Radiology Flashcards
1
Q
what is a radiograph?
A
an image produced by radiation, commonly by x-rays
2
Q
what is the difference between radiography and radiology?
A
radiography is the technique of taking radiographs
radiology is the interpretation of radiographs
3
Q
what are the main types of radiograph in dentistry?
A
bitewings
periapicals
OPG
4
Q
wavelength and frequency of x-rays
A
short wave lengths with a high frequency
5
Q
what determines whether x-rays are penetrated or passed through?
A
penetrates liquids, solids and gases. composition of substance determines whether x-rays penetrate or pass through or absorbed.
6
Q
what is ionisation capability?
A
x-rays interact with materials they penetrate and cause ionisations.
7
Q
what is fluorescence capability?
A
x-rays can cause certain substances to fluoresce or emit radiation in longer wavelengths (e.g., visible light and ultraviolet light)
8
Q
how do x-rays travel?
A
in straight lines but can be deflected or scattered
9
Q
are x-rays waves or particles?
A
they are waves and energy. the packets of energy that x-rays travel in are called photons.
10
Q
what are photons?
A
the packets of energy that x-rays travel in
11
Q
what is needed to create an x-ray?
A
a power source, and a circuit
12
Q
which way do electrons flow in the circuit?
A
from negative side of battery around the tube to create x-ray
13
Q
what is needed to create an x-ray?
A
a power source, and a circuit
14
Q
which way are the filament and anode connected?
A
filament is connected to negative side of battery
anode on positive side of battery
15
Q
what is x-ray tube made out of?
A
glass, vacuum inside it
16
Q
what is the filament made of and why?
A
tungsten due to its very high melting point
17
Q
what is the anode made out of and why?
A
tungsten mounted on copper
copper is used as a conduction metal for electricity and heat. allows heat to dissipate so it doesnt get too hot and melt.
18
Q
process? how are electrons converted into x-ray photons?
A
electrons heat up the filament and they build up in vacuum (at negative side). they boil off the filament. anode is positive, so electrons fly across the vacuum and hit it, flying at high speeds. when hitting tungsten on other side they are converted into heat. anodes rotate so electrons don’t constantly hit the same part. all in oil sealed container to aid heat dissipation. produces x-ray photons.
19
Q
what is the anode made out of and why?
A
tungsten mounted on copper
copper is used as a conduction metal for electricity and heat. allows heat to dissipate so it doesnt get too hot and melt.
20
Q
how is the x-ray beam created?
A
whole tube is held in a lead casing with a little window where electrons can flow out and create the x-ray beam.
21
Q
what is the braking effect?
A
electron gets attracted to a nucleus and swings around it, producing a heat causing collision by hitting the outer shell electrons. it swings around and exits the other side. it slows down to the stop because electron has a lot of kinetic energy as it comes around but it is lost as it swings around the nucleus of the atom. kinetic energy is lost and transferred in/and produces an x-ray photon.
22
Q
what happens if the electron does not swing all the way around?
A
it sometimes does not swing all the way around but changes direction slightly. this produces an x-ray photon but with not as much energy.
23
Q
do short or long wavelengths correlate to high energy?
A
long wavelength = low energy
short wavelength = high energy
24
Q
which electrons produce short wavelength photons?
A
electrons that slow down more, lose more energy, so photon released has more energy, producing a shorter wavelength and more of them
25
which electrons produce long wavelength photons?
electrons that are slightly deflected can lose more energy and create more photons by interacting with more nuclei. produces more lower energy long wavelength photons.
26
what is characteristic radiation?
electron smashes into an inner electron. both electrons go off in different electrons, creating a hole in the inner shell. an outer shell electron will drop down into the inner shell etc. this creates a release of energy when it drops down, creating a photon. occurs again when electrons drop down again to another shell, but further out is less so lower energy and photons are not detectable. it is characteristic of specific elements - always same wavelength and energy for that element.
27
which shell electrons have the highest energy?
K shell has the highest energy
28
which shell, when filled, produces the highest energy photons?
K shells
their electrons have the highest energy so when an electron in K shell is filled, they produce higher energy photons
29
what is the combined spectrum?
combining bremsstrahlung and characteristic radiation
30
what are the 4 situations that can occur when photons interact with matter?
- absorbed with total loss of energy
- scattered with some absorption and loss of energy
- scattered but no loss of energy
- pass through unchanged
energy/directional changes
31
what is scattering?
change in direction of a photon with or without a loss of energy
32
what is absorption?
deposition of energy, loss of energy from the photon
33
what is attenuation?
reduction in the intensity of the main x-ray caused by absorption and scattering
34
what is ionisation?
removal of an electron from a neutral atom, producing a positively charged atom
35
how does ionisation occur?
short wavelength, high energy x-rays (anything above it in the EMS, e.g., gamma)
energy deposited into atoms is deposited into electrons in the shells. when there is more energy than the energy holding the negative electron to the positive nucleus, it results in that electron being hoisted out of the cell, resulting in a positively charged ion.
36
what is the photoelectric effect? (summary)
complete absorption - x-ray photon hits the matter and is completely absorbed. mechanism of absorption = photoelectric effect.
37
what is compton scattering? (summary)
absorption and scatter. as the x-ray photon passes out of the material, it has changed in photon energy. travels in with the same energy as photon 1, but interaction that happens in the matter results in a change in direction and a loss of energy of that photon.
38
describe the photoelectric effect
incoming photon collides with an electron in the inner shell, so it is bounced out and displaced. this displaced electron is the photoelectron. it has a high energy and will go on to eject other electrons from other adjacent atoms and cause further ionisation. thus complete absorption results in ionisation.
39
what type of electrons predominate the photoelectric effect?
the photoelectric effect predominates with low energy electrons. x-ray photon energy = binding energy of electron
low energy photons can displace more inner shells.
40
what happens to the photoelectric effect as Z increase?
as atomic number increases, number of inner shell electrons increase, so more photoelectric interactions, meaning more absorption.
41
the probability of photoelectric interactions occurring is proportional to?
atomic number^3
42
the probability of photoelectric interactions occurring is inversely proportional to?
(energy of the x-ray beam)^3
(as energy of x-ray beam increases, photoelectric effect decreases)
43
describe the compton effect
x-ray photon comes in and interacts with an outer shell electron. it collides but the photon still has more energy to impar. the outer shell electrons are less tightly bound so do not need as much energy to be released from their shell. so compton scattered electron is produced as well as a photon scattered in the form of an x-ray.
44
does the compton effect result in ionisation? why?
yes because atom has lost an electron.
45
what happens to the incoming photon from the compton effect?
the incoming photon is attenuated. lower energy photon leaves the matter in an altered direction - it is scattered.
the incoming photon energyv > binding energy of the photon, thus the excess energy is released in the form of another photon
46
where are scattered photons deflected?
any direction
47
what happens if scattered photons are deflected to a different area of the x-ray film?
they cause noise in the final image
48
which photons produce more forward and backward scatter?
high energy photons produce more forward scatter (forward through the matter); low energy photons produce back scatter
49
what is detected in radiography?
transmission
50
which parts are white and black in radiographs?
anything absorbed is white. x-rays pass through the bits through the teeth so show up as black.
51
does the photoelectric effect occur inside teeth?
yes - so teeth absorb x-rays
52
putting a detector (plate) behind the matter, we can detect the x-rays/photons that pass through. we want to detect transmission. what is white and black?
white bit is where transmission is blocked
black is where x-rays transmit through
53
what direct damage occurs to cells?
direct hit on DNA or RNA from a photon radiation disrupts chemical bonds causing molecular changes, e.g., mutations
54
what indirect damage occurs to cells?
formation of free radicals, ions and ejected photoelectrons which bring about molecular changes
55
are direct and indirect damage micro or macroscopic effects?
microscopic effects
56
what are deterministic effectss?
they will definitely happen in the threshold of a high dose of radiation is reached
57
what happens with deterministic effects of radiation?
eg sunburn
skin redness, mucositis, xerostomia, blood and gut changes, cataract formation
58
what is stochastic effect?
no known threshold dose. every time you expose to ionising radiation, you have a chance of causing damage to the tissues.
probability: the lower the dose the lower the probability of causing cell damage. the lower the number of x-rays, the lower the probability of causing cell damage.
59
which effects are dentistry affected by?
stochastic - each time we take a dental radiograph, we have a chance of causing a stochastic change. no deterministic effect since dose of radiation is low.
60
who is most at risk of stochastic effects?
any rapidly dividing cells - due to more mitosis and more chance of developmental problems.
unborn children - concerns pregnancy ladies.
children more at risk than adults since still growing
61
does photoelectric effect or compton scatter cause image contrast?
photoelectric effect helps produce contrast between different tissues of different atomic numbers
62
does compton or photoelectric effect contibute to fogging or noise of image receptor?
compton
63
what increases proportion of compton interactions?
higher kV
64
is there a safe dose?
no
65
why is there no safe dose?
every exposure to ionising radiation has a possibility of causing damage
the dose does not effect severity unless it is above the dose to cause a deterministic effect
an increase in dose does increase the probability of a stochastic effect
66
what legislation protects works and the public from radiation?
ionising radiations regulations 2017 (IRR 17)
67
what legislation protects patients?
ionising radiation (medication exposure) regulations 2017
68
are low doses of radiation linked to increases of cancer?
yes, low doses are associated with increases with cancer
69
why is lead good at absorbing x-ray radiation?
because it has a high atomic number of 82
70
how do we control that we are only dosing patient with only what we need?
filtering/collimating out excess x-rays
controlling distance to the patient
controlling energy (voltage)
controlling tube current (ampage)
controlling exposure time
71
how are x-rays filtered?
aluminium filtration blocks low energy x-rays from coming out of the tube.
1.5mm of aluminium sets upto 70kV
2.5mm of aluminium for x-ray tube voltages of above 70kV
72
what is collimation?
restricts the beam size
73
what should the focal point to skin distance be for equipment operating at 60kV or greater?
20cm
74
what is the inverse square law?
the intensity of the beam is inversely proportional to the distance from the source
(as distance increases, intensity decreases)
75
do we want the tube close or far away from patient and why?
close to patient as possible to prevent unwanted spread of the beam. a small focused beam is ideal so we dont emit x-ray bits we dont need.
76
what is energy measured in?
volts or potential difference
77
what effect does potential difference have on the x-rays?
increasing p.d. will result in greater energy given to the electrons transferred from the cathode to anode, so greater probability it will be converted into x-ray photons.
78
how does electric current (amps) control beam quality?
the higher the amperes, the greater the quantity of x-rays. tungsten filament is supplied with more electrons and so more are liberated and travel across the vacuum to cause x-ray producing collisions.
79
what happens if you increase exposure time?
the longer you expose the patient, the more x-rays they receive.
80
what factors can we control about the x-ray beam?
filration - fixed at 2.5mm for over 70kV sets
collimation -- always use for intraoral radiography
focal spot to skin distance - aim for 20cm
beam energy - machines are set at 70kV sets
tube current - milliamperage can be changed
exposure time - milliseconds how long machine is on
81
what is radiation absorbed dose?
a measure of amount of energy absorbed from radiation beam per mass of tissue (does not account for type of radiation used)
82
what is equivalent dose?
equivalent dose = radiation absorbed dose x radiation weighting factor
numerical weighting factors represent the biological effects of different radiations
83
what is effective dose?
takes into account different body parts and risks associated. gives organs a weighting factor. some parts of body are more sensitive to raidation changes than others.
effective dose = equivalent dose X tissue weighting factor
84
which tissues have high tissue weighting factors?
bone marrow, colon, lung, stomach, breast
85
where does natural background radiation come from?
cosmic radiation from earths atmosphere. gamma radiation emitted from the earth crust. radiation from ingested isotopes eg banana. radon is a natural gaseous decay product of uranium.
86
artificial sources of background radiation
fallout from nuclear explosions
nucleus accidents
radioactive waste from closed power plants
medical sources
87
what is average UK radiation dose?
2.7mSv
88
what is the threshold for deterministic changes?
50mSv
89
what does is given by periapical radiograph and OPG?
0.005mSv (less than day of background radiation)
0.01mSv (1/8th flight to disneyland)
90
do we need to inform patients of the amount of radiation they are being exposed to?
yes
91
are low energy or high energy photons more damaging to biological tissues?
low energy photons
92
what does using constant potential do?
x-ray production per unit time is more efficient
more high-energy diagnostically useful photons are produced per exposure
fewer low energy harmful photons produced
shorter exposure times possible
93
unit of radiation absorbed dose?
Gray (Gy) or joules/kg
94
unit for effective dose
millisieverts (mSv)
95
what is direct radiographic film used for?
intraoral radiography
96
what is indirect radiographic film used for?
extraoral radiography, such as OPTs
97
what digital receptors are there?
phosphor plate scanning system
charge-coupled device system
photostimulable phosphor plate
98
what are films made out of?
an emulsion and a base
99
why is base coated on both sides with emulsion?
to help produce an image with a lower dose
100
what is base made of and what is its purpose?
plastic - provides a medium for emulsion
101
what is emulsion made out of and why?
silver halides (usually AgBr). AgBr is sensitive to light and x-ray photons.
crystals of silver bromide is held in a flat matrix on the base. these crystals are sensitised when hit by photons and perform a latent image.
102
why is the outer transparent sealed plastic wrap needed?
for cross infection control
103
what is the inner white/coloured plastic wrapper for?
sealed to prevent ingress of light. tube side is white and non-tube side is white and purple.
104
what is the black paper sleeve for?
to protect film against light and damage when unwrapping the packet
105
what is sheet of lead foil for?
to absorb residual and scattered radiation
106
where should the raised dot be when taking x-ray?
the side with the raised dot is always placed facing the x-ray tube.
107
where should the raised dot be once processed?
once processed, the films are mounted and the raised dot is always facing towards the operator
108
what might dark films be due to?
overexposure, light fogging, over development: temperature, concentration, time excessive
109
what might pale films be due to?
underexposure, underdevelopment, excessive fixation, processing chemicals depleted or worn out
110
indirect films make images of inferior quality to direct films, so why are they used?
they require fewer x-ray photons, so reduce patient dose
111
is there an embossed dot in indirect films?
no, left and right markers used in or on the cassette
112
how do indirect films work?
sensitive to primarily light photons. silver halide emulsion. used with intensifying screens in a casette - light emanates from these screens when X-ray photons interact with them.
x-ray photons interact with the phosphors by the photoelectric effect and light photons are produced. one x-ray photon will produce many light photons and this will cover a relatively large area of the radiographic emulsion. this reduces x-ray dose but causes a loss of detail (resolution) on resultant image
113
what is limited in digital radiography?
resolution
114
what can sharpening and smoothing effects do?
removes blur or noise
115
what is noise on a radiograph?
high frequency (speckling)
low frequency (intensity changes)
116
what is a photostimulable phosphor plate? PSP
reusable PSP instead of film - plate is scanned by a laser beam and relayed to computer. used at DH
typically consists of layer of barium fluorohalide on a plastic backing support
117
how does a PSP work?
they absorb and store energy (not attenuated by patient) from x-ray photons and release this energy as light when scanned by laser beam. converted into voltage relayed to the computer. image is wiped and plate reused.
118
why should PSP plates be processed away from strong light and what else might happen which is why they must be handled with care?
light photons will remove the image
scratching the surface is easy
119
advantages to PSP
lower radiation dose to patient
easy storage of images
can transfer electronically
image enhancement with software
120
disadvantages of PSP
expensive
need good backup and security in computer software
memory needed
loss of image quality once printed
monitor with good luminance is required
121
what is the ICRP?
international commission on radiological protection ICRP
122
ICRP general principles
justification - practice only if benefits patient
optimisation - ALARP
limitation - dose equivalent should not exceed limits recommended
123
what is ALARP?
keep exposure As Low As Reasonable Practicable
124
when no radiation shield is available, how far should the operator stand out of the primary x-ray beam and a distance from patient head?
at least 1.5m
125
what is the ionising radiations regulations concerned with?
safety of works and general public
safety checks for x-ray equipment
radiation protection advisor and supervisor for every practice
126
which photons are more likely to cause backscatter?
low energy photons
127
what is the 'controlled area'
area that should be clear when taking the x-ray
always stand at least 2 metres away from patient and x-ray beam, or behind protective lead screen - never in line of main beam
stand outside of area but where you can see your patient
only patient should be in it
128
when does the controlled area exist?
when the x-ray machine is on
129
what happens when the x-ray tube is turned on?
warning signs and light present when power is on
audible noise/beep is made when the tube is on
130
what is RPA?
radiation protection adviser
trained in radiation, competent
131
what does RPA advise on?
advises on identification and designation of controlled areas
calibration of monitoring equipment
risk assessments
drawing up of local rules and contingency plans
quality assurance programmes
132
what is RPS?
radiation protection supervisor
appointed by employer
ensures local rules are complied with
need to know what to do in emergency
can be more than one
133
where do you wear radiation monitoring badge?
on chest at front
134
dose limitations?
20 mSv trainees and employees >18
6mSv trainees <18
1 mSv public
13mSv in any 3 consecutive months for abdomens of reproductive capacity
1mSv foetus of pregnant employees
135
what is a classified worker?
anyone likely to receive:
effective dose of >6mSv (3/10 dose limit)
dose of greater than 3/10 of any dose limit (15mSv/year to lens, >150mSv/year to skin or extremities)
136
IR(ME)R 17 is concerned with?
protecting patients
137
what are the 4 positions of legal responsibility in the IR(ME)R 17?
employer, referrer, practitioner, operator
138
what is justification?
net benefit outweighing risk
exposure must be assessed to ensure it will lead to a change in patient's diagnosis, treatment or prognosis
139
how to justify radiographs for patient?
availability and findings of previous radiographs
total potential diagnostic benefit to patient
relate need for radiographs to history and examination you have performed on patient
radiation risk of radiographic examination
any alternative techniques available?
140
considerations for pregnant patients
can you defer radiograph until next visit
is it urgent
is patient in pain, able to eat?
can you make temporary judgement without?
141
what is optimisation?
how we reduce risk of radiation or lower the dose
exposures kept ALARP
142
how do we optimise dose through radiographic equipment?
high kV (70kV)
constant potential (DC current)
rectangular collimation
adequate aluminium filtration
long focus to skin distance
digital receptor
intensifying screens
143
when are thyroid collars used and why?
thyroid gland is very radiosensitive, used for certain types of intra-oral radiography
144
which form is for you or downstairs at BDH?
white form for x-rays downstairs
green form for yourself on clinic
145
who is the employer, referrer, practitioner, operator?
employer - responsible for installation, conformation of regulations and framework of procedures
referrers - registered practitioner referring individuals for medical exposure. provides justification
practitioner - ensures justification to proceed
operator - carry out the x-ray
146
what does the operator do?
patient identification
position film, patient, x-ray tubehead
setting exposure parameters
pressing exposure switch
processing films
clinical evaluation of radiographs
147
what is radiographic report?
written report of findings must be recorded in patients notes
legal requirement
spotting pathology etc
148
what do you need to record for radiographs?
type of image taken and how many, patient name, patient registration number; date; clinician name and GDC number; record of dose received in seconds
