Oral and Dental Radiography Flashcards
what is ionising radiation ?
x-ray interacts with atom in human tissue, electron can go on to cause further ionisation and free radical formation
what are the biological effects of ionising radiation?
stochastic effects e.g. cancer induction, non stochastic effects e.g. cataracts, radiation burns, sterility
what is the role of the international commission on radiological protection (ICRP)
produce advice for creation of national legislation to govern use of ionising radiation
what is the main source of radiation int he environment ?
background radiation
what is the radiation dose of an OPG?
0.02mSv
what is the radiation dose of a periapical?
0.001mSv
what is the radiation dose of a chest x ray ?
0.02mSv
what is the radiation dose of a whole body CT ?
15-20mSv
what is the purpose of ionising radiation regulations 1999 (IRR99) ?
ensure ionising radiation from work activities are kept as low as reasonable practicable (ALARP) and does not exceed specified limits
relates to workplace, employees and public
what are the requirements of IRR99?
risk assessment employers written procedures radiation protection adviser and supervisor local rules controlled areas restriction of exposure e.g. PPE quality assurance program dose limits/constraints notification of equipment related incidents
what are the stages of a risk assessment ?
identify hazards (dose)
determine who may be harmed
evaluate risks and implement control measures (protection)
record findings
periodic review and revision of risk assessment
what must the RPA be consulted on ?
requirements for controlled areas
new equipment
regular calibration of dose monitoring equipment
testing safety features and warning devices
risk assessment and contingency plans
investigation after a radiation incident
training
what is the role of the RPS ?
ensure local rules are followed
what are local rules ?
rules on how to work safely in a controlled area
what must local rules for radiation rooms/equipment contain ?
PRS and RPA name and contact info
identification of controlled area
summary of working instructions
contingencies for foreseeable accidents
what is the controlled area ?
any area where it is necessary to follow special procedures to restrict significant exposure or
any area where >6mSv/y or 3/10 of any dose limit is likely
what are dose limits ?
upper limits of dose that must not be exceeded
to whom do dose limits apply ?
staff, trainees and other persons excluding the patient
what are dose constraints ?
recommended limits that should not normally be exceeded with standard practice
what are the recommended dose contracts for dental radiography ?
1mSv for operators directly involved with radiography
0.3mSv for employees not directly involved and comforters and carers
what is a quality assurance programme?
regular testing and review of equipment, procedures and training to ensure optimal diagnostic results at minimal level of radiation dose
what os the purpose of the ionising radiation (medical exposures) regulations 2000 (IR(ME)R 2000)
minimise the risks to patients undergoing medical exposures
who enforces IR(ME)R 2000?
CQC, helathcare inspectorate wales
what are the requirements of IR(ME)R 2000?
guidelines for referral criteria for radiographic examinations
written protocols for every type of standard radiographic examination
correct identification of the patient
identification of referrers, practitioners and operators
ensuring QA programmes are followed
assessment of patient dose
use of diagnostic reference values
carrying out and recording clinical evaluation of the outcome of each exposure
medical physics expert
clinical audit
what are the 4 classes of duty holder defined by IR(ME)R 2000 ?
referrer, practitioner, operator, employer
what does justification mean with regards to radiography ?
the benefits to the patient must outweigh the risks
what does authorisation mean with regards to radiography ?
recording that the justification has been carried out prior to the exposure in patients notes
what is the role of the operator ?
carry out investigation
optimisation (ALARP)
how is optimisation (ALARP) achieved ?
justification
selection criteria
sensitive image detector systems
field reduction to minimum required for OPG’s
rectangular collimation for intra orals
effective QA and equipment management programme
what os the role of the employer ?
legal person implement IRR99 and IR(ME)R 2000 notification of HSE risk assessment training dose limits
what must HSE be notified of ?
installation of new equipment
new ownership of practice
change of address
not required when x ray equipment changed or renewed
what are the duties of the employee ?
not knowingly expose themselves or others to ionising radiation greater than necessary
use PPE
report equipment defects
training
what should the medical physics expert give advice on ?
patient dosimetry
use of new/complex techniques
what are diagnostic reference levels (DRL’s) ?
doses for typical examinations for groups of average sized patients
based on entrance surface dose (skin entry dose)
how is an IRMER incident reported ?
online
what is the recommended amount of training in radiography for DCP’s ?
1 day course every 5 years
what should dental nurses/therapists/hygienists possess in order to operate x ray equipment ?
NEBDN certificate
what are x-rays ?
a form of electromagnetic radiation,
each x-ray is a photon and is equivalent to a packet of energy,
can be thought of as a wave with frequency and wavelength,
the x -ray beam used in dentistry is made up of trillions of individual photons
what are the properties of x-rays ?
invisible, weightless, no charge, travel in straight lines, travel at speed of light in a vacuum, penetrating, ionising, obey inverse square law (intensity of radiation reduces to one quarter as distance from source is doubled
what is the wavelength range of x-rays ?
0.01-0.05 nm
what is an atomic mass unit (amu) ?
1/12 mass of 12C atom
what is the charge and mass of a proton ?
+ charge and 1 amu
what is the charge and mass of a neutron ?
no charge and 1 amu
what is the charge and mass of an electron ?
- charge and 1/1840 amu
what is meant by atomic number ?
Z, number of protons in the nucleus
what is meant by atomic mass number ?
A, number of proteins and neutrons in a nucleus
what determines the chemical properties of an atom ?
number of electrons
what is electron binding energy ?
the work required to overcome attraction between the negative electron and positive nucleus and remove the electron from an atom
for which electron shell is binding energy greatest and why?
K shell as closest to nucleus
what is ionisation ?
the removal of one or more electrons form an atom, creates an ion pair - positive ion and an electron
what is excitation ?
raising an electron to a higher energy level
what are the stages in the production of x-rays ?
produce lots of electrons,
accelerate electrons to a high energy,
smash electrons onto heavy metal target,
process conducted in a vacuum to prevent collision of electrons with atoms of air or gas
what are the main components of an x-ray tube head ?
glass x-ray tube insert (filament, coper block and tungsten target),
step up transformer (high voltage to accelerate electrons from cathode to anode),
step down transformer (low voltage to heat filament),
lead-lined casing,
oil surrounding insert,
aluminium filtration,
collimator,
beam indicating device
what is the production process of x-rays in a tube head?
electrons produced by filament heating, thermionic emission at the cathode,
extent of filament heating controls the amount of electrons produced and hence the tube current (mA),
electrons accelerated to anode by high potential difference (kV),
rapid deceleration of electrons by target at the anode
what causes heat producing collisions during x-ray production ?
when electrons bombard the tungsten target they are suddenly brought to rest, the energy lost by the electrons is transferred into heat (95%) or x-rays (1%)
where does the heat produced during x-ray production go ?
removed and dissipated by copper block and surrounding oil
why is the x-ray target tungsten?
high melting point,
high atomic number ensures lots of interactions between electrons from filament and target atoms
what is meant by kV with reference to x-rays?
determines quality of x-ray beam i.e. energy of the photons,
determines penetrating power of the photons,
increased kV reduces image contrast
what is meant by mAs ?
determines quantity of the x-ray photons,
affects degree of blackening of film (optical density)
which 2 components are involved in the production of x-rays ?
Bremsstrahlung Radiation
Characteristic Radiation
what causes Bremsstrahlung radiation ?
incoming electron penetrates the outer electron shells and passes close to the nucleus of the tungsten atom,
the electron is slowed down and deflected by the nucleus with a loss of energy which is emitted in the form of x-rays
what is meant by filtration in x-ray production ?
the removal of low energy photons from the final x-ray beam due to their lack of penetrating power
what causes characteristic radiation ?
the incoming electron collides with an inner shell tungsten electron displacing it to an outer shell or displacing it from the atom
which electrons are of diagnostic importance in characteristic radiation ?
K shell electrons
what energy does a bombarding electron need in order to displace a K shell electron in characteristic radiation ?
69.5kV
how is an x-ray photon produced in characteristic radiation ?
following ionisation or excitation of tungsten atoms the orbiting tungsten electrons rearrange to return the atom to a neutral state,
this involves the electrons jumping from one energy level to another,
the jump result in an x-ray photon with a specific energy
describe the photoelectric effect
process of pure x-ray absorption,
the incoming x-ray photon interacts with a bound inner shell electron of the tissue atom,
the inner shell electron (photoelectron) is ejected with considerable energy into the tissues and will undergo further interactions,
the x-ray photon disappears having given up all of its energy,
vacancy exists in the inner shell
how is vacancy caused by the photoelectric effect filled ?
electrons drop from outer shells, the excess energy is released in the form of light or heat
how is atomic stability achieved following the photoelectric effect ?
capture of a free electron
what is the probability of a photoelectric effect proportional to ?
Z^3 (atomic number3) of tissue
1/KeV^3 (1/energy of x-ray beam ^3)
what is the purpose of the photoelectric effect ?
produces the contrast between different tissues of different atomic numbers
what is the significance of the photoelectric effect being a process of pure absorption ?
contributes to dose received by patient
describe the compton effect
x-ray absorption and scattering process,
predominates with high energy photons,
the incoming x-ray photon interacts with a free or loosely bound outer shell electron of the tissue atom,
the outer shell electron (recoil electron) is ejected with some energy taken from the incoming photon (absorption),
the remaining incoming photon energy is scattered
in which direction does the recoil electron travel ?
forwards
what can happen to the scattered photon following the compton effect ?
undergo further compton interactions in the tissues,
undergo photoelectric interactions in the tissues,
escape the tissues as scattered radiation
what are the differences between the photoelectric and compton effects ?
in the compton effect the incoming x-ray photon does not distinguish between one electron and another so the interaction is not dependent on the atomic number as with the photoelectric effect
the compton effect does not give much diagnostic information as there is not good discrimination between tissues on the final radiograph
in which 2 ways can x-rays case harm?
direct and indirect damage
how can x-rays cause direct damage ?
the x-ray photon or ejected high energy electron breaks nucleic acid bonds leading to defective chromosomes
what are the potential effects of defective chromosomes ?
failure to pass on information
abnormal replication
cell death
temporary damage
what is the possible effect of direct damage on somatic cells ?
radiation induced malignancy
what is the possible effect of direct damage on stem cells?
congenital abnormality
how can x-rays cause indirect damage ?
ionisation of intracellular water,
production of free radicals,
recombination of free radicals to form hydrogen peroxide,
hydrogen peroxide damages the cell by breaking down proteins e.g. DNA
what are the biologically damaging effects of radiation ?
tissue reactions (deterministic effects) - early and late tissue reactions stochastic effects - cancer induction, heritable effects
what are the effects of therapeutic doses of radiation on the oral cavity ?
mucositis, loss of taste, atrophic mucosa, dry mouth, radiation caries, tooth defects during development
what are the differences between stochastic and tissue effects ?
stochastic effects -
have no known threshold dose,
the size of exposure to ionising radiation does not effect the severity of the damage induced, only the pronanility of it occurring
what are the possible heritable effects of ionising radiation ?
damage DNA in sperm or egg cells,
congenital abnormality,
dose of 0.5-1.0 Sv doubles rate of spontaneous mutation
what is the absorbed dose (D) ?
a measure of the amount of energy absorbed form the radiation beam per unit mass
what unit is used to measure absorbed dose ?
Gray (1 joule/Kg)
what is the equivalent dose (H)?
a measure which allows the potential harm (radiobiological effectiveness) from different types of radiation to be considered
what is the equation for the equivalent dose ?
H = absorbed dose X radiation weighting factor (Wr)
what unit is sued to measure equivalent dose ?
Sievert (Sv)
what is the radiation weighting factor of x-rays, gamma rays and beta particles ?
Wr = 1
what is the radiation weighting factor of protons and neutrons ?
Wr = 5-10
what is the radiation weighting factor of alpha particles ?
Wr =20
why do protons, neutrons and alpha particles have a higher Wr than x-rays, gamma rays and beta particles ?
have mass and charge so are more ionising
what is the relationship between equivalent and absorbed dose for x-rays ?
the equivalent dose measured in sieverts = the absorbed dose measured in Grays
what is the purpose of the effective dose (E) ?
allows doses from different investigations of different parts of the body to be compared
why is the effective dose important ?
some parts of the body are more radiosensitive e.g. gonads, lens
can be thought of as a broad indication of the risk to health form any exposure to ionising radiation
what is the equation for effective dose ?
E = dose equivalent x tissue weighting factor (Wt)
if more than one organ is exposed the effective dose is the sum of effective doses to all exposed organs
what units are used to measure effective dose ?
sieverts
how much dose can a patient receive in a year ?
as much as required to diagnose and treat effectively
how much background radiation is a periapical radiograph equivalent to ?
16 hours
how much background radiation is an OPG equivalent to ?
3 days
what is the risk of malignancy from 1 intraoral film?
traditional x-ray set and D speed film - 1 in 2000000
70 kV x-ray set and E speed film - 1 in 20 000000
what is the risk of malignancy from an OPG ?
0.21-1.9 per million exposures
when is collective dose measure used ?
when considering the total effective dose to the population
what is the equation for collective dose ?
CD = effective dose X population
what unit is used to measure collective dose ?
man-sievert
which 3 groups are the population divided into for the purpose of limiting radiation dose ?
patients, occupationally exposed, general public (by the ICRP)
what should the decision to perform a radiograph on a patient be based on ?
correct assessment of indications,
expected diagnostic yield,
how results will influence diagnosis,
clinician having adequate knowledge of ionising radiation
what is the definition of a classified worker ?
a worker who receives >6mSv per year
what are the practical methods of dose reduction ?
distance , shielding, time
how big should the controlled area be for an x-ray set operating up to 70Kv?
1.0M
how big should the controlled area be for an x-ray set operating above 70Kv?
1.5 M
what materials are appropriate to shield from x-rays ?
lead, lead rubber/glass, concrete, barium plaster
how can dose be limited by x-ray set design and use ?
higher Kv (60-70KVp), rectangular collimation, aluminium filtration, > 20 cm away from skin, accurate timer, adequate warning signals
how can dose be reduced by quality assurance ?
check x- ray equipment every 3 years,
check processing equipment,
image quality evaluation and audit
what is meant by the entrance surface dose ?
max dose to tissues, measured using thermoluminescent dosimeters
what are the 2 dose measurements in radiography ?
ESD and dose area product
what are the advantages of film badges to measure personal dose ?
cheap, permanent record, can be reassessed, record type of radiation
what are the disadvantages of film badges to measure personal dose ?
processing required
what is the definition of thermoluminescence ?
a form of luminescence where stored radiation energy is emitted as light on heating
what is the active component in TLD’s ?
lithium fluoride crystals
what are the advantages of TLD’s to measure personal dose ?
sensitive, re-usable, quick read out, no processing
what are the disadvantages of TDL’s to measure personal dose ?
destructive read out, expensive, provide limited information on energy of radiation received
what are the 3 types of intra oral radiographs ?
periapicals, bitewings and occlusals
what does a periapical radiograph show ?
2-3 teeth from crown to apex and the surrounding apical tissue
what does a bitewing radiograph show ?
the crowns of upper and lower pre-molars and first and second molars (8 teeth on one film)
what does a vertical bitewing radiograph show ?
more root but fewer teeth than regular bitewing
what extra-oral radiographic techniques can be used ?
panoramic radiography, lateral cephalometric radiography, oblique lateral, postero-anterior mandible, occipito-mental (OM)
what does a DPT show ?
all teeth and supporting structures in one image
what does a lateral cephalometric radiograph show ?
lateral view of the facial bones and jaw,
relationship of upper and lower arches and the soft tissue outline
what does an oblique lateral radiograph show ?
upper and lower posterior teeth on one side
when is an oblique lateral radiograph useful ?
poor tolerance of film in mouth/small children
what are the alternative methods to radiography to obtain diagnostic images ?
cone beam computed tomography (CBCT), computed tomography (CT), ultrasound, magnetic resonance imaging (MRI), radionuclide imaging
what is CBCT useful for ?
imaging in multiple planes, good for bone not soft tissue
what is CT useful for ?
imaging in multiple planes, good for bone and soft tissue
how does ultrasound work ?
probe gives off high frequency sound waves,
sound waves reflected back at the interfaces between different tissues,
the reflection is picked up by probe which produces the images
does not use ionising radiation
how does MRI work?
strong magnetic field lines up the protons in hydrogen atoms,
short bursts of radio waves knock protons out of alignment,
as the protons realign with the magnetic field their rotation produces an electrical signal in a receiving coil
does not use ionising radiation
what os MRI useful for ?
soft tissue imaging
how does radionuclide imaging work ?
uses a pharmaceutical attached to a radioisotope,
small amount introduced to body,
different pharmaceuticals go to different organs,
radioactive part emits gamma rays,
gamma rays detected by gamma camera
what does a dental x-ray set consist of ?
tubehead, positioning arms, control panel and security
what are the dental x-ray set requirements ?
safe, accurate, capable of generating x-rays of appropriate Kv, small, easy to manoeuvre, easy to position, stable and balanced once positioned, easily folded and stored, simple to operate, robust
what does the dot on the tube head indicate ?
position of the target
what is used for filtration of the x-ray beam?
- 5mm al below 70Kv,
2. 5mm al above 70Kv
what is the purpose of the x-ray beam filter ?
removes low energy photons,
decreases dose to patient
what is the advantage of rectangular collimators over round collimators ?
rectangular matches the beam size and shape to the image receptor decreasing dose to the patient by 50 %
what features are on the control panel of an x-ray machine ?
on/off switch, timer, exposure time selection, warning lights/audible signals, exposure button
what does the Kv control ?
quality or penetrating power of the beam
what will a higher Kv do ?
decrease patient dose,
decrease contrast,
increase scatter,
give photons higher energy so more penetrating power
what does mA/time control ?
quantity of x-ray photons
what does a higher mA do ?
increase patient dose,
increase film blackening
what are the advantages of constant potential ?
x-ray production per unit time is more efficient,
more high energy photons per exposure,
fewer low energy harmful photons are produced,
shorter exposure times
why is the beam indication device better than the spacer cone ?
spacer cone has a short focal skin distance,
spacer cone has a divergent beam leading to image magnification and irradiation of a greater areas
beam indicating device - 20 cm long focal skin distance,
near parallel beam
what is a direct action film ?
the x-ray photons interact with the film
what is an indirect action film ?
the x-ray photons interact with an intensifying screen producing light which then interacts with the film
what is inside a film packet ?
black paper, film, lead foil, moisture resistant outer cover,
describe the cross sectional structure of x-ray film
protective coating, emulsion, adhesive on both sides of a blue tinted transparent plastic base
both sides of the film are active
what does the emulsion in x-ray film contain ?
90% silver halide crystals in a gelatin matrix,
10% iodo - bromide (increases sensitivity)
what is the function of the emulsion in x-ray films ?
the silver halide crystals are sensitised by x -ray or light photons forming the latent image,
the sensitised crystals are reduced to black metallic silver int the developer
what does film speed control ?
the exposure required to produce an optical density of 1.0 above background fog
the faster the film the less exposure required so less dose to the patient
what are the slowest to fastest x-ray films and how do they reduce dose ?
slowest - D speed E speed (1/2 dose of D speed) F speed (60 % dose of E speed) fastest - digital (50% dose of F speed)
what factors determine film speed ?
the number and size of silver halide crystals in the emulsion - more crystals with larger size means greater speed but some loss of image quality
how do indirect action films work ?
x-ray photons interact with intensifying screens which sandwich the film between them and produce light which then interacts with the film
what is the purpose of a cassette ?
light tight aluminium or carbon fibre casings which contain the intensifying screens and film
used to penetrate thicker structures
what are intensifying screens ?
fluorescent phosphors embedded in a plastic matrix which emit light when excited by x rays via the photoelectric effect
how do intensifying screens reduce patient dose ?
one x-ray photon produces many light photons therefore fewer x-ray photons are required to produce an image
what is image resolution ?
the ability to differentiate between different structures that are close together on the radiograph
what is the resolution of direct action film ?
10 line pairs per mm
what is the resolution of indirect action film ?
5 line pairs per mm
what is intensification factor ?
exposure required when screens not used / exposure required with screens
what are the advantages of rare earth screens ?
they are 5 times faster than calcium tungstate screens therefore lower dose to patient
what colour light do terbium activated screens emit ?
green
what screen emits blue light ?
thulium activated screens
what colour light does yttrium emit ?
ultraviolet
what is important to remember with rare earth screens ?
films must be matched to the screens
what happens during film processing ?
the invisible latent image is converted into the visible radiographic image
what are the advantages of automatic x-ray processing ?
time saving,
no darkroom required,
controlled, standardised processing conditions,
automatic replenishment of chemicals
what are the stages of film processing ?
development, fixation, washing, drying
describe the developing solution used in x-ray processing
alkaline pH 10.5,
oxidised by air over time making it less effective,
should be changes every 14 days
what conditions of the developing solution will produce an overdeveloped image ?
concentration too high, left in for too long, too hot
what conditions of the developing film will produce an underexposed image ?
concentration too low, solution too old, too cold
describe the fixation stage of x-ray processing
unsensitised silver halide emulsion is removed to reveal the transparent/white parts of the image
the fixer firmly anchors the silver grains onto the film base
2 stages :
clearing - time taken for unsensitised silver bromide crystals to be removed from the film
fixing - 2X clearing time
what is the pH of the fixing solution ?
4.0-4.5
what does under fixed film look like ?
greenish yellow/milky
over time will discolour to brown
what is the purpose of the washing stage of film development ?
remove residual fixer
if fixer remains on the film it will be stained brown
how is a digital image constructed ?
digital images are made up of pixels,
each mixl has a specific grey shade ranging between black and white,
pixels are arranged in a matrix of fixed dimension,
smaller pixels allow finer image detail
what is spatial resolution ?
sharpness of the image,
measured in line pairs per mm,
human eye can only resolve 8 lp/mm without magnification,
current dental systems have resolutions between 6 and 22 lp/mm
what determines the pixel shade in digital imaging ?
the amount of radiation that has reached the sensor assigns each pixel a shade of grey
what determines the number of grey shades possible in a digital image ?
bit depth of the image file
what is the main difference between direct digital and indirect digital imaging techniques ?
direct digital is a virtually instant image but with indirect the plate must be read so there are several seconds before the image is available
describe the process of direct digital imaging
2 stage process:
- scintillation layer converts x-rays to light,
- semi conductor based pixel ray converts light to electron charge
which imaging technique are charged coupled devices (CCD) involved with ?
direct digital imaging
why are CCD’ s expensive to manufacture ?
have to transport charge across the chip without distortion
what are the advantages of CCD’s ?
create high quality low noise images, higher fill factor, better pixel uniformity
which digital imaging technique are complementatry metal oxide semiconductor active pixel sensors associated with ?
direct
compare CCD’s and CMOS-AP’s
CMOS-AP: lower power requirements, easier to manufacture, cheaper, lower light sensitivity, noisier
what type of digital imaging are photostimulable phosphor plates (PSP’s) involved in ?
indirect digital
what are PSP’s ?
plastic plate coated with a storage phosphor material sensitive to x-rays
how do PSP’s work ?
the phosphor stores the x-ray energy,
psp plate placed in a laser reader/computer which releases the photon energy as light,
image generation is not instant
what are PSP’s also known as ?
computed radiography
describe the process of computed radiography
phosphor material is europiam activated barium fluorohalide,
the stored energy is released as blue light when stimulated by red light from a helium/neon laser,
the released light is detected by a photomultiplier which converts the light signal to an electrical signal,
the signal is amplified and converted into a digital signal by an analogue to digital converter (ADC),
data is transferred to a workstation for computation into an image,
the imaging plate is erased after use by exposure to an intense light source
what are the advantages of PSP over CCD/CMOS ?
larger variety of imaging areas, no connecting cable, slimmer imaging plate, cost, has a linear response to x-rays over a wider range than most CCD/CMOS
what does blooming mean in digital imaging ?
overload of pixels and bleeding of signals into adjacent pixels
what are the disadvantages of PSP ?
plates must be processed within 8 hours,
require separate processing,
requires careful handling to prevent scratches
what happens to a digital image when the brightness is altered ?
all the grey levels are raised or lowered by the same amount
what are the disadvantages of the physical archival of images and notes ?
requires lots of space,
staff must manage archive and retrieve notes,
may only be viewed in one place at a time,
limited options for electronic transfer,
risk of data loss e.g. fire/flooding,
misfiling
what is DICOM ?
digital imaging and communications in medicine,
industry standard for the communication and management of medical imaging information
what are the advantages of digital imaging compared to film ?
potential reduced radiation dose, instant image, electronic storage, manipulation possible, reduced consumables as sensors are reusable, no noxious chemicals so safer, fewer processing errors
what are the disadvantages of digital imaging ?
outlay cost, cross infection control, bulky rigid sensors, damage to sensors, limitation on size of sensors, images may be manipulated by fraud
