radiology need to know Flashcards
what radiographs should be used to view retained roots?
periapical
OPT if poor pt cooperation
what is the bisecting angle technique?
- x-ray beam at 90 degrees to line bisecting angle formed by the long axis of the tooth and the plane of film packet
- image receptor and object partly in contact but not parallel
- receptor and object close together except at paices
- can be done without film holders
what is the parallel technique?
- image receptor and object parallel but not in contact
- divergent x-ray beam
- image receptor and object some distance apart-potential for undesirable magnification
- use long spacer cone to reduce magnification- 30cm
what is the purpose of the coin test?
to determine how long films can be exposed to safelight
what is the ideal projection geometry?
- image receptor and object in contact and parallel
- parallel beam of x-ray beam perpendicular to object plane and image receptor
- image size identical to oject size
in an oblique radiograph, what lines are used for references and what are their positions?
maxilla- 1cm above ala-traguc line
mandible- through lower border of mandible
what are the oblique occlusal guideline vertical angles?
- upper anterior- 60 degrees
- upper occlusal centred on canine- 55 degrees
- upper occlusal centred on premolar- 50 degrees
- upper occlusal centred on molar- 45 degrees
- lower occlusal- 40 degrees to occlusal plane
- lower occlusal centred laterally- 35 degrees to occlusal plane
when would you use a mandibular true occlusal?
- detection of submandibular duct calculi
- assessment of bucco-lingual position of unerupted teeth- unless advanced imaging indicated
- evaluation of pathological bucco-lingual expansion
- horizontal displacement of fractures
why is rectangular collimation preferred?
has a greater dose reduction than circular
what are the 2 curves in bitewing radiographs?
- curve of spee
- curve of monson
describe the curve of spee
- has antero-posterior direction
- curves up posteriorly
- produces a happy smile
describe the curve of monson
- has a bucco-lingual direction
- influences x-ray technique e.g. bitewings and panoramic radiography
what is cervical burnout?
- relative lower x-ray absorption on mesial/distal aspect of teeth, between edge of enamel and adjacent to crest of alveolar ridge
- these areas appear relatively radiolucent with ill-defined margins
- may mimic root surface caries
what do panoramic radiographs show?
- all teeth
- structures above and below the teeth
- structures superficial and deep to the teeth (provided they are close)
What is another term for the coin test?
Safelight testing
Explain the coin test
In the dark, place coins at intervals on an extra-oral film
Cover completely with card
Turn on safelights
Uncover each coin at intervals of 30 seconds, leaving the last coin covered
Process and observe which coin can be seen first
What causes ghost images?
When there is horizontal distortion if the patient is in the incorrect position to the focal plane
Name typical ghost images
Earrings
Metal restoration
Sodt tissue calcification
Soft palate
Hyoid bone
Dentures and fixed appliances
What are indications for an OPT?
When you require a full view of the dentition and surrounding structures including the TMJ and condyles
Fractures and evaluation of trauma
3rd molar relationship to ID canal on lowers
Bone loss in generalised periodontal disease
Large lesions that wouldn’t be seen on occlusal, bitewings or periapical
Retained/unerupted teeth and development of dentition
Developmental and acquired anomalies
TMJ evaluation
Inability to tolerate intra-oral radiographs
Name 3 positioning faults that can occur on a radiograph
- Speed of beam through the teeth and image receptor through the beam must be synchronised to produce an accurate image
- Patients canine must be synchronised behind the canine guide line which means it is closer to the x-ray source than the machine expects- cases speed of beam to be slower through the teeth as it is closer to the rotation centre- causes horizontal magnification
- Patients canine in front of the canine guide line means it is further from the x-ray source than the machine expects- causes speed of beam to be faster through teeth as it is further from the rotation centre- image reduced horizontally
Name 2 forms of bone loss that can be seen on a radiograph
Horizontal
Vertical
Describe horizontal bone loss
Most common pattern of bone loss
Occurs when the path of inflammation is to the alveolar bone crest
Perpendicular to the tooth surface
Describe vertical bone loss
Less common pattern of bone loss
Occurs when the pathway of inflammation travels directly into the PDL spaces and occurs intra-orally
Name 3 characteristics of a ghost image
- Will be present higher due to vertical beam angulation of bra
- Horizontally magnified
- Usually further forward due to change in antero-posterior position
Give 3 ways you can reduce the radiographic dose to the patient
- Use of rectangular collimator combined with a beam-aiming device and film holder which reduces x-ray dose by 30%
- Reducing the area irradiated and therefore volume irradiated will also reduce the number of scattered photons produced as well as patients dose
- High tube kVp which produces higher energy photons meaning the photoelectric interactions and the contract between different tissues is reduced, meaning the dose absorbed by the patient also reduces
Describe the Compton effect
- X-ray photon interacts with loosely bound over shell electrons
- The photon energy is much greater than the electron binding energy
- The electron is ejected, taking some of the photon energy as kinetic energy causing a recoil electron- this gives off an atom that is positively charged
- Photon has lower energy after collision- now a scatter photon
What factors affect the probability of Compton scatter occurring
- Proportional to density of material
- Independent of atomic number
- Not related to photon energy
Describe the photoelectric effect
- X-ray photon interacts with inner shell electron- generally the k shell which has the highest energy
- This photon has energy higher than the binding energy of the electron which makes the x-ray photon disappear
- The difference in energy between the 2 levels is emitted as light and heat
- Most of the energy used to overcome binding energy of the electron remainder gives electron kinetic energy meaning the electron is ejected as a photon -results in complete absorption of photon energy meaning the photon does not reach the film and preventing any interaction with component of the image receptor
- Images appear white if all photos are involved
- Images appear grey if some photons are involved
What factors affect the occurrence of the photoelectric effect
- Atomic number
- Photon energy
- Density of material
What metal is used to absorb the jets generated during x-ray production?
- Lead is used to prevent leakage
- Lead film is for photoelectric absorption which absorbs scatter x-rays to prevent image degradation and its 2nd function is to absorb some of the primary beam
Name other metals used in x-ray production, other than lead
- Zinc- prevents leakage in shielding
- Aluminium and zinc- used for final spectrum of x-ray energy filtration
How are x-rays produced?
Produced when fast-moving electrons are brought rapidly to a stop
What are the 2 types of collimator used?
Rectangular
Circular
What is the maximum beam diameter of collimators?
60mm at the patient end with spacer cone
what plane should be horizontal to the floor whilst taking an OPT?
frankfort plane
what x-ray would you take for a patient who cannot tolerate bitewings?
OPT on setting 4
where is the Frankfort plane located?
lower border of orbit to the upper border of external auditory meatus
what are the limitations of a panoramic radiograph?
- horizontal distortion
- long exposure time not suitable for nervous pts or pts with additional needs
- big shoulders
- positioning difficulties
what is image processing?
the series of actions by which the invisible latent image is converted into a visible permanent image
why are films processed in a dark room?
to prevent light from affecting the films
what are the chemical processing steps when developing films?
- development
- rinse
- fixation
- washing
- drying
what is attenuation?
- reduction in the number of photons within th ebeam
- occurs as a result of absorption and scatter
- affects number of photons reaching film
how can you reduce the effects of scatter on the image?
- increase the pt-film distance- obliquely travelling scattered photons miss the film
- lead foil within the film packet prevents back scattered photons from oral tissues reaching film
- collimation
what is the radiographic baseline?
outer canthus of the eye to centre of external auditory meatus
what is the difference between true and oblique lateral radiography?
oblique occlusal comes at an angle
what is IRMER?
ionising radiation medical exposure regulations
when would you use setting 4 on an OPT?
- if focussing intraorally
- this programme reduces overlap between teeth allowing easier interprox caries detection
when would you use setting 1 on an OPT?
- if you want to see extra and intra oral
- allows vision of eaxtra oral features such as TMJ and body of mandible
list oral implications of radiotherapy
xerostomia due to damage of salivary glands
increase risk of osteoradionecrosis
mucositis
radiation caries affecting incisal edges and cervical margins
limited opening due to trismus
hypogeusia
what position fault causes anterior teeth to appear magnified on a radiograph?
canine is positioned behind the canine guidance line
what position fault causes one side of the posterior region to appear wider than the other on a radiograph?
patient’s head rotated slightly in the OPT machine
in an OPT, what part of the maxillary sinus is immediately above premolars?
inferior border
in an OPT, what part of the maxillary sinus is immediately above the third molar?
posterior border
what x-ray would you use to determine working length?
periapical
what x-ray would you take for extraction of 48, with no sign of 38?
- OPT of right side only, on setting 4
give features of a ghost image
image is always higher
the image is horizontally magnified
on theopposite side
can interfere with diagnosis
what are radiographic signs that a tooth is non-vital?
internal inflammatory resorption
external inflammatory resorption
periapical abscess
widened pdl
loss of lamina dura
what position fault causes one side of the posterior region to appear wider than the other on a radiograph?
patient’s head rotated slightly in the OPT machine
what are radiographic signs that a tooth is non-vital?
internal inflammatory resorption
external inflammatory resorption
periapical abscess
widened pdl
loss of lamina dura
name complications of radiotherapy to the head and neck
mucositis
xerostomia
osteoradionecrosis
radiation induced caries
What radiation dose increases the risk of osteoradionecrosis?
doses over 60 Gy
What are oral complications of radiotherapy?
osteoradionecrosis
radiation caries
hypogeusia - loss of taste due to radiation affecting taste buds
xerostomia - may be due to damage of salivary glands
difficulty wearing dentures
more prone to fungal infections
trismus may occur due to replacement fibrosis of muscles of mastication
what sites of the teeth are affected by radiation caries?
gingival margins and incisor edges
what are causes of radiation caries?
dry mouth
loss of taste
change in diet
hypersensitivity of teeth makes OH difficult
What do you need to know about patients who have had radiotherapy?
what dose of radiation was given
what area of the body was exposed to the radiation
duration of treatment
What are preventative measures used for patients who have had radiotherapy?
OHI
higher concentration of fluoride toothpaste
fluoride varnish
how do you treat osteoradionecrosis?
irrigation of necrotic debris
remove loose sequestra
What methods help prevent risk of osteoradionecrosis?
scale teeth near extraction site and use chlorohexidine mouthwash
careful extraction technique
antibiotics, chlorhexidine mouthwash and review
hyperbaric oxygen before and after extraction to increase local tissue oxygenation
close soft tissues
What is a wavelength
The distance over which the waves shape repeats
what is frequency
how many times the waves shape repeats per unit time
how do you calculate speed
frequency x wavelength
what unit is energy measured in
electron volts eV
how do you calculate intensity of the xray beam
1 / distance ^2
Double the distance you quarter the dose
what metal is the focusing cup made of
molybdenum
what is the charge of the cathode
negative
What is the cathode composed of
filament and focusing cup
what is the charge of the anode
positive
what is the anode composed of
target and heat dissipating block
what is the filament
a component of the cathode
a coiled metal wire that high current electricity is passed through
what metal is the cathode filament made of
tungsten
explain how the cathode works
increased current in the filament causes an increase in heat and increase in electrons
explain the anode and cathode relationship
high potential difference between negative cathod and positive anode
high voltage electricity passed through the xray
electrons released by the filament are repelled by the cathode towards the target in the anode
electrons have a high kinetic energy when colliding with the anode target
explain the kinetic energy of electrons between the anode and cathode
kinetic energy is gained as the electrons move from the cathode to the anode
if potential difference across xray tube is 70kV then each electron gains 70kV of kinetic energy when reaching the anode
what is the target in the anode
the metal block bombarded by electrons producing photons and lots of heat
what is the focal spot
precise area on target (anode) where electrons collide and xrays are produced
wht metal is the target made of
tungsten
what metal is the heat dissipating block made of and why
copper
it is a high thermal conductor - heat produced in the target dissipates into the block by thermal conduction which prevents target overheating
what is the penumbra effect
blurring of radiographic image due to focal spot not being a single point
minimised by shrinking focal spot
what happens if you decrease the focal spot size
increase image quality BUT increase heat concentration
how do you solve the penumbra effect
angle target - reduces surface area where xray is emmitted
increases heat tolerance - increases surface where electrons impact
what is the glass envelope and what is its function
leaded glass that produces an air tight enclosure
- absorbs xray photons ensuring photons travelling in desired direction escape the xray tube
- supports cathode and anode
- maintains a vaccum
why is aluminium in the tubehead important
it removes low energy photos from xray beam as the patients tissues would absorbing these and they don’t contribute to the image
this ensures xray beam contains of mainly diagnostic xray photons
what is the function of the spacer cone
Dictates the distance between the focal spot (on target) and the patient
what is the function of the lead collimator
reduces the patient dose
what are the types of collimator and what is recommended to use/why?
circular
rectangular
rectangular can reduce the surface area and dose of radiation the patient receives
what is continuous radiation
bombarding electron passes close to target nucleus causing it to be rapidly decelerated and deflected
lost kinetic energy release as xray photons - continuous range of energy
what is characteristic radiation
bombarding electron collides with inner shell electron and either displaces is to a more peripheral shell or removes it completely
creates energy specific to the element used for target
what is the k shell binding energy of tungsten
69.5 keV
remember dental xrays use 70kV to displace k shell electrons
what is transmittion
photon passes through the matter unaltered
What is absorption
photon is stopped by the matter
what is scatter
the matter causes the photon to change direction
what are the fates of photons in xrya beams
transmitted
absorbed
scattered and absorbed
this results in attenuation of the beam - reduced intensity
explain attenuation in terms of colour of xrays
minimal attenuation - black
partial attenuation - grey
complete attenuation - white
what is the photoelectric effect
photon interacts with inner electron shell - absorption of photon creating photoelectron
occurs when energy of photon is =/> binding energy of electron
inner shell electron is ejected (photoelectron) - this can ionise and damage adjacent tissues
vacancy in inner electron shell filled by outer shell electron producing light photons and/or heat
NECESSARY FOR IMAGE FORMATION
what is the compton effect
photon interacts with outer shell - partial absorption and scattering of photon
occurs when energy of photon is > binding energy of electron
electron in outer shell removed (compton recoil electron) - this can ionise and damage adjacent tissues
remaining photon is scattered
DOESNT CONTRIBUTE TO IMAGE
explain scatter for high energy photons
forward scatter
explain scatter for low energy photons
back scatter
what is implemented to account for radiation scatter
controlled area - 1.5m from patient
how does scatter affect radiographic image
backwards and sideways - DO NOT affect the image
forward scatter - may reach receptor and interact with wrong area
causes darkening/fogging of image in the wrong place
reduces image quality/contrast
what is the probability of photo electric absorption effects occuring in radiography is proportional to
- atomic number cubed (Z3)!!
- physical density of the material
- inversely to photon energy cubed (1/E^3)
give examples of how to reduce scatter
decrease surface area radiated
decrease volume of irradiated tissue
decrease number of scattered photons produced in the tissue
decrease the scattered photons interacting with the receptor
what effect does lowering kV have on xray unit
increases contrast between tissues with different Z - GOOD
increases dose absorbed by patient - BAD
what effect does raising kV have on the xray unit
decreases dose absorbed by patient - GOOD
decreases contrast between tissues with different Z - BAD
what is the UK guidance range for kV
60-70kV
what types of DNA damage can occur from radiation and explain them
direct - radiation interacts with the DNA molecule
indirect - radiation interacts with water in the cell producing free radical that causes damage
explain how dose rate affects celss
higher dose - Cell cannot repair DNA damage
lower dose - cells can repair damage before further damage occurs
what tissues are most radiosensitive
tissues with rapidly dividing cells
what is the unit of measurement for equivalent dose
sieverts (Sv)
what is the unit of measurement for absorbed dose
Gray (Gy)
what are the two types of radiation biological effects and explain
deterministic - tissue reaction occurs above a certain threshold, severity related to the dose received
stochastic - the probability of occurence is related to dose received
define justification in terms of radiology
practise must have sufficient benefit to the individual or society in order to offset the deteriment
what are ways to reduce patient doses of radiation
use E speed film or faster
Use kV range of 60-70
focus skin distance should be >200mm
use rectangular collimation
What does ALARP mean
as low as reasonably practicable
what effects does radiation have on pregnancy
- increased risk of childhood cancer
- can retard growth
what are DRLs
Diagnostic reference Levels - establish dose level for standard sized patients
when is radiographic localisation used
- locate position of unerupted teeth
- location of roots
- relationship of pathological lesions
- trauma - bone or dental fracture
what is the rule for parallax
same lingual opposite buccal
what is a cephlostat and why is it important
standardised positioning of equipment and the patients head (ear rods and forehead support)
produces standardises and reproducible radiographs
reduce magnification/ distortion of image
what is the collimation rule for all radiographs
field of view should be no bigger than what is clinically required
how do pixels affect the xray image
more pixels = better detailed image
overall higher resolution
what are the types of receptors used in digital intra oral radiographs
solid state sensors - connected to the computer/instant image
phosphor plates - put through a scanner
why must you use adhesive plastic covers in radiology
to prevent saliva contamination
cross infection control
what are advantages of digital radiology
no need for chemical processing
easy storage and archiving of images
easy back up of images
images can be integrated into patient records
easy transfer and sharing of images
images can be manipulated
What are disadvantages of digital radiology
worse resolution
requires diagnostic level computer monitors for optimal viewing
risk of data corruption/loss
hard copy print outs have decreased image quality
image enhancement can create misleading images
what is radiographic emulsion
silver halide crystals (silverbromide) in a gelatin binder - becomes pixels in the final image
sensitised crystals - dark parts of image.
non sensitised - light parts of image
what affects film speed
number and size of silver halide crystals
what are factors that cause issues in film radiology
developing - involves chemicals which are affected by time, temp and solution concentration
fixing - chemical reaction that remobes non-sensitised crystals
washing - developer continues to act if not washed off
what are disadvantages of solid state sensors
bulkier
usually wired
expensive
What causes the incisor teeth to be horizontally magnified in a panoramic
the patient is too far back in the machine
vertical guide line in front of canine
canine behind guide line
what are radiographic signs a tooth is non vital
internal inflammatory resorption
external inflammatory resorption
periapical abscess
widened lamina dura
loss of lamina dura
what are planes and reference lines used in radiology
mid saggital plane - line down the middle of face
interpupillary line - horizontal across pupils
Frankfort plane - inferior infraorbital margin to superior border eof external acoustic meatus
Orbitomeatal line - through middle of orbit
