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102 Cards in this Set
- Front
- Back
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What type of wace are X rays? |
Electromagnetic with a wavelength below 100nm. High frequency, high energy.
Also described as a beam of photons |
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Equations for photon energy |
E=hf E=hc/lamda |
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Basic requirements for an x ray image |
X ray source Object of interest (patient) Recording device - film, digital recorder |
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Mechanisms of x-ray production |
1- Electron - Nucleus interaction - electron approaches atom, curves around the nucleus, change of direction causes it to lose energy which is "screeched" as an x-ray. - no collisions involved -many possible paths = many possible energies of x-ray 2- Electron - electron interaction -electron approaches atom, collides with orbital electron, both are ejected, leaves vacancy, higher orbital electron drops into vacancy, emits excess energy as x-ray, creates vacancy, electron drops etc. - gives discrete energies of electrons as shells have discrete levels
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Practical x-ray production |
Produced in a vacuum. Cathode with current passing through it to heat it and produce high voltage between it and the anode which has the target material.
Electrons are produced at the cathode and accelerated by the high voltage between the cathode and anode. The electrons hit the target material and produce x-rays in all directions.
Current flows in the cathode (filament current) separately to between the anode and cathode (tube current). |
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Notes on x-ray production |
Electron energy is proportional to the potential (voltage) between anode and cathode
X-rays produced at the target anode have a range of energies between zero and the electron energy |
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Tube current |
This is the flow of electrons from the cathode to the anode.
It can be measured in milliamperes (mA).
This current affect the number of photons produced but not the energy of the photons. |
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Effect of filtration |
Filtration is use to remove low energy photons.
These photons will not traverse the patient to produce an image but would contribute to patient dose.
Inherent - from parts of the tube already there (glass window)
Added - sheet of aluminium
Inherent + Added = total
Effect on the photon distribution: Lowers overall beam intensity Increases average photon energy
Image contrast is determined by the beam energy. Therefore filtration is a balance of dose and contrast. |
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Focal spot size |
Ideally the picture produced will be sharp.
A small focal spot gives a sharp picture - it reduce umbra and penumbra.
A small focal spot gets hot and degrade the target material
To obtain a small focal spot: - focussed electrons - steep angle of target material |
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Heat removal |
Heat removal is necessary to: - prevent damage to focal spot and target - to prevent general overheating of tube
Heat build up limits how soon x-rays can be repeated
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X-ray attenuation
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An X-ray is attenuated (reduced in intensity) as it passes through matter. There are two mechanisms for this: - Photoelectric absorption - the incident photon collides with an electron, gives up all its energy and ceases to exist. -The probability of the PE decreases as the energy of the photon increases. -The probability of the PE increases as the atomic number of the absorbing material increases
-Compton scatter - Photon collides with an electron, transfers some energy to electron, photon changes direction with reduced energy. -the probability of the CE is fairly constant with both energy and atomic number
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Possibilities for an x-ray photon |
1 - pass through 2 - photoelectric effect 3 - crompton scatter |
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Picture detail |
Contrast - a high contrast is prefered - crompton scatter reduces contrast - high energy reduces contrast (crompton scatter more likely at high energy)
Scatter possible outcome 1 - scatters and hits film - creates noise - photons hit different part of film compared to where they interacted with matter 2 - doesn't hit film - doesn't contribute to image but give patient dose
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What energy x-rays should we use? |
High energy = more penetrating - lower dose - lower contrast
Low energy = less penetrating - higher dose - better contrast
Solution: keep energy high enough to traverse the tissue thickness of interest and minimise scatter but low enough to be attenuated in the appropriate tissue - Generate X-rays at 30 keV to 70 keV 70kV with ~2mm Al filtration |
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What is ionisation? |
When any type of radiation interacts with a target atom and causes an electron to be ejected giving the atom an overall charge. |
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Radiation ranges |
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Ionisation measures |
Absorbed Dose (D) - energy absorbed from any type of radiation per unit mass - unit:Gray
Equivalent Dose (H) - derived from absorbed dose using radiation weighting factor, modifies for the type of radiation and summed over all types of radiation - unit: sievert (Sv)
Effective dose - derived from equivalent dose by modifying for the sensitivity of tissue, summed over all exposed tissues |
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Risk models |
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Radiation effects on tissue |
Tissue Reactions - Occurs above a threshold - Severity increases with dose - Severity increases with dose rate - Effects include - radiation sickness, erythema, epilation, loss of fertility, death - The threshold for tissue reactions is high relative to medical exposures - Effect of fertility could be reached by CT scanning
Stochastic (random) effects - no threshold - Severity independent of dose - Probability depends on dose and a bit on dose rate - effects: cancer induction and genetic effects
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Percentage of average dose to UK population from medical sources |
15% |
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Effective from intraoral x-rays |
Technique (2 bite wings) MicroSieverts
70Kv, 20cm fsd, rectangular 2 collimation,E-speed film/CR (modern technique)
Round collimation, 8 D speed film
50kV, 10cm fsd, round 16 collimation, D speed film (old technique)
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Effective doses from panoral x-rays |
Technique MicroSieverts
Panoramic, rare earth 7 screens/CR
Panoramic, Ca tungstate screen 14
2 oblique lateral jaws, 70kV, 15 20cm fsd, rare earth screens |
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Methods of explaining dose risk to public |
Natural dose years - converting an exposure to the equivalent time for natural exposure
Bananas - converting the dose to the amount of bananas that would give the same dose - disadvantage of the number of bananas being more harmful than the radiation/people don't know how radioactive a banana is
Comparing to other risks of death - eg RTA, natual causes etc |
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Aim of dose limits |
Avoid tissue effects completely Reduce risk of stochastic effects to "acceptable" level |
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What is an acceptable risk? |
Societies will only accept risk of death between 1:10,000 to 1:100,000 per year
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ICPR principles of protection |
JUstification -benefits must outweigh risk
Optimisation dose must be as low as reasonably achieveable
Limitation Dose must not exceed limits |
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Annual dose limits (effective dose to the whole body) |
MicroSieverts Employees 20 Trainees under 18 6 Other people 1 Patients No limit but must be justified
Employee limit can be 100 in 5 years with no year being over 50 |
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Dose limits for women |
Of reproductive capacity - 13milliSievert in 3 month period
Pregnant women 1 milliSievert in declared term |
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Dose limit for medical exposure? |
No limit but must be justified
Public exposed due to treatment of others must be <5mSv over 5 consecutive years
Comforters & carers - knowingly and willing accept dose, voluntary - 5mSv per episode |
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IRR '99 |
Primarily related to exposures of people we did not intend to expose.
Concerned with protection in the workplace - enforced by HSE.
Framework: Consult an RPA Notify intention to use radiation - 28 days before Assess radiation risks - must be written record Manage risks (design ,controls etc.) Write safety procedures Mark & control hazardous areas Train & supervise staff in hazardous areas Monitor staff doses Investigate incidents Maintain & test engineering controls
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What is an RPA? |
Radiation Protection Adviser
Employer must consult RPA on: - controlled and supervised areas - prior inspection of plans for installation - calibration of monitoring equipment - checking of engineering controls and systems of work
RPA must be certified as competent by approved body
Employer must ensure RPA is suitable |
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Restriction of exposure as determined by IRR '99 |
Employer must restrict exposure by: -engineering controls, design features and warning controls - maintained and tested - systems of work - PPE - thoroughly examined at regular intervals
Employees must: - not expose themselves or anyone else to radiation when not warranted - Use PPE provided by employer - Report faults
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IRR '99 - Classified persons |
Persons likely to receive dose greater than 6mSv effective dose or 30% of any relevant limit.
Based on prior risk assessment.
Requirements: - personal dose assessment - medical surveillance - dose records kept for 50 years - dose summary sent annually to HSE
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IRR '99 - Investigation |
Employer must investigate if employee exposure exceeds: - 15mSv during the year - a lower investigation threshold set by employer
Hospitals normally set level at 4mSv
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IRR '99 - Overexposure |
If a dose limit is exceeded then employer must: - Investigate - Inform employee - inform HSE
Patient overexposure - "much greater than intended" resulting from equipment fault must be reported to HSE
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IRR '99 - controlled areas |
Needed if: - special procedures have to be followed to avoid a significant dose - any person is likely to exceed 6mSv effective dose or 30% of limit |
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IRR '99 - Supervised areas |
needed if: - conditions have to be kept under review to ensure controlled area is not exceeded - any person is likely to receive dose of 1mSv or 10% of limit
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IRR '99 - Radiation equipment |
Manufacturer design must be capable of reducing exposure by: - controls - shielding - warnings
Installer must perform a "critical examination" with RPA |
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IR(ME)R 2000 |
Ionising Radiation (Medical Exposure) Regulations 2000
Concerned with protection of patients Enforced by Care Quality Commission
General Aims: -Protection of patients -Justification of exposure -Ensuring medical doses are appropriate -Ensuring those that expose patients are fully trained |
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IR(ME)R 2000 - Duty Holders |
-Employer - main duty holder, must employ people who are correctly trained -Referrer - examines the patient and then passes info to practitioner -Practitioner - judges whether referral should proceed to exposure -Operator - carries out exposure - Medical Physics Expert - gives advice on equipment, technique, settings and training
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IR(ME)R 2000 - Duty holder's duties |
Employer - identify responsible staff - have procedures to identify each patient - positive and active -ensure outcome of every exposure is recorded - reduce likelihood of accidental exposure - establish referral criteria - ensure written procedures -determine dose constraints
Referrer (any health prof declared trained by employer) - supply sufficient data to practitioner to decide if procedure will have a net benefit - info to allow id - med history to demonstrate: what you want, why and action to be taken
Practitioner - justify the exposure in terms of radiological risk and medical benefit - authorise exposure or provide guidelines for the operator to authorise it
Operator -ensure correct patient - ensure correct exposure - ask about pregnancy - use correct settings - position pt correctly -minimise field size
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IR(ME)R 2000 - overexposures |
an exposure "much greater than intended" due to human error must be reported to CQC
Much greater than intended depends on exposure
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Ideal qualities for an image receptor |
Record all available information • Good contrast and detail • Minimal dose • Easy to handle (? Eliminate processing) • Image available to view immediately • Doesn’t deteriorate with time • Easy storage • Cheap |
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What is a conventional film? |
A conventional film radiograph is x-ray film which has been exposed to light or xrays and due to a light sensitive salt in the emulsion, records the image. The latent image which is produced, becomes visible to the naked eye following processing. |
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What is a digital film? |
Also produced by passage of x-rays through a patient, but the receptor is either a storage phosphor plate or CCD/CMOS which then stores the image on a computer. This can then be viewed on the monitor or printed. |
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Differences in receptors for intra and extraoral radiographs? |
Intraoral radiographs = non screen, direct action film or digital
Extraoral radiographs = screen, indirect action film or digital |
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Cross section of conventional film |
Layers: Supercoat Emulsion Adhesive Base Adhesive Emulsion Supercoat
Emulsion is the important part |
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What is the emulsion of a conventional film? |
Suspension of light sensitive salt in a gelatin binder. Salts are silver halides Sensitive to light up to blue wavelength Salts can either be: - globular - light absorbed in blue spectrum - Tabular - light absorbed in green spectrum A combination of the two is used in twin emulsion |
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Parts inside conventional film packet and their function |
Plastic outer - waterproof Lead foil - prevents reflection and increased dose Black card - either side of film, stops visible light, absorbs moisture
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How to reduce the dose using the film? |
Using the fastest possible film (E or F) will reduce the exposure time required. |
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Extraoral x-rays |
X-ray doesn't act directly on emulsion Acts on intensifying screens New ones are "rare earth" - blue/green light -absorb more energy - more conversion to light -more efficient/faster |
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Film processing |
Non exposed film-green silver halide emulsion | Exposure - green sensitized and green non-sensitized emulsion | Developer - alkaline reducing action, sensitized silver halide crystals are converted to black metallic silver | Washing - removes residual developer | Fixation - unsensitized silver halide crystals removed, acetic acid and sodium thiosulfate | wash - removes residual fixer | Dry
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Advantages of automatic processing |
-Time saving, films dry in 5 mins -No need for a dark room -Controlled, standardised conditions, easy to maintain -Some machines automatically replenish chemical |
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Disadvantages of automatic processing |
-Strict maintenance and regular cleaning essential -Dirty rollers produce marked film -Some machines transport films on a mesh and this can leave marks -Equipment relatively expensive -Small machines cannot process extraoral films -depending on chemicals, cannot always process intra and extraoral films in same machine |
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Conventional film errors |
Pale- too short time in developer, too cold, too dilute, exhausted developer, underexposed
Dark - too long in developer, too concentrated, too hot, fogged, over exposed |
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Grading of image quality |
Excellent: no errors Acceptable: errors but diagnostically useful Unacceptable: needs to be repeated
Quality is task dependent It is the ability of the receptor to reproduce the desired information |
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Aspects of image quality |
Geometric accuracy Anatomical accuracy Absence of artifacts Adequate coverage Sharpness- clarity, definition, detail Contrast
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What can affect contrast? |
receptor contrast - characteristic curve/digital algorithm subject contrast - too fat, thin enamel, decay too early Exposure factors - kV, Compton scatter etc Viewing conditions - correct illumination for film |
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Blurring causes |
Patient movement Geometric blurring - focal spot size, fsd, object-receptor distance Receptor blurring - film: grain size and shape, screen: phosphor thickness, particle size reflective layer, screen-film contact |
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Compare digital and film radiographs |
Poss exam question |
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Types of digital receptors |
Solid state - Charge Coupled Device (CCD) or Complimentary Metal Oxide Semiconductors (CMOS) -expensive - not issue for dental as small
Photostimulable phosphor storage plates - range of sizes, wireless, Europium doped barium fluorohalide on a flexible plastic plate |
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Charged Coupled Device |
A silicon chip embedded in an electrical circuit An array or matrix of pixels of silicon chips - P and N type. Linked together in rows - 1 faulty pixel affects a whole row Has surface scintillation layer of rare earth - produces light from x-ray, light then interacts with silicon
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Complementary Metal Oxide Semiconductors |
Similar to CCD but each pixel is individually linked to a tranisitor - one faulty pixel doesn't affect whole row |
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PSPL mechanism |
X-ray hits europium and excites it to higher energy level. Plate is put in reader and scanned by a laser which causes Europium to move back to lower energy level. Emits energy as light which is converted into voltage and relayed to the computer.
Plate is then clear for reuse. |
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Image editing tools for digital radiographs |
Contrast - difference between black and white Brightness - degree of blackening Magnification Sharpness Grey scale inversion Edge enhancement Pseudo Colour measurements
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resolution of different radiograph techniques |
Resolution - the ability to distinguish between two points close together - measured in line pairs per mm Direct action - 20 lp/mm PSP 10 lp/mm CDD and CMOS 20-30lp/mm |
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Advantages of digital dental radiography |
Instant image lower patient dose image processing/enhancement computer can compensate for exposure error avoids chemical processing errors and hazards easy storage easy transfer of images Phosphor plates have a wide latitude for exposure |
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Disadvantages of digital dental radiography |
CCD requires connecting wire to the computer for intraorals CCD physically large detector compared to film for intraoral CCD low dose but narrow exposure latitude Monitor quality and ambient light need for back up? - computer failure over exposure of CCD can cause blooming Manipulation - can misread |
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Possible errors |
Patient preparation Positioning Exposure Processing Film handling |
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Film too pale |
Underexposed - incorrect exposure time, incorrect mA, faulty equipment, taken finger of button too soon Underdevelopment - inadequate time in developer, too, cold, too dilute, developer exhausted, developer contaminated by fixer Patient tissue excessively thick Film packet back to front - lead sheet in way |
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Film too dark |
Overexposure - faulty equipment, incorrect exposure time, timer of intraoral not panoramic Overdevelopment - too long, too hot, too concentrated Fogging - films poorly stored, too warm, faulty cassettes, faulty darkroom Patient small or thin tissue |
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Film with low contrast |
underdevelopment overdevelopment double exposure contaminated developer inadequate fixation/fixer exhausted poor storage old film faulty cassette poor dark room |
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Image blurred |
movement of patient bending of film during exposure poor film-screen contact flim type Overexposure of film may lead to "burn out" of thin edges |
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Dark Marks |
Film bent Poor handling - finger prints/nail marks Processing errors - roller marks, splashes Patient biting film packet Damp environment
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White marks |
Fixer splashes Inadequate fixation -> may look milky Films stuck together in processor Insufficient chemicals to cover film Dirty intensifying screens Film bent such that beam passes through lead foil along its long axis |
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Incorrect positioning - intraoral |
Incorrect vertical angulation Foreshortened/elongated Incorrect horizontal angulation overlap Cone cutting Missed off tooth |
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Incorrect positioning - panoramic |
Too far forward Too far back Rotated Chin down Chin up Slumped |
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3 types of intraoral radiograph |
Bitewing Periapical Occlusal |
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Bitewings |
Aim to show the crowns of premolars and molars of both jaws with no or minimal overlap (up to half the thickness of enamel is acceptable). Should see contact point of distal canine/mesial first premolar to the most distal contact point.
Horizontal will also show bone level. |
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What can you see from a bitewing? |
Detection of approximal caries Detection of occlusal caries Detection of recurrent caries - under restorations Asses depth of caries Check for overhangs Check for calculus deposits - hard to see assess bone levels May see pins/perforations |
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Bitewing technique |
Technique 1 Sticky tab attached to the middle of the film. Patient bites on wing attached at right angle to film. Good for children as smaller. Harder to align beam. Cheap. Simple.
Not reproducible. More chance of coning off. Operator dependant.
Technique 2 - more prefered Generally use film holders with beam aligning device. Long axis of film horizontal Use size 2 for adults (0 or 1 for kids) Bite block in middle of film and film held as close to teeth as possible Beam projects at right angles to film both horizontally and vertically although because of curve of Monson, beam will be angled slightly downwards.
Simple. Film not displaced by tongue. Beam always right angles to film. Less chance of coning off. Reproducible.
More expensive initially. May be uncomfortable. |
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Vertical bitewings |
long axis of film is vertical Each film covers fewer teeth but shows more alveolar bone so if bone loss >6mm will be more diagnostic
Usually need 2 to cover posterior teeth
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Film placement for the best image |
Film and object as close together as possible. Film parallel to object. Film beyond apices X-ray source to object distance as great as possible X-ray beam perpendicular to film |
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Aim of a periapical |
To show all of tooth (crown and root) and periapical tissues (approx 3mm around apex) |
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What can be seen on a periapical? |
Apical pathology - rarefying osteitis, cyts, root resorption Perio disease - bone levels Endodontics Root morphology Impacted teeth Post op trauma |
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Paralleling technique - periapicals |
Film is held parallel to tooth by the use of film holders Most areas of the mouth - due to anatomical restraints - the film has to be a distance from the tooth This causes magnification so it is very important to increase source-object distance (30cm)
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Paralleling advantages and disadvantages |
Geometric accuracy with minimal magnification Sharper image Anatomical accuracy of alveolar crest less superimposition Less foreshortening or elongation Approximal caries well shown Patient's head can be in any position Lower dose to thyroid, gonads, no dose to finger
Expensive to start Careful and accurate placement required Some patients find it uncomfortable Longer to perform full mouth survey Cannot use short cone |
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Bisecting angle technique |
•The original periapical technique •Not routinely used in LDI
•Occasionally can be useful adaptation of paralleling technique if can’t get a very long root onto film then by changing the angle of the tube ie no longer paralleling, and thereby causing foreshortening can project all of tooth
•Relies on film being as close to tooth as possible •Crown edge touching film and root diverging away •X-ray beam is directed perpendicular to a line which bisects the angle between the long axis of tooth and film
•Patient must have relevant occlusal plane parallel to floor
•Film holders can be used but more common for patient to hold film in place with finger •Average angles that tube head is set at for different areas of mouth making the occlusal plane positioning important •Should take into account any obvious variations in anatomy e.g. class 2 div 1 malocclusion
•Use largest periapical film anteriorly due to increased risk of cone cutting |
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Bisecting advantages and disadvantages |
•Cheap •Quick •More comfortable for patient
•Difficult to assess line of bisection •There can be foreshortening/elongation •Finger irradiated if holding film in place •Patient must have occlusal plane parallel to floor •Beam angles have to be remembered •Bone levels not accurate •Zygoma superimposed over roots of maxillary molars •Increased likelihood of coning off •Not reproducible •Thyroid more likely to be irradiated |
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Occlusal aim |
Similar to large bisecting angle |
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What can you see on an occlusal? |
•Pathology not fully covered by periapical •Assess impacted teeth such as maxillary canines •Used in localisation in conjunction with other films (parallax principle) •Trauma especially in children •Bony expansion of mandible •Submandibular duct stones |
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Difference between true and oblique occlusals? |
•TRUE: x-ray beam perpendicular to film from all directions
•OBLIQUE: x-ray beam angled other than right angles to film from at least one direction |
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Maxillary, oblique occlusal |
•Midline is also known as “upper standard” or anterior oblique AO or maxillary midline. Common angulation is 60-70 degrees through tip of nose
•Other than the midline may be known as lateral maxillary occlusal or upper oblique occlusal of whichever tooth centred over |
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Maxillary, true occlusal |
•Virtually useless film •Due to inclination of maxillary incisors one does not obtain a cross sectional view
•Due to the bones of face and skull being between beam and film there is too much superimposition to obtain clear view of incisors |
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Maxillary, vertex occlusal |
•Rarely used in LDI •Projects down through the vertex of skull along long axis of incisors so resulting in cross sectional view •Not true occlusal as beam angle is more than 90o to film •Mini cassettes with intensifying screens used due to the amount of bone that need to be penetrated •X-ray beam angled towards abdomen so use of lead apron is prudent
•Does not give a detailed image, teeth look like “a string of pearls” |
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Mandibular oblique occlusal |
•Looks like big bisecting angle periapical •midline might also be known as “standard” Angulation of beam is approximately 45o to the chinpoint
•Other than the midline may be known as lower oblique |
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Mandibular, true occlusal |
•As the teeth in the mandible are more upright, if the x-ray beam is 90o to film a cross sectional view will be achieved •Can be midline or one side or the other •Useful for fractures of mandibular symphysis, submandibular stones, buccolingual expansion
•Posterior placed stones can be imaged by “shooting” beam over patients shoulder, projecting the stone anteriorly onto the film |
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Localisation |
•Often need to localise impacted teeth or foreign bodies •Orthodontist may wish to know whether a tooth is positioned such that it will interfere with tooth movement
•Surgeons may need to know whether a tooth is better approached buccally or palatally •2 views at angle to each other, PARALLAX. Vertical ( e.g. paralleling periapical and oblique occlusal), horizontal (e.g. 2 periapicals at different horizontal angulations) •Object further away moves with the direction of x-ray source |
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Define radiolucency and radiopacity |
Radiolucency: will appear blacker on image, less to stop the x-rays passing through to interact with receptor, e.g. air, less bone
Radiopacity/radiodensity: will appear whiter on image, more tissue that stops xrays reaching receptor e.g. bone |
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Writing a radiographic report |
Does not have to be a full radiology report Should be able to demonstrate that each radiograph has been evaluated Should provide enough info so that it can be subject to later audit |
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What to do when first viewing an image? |
Check is the correct patient and correct image date Check it is orientated correctly Are there any faults that make it non diagnostic ie do you need to repeat it Is the quality acceptable ie contrast/brightness Look round the image methodically |
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Describing a lesion |
Where is lesion - ID canal What size -cm/mm beware distortion What shape - Circular • Lobulated • Sausage shaped • Expansile What are its borders/margins like - irregular /smooth, Corticated • Partially corticated • Well defined Is it radiolucent/ radiopaque/mixed density - homogenous or heterogenous, unilocular, multilocular, pseudolocular Effects on other structures - Teeth:displaced/ resorbed • Inferior dental canal • Maxillary antrum |
