Radiography Start PDF

X-Ray Revision pre start Poppy Evans Nucleus = Positive Protons (in nucleus) = Positive Neutrons (in nucleus) = Neutral Electrons = Negative Who discovered X-rays? Roentgen in 1895 What is an X-ray? High frequency and high energy waves of electromagnetic radiation Where do X-...

X-Ray Revision pre start Poppy Evans Nucleus = Positive Protons (in nucleus) = Positive Neutrons (in nucleus) = Neutral Electrons = Negative Who discovered X-rays? Roentgen in 1895 What is an X-ray? High frequency and high energy waves of electromagnetic radiation Where do X-rays sit on the electromagnetic spectrum? Between ultraviolet radiation and gamma rays. What are X-rays made of? Wave packets of energy called photons What is a photon? One quantum of energy (smallest unit of energy) What are X-ray beams made up of? Photons What is matter? Matter is a substance made up of various types of particles that occupies physical space What is matter made of? Made up of protons and neutrons and electrons Fundamental unit of matter is called? Atom What is an atom? Basic building blocks of matter. What are atoms composed of? Fundamental/Elementary particles = Nucleus (protons and neutrons) + orbiting electrons (in surrounding orbits/shells) How are the particles all held together? By electric and nuclear forces Neutral atom = number of electrons are equal to number of protons What determines chemical behaviour? - Z = atomic number (protons) - Number of electrons Atoms in ground state are electrically neutral due to : Positive charge (protons) balanced by Negative charge (electrons) What is the unit of energy called within the atomic system? Electron volt (eV) 1 UNIT of eV = 1.6 x 10 (-19) Joules Joules = one unit of energy Electron being removed = atom no longer neutral + becomes positively charged and now called positive ion. This process is called Ionization. What is ionisation? When an electron is removed from an atom Creating a no longer neutral atom Atom becomes positively charged Now called positive ion What is excitation? Electron moving from inner shell to outer shell (to higher energy level) The atom remains neutral = excited state This process is called excitation  Short name Name Meaning Z Atomic number Number of protons in nucleus N Neutron number Number of neutrons in nucleus A Atomic mass number (sum) Z+N=A Isotopes One of two or more types of atoms with the same number of protons but with different numbers of neutrons and therefore different atomic masses. Radioisotopes Isotopes with unstable nuclei which undergo radioactive disintegration Main features of an atom Protons Mass - 1.66 x 10 (-27) kg Charge - Positive 1.6 x 10 (-19) Coulombs Coloumbs - 1 unit of electrical charge Neutrons Mass - 1.70 x 10 (-27)kg Charge - nil Neutrons act as binding agents in the nucleus Neutrons counteract repulsive forces between protons Electrons Mass - 1/1840 of the mass of a proton Charge - negative 1.6 x 10 (-19) coulombs Electrons move circular or elliptical shells/orbits around the nucleus each shell represents different energy levels Energy levels increase further out of the nucleus. Shells are labelled K,L,M,N,O (Outwards from nucleus) Each shell can contain maximum electrons : K shell - Maximum 2 electrons L shell - Maximum 8 electrons M shell - Maximum 18 electrons N shell - Maximum 32 electrons O shell - Maximum 50 electrons Electrons can move from shell to shell but cannot exist in between (forbidden zone) What is the X-ray generating component called? Tube head What do all X-ray tubes contain? small evacuated glass container called the X-ray tube. How are X-rays produced? Energetic electrons hit the target and are brought suddenly to rest. What are the main features of an X-ray tube? - Cathode (negative) - Anode (positive) - Focusing device - High voltage (kV) - A current - Surrounding lead casing - Surrounding oil Feature Function Cathode (negative) Heated filament of tungsten providing source of electrons Anode (positive) Small target made of tungsten in large copper block providing removal of heat Focusing device Aims the stream of electrons at the focal spot on target High voltage (kV) Connected between cathode and anode pushes electrons from negative filament to positive target = kilovoltage peak A current (milliamperage) Flows from cathode to anode. The measure of quantity of electrons being accelerated (moved). Surrounding lead casing Absorbs unwanted X-rays Surrounding oil Facilitates removal of heat Practical considerations Production of X-ray steps : - Filament is electrically heated = produces electrons - High voltage across X-ray tube accelerates electrons towards anode at high speed. - Focusing device aims electron steam at focal spot on target - Electrons bombard the target and brought suddenly to rest - The energy lost by electrons is transferred into either heat (99%) or X-rays (1%) - Heat produced is removed and dissipated by copper block and surrounding oil - X-rays are emitted in all directions from target. - X-rays emitted through small window in lead casing apart of the beam creates the image of purpose. 1. Electrons are accelerated through x-ray tube by a voltage (KvP) 2. Electrons (negative) are decelerated when interact with anode target (+) Electrons hitting the target have 2 types of collisions with tungsten atoms 1. Heat producing collisions (most common) 2. X-ray producing collisions (Bremsstrahlung - breaking radiation) Heat producing collisions 1. Incoming electron is deflected by outer shell tungsten electrons = causing small loss of energy in the form of heat. 2. Incoming electron collides with outer shell tungsten electron = displacing it to an even more peripheral shell (excitation - further out shell) 3. Or displacing electron entirely from the atom (ionisation) = small loss of energy in form of heat. X-ray producing collisions 1. Electron gets through the outer electron shell, passing close to the nucleus of the atom. The electron is slowed down and deflected from nucleus with large loss of energy (emitted in X-rays - photons) CONTINUOUS X-RAYS. - Incoming electron energy of 90 keV - Outgoing electron energy of 60 keV - 90 keV - 60 keV = photon energy (30 keV) 2. Electron collides with an inner shell electron and displaces it into the outer shell (excitation) OR displaces it completely from the atom (ionisation) with a large loss of energy and outer shell electrons move into inner shell which causes emission of x-rays. CHARACTERISTIC X-RAYS Spectra What is X-Ray Spectra? Collection of x-ray wavelengths emitted. Intensity vs wavelength (graph) Two X-ray producing collisions (heat + X-ray) result in what? Production of 2 types of X-ray spectra What is the 2 types of X-ray Spectra? 1. Continuous 2. Characteristic Continuous X-ray spectrum - X-ray photons produced by rapid deceleration of bombarding electrons passing close to the nucleons (bremsstrahlung) - The amount of deceleration and degree of deflection determines how much energy is lost. - A wide range/spectrum of photon energies is possible = continuous spectrum - BASICALLY = The wide range of photon energies produced in an x-ray tube due to the properties of Bremsstrahlung radiation (Electron deceleration near nucleus). The energy of x-ray photons can value from zero to the maximum kinetic energy of the electrons. Characteristic spectrum Characteristic X-rays are emitted when electrons rearrange themselves to return to natural or ground state. - Ionisation (electron removed) or excitation (electron moves to higher energy shell) occurs. - Outer-shell electrons fill a vacancy in the inner shell of an atom - Releasing X-rays in a pattern that is "characteristic" to each element. Vocabulary Word Meaning Scattering Change in direction of a photon with or without loss of energy. Absorption Deposition of energy ; removal of energy from the beam (materials absorb X-ray radiation/photons) Attenuation The X-ray beam (photons) weaken as it travels through matter. Caused by = Absorption + Scattering Ionisation Removal of an electron from a neutral atom producing a negative ion. Compton effect Scatter and absorption of photons 1. Incoming x-ray photon interacts with outer shell electron. 2. Outer shell electron ejected that electron is now called = Compton recoil electron. 3. Some loss of energy occurs due to some absoprtion. 4. The ejected electron undergoes further ionoizing interactions within tissues. 5. remaining photon energy is scattered. Photoelectric effect Pure absorption of photons 1. Incoming X-ray photon interact with inner shell electron. 2. Ejects the inner shell electron out of atom. 3. X Ray photon totally absorbed. 4. Outer shell electrons all move in to the empty shell spaces and energy is released in the form of low energy radiation (ie light). Vocabulary Word Meaning Effective dose Calculated for the whole body. Expressed in millisieverts (mSv) Calculated by : multiplying the equivalent dose (HT) by a tissue weighting factor (WT) 3 Equivalent dose (HT) Calculated for individual organs. Expressed in millisieverts (mSv) Characteristic effect Characteristic X-rays are emitted when outer-shell electrons fill a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is "characteristic" to each element. Continuous effect (bremsstrahlung) Bremsstrahlung is the radiation produced when a charged particle decelerates suddenly.  Johns 1st lecture notes Intro to X-rays and Physics Part 1 Why take an X-Ray? - Aid diagnosis - Plan treatment accordingly - Justify plans = medico legal record - Assess disease and out come of treatment - Patient education - Referral The term ‘radiography’ means the process/technique of image taking. What is a cap scan? CT scan - creates a 3D image Shades of radiographs The more x-rays (photons) hitting a film (receptor) the DARKER the film will be. Example : - Crown is dense and blocks X-rays from getting through = White on film. - Soft tissue not dense so X-rays go straight through and hit receptor (film) = Black on film. - Caries is present = grey/black shadow Terminology to know: Term Meaning Radiodensity How X-rays appear. The amount of X-rays stopped by an object determines radiodensity. Radiopaque White Radiolucent Black Example : 100% radiopaque = metal filling / Crown 100% radiolucent = Gingiva/ open matter/air Factors to consider? When more energy is in the X-ray beam more likely to go through an object. Principles of shadows? (how are shadows formed) They represent themselves in variations of the density. Superimposition = layers Magnification and distortion X-Ray absorption Final shadow density is determined by: - Type of material - Thickness and density - Shape of object - Intensity of X-ray beam - Position of X-ray beam/object/receptor What does superimposition mean? Misleading = unable to tell by the X-Ray its full info. Example = Upper molar has 3 roots = image can be superimposing and can only view 2 roots. What factors can make an X-ray superimposed? - Positioning - Contrast = shades of grey, black and white - Context = prejudgment can distract correct answers Quality of radiographic image is due to : - Contrast = visual difference of shades - Image positioning - Tube, person, film - Characteristics - Image sharpness (focus) - Resolution (details) Visual Characteristics - Related to the X-Ray beam (energy) as energy penetrates through tissues - Parallel ie non diverging - From a point source. - Contrast, sharpness, resolution Geometric characteristics - Related to technique - Object and receptor closeness - Beam meets object / receptor at right angles - Being accurate and no magnification Plaque retentive factors on X-Rays : - Furcation - Crowns + bridges - Ledges or overhangs  - Lack of contact points (Spacing) Physics side of the lecture What does polarity mean? Separation of electric charge leading to a molecule to have a negatively charged end as well as a positively charged end. Where do ranges of energies originally come from? The sun How are wavelengths measured? From one peak to another. Why are X Rays ionising? - Ability to remove electrons from atom - Can cause damage - X-rays and Gamma rays both are ionising radiation Ionic pair = unstable atom = 1 less electron = 1 free electron. Nature and Characteristics of X-Rays - Electromagnetic energy - Produced by the sun - Ionising radiation - Absorbed by the atmosphere - Travels in straight lines - Undetectable by human senses Properties of X-Rays - Electromagnetic waves - Packets of energy called photons - Xray beam has millions of different photons with different energy levels - Short wavelength = High frequency = Higher energy - Long wavelength = Low frequency = Low energy - Travel in straight lines @ speed of light - X-rays obey the inverse square law - Energy of x rays can be attenuated by matter - X-rays can cause biological damage in living tissue due to ionisation Inverse square law Radiation intensity decreases as the square of the distance from the source increases. Attenuation (distance) reduces energy. Polyenergetic Lots of different levels of energy X-ray beams have millions of photons (wide range of energies) Binding energy Tungsten atom K electrons have binding energies of 69.5 keV L electrons are bound by 12.1 keV. A K-shell electron is removed from a tungsten atom and is replaced by an L shell electron. What is the energy of the characteristic X-ray that is emitted (in keV)? Answer: 57.4 keV (the difference in the energies of the shells) = 69.5 - 12.1 Electrical current - The flow of electrons in a circuit - Measure in amperes (amps) Voltage - Amount of force pushing the flowing electrons - Higher the voltage more current will flow - Lower the voltage = weaker current - Measured in volts Measurement shorter names - Milliamps = mA (determines quantity of electrons produced) - Kilovolts = Kv (determines the quality of x rays) - Milliamp-seconds mAs High atomic number = more protons and electrons Soft tissues = less electrons Metal = Lots of electrons AC = Alternate The direction of electricity periodically changes Changes from positive to negative. DC = Direct current Electricity flows in one direction Voltage is always constant Exposure time = time the patient is exposed = the amount of x rays patient exposed to.  Pre reading notes before radiography lecture 2 14/10/24 What is an atom? Basic building block to matter What are the components of an atom? Nucleus (positive) containing protons (positive) and neutrons (neutral) Electrons (negative) Orbiting shells which hold the electrons How can electric current be transformed to light or other forms of energy? ?????? Normal household electrical voltage? 230 volts 50 Hz frequency Types of reactions within an atom when X-rays are being created Heat producing reactions : Incoming electron DOESNT have enough energy to penetrate through atom so: doesn’t interact with nucleus, interacts with the orbiting electrons. Either by : 1. Incoming electron hits the outer shell electron and get deflected away and causes heat. 2. Incoming electron hits the outer shell electron and displaces it from the shell and causes loss of energy through heat. 3. Incoming electron knocks an electron into a further out shell (excitation) causing loss of energy through heat. Bremsstrahlung reaction : Primary source of x-rays photons (Continuous spectrum) Incoming electron has enough energy to penetrate through the atom. Interacting with the nucleus. 1. Incoming electron strikes a target and brakes suddenly near nucleus giving off energy (photons) 2. The incoming electron from the cathode interacts with the nucleus not the shells. Characteristic reaction : Secondary source of x rays photons 1. Electron knocks into another electron displacing it then an electron from the outer shell drops into a lower energy shell. 2. Emits photons of specific energy. - Electron from cathode interacts with an electron in K shell of an atom in the anode - Knocks electron out from k shell - Atom is unstable - So electron from outer shell jumps in = emission of xray photons - The energy from xray photons is dependent on the binding energy between shells. - Binding energy is characteristic to each material. Number of kV set by xray unit determines the maximum energy produced. E.g. 70kVp = 70keV then when increasing the kvp to 90 will mean the energy will also increase to 90keV. X-Ray production 1% of interaction of electrons and target = X-rays 99% of interactions result in heat production Excess heat is absorbed by the high tungsten target, oil, and copper sleeve. Know the equipment : Inside the X-ray machine : Johns Lesson 2 X-Ray production Johns 2nd lesson  X-ray production Johns 2nd lecture Xray production Normal household voltage (electrical) - 240 volts - 50 Hz frequency Know the equipment and how its works : Outer casing (lead lined - high atomic number blocking X-rays) - Stop escape of X-rays Glass envelope (vacuum) - Vacuum stops particles from interacting. - Allows electrons to move from cathode to anode Cathode (-) Focusing cup/device - surrounds the filament directing/repelling electrons to anode Step down transformer - reduces the 240 volts into 6 volts in cathode Filament - electronically heated and forms a cloud of electrons. Anode (+) Tungsten target - Produces X-rays (attracts electrons from cathode) Abrupt deceleration or collision at tungsten target = produces the X-rays Copper block - dissipates heat Surrounding oil - Dissipates heat Cone - beam indicator (directs the beam) Filter (aluminium) - removes low energy X-rays Exam question example: Describe the process of electrons emission at the cathode? 1. Electric current fed to cathode 2. Step down transformer changes the voltage from 240v to 6v 3. Current heats up the filament 4. Cloud of electrons are formed and become agitated 5. Thermionic emission occurs - heat causes ionisation (loss of electrons) 6. Step up transformer changes 6v to 70,000v 7. Focusing device is negative aims and repels the electrons towards the anode 8. Electrons bombard tungsten target and brought to rest. Process at the anode : 1. Anode is tungsten (high atomic number) 2. Tungsten is positively charged = attracting electrons from cathode. 3. Abrupt deceleration or collision occurs at tungsten target = producing x-rays. 4. Energy is lost when deceleration/collision occurs transferred into heat (99%) or X-rays (1%). 5. Heat is removed/dissipated by surrounding oil and copper block. 6. X Rays are emitted in all directions. 7. The opening in the tube head allows photon beam to create image. 8. The filter removes low energy photons/x rays Binding energy Binding energy between shells K + L = 69.5 Kv K shell electron in tungsten have binding energy of 69.5kv To remove an electron from this shell incoming electron must equal or greater than 69.5 kv. The closer the incoming electron is to the nucleus the: - Greater deceleration - Greater deviation - Greater energy. 3 types of reactions at the anode : 1. Heat 99% 2. Bremsstrahlung / breaking / continuous / general - X-ray 1% 3. Characteristic - X-ray 1% 2 types of X-ray production 1. Bremsstrahlung/breaking/continuous = diversion of direction 2. Characteristic = collision causing electron to be ejected from atom (high energy) Heat producing reactions (99%) (Low energy - deviate or deflect) 1. Deviation : incoming/incident electron doesn’t interact with atom it deviates before touching atom causing heat. 2. Deflect : incoming/incident electron hits outer shell and gets deflected away causing heat. Description: Within heat producing reactions incoming/incident electrons do not have enough energy to penetrate through the atom resulting in the incoming electron being deviated or deflected causing loss of energy in the form of heat (99%). X-Ray producing reactions (2) 1. Bremsstrahlung / Breaking / Continuous / General 2. Characteristic Bremsstrahlung / Breaking / continuous / General : (1%) Electron (-) interacts with nucleus (+) = opposites attract - Doesn’t have enough energy to displace electrons - Electron suddenly slows (breaks) in atom near nucleus - Electron is then deviated in different direction - Deviation creates energy = X-ray photons The closer the electron is to the nucleus the more breaking occurs causing larger deviation and more energy produced. The further away the electron passes from the nucleus the less breaking and less deviation made meaning less energy produced. Characteristic : 1% X-ray - Has enough energy to displace electrons from k shell (inner) = ionisation - Atom = unstable state (becomes a positive ion as its positively charged) - Electrons jump from one shell to another to stabilise and fill empty space - Jumping electrons = creates energy = X-ray photons Energy of photons is consistent and predictable. Xray production Number of X-rays produced is controlled by maximum energy on xrays tube (KV) Increasing the speed of x rays (anode Increases the number of electrons that charge) penetrate through tungsten atoms = more energy, more X-rays. Reducing the speed of X Rays Reduce average energy of electrons, less interaction = fewer x rays = more heat Three factors affecting X-Ray production: 1. The current (mA) 2. The energy (kvp) 3. The time exposure Quality of image Contrast The teeth present Tilted, overerupted, submerged Bone levels Normal (2mm below CEJ) or Bone loss (horizontal or vertical). Restorations Type, defects, overhangs. Plaque retentive factors Calculus spurs, cavities, ledges, poor contact points, tooth position Presence of disease Caries, resorption  Tissue interactions When X-rays pass through tissue/objects what happens? Absorption TOTAL energy is transferred to target material in one or more interactions Does not reach receptor Scatter (deviation) Photons change direction with or without loss of energy. Does not go to the primary beam/path. Unmodified Traverses the atom Goes straight through and avoids any physical touch. Straight to receptor. Terminology to know : Scattering - change of direction of photon with or without loss of energy. Absorption - total loss of energy from beam. Attenuation - reduction of energy of X-ray beam due to absorption + scatter. Ionisation - Ability photon to knock out electron (when both absorption and scatter occur with loss of energy) Attenuation What is it? Reduction of intensity (energy) of main X-ray beam How? By absorption and/or scattering. Example: - 1000 photons - 200 scatter - 100 absorbed This means 300 photons have attenuated 700 have transverse through tissue without any interaction. Soft tissue - little attenuation (hits receptor) Lead - completely attenuated (wont go through to receptor) Interactions of Xrays at atomic level (when it gets into tissue) Coherent / un modified/ Rayleigh scattering = PURE scatter Photoelectric effect = PURE absorption (bounces around + loses energy) Compton effect = Scatter AND absorption (partially absorbed then deviated direction = poor image) Pair production = PURE absorption (ionic pair) Two most important in dentistry : 1. Photoelectric effect = PURE absorption 2. Compton effect = Scatter AND absorption Coherent scattering/Rayleigh - Incoming photon hits outer electron - Energy of the photon temporarily absorbed and then released as scattered photon - No ionisation and no free electron - Decreases contrast - 8% of interactions in dental X-ray beam Photoelectric absorption (creation of unstable atom) - least desirable total absorption - knocks out inner electron subsequent photoelectron - never escapes the tissue - Incoming photon hits inner electron and forms ion pair - Increases contrast - 30% of interactions in dental X-ray beam. - Pure absorption - Ejected electron undergo further interactions - Emits low energy ionising radiatiin - Contributes to higher absorption for patient - The higher atomic number = more likely the photoelectric effect. Compton scattering (most common + least describable) Absorption and scatter - Incoming photon is partially absorbed by outer electron - Electron gets knocked out of atom (ionisation) = Compton electron / Compton recoil - Rest of photon energy exits the atom in other direction as scatter (less energy) - Photon in within an electron AND scattered photon out. - Decreases contrast (lower energy - more xrays getting through) - 62% of interactions in dental X-ray beam. Shorter range (higher energy) = more grey values Lower energy - more absorbed - fewer grey values. Low kvp - Photoelectric higher kvp - Compton scatter Angle of scatter depends on energy - High energy = Forward scatter (could reach receptor and degrade image) - Low energy = Back scatter (concern of clinical environment) Exposure factors and X-Ray beam modification What factors regulate the energy of X-ray beams/ number of xrays? 1. Kvp (kilovoltage peak - potential difference between cathode and anode ie 70kvp) 2. mA setting - quantity of xrays produced 3. Exposure time - increased time - increased xrays. These factors are adjusted to suit pt : patient head size. Intensity: - Quantity of electrons (Number of photons) Energy - Quality of electrons (Energy of photons) Density : degree of darkness of image Contrast : difference among grey values - higher the average energy of X-ray beam - greater of grey values close together. Contrast - ability to differentiate between structures ie caries and dentine. Exposure time (s) Affects Intensity. Most frequently changed. Too long = too dark (Overexposed) Too short = too light (Underexposed) Double the time = double the amount of xrays = Darker the image. Less time = less amount of xrays hitting receptor = lighter the image. Tube Current (mA) Doesnt affect energy of beam Affects intensity Usually can’t adjust setting. Too much tube current = too dark (over exposed) Too little tube current = noisy??? (Underexposed) Half exposure time and double ma = same image produced half the ma and double the exposure time = same picture Tube potential (kvp) Affects intensity and energy (Average energy = ⅓ of kvp) Too high = too grey = not enough contrast (Compton scattering) Too low = too light = high contrast (photoelectric absorption) Increase kvp = increase Compton scatter Lower kvp = Filtration Aluminium filter (sufficient atomic number) Removes lower energy photons from beam = reducing pt exposure ie pt absorption Similar to ‘beam hardening’. Collimation Involved lead Reduces beam size = to reduce patient exposure/dose Rectangular collimation is the best method = reduce radiation dose as its narrow. The more narrow the beam = less damage. Increase quality of image. Round Collimation (7cm) Distance Inverse square law Further away = less photons per unit area / lower radiation Operator should be at least 6 feet away from source Radiation intensity decreases as the square of the distance from the source increases. Attenuation (distance) reduces energy. Double the distance (16th) Aim of the beam : Too close - too dark Too far away - too light Tube current Flow of electrons in X-ray tube In 2 forms - AC + DC AC = Alternate The direction of electricity periodically changes Changes from positive to negative. DC = Direct current Electricity flows in one direction Voltage is always constant Milliampere (mA) - Determines heating of filament = number of electrons - Doubling mA setting = twice as many xrays Scatter - compromise quality of image Absorption - influence patient dosage Modify the beam for a better picture by: filtration and collimation Types of filtration 1. Inherent filtration (oil/ beryllium window) 2. Added filtration Why do we use filtration? Remove the low energy xrays because unnecessary photons Increase pt dose and don't improve image. Adjust filtration by the thickness of aluminium Geometry Umbra - Shadow - penumbra (multiple focal spot size (FSS) by OID divide by SOD) Exposure factors too high = too dark Exposure factors to low = too light