Production of xrays Flashcards
What are the four ways x rays interact at the atomic level?
Photoelectric effectCompton effectRayleigh scatteringPair production
What is the photoelectric effect?
process of pure x ray absorption
What happens between the electron and the x ray photon in the photoelectric effect?
incoming x ray photon interacts with a bound inner shell electron of tissue atomthe inner shell electron is then ejected with large amounts of energy into tissues and undergoes further interactions
What is the name of the electron that becomes knocked off in the photoeectric effect?
photoelectron
What happens to the x ray photon once it has given its energy to the electron in the photoelectric effect?
the photon disappears
What happens to the remainder of the electrons in the tissues during the photoelectric effect once the photoelectron becomes ejected? WHat happens in this process?
the electrons then drop down from outer shells to inner shells. this process produces energy in the form of light or heat
How is atomic stability then achieved once the electrons drop down from the outer shell to the inner shell in the photoelectric effect?
free electrons are captured
What is the effect of the high energy photoelectron on the rest of the tissues?
it is then free to interact with other tissues and maybe the cause of ionising radiation within the tissues which could lead to tissue damage
What is the probability of the photoelectric effect occurring within the tissues?
it is proportional to the atomic number of the protein ^3
Which tissue out of bone, dentine, enamel and pulp has the greatest atomic number?
bone hence why bone appears white because more x ray photons are absorbed (photoelectric effect)
What is the relationship between KV and photoelectric effect?
the lower the Kv the more likely the photoelectric effect will take place photoelectric effect proportional to 1/Kv^3
How is contrast produced on an x ray?
Photoelectric effect
T/F the photoelectric effect contributes to the total dose recieved by the pt?
Tbecause it is a process of pure absorption
What type of radiographic tool uses the photoelectric effect?
intensifyng screens
What is the compton effect?
this is the process of x ray absorption and scattering
WHen does the compton effect occur?
When there is higher energy photons
How does the compton effect work?
x ray photon interacts with a free/lossely bound outer shell electron of the tissue atomthe outer shell elctron is then ejected by using some energy from then incoming photon
What happens to the photon energy in the compton effect?
some is absorbedthe reminader is scattered
What happens to the direction of the x ray photon in the compton effect when an outer shell electron is encountered?
the photon changes direction and loses energy
WHat is the name of the electron in the compton effect that gets knocked off and what direction does it travel in?
recoilforward
In which tissues does the Compton effect occur more commonly in?
Any tissues since it is not dependant upon the atomic number rather it is dependant on the energy of the photon
WHat happens to the scattered photon in the Compton effect?
can undergo further Compton reactions with more tissuesundergo the photoelectric effect with tissuesescape the tissues and form scattered radation
T/F the Compton effect contributes greatly to the diagnostic information on the xray?
falseit does not provide information about the tissues s
What is the overall effect of both the photoelectric and Compton effect?
ionisation of the tissues
What are the two ways in which x rays can cause damage?
Direct damageIndirect damage
Which two things can cause direct damage?
the x ray photon or elected high energy electron
How do the photons or high energy electrons cause tissue damage?
they break the bonds between the nucleic acids causing defective chromosomesleads to mutations
What happens if there is direct damage to somatic cells?
radiation induced malignancy
WHat happens if there is direct damage to the stem cells?
congenital abnormality
How does indirect tissue damage occur from x rays ?
Ionisation of intracellular water creates free radicals which recombine to form Hydrogen peroxide
WHat is the effect of hydorgen peroxide on DNA?
breaks down proteins
What are the 3 biologically damaging effects of radiation?
somatic non stochiastic effectssomatic stochiasitcGenetic Stochiastic
What are somatic non-stochiastic effects?
these are deterministic effects (they will certainly happen)
How can the somatic non-stoch effects be divided?
acutechronic
Give an example of a somatic non stoch effect?
erythema
T/F somatic non stock effects have a threshold value?
Tthey will occur above a certain level
T/F somatic non stock effects occur frequently in dentistry?
FALSEdoses are too low for this
T/F there is no known threshold for stochastic effects?
Trueevery exposure to ionising radiation carries its risks
How does the size of the exposure relate to the stochastic effect?
this has no relation to the severity of damage only the probability of damage occurring
Stochastic effects are important where?
in diagnostic medicine
What are the genetic stochastic effects?
this is when radiation may damage DNA in sperm or egg cells leading to some kind of genetic abnormality
T/F genetic stochastic effects have a threshold dose?
F
What effect does a radiation dose of 0.5-1.0 Sv have on the chances of spon mutation?
doubles the chances
What does D refer too in radiography?
radiation absorbed dose
What does H refer to in radio?
Equivalent dose
What does E refer to in radio?
Effective dose
What is the radiation absorbed dose measured in?
Gray (Gy)
What is the radiation absorbed dose?
A measure of the amount of energy absorbed from the radiation beam per unit mass of tissue
WHat is the equivalent dose?
allows different radiobiological effectiveness of different types of radiation to be considered
What is equivalent dose measured in?
Sievert (Sv)
What is the effective dose?
allows doses from different investigations of different parts of the body to be compared
What is the effective dose measured in?
Sv
What is the collective dose?
totoal effective dose to the population (Man Sv)
T/F younger people have the greatest risk from radiation compared to older people?
T
What is the radiation dose from 1 intra oral filM?
0.001-0.008mSv
What is the radiation dose from DPT?
0.016-0.026 mSv
A periapical is equivalent to how many hours outside?
16 hours of natrual background radation
A DPT is equivalent to how many hours outside?
72 hours (3 days)
How many congenital abnormalities occur as a result of dental radiography?
1 every 3 years
What are the dose limits for patients having x rays?
no dose limitsneed to follow ALARA principle
What are the dose limits for comforter and carer?
there are no dose limits
What is the exposure time for dental x rays?
0.25s
What are X-rays and name their properties?
Wave packets of energy. Each packet is a photonForm of EM radiation They are invisible and weightlessThey travel in striaght lines and at the speed of light in a vaccummRange of wavelength 0.01-0.05nmObey inverse square law
What are the components of the x ray tube head?
class x ray tube step up transformer and step downlead casingOilaluminium filtrationCollimatorbean aiming device
What is inside the glass x ray tube?
filament and copper block with target
Where are electrons produced?
at the cathode W
What surrounds the cathode?
a molybdenum focussing cup
Once the electrons are produced at the cathode what happens?
they are accelerated to the anode by a high potential differnce
Where do the electrons bombard the anode?
At the tungsten target
What happens to the electrons once the tungsten target has been bombarded?
the electrons lose their energy which is transferred mainly to heat 99% and some into x rays 1%
How is the heat produced removed from the x ray unit?
the oil inside and copper block
What two methods explain how x rays are produced?
Bremsstrauhling radiation and characteristic radiation
WHat is the bremsstrualing radiation process?
incoming electron penetrates the outer electron shells and passes close to the nucleus of the tungsten atom.this electron is then slowed down and reflected by the nucleus and this causes a great loss in energy which is then emitted in the form of x rays
How are most x rays produced?
via the bremsstauling way 90% Brem
How does characteristic radiation occur?
incoming electron collides with an inner shell tungsten electron and displaces this to an outer shell or out of the atom via excitation and ionisation. is it the large loss in energy which causes x rays to be produced
Which electrons are of diagnostic value?
those in the K shell
How are x ray photons created?
they are created by electrons jumping from one energy level to another which then causes x ray photons with specific energy to be produced
What is the purpose of the aluminium filter?
This removes low energy photons and decreases the overall dose to the patient
How thick should the Al filter be when using xrays below 70Kv?
1.5mm
What is the purpose of the rectangular collimator?
This reduces the dose by approx 50%. it matches the beam sixe to the image receptor size
What is the purpose of kV?
this determines the quality or penetrating power of the x ray beam
What effect does increasing Kv have on patient dose?
it decreases it
What effect does increasing Kv have on contrast?
it decreases contrast
What effect does increasing Kv have on scatter?
increases catter
What is the purpose of mA/time?
determines quantity of x ray photons
What is the effect of increasing mA ot rime?
increases patient dose and increases film blackening
Are AC or DC units preferred for x ray machines?
Direct current are better
How long should the beam aiming device be?
20cm to minimise magnificaton
What are the two types of conventional image receptors?
Direct action film and Indirect action film
How do direct action films work?
The x ray photons interact with the xray film
Who do indirect action films work?
X ray phtons interact with an intensifying screen which then produces light and interacts with the filmFilm is sensitive to light
What are the four compontns of direct action films?
gren filmblack papermositure resistant cover and lead foil
What is the purpose of the lead foil?
this prevents any x rays going back onto the film and destroying the final image produced and prevents x tays going to the tongue
What is inside the xray film?
emulsion
What is the emulsion composed of? And what is its purpose?
90% Silver halide crystals in a gelatin matrix 10% silver iodo-bromideThey increase the film sensitivity as the silver halides become sensitised by x ray photons and when they become sensitised they become blackened by the phtons
What is the film speed definition?
The exposure required to produce an optical density of 1.0 above background fog
Faster films require more or less exposre?
Less exposure
What film speed is better, fast or slow, and why?
fastbecause reduces overall exposure to the patient
What does filmspeed relate to?
the number and size of the silver halide crystals in the emulsionLARGER CRYSTALS= FASTER FILM
What happens if the crystals are too large?
rhere will be some loss of image quality
What intr oral film speed do we use?
F speedoffers good film speed with adequate diagnosis
What are intensifying screens?
fluorescent phosphors embedded in a plastic matrix they emit light when x ray photons hit them
How do intensifying screens reduce dose?
one x ray phtoton produces many light photons therfore fewer x ray photons needed to produce image
What is one disadvanatge of intensifying screens?
they reduce the resolution of the image
What does the term resolution refer to?
ability to differentiate between differnt structures that are close togther on the xray
What is special about rare earth screens?
they are 5x faster than calcium tungstate screens and thefore they lower the overall dose to the pt.
What compound is inside the rare earch screns?
phosphors which emit differnt coloured light
Which type of phosphor emits green light?
Terbium activated
Which type of phosphor emits Blue light?
Thilium activated
Which type of phosphor emits UV light?
Yttrium
What must be matched to the screen when using rare earth screens>
the film
What are the advanatges of automatic film processing compared to manual?
time savingNo darkroom requiredControlled standardised processingr
What are the 3 stages to film development?
STage 1” DevelopmentStage 2: FixationStage 3: WashingStage 4: Drying
What happens in stage 1?
DevelopmentSilver halide crystals that have been sensitised are converted to black metallic silver once placed in he developing solution producing a black and grey image
What pH is the developing solution?
pH 10.5
How do you get an overdevelopped film?
Placed in developing solution for 1. Too long2. Too strong3. Too hot
How often should the developing solution be changed and why?
every 14 days because it slowly becomes oxidised
How do you get a film too pale?
Underdevelopeddeveloping solution1. Too old2. Too cold3. Too weak
What happens in stage 2?
FixationAny silver halide emulsion which was not sensitised by the xray photons is removed. This exposes the white parts of the film
What is the purpose of the fixer?
this firmly anchors the silver grains to the base
What is the pH of the fixer?
4.0-4.5
WHat is more critical, fixing time or developing time?
Developing
What is the clearing time?
Time taken for the unsensitised silver bromide crystals to be removed from the film
How long is the fixing time relative to the clearing time?
fixing is twice as long as clearing time
What colour are under fixed films?
Greenish/yellow/milky
How do you get brown films?
overtime any underfixed films begin to turn brown, any films with remaining fixer on
What is the purpose of washing the film?
To remove any residul fixer
What is a photon equivalent to?
A quantum of energy
How much does the step up transformer step to?
From 240kv to 70000kv
How much does the step down transformer step to?
240kv to 810v
