from an inner shell The incident electron transfers sufficient energy to remove an electron from an inner shell. The incident electron transfers sufficient energy to remove an electron from an inner shell. To do this the electron must have energy equal to or grater than the binding energy for that shell. To do this the electron must have energy equal to 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 electron moving inwards from another shell. The vacancy in the inner shell is filled by an electron moving inwards from another shell. It is accompany by the emission of an X-ray photon of energy equal to the difference between the binding energy of the two shells. It is accompany by the emission of an X-ray photon of energy equal to the difference between the binding energy of the two shells. This photon is known as a Characteristic X-ray photon. This photon is known as a Characteristic X-ray photon. Its energy depend on the element of which the target is made. Its energy depend on the element of which the target is made. The photon energy for Characteristic X-ray for Tungsten is between 57 to 69 KeV. The photon energy for Characteristic X-ray for Tungsten is between 57 to 69 KeV.

Ionization of the inner shell

Bremsstrahlung production The incident electron passes close to the nucleus of an atom in the target. The incident electron passes close to the nucleus of an atom in the target. The electron is negatively charged and the attraction of the positive electric charge of the nucleus makes it decelerate. The electron is negatively charged and the attraction of the positive electric charge of the nucleus makes it decelerate. The electron loses energy in the form of an X-ray photon. The electron loses energy in the form of an X-ray photon. The energy of the X-ray photon depends on the degree of deceleration. The energy of the X-ray photon depends on the degree of deceleration. The photon energy can take any value from zero to a maximum. The photon energy can take any value from zero to a maximum. The maximum photon energy occurs when the electron passes very close to the nucleus and the deceleration is so great that the electron comes to rest. The maximum photon energy occurs when the electron passes very close to the nucleus and the deceleration is so great that the electron comes to rest. This is known as Braking radiation and it gives rise to the continuous spectrum of X-rays. This is known as Braking radiation and it gives rise to the continuous spectrum of X-rays.

Bremsstrahlung production

Interaction of X - ray with matter

Interaction of X ray with matter There are 5 process by which X or gamma ray may absorbed or scattered. There are 5 process by which X or gamma ray may absorbed or scattered. 1) Classical or unmodified scattering. 1) Classical or unmodified scattering. 2) Photoelectric scattering 2) Photoelectric scattering 3) Compton unmodified scattering. 3) Compton unmodified scattering. 4) pair production 4) pair production 5) Photo – nuclear disintegration 5) Photo – nuclear disintegration

Classical or unmodified scattering

It can occur when an photon with low energy hits an atoms with high atomic number. It can occur when an photon with low energy hits an atoms with high atomic number. An incident photon collides with an electron and rebounds without causing it to recoil because electron is tightly rebound. An incident photon collides with an electron and rebounds without causing it to recoil because electron is tightly rebound. No kinetic energy is acquired by the electron because it does not recoil. No kinetic energy is acquired by the electron because it does not recoil. The photon is scattered without loss of energy and with unmodified wavelength. The photon is scattered without loss of energy and with unmodified wavelength.

Classical or unmodified scattering In this process, scattering occurs but there is no absorption. In this process, scattering occurs but there is no absorption. The process makes only a small contribution to the attenuation of a beam in radiology. The process makes only a small contribution to the attenuation of a beam in radiology. It is also called Thomson scattering. It is also called Thomson scattering.

Classical scattering

Photoelectric absorption

It can occur when an incident photon has energy equal to or greater than binding energy of an electron in an atom of the medium. It can occur when an incident photon has energy equal to or greater than binding energy of an electron in an atom of the medium. The incident photon gives up all its energy. The incident photon gives up all its energy. The electron,known as secondary electron or photoelectron. The electron,known as secondary electron or photoelectron. Photoelectron is ejected with kinetic energy equal to the energy of the incident photon minus the binding energy. Photoelectron is ejected with kinetic energy equal to the energy of the incident photon minus the binding energy.

Photoelectric absorption The vacancy is then filled by an electron from outer shell (characteristic radiation). The vacancy is then filled by an electron from outer shell (characteristic radiation). In this process, no scattering occur. In this process, no scattering occur. Attenuation coefficient for photoelectric process is proportional to ZxZxZ. Attenuation coefficient for photoelectric process is proportional to ZxZxZ.

Photoelectric absorption

Compton scattering

It can occur when incident photon has much energy than the binding energy of electron in an atom of the medium. It can occur when incident photon has much energy than the binding energy of electron in an atom of the medium. In this process, both scattering and absorption occur. In this process, both scattering and absorption occur. The increase of the wavelength of scattered photon depends on the angle through which it is scattered. The increase of the wavelength of scattered photon depends on the angle through which it is scattered. Larger the angle, greater the increase of the wavelength. Larger the angle, greater the increase of the wavelength.

Compton scattering Wavelength is greatest, when the angle is 180. Wavelength is greatest, when the angle is 180. The increase in wavelength depend only on the angle and independent of the medium and of the actual wavelength. The increase in wavelength depend only on the angle and independent of the medium and of the actual wavelength. For example: For example: The increase in the wavelength is always 0.0024 nanometer when the angle is 90 degree. The increase in the wavelength is always 0.0024 nanometer when the angle is 90 degree.

Compton scattering

Pair production

It can occur when an incident photon has energy equal to or greater than 1.02MeV. It can occur when an incident photon has energy equal to or greater than 1.02MeV. At these energies,a photon can interact with the field around the nucleus of an atom of the medium. At these energies,a photon can interact with the field around the nucleus of an atom of the medium. This results in spontaneous creation of a pair of electrons,one negatively charged (Negatron ) and the other positively charged ( positron ). This results in spontaneous creation of a pair of electrons,one negatively charged (Negatron ) and the other positively charged ( positron ). In this process, mass and energy are interchangeable ( Einstein law ). In this process, mass and energy are interchangeable ( Einstein law ).

Pair production

When positron and negatron are annihilated secondary annihilation radiation produced each having 0.51MeV traveling at 180 degree to each other. When positron and negatron are annihilated secondary annihilation radiation produced each having 0.51MeV traveling at 180 degree to each other. No scattering occur in this process. No scattering occur in this process.

Photo - nuclear disintegration

It can occur when an incident photon has energy enough to disintegrate the nucleus of an atom ( to eject proton or neutron ). It can occur when an incident photon has energy enough to disintegrate the nucleus of an atom ( to eject proton or neutron ). It can occur at the energies range between 20 to 25 MeV It can occur at the energies range between 20 to 25 MeV

PHYSICS OF ULTRASOUND

Ultrasound 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 commonly employed frequencies. Dog and cat may perceive ultrasound up to 100 KHz but no disturbance by the commonly employed frequencies. Sound waves are cyclic alterations of matter in time and space caused by a force ( in this case mechanical pressure ). Sound waves are cyclic alterations of matter in time and space caused by a force ( 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 ( λ ) consists of the distance between compressed and rarefied particles in one cycle. Wavelength ( λ ) consists of the distance between compressed and rarefied particles in one cycle. Wavelengths are inversely proportional to frequency ( f ) or cycles per second. Wavelengths are inversely proportional to frequency ( f ) or cycles per second. High frequencies have shorter wavelengths and vice versa. High frequencies have shorter wavelengths and vice versa. λ = c / f or c = λ x f λ = c / f or c = λ x f One – ten MHz and a mean velocity of 1540 m/s in soft tissues has a wavelengths of 1.5 and 0.15 mm. One – ten MHz and a mean velocity of 1540 m/s in soft tissues has a 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 tissue Sound intensity Sound intensity Velocity Velocity Acoustic Impedance Acoustic Impedance Reflection Reflection Transmission Transmission Refraction Refraction Scattering Scattering Absorption Absorption Divergence. Divergence.

Sound intensity Amplitude ( j ) : is the maximum extension of its oscillation. Amplitude ( j ) : is the maximum extension of its oscillation. Higher amplitude may be attained by increasing the energy supply. Higher amplitude may be attained by increasing the energy supply. High amplitude or high sound intensity is indicative of high sound valium. High amplitude or high sound intensity is indicative of high sound valium. In real time ultrasonography the higher the sound intensity the brighter the echoes will be on monitor. In real time ultrasonography the higher the sound intensity the brighter the echoes will be on monitor.

Sound waves

Velocity Sound velocity varies in different media. Sound velocity varies in different media. Sound velocity ( c ) is dependent on the wavelength and frequency of sound beams and the density of the media in which the sound wave transmitted. Sound velocity ( c ) is dependent on the wavelength and frequency of sound beams and the density of the media in which the sound wave transmitted. Stiffness and compressibility of the material probably more important than density. Stiffness and compressibility of the material probably more important than density. Examples : Ag density is 13.9 times of water., Water density is one., the velocity of sound in the Ag is 1450 and in the water is 1520 (almost the same) and it is due to stiffness. (stiffness of the Ag is 13.4 times more than water or compressibility of the water is 13.4 times greater than Ag). Examples : Ag density is 13.9 times of water., Water density is one., the velocity of sound in the Ag is 1450 and in the water is 1520 (almost the same) and it is due to stiffness. (stiffness of the Ag is 13.4 times more than water or compressibility of the water is 13.4 times greater than Ag). 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. 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. 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 Impedance Acoustic impedance ( Z ) is tissue characteristics such as molecule connection and elementary substance inertia counteract sound beam transmission. Acoustic impedance ( Z ) is tissue characteristics such as molecule connection and elementary substance inertia counteract sound beam transmission. Z = density X velocity Z = density X velocity Examples : Air 0.004 ( g / cm.cm / second X 1/100000 )., water 1.54., liver 1.65., bone 7.8. Examples : Air 0.004 ( g / cm.cm / second X 1/100000 )., water 1.54., liver 1.65., bone 7.8.

Acoustic Impedance

Reflection Tissues with impedance differences have acoustic interfaces that reflect sound waves with proportional intensity to the degree of difference in impedances. Tissues with impedance differences have acoustic interfaces that reflect sound waves with proportional intensity to the degree of difference in impedances. Sound beams perpendicular to an interface at a 90 degree angle (α) will be reflected at a 90 degree angle (β) to the interface ( α = β = 90 degrees ). Sound beams perpendicular to an interface at a 90 degree angle (α) will be reflected at a 90 degree angle (β) to the interface ( α = β = 90 degrees ). The sound receiver, scanner or transducer can register these echoes. The sound receiver, scanner or transducer can register these echoes. The none reflected sound beams continue transmitting through the new medium. The none reflected sound beams continue transmitting through the new medium. Only sound beams perpendicular to an interface will produce ultrasound images that can be accurately assessed for the thickness and echogenicity. Only sound beams perpendicular to an interface will produce ultrasound images that can be accurately assessed for the thickness and echogenicity. At an interface with a high acoustic impedance nearly all sound intensity is reflected. At an interface with a high acoustic impedance nearly all sound intensity is reflected. Small differences in acoustic impedance will cause the reflected intensities to be small. Small differences in acoustic impedance will cause the reflected 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.

Reflection

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

Reflection 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%.

Transmission The none reflected sound beams continue transmitting through the new medium. The none reflected sound beams continue transmitting through the new medium. Reflected sound beams + Transmitted sound beams = 100%. Reflected sound beams + Transmitted sound beams = 100%. The relationship of reflected to transmitted echo amplitude depend on the impedance difference of two tissues at an interface. The relationship of reflected to transmitted echo amplitude depend on the impedance difference of two tissues at an interface.

Refraction When the sound beam angle ( α ) is not 90 degrees some of the reflected sound waves do not return directly to the transducer, the result is production of the ARTIFACT. When the sound beam angle ( α ) is not 90 degrees some of the reflected sound waves do not return directly to the transducer, the result is production of the ARTIFACT. Artifacts is a false position in this case. Artifacts is a false position in this case. Refraction is due to changes of wavelength in second medium. Refraction is due to changes of wavelength in second medium. Changes of the wavelength is due to changes of the velocity. Changes of the wavelength is due to changes of the velocity. Frequency doesn’t change. Frequency doesn’t change. Refraction angle can be measure by Snell’s law. Refraction angle can be measure by Snell’s law.

Snell’s low Angle of incidence Angle of refraction Velocity in first medium Velocity in second medium

Refraction

Scattering, Absorption & Divergence Ultrasound waves encountering small, uneven and inclined acoustic interface are DIFFUSELY REFLECTED also termed SCATTERING. Ultrasound waves encountering small, uneven and inclined acoustic interface are DIFFUSELY REFLECTED also termed SCATTERING. REFLECTION, TRANSSMITION & REFRACTION are usually associated with relatively LARGE OBJECTS, while SCATTERING & DIVERGECNCE occur with SMALLER STRUCTURE. REFLECTION, TRANSSMITION & REFRACTION are usually associated with relatively LARGE OBJECTS, while SCATTERING & DIVERGECNCE occur with SMALLER STRUCTURE. Fine tissue structure, e.g. capillaries and cells which are smaller than ultrasound wavelength, show distinct texture in which the separate echoes are not represent by an actual dote on the image. Fine tissue structure, e.g. capillaries and cells which are smaller than ultrasound wavelength, show distinct texture in which the separate echoes are not represent by an actual dote on the image.

Scattering, Absorption & Divergence Longitudinal waves travel straight trough a homogeneous medium at a specific velocity. Longitudinal waves travel straight trough a homogeneous medium at a specific velocity. At the same time part of the sound waves mechanical energy is converted to heat. At the same time part of the sound waves mechanical energy is converted to heat. The decrease in sound energy and intensity through absorption is dependent upon the frequency and the tissue texture ( viscosity and resilience ). The decrease in sound energy and intensity through absorption is dependent upon the frequency and the tissue texture ( viscosity and resilience ). Increase frequency gives increase attenuation. Increase frequency gives increase attenuation. High frequencies lead to increase attenuation and decreased sound wave dept penetration. High frequencies lead to increase attenuation and decreased sound wave dept penetration. Absorption in soft tissues is relatively minor. Absorption in soft tissues is relatively minor.

Scattering, Absorption & Divergence In bones, attenuation becomes squared with each increase of frequency. In bones, attenuation becomes squared with each increase of frequency. Absorption in soft tissues is relatively minor. Absorption in soft tissues is relatively minor. Bones, calcifications and calculi show Acoustic Shadowing. Bones, calcifications and calculi show Acoustic Shadowing.

Frequency and Penetration

Scattering

Divergence

Biological Effects Comments The intensities approved for commercial, 2D ultrasound systems in human medicine are around 10 mW / cm.cm. The intensities approved for commercial, 2D ultrasound systems in human medicine are around 10 mW / cm.cm. Duplex ultrasonography, displaying both 2D images and blood flow, may reach intensities of 60 – 90 mW / cm.cm. Duplex ultrasonography, displaying both 2D images and blood flow, may reach intensities of 60 – 90 mW / cm.cm. Non-Doppler diagnostic ultrasound may be safely used continuously over a reasonably extended period. Non-Doppler diagnostic ultrasound may be safely used continuously over a reasonably extended period. Constant testing for adverse effects is done with any new and improved technique to avoid damage safely intensity of over 100 mW / cm.cm should be applied for a limited time only. Constant testing for adverse effects is done with any new and improved technique to avoid damage safely intensity of over 100 mW / cm.cm should be applied for a limited time only. Diagnostic ultrasonography is a safe method when using approved equipment Diagnostic ultrasonography is a safe method when using approved equipment

Biological Effects Comments High frequencies and high intensities have been shown to cause damage. High frequencies and high intensities have been shown to cause damage. Long exposure to ultrasound may lead to tissue lesions and necrosis, and even to teratogenic change chromosomal damage and mutation. Long exposure to ultrasound may lead to tissue lesions and necrosis, and even to teratogenic change chromosomal damage and mutation. Numerous animal experiments and human statistics show that adverse side-effects are not found with diagnostic ultrasound. Numerous animal experiments and human statistics show that adverse side-effects are not found with diagnostic ultrasound. No biological effects of ultrasound were noted with low MHz frequencies, when intensities less than 100 mW / cm.cm were applied to mammalian tissue. No biological effects of ultrasound were noted with low MHz frequencies, when intensities less than 100 mW / cm.cm were applied to mammalian tissue.

Biological effects of Ultrasound Mechanical Effects. Mechanical Effects. Thermal Effects. Thermal Effects. Chemical Effects. Chemical Effects.

Mechanical Effects Ultrasound causes mechanical vibration in tissues. Ultrasound causes mechanical vibration in tissues. The particles are compressed (pressure phase) and then dispersed (suction phase). The particles are compressed (pressure phase) and then dispersed (suction phase). Small cavities form in fluids during the suction phase and disappear in the pressure phase. Small cavities form in fluids during the suction phase and disappear in the pressure phase. This phenomenon is describe as cavitation in gas-free fluid and psudocavitation in fluid with gas. This phenomenon is describe as cavitation in gas-free fluid and psudocavitation in fluid with gas. The amount of cavitation and pesudocavitation depend on the frequency and the intensity (sound energy per area (. The amount of cavitation and pesudocavitation depend on the frequency and the intensity (sound energy per area (. High frequency combine with high intensities have great mechanical effects. High frequency combine with high intensities have great mechanical effects. There are no confirmed adverse effects or mechanical damage to cell membranes or chromosomes by exposure to diagnostic levels of ultrasound. There are no confirmed adverse effects or mechanical damage to cell membranes or chromosomes by exposure to diagnostic levels of ultrasound. Therapeutic ultrasound which applies higher intensities than diagnostic sonography, uses this mechanical forces for generation of heat or in a more sophisticated application, for destruction of renal calculi (Lithotripsy). Therapeutic ultrasound which applies higher intensities than diagnostic sonography, uses this mechanical forces for generation of heat or in a more sophisticated application, for destruction of renal calculi (Lithotripsy).

Thermal Effects Thermal effects of ultrasound are due to ultrasound energy absorption and its transformation into the heat. Thermal effects of ultrasound are due to ultrasound energy absorption and its transformation into the 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 not thought to cause significant thermal effects. Intensities used in diagnostic Ultrasonography are not thought to cause significant thermal effects. Beam characteristic and the heat reducing effect of vasculariztion are thought to contribute to the lack of thermal effects,provided the vascular system is intact and moves the heat away. Beam characteristic and the heat reducing effect of vasculariztion are thought to contribute to the lack of thermal effects,provided the vascular system is intact and moves the heat away. Hyperthermia, however, is used in therapeutic Ultrasonography. Hyperthermia, however, is used in therapeutic Ultrasonography.

Chemical Effects The chemical effects of ultrasound are oxidation, reduction and depolymerization. The chemical effects of ultrasound are oxidation, reduction and depolymerization. The ability of ultrasound to depolymerize macromolecules like polysaccharides, various proteins or isolated DNA has been demonstrated experimentally. The ability of ultrasound to depolymerize macromolecules like polysaccharides, various proteins or isolated DNA has been demonstrated experimentally. These adverse biological effects, however, are not found with diagnostic ultrasound. These adverse biological effects, however, are not found with diagnostic ultrasound.

Mode of Display

Mode 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 scan 3) Compound scan

Real- time Ultrasonography The resulting image is either a: The resulting image is either a: 1) Triangular or Pie-shaped 1) Triangular or Pie-shaped 2) Rectangular 2) Rectangular 3) Convex 3) Convex The same classification applies to transducers. The same classification applies to transducers.

Transducers & Sonograms

Sector transducer – sector sonogram. Sector transducer – sector sonogram. Linear or parallel transducer –parallel sonogram Linear or parallel transducer –parallel sonogram Curved – array transducer – convex sonogram. Curved – array transducer – convex sonogram.

Sector transducer Sector sonogram

Sector transducer – sector sonogram Sector transducers produce a triangular or pie- shaped image. Sector transducers produce a triangular or pie- shaped image. The scan line density of the display is higher in the near field, while the lines diverge in the far field. The scan line density of the display is higher in the near field, while the lines diverge in the far field. Most commercial sector scanners are mechanical. Most commercial sector scanners are mechanical. One to eight crystals are mounted on the transducer and are either rotated in a circular motion or oscillated to-and-fro. One to eight crystals are mounted on the transducer and are either rotated in a circular motion or oscillated to-and-fro.

Sector sonogram

Sector transducer – sector sonogram An angle of 60 -120 can be scanned within a short time. An angle of 60 -120 can be scanned within a short time. Echoes from a dept of 10 cm return to transducer 0.13 ms after being pulsed. Echoes from a dept of 10 cm return to transducer 0.13 ms after being pulsed. Electronic sector scanners are made of several ceramics, each holding numerous piezoelectric elements. Electronic sector scanners are made of several ceramics, each holding numerous piezoelectric elements. Triggering of these crystals must follow at exact sequence or phases, which is why these electronic transducers are called phased-array scanners. Triggering of these crystals must follow at exact sequence or phases, which is why these electronic transducers are called phased-array scanners.

Sector transducer – sector sonogram The crystals in some newer sector scanner are mounted in an annular fashion. The crystals in some newer sector scanner are mounted in an annular fashion. This is referred to as an annular- (phased-) array transducer. This is referred to as an annular- (phased-) array transducer.

Linear or parallel transducer Parallel sonogram

Linear or parallel transducer Linear transducers produce rectangular display format. Linear transducers produce rectangular display format.

Linear or parallel transducer

Parallel sonogram

Curved – array transducer Convex sonogram

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

Curved – array transducer

Convex sonogram

Comparison of transducer types

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

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