Radiology Flashcards
List three reasons why radiographs are useful…
- Provide the ability to see structures within the body, particularly mineralised tissues - can show both normal anatomy and pathology - aid diagnosis and planning/monitoring of treatment
What are the four properties of electromagnetic radiation?
- no mass - no charge - always travels at the speed of light - can travel in a vacuum
what is the inverse square law?
the intensity of the x-ray beam is inversely proportional to the square of the distance between the x-ray source and the point of measurement. Therefore, doubling the distance will quarter the dose
what range should new equipment operate within?
60 - 70 kV
list the order of target interactions
- incoming electron passes close to nucleus of a target atom - electron rapidly decelerated and deflected (amount proportional to energy loss) - energy loss in form of electromagnetic radiation - incoming electron collides with inner shell of target electron - target electron displaced to an outer shell or completely lost from atom - target atom unstable - orbiting electrons rearranged to fill vacant orbital slots to return atom to neutral state
what is the advantage of rectangular collimation?
it reduces the exposure to the patient by 30% in comparison to circular collimation
what is the ideal focus to skin distance (fsd)?
at least 20cm
what are the four possible outcomes for x-ray photons transversing tissue?
- pass through unaltered - change direction with no energy loss (scatter) - change direction losing energy (scatter and absorption) - be stopped, depositing all energy within tissue (absorption)
What is attenuation?
- attenuation is the gradual decrease in energy as the x-ray passes through absorbing material (eg flesh) -reduction in number of photons (x-rays) within beam -occurs as a result of absorption and scatter -affects the number of photons reaching the image receptor
as per the effect of photon absorption on an image, what do the following colours on an image suggest; black, grey, white
black - all photons reach the film grey - partial attenuation white - complete attenuation
what is the effect of photoelectric absorption?
results in complete absorption of photon, preventing any interaction with the active component of image receptor. Image appears white if all photons involved, grey if some photons are not involved
what are the effects of compton scattered photons?
- scattered photons produced before the image receptor is reached, and scattered backwards, do not reach the image receptor and do not contribute to the image - scattered photons produced beyond the image receptor and scattered back towards it, may reach image receptor producing darkening. As their path is randomly altered they do not contribute useful information to the image Results in fogging of image, reducing contrast and image quality
what are the effects of photoelectric absorption and compton scatter on dose?
photoelectric absorption results in deposition of all photon energy within tissue. Increased patient dose but necessary for image quality Compton scatter results in deposition of some photon energy within tissue. Adds to patient dose but does not give useful information. May also increase dose to operator
Describe ionising radiation
-Atoms have equal numbers of protons and electrons, ions do not. Ionising radiation has enough energy to turn atoms into ions. It does this by knocking away electrons orbiting the nucleus of an atom. -When radiation passes through matter, it will ionise atoms along its path. -Each ionisation process will deposit a certain amount of energy locally. This energy is greater than the energy involved in atomic bonds.
What is the direct effect of DNA damage from radiation?
radiation interacts with the atoms of a DNA molecule or another important part of the cell
What is the indirect effect of DNA damage from radiation?
radiation interacts with water in the cell, producing free radicals which can cause damage. Free radicals are unstable, highly reactive molecules. Double strand breaks are more difficult to repair and usually occur as a result of alpha radiation.
What does the biological effect of DNA damage from radiation depend on?
-type of radiation -amount of radiation (dose) -time over which the dose is received (dose rate) -the tissue or cell being irradiated
Describe tissue radiosensitivity
the radiosensitivity of tissues depends on two factors; the function of the cells that make up the tissue -if the cells are actively dividing the more rapidly a cell is dividing, the greater its sensitivity
In regards to tissue radiosensitivity, what are the possible outcomes after radiation hits a cells nucleus?
In regards to dose quantities, what is the absorbed dose?
measures the energy deposited by radiation and has units of gray
In regards to dose quantity, what is equivalent dose?
absorbed dose multiplied by a weighting factor depending on the type of radiation.
For beta, gamma and xrays the weighting factor is 1. For alpha particals it’s 20
What is a deterministic effect of radiation?
tissue reactions
only occur above a certain (threshold) dose
the severity of the effect is related to the dose received
What is stochastic effects of radiation?
the probability of occurrence is related to the dose received.
No known thershold.
Cannot predict if these effects will occur in an exposed individual or how severe they will be
Effects can develop years after exposure
Can be somatic (results in disease or disorder (cancer))
Can be genetic (abnormalities in descendents
What are the four philosophies of radiation protection?
Justification
Optimisation
Dose limitation
Protection of staff
In relation to radiation protection, what is justification?
practices must have sufficient benefit to individuals or society in order to offset the detriment
In relation to radiation protection, what is optimisation?
Individual doses and the number of people exposed should be as low as reasonably practicable, taking into account economic and social factors
In relation to radiation protection, what is dose limitation?
System of individual dose limits so that the risks to individuals are acceptable
In relation to radiation protection, what is a controlled area?
an area that should extend at least 1.5m from the xray tube and patient.
The xray beam should always be directed away from staff members
In relation to the protection of patients, what is dose optimisation?
it is a legal requirement.
Dose to patient is ALARP while still maintaining adequate image quality.
Rectangular collimators should be used (reduce dose by up to 40%)
Patient dose can be reduced by using e speed films, using a kV range of 60-70kV, FSD should be more than 200mm
What are diagnostic reference levels?
- legislation requires employers to have established dose levels for typical examinations for standard size patients
- they are a comparative standard that is used in optimisation
- they are compared to national reference levels
- individual xray units are compared to DRLs and national reference levels
- enables the identification of units giving higher doses
How are xrays produced and what are their properties?
- X-rays are produced when fast-moving electrons are brought
rapidly to a stop - An electron is a negatively charged particle in an atom which
conceptually sites itself in the orbits around the nucleus as
stated by the Bohr model. - Process:
— Source of the x-ray from the x-ray machine and the
object is the teeth and jaws with the interaction of xrays
with matter
— Image receptor will be digital or film
— Processing is the conversion of latent image to
permanent visible image by computer technology or by
chemical processing means
How is a ghost image produced?
- Ghost images are produced as the x-Ray tube start position
directs the beam posteriorly towards then opposite TMJ region
and then moves round behind the patient’s head, when the
image of the premolar region is being created the beam is
coming from a more posterior point on the opposite side and
the ghost products such as earrings are usually more anterior
due to this. - Ghost images that occur are always higher due to vertical
beam angulation of 8o and be horizontally magnified and
usually further forward due to change in anterior-posterior
position - Ghost images can occur when there is horizontal distortion if
the patient is in the incorrect position relative to the focal
plane - Typical ghost images:
— Earrings
— Metal restoration
— Soft tissue calcification
— Soft palate
— Hyoid bone
— Dentures and fixed appliances
How can radiation dose be reduced?
- Use of rectangular collimating 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 reducing patients dose. - High tube kVp which produces higher energy photons meaning
the photoelectric interactions and the contrast between
different tissues is reduced, meaning the dose absorbed by the
patient also reduces.
What is the coin test?
- For 150,120,90,60,30,0:
— 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 30seconds, leaving
the last coin covered
— Process and observe which coin can be seen first - For 50,40,30,20,10,0:
— In the dark, place the coins at intervals on an Extra-oral
film
— Cover completely with card
— Turn on safe lights
— Uncover each coin at intervals of 10seconds, leaving
the last coin covered
— Process and observe which coin can be seen first
What are the differences between the frankfort plane and the orbitomeatal line?
FP = lower border of orbit-EAM OM = outer canthus of eye - EAM about 10 degrees out
What are the indications for taking a lateral skull?
BoS # AP displacement of facial fracture skull pathology (Pagets)
What view would you take for maxillofacial view - PA or AP? why?
PA - posterioanterior (anterior (face) is closer to film, less magnified, low energy photons attenuated before reaching most radiosensitive tissues)
what are indications for CBCT?
implant planning impacted teeth pathology orthognathic surgery hypodontia CLP dental abnormalities
Midline maxillary radiolucency well defined corticated not associated with apices of 11/21 - PDL space is clear. what is it?
nasopalatine cyst
multiple mandibular radiolucencies in mixed dentition all assocated with crowns of unerupted teeth. some are deeper, some are superficial. what are they?
deeper ones are dentigerous cysts and need excision if they delay eruption superficial ones are eruption cysts and need marsupialisation
why is swelling in the palate concerning?
if there is odontogenic pathology of the max teeth, it causes buccal swelling. palatal can be more sinister and from parotid
Pa radiolucency after tooth has had RCT. well defined radiopaque margin. what is it?
periapical granuloma (healing infection from before RCT)
What are some developmental abnormalities of bone?
- osteogenesis imperfecta - achondroplasia - osteopetrosis - cherubism
if a patient presenst with slow growing, asymtomatic bony swelling and precocious puberty - what would you diagnose?
albrights syndrome
What are some inflammatory bone diseases?
alveolar osteitis osteomyelitis actinomycosis periositis MRONJ ORNJ
In digital radiology, describe the conversion of x-ray shadow into image
- When the x-ray beam passes through an object, some of the x-ray photons are attenuated, creating an x-ray ‘shadow’
- The x-ray shadow is basically the image information held by the x-ray photons after an x-ray beam has passed through an object
- The image receptor detects this x-ray shadow and uses it to create an image
In digital radiology, describe the transition from x-ray shadow to digital image
- The detector measures the x-ray intensity at defined areas (arranged in a grid)
- Each area is given a value relating to the x-ray intensity (typically 0-255)
- Each value corresponds to a different shade of grey; 0 = black -> 255 = white
- More pixels = better detail = higher resolution
In digital radiology, what are phosphor plates?
- Not connected to a computer
- After receptor is exposed to x-rays, it must be put in a scanner and ‘read’ to create the final image
In digital radiology, describe the image creation on a phosphor plate
- Within the patients mouth; 1) receptor exposed to x-ray beam 2) phosphor crystals in receptor excited by the x-ray energy, resulting in the creation of a latent image
- Within the scanner; 3) receptor scanned by laser 4) the laser energy causes the excited phosphor crystals to emit visible light 5) this light is detected and creates the digital image
In digital radiology what is a solid state sensor
- Connected to a computer. Usually wired but can be wireless.
- Latent image created and immediately read within the sensor itself. Final image created virtually instantly
what can be used to control cross infection in digital radiography?
- Intra oral receptors have purpose made covers (single use) to prevent saliva contamination
- Receptor is still disinfected between uses
Describ a radiographic film
- Material in which the actual image is formed
- Sensitive to both x-ray photons and visible light photons
- Photons interact with emulsion on film to produce latent image which only becomes visible after chemical processing
In film radiography, explain how film speed is relevant
- Relates to the amount of x-ray exposure required to produce an adequate image
- Greater speed = less radiation required to achieve an image
- Affected by number and size of the silver halide crystals
- Larger crystals -> faster film but poorer image quality
- If changing to a different film speed, you must install a filter to absorb part of the primary x-ray beam
What is film processing and what are the different methods?
- Sequence of steps which converts the invisible latent image to a visible permanent image
- Must be carried out under controlled, standardised conditions to ensure consistent image quality
- Different methods; manual, automated, self developing
What are the five common steps in film processing?
1) Developing - converts sensitised crystals to black silver particles
2) Washing - removes residule developer solution
3) Fixing - removes non sensitised crystals. Hardens emulsion (which contains the black silver)
4) Washing - removes residule fixer solution
5) Drying - Removes water so that film is ready to be handled/stored
What are some potential causes of a pale image?
- Exposure issue (radiation exposure factors too low)
- Developing issue (film removed from solution too early. Solution too cold. Too old/dilute)
- Opposite will result in a dark image
What can be the result of inadequate fixing?
- Image greenish-yellow or milky
- Image becomes brown over time
Give some advantages of digital radiography
- 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/sharing of images
- Images can be manipulated
Give some disadvantages of digital radiology
- Worse resolution - risk of pixilation
- Reqires diagnostic level computer monitors for optimal viewing
- Risk of data corruption/loss (solved by backing up)
- Hard copy print outs generally have lower image quality
- Image enhancement can create misleading images
How is radiographic image quality rated?
- Excellent. - No errors of patient preparation, exposure, positioning, or film handling
- Diagnostically acceptable. - some errors of above but they do not detract from diagnostic utility of radiograph
- Unacceptable. - errors make film diagnostically unacceptable, needs retaken
What are the requirements of a periapical radiograph?
- Must contain full length of root
- Ideally full crown
- Done around roots
What are the requirements of a bitewing radiograph?
- To show posterior teeth from mesial of first premolar to distal of last tooth
- Upper and lower teeth equally
- Critical to see EDJ
- Desirable - no overlap
What is quality assurance?
The establishment of procedures, at every stage of image formation and utilisation, to ensure optimum image quality and maximum acquisition of information
What are five stages involves in quality assurance?
- Selection criteria
- Production of x-rays
- Image geometry
- Image receptor
- Image processing
- Image viewing
- Reject analysis
- Right view when needed
- Correct kV
- Film holders with beam aiming devices
- Fastest film or digital
- Test tool
- Light box or monitor quality
What are some causes of dentisty variation?
- Exposure factors
- Object factors
- Processing factors
- Viewing facilities
What are the indications for an OPT?
- When you require a full view of the dentition and surrounding
structures including the TMJ and condyles - It will show:
— Fractures and evaluation of trauma
— 3rd molar and relationship to ID canal on lowers
— Bone loss in generalise 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 2 forms of bone loss that can be seen on a radiograph
- Horizontal:
— Most common pattern which occurs when the path of
inflammation is to the alveolar crest which is
perpendicular to the tooth surface - Vertical:
— Less common pattern which occurs when the pathway
of inflammation travels directly into the PDL spaces
and occurs intra-dentally.
Name 3 characteristics of a ghost image
- They will present higher due to vertical beam angulation of 8o
- Be horizontally magnified
- Usually further forward due to change in Antero-posterior
position.
Name positioning faults and what would occur on radiograph
- Speed of beam through the teeth and image receptor through
the beam must be synchronised to produce an accurate image - Patients canine behind the canine guide line which means it is
closer to the x-ray source than the machine expects. This
causes the speed of the beam to be slower through the teeth
as it is closer to the rotation centre. If not compensated, the
image receptor will be too fast and the image will be
magnified horizontally. - Patients canine in front of the canine guide line means it is
further from the x-ray source than the machine expects. This
causes the speed of the beam to be faster through the teeth
as it is further from the rotation centre. If not compensated
the image receptor will be too slow and the image of teeth will
be reduced in width horizontally.
