Radiology Flashcards
What is the focal trough?
Image layer –> the cross section of the tomograph that’s in focus (mandible and maxilla)
Indications for panoramic radiograph
- Evaluation of third molars
- Evaluation of trauma
- Evaluation of large lesions
- Inability to visualize the entire lesion on smaller film
- Generalized disease (diseases affecting jaw bone)
- Intolerance to intraoral films
- Assessment for surgical procedures (implants, TMJ disorders, craniofacial anomalies)
Advantages of panoramic radiographs
- Well tolerated by patients
- Minimal time of exposure when compared to FMS
- Easy technique
- Broad anatomical coverage
- Relatively low patient dose
- Useful for patient education (secondary to diagnostic purpose)
Disadvantages of panoramic radiographs
- Lower resolution than intraoral film (decreased detail)
- Only objects in the focal trough can be clearly seen
- Distortion
a) overlapping teeth
b) magnification and minification (we can’t use it to get accurate measurements of structures)
c) objects outside of the focal trough will appear blurred
How panoramic radiographs work?
Utilizes principles of scanography:
- slit-shaped collimator is used to produce a thin moving beam of x-rays that scan different parts of an object onto a moving film/receptor
Utilizes principles of tomography:
- imaging of a layer or section of the body by intentionally blurring images of structures in other planes
- during exposure, the x-ray source and film move in synchronized movement parallel to each other in opposite directions
Position of panoramic x-ray tubehead
Negative angle (approximately - 10”) to allow beam to pass under the occipital bone
of collimators for panoramic x-ray
2 collimators:
- 1st at the source - 2nd between the image receptor and object
Type of collimators used in intraoral x-ray units
- Round or rectangular x-ray collimator
- Projected beam slightly larger than the receptor
Thickness of focal trough
- Anterior teeth is thin, while posterior is thick.
- Key: thicker focal trough, more tolerant of slight changes in positioning (better for posteriors than anteriors)
Center of rotation principle as used by Panorex machine
COR would create two arcs, halfway through the process the patient would shift over
of COR
Divides the arch into 3 segments:
- Condyle to 1st premolar
- Canine to canine
- Contralateral condyle to 1st premolar
Appearance of structures outside focal trough
Blurred
Appearance of structures within focal trough
Clear
Position of the patient during panoramic radiograph
- Patient needs to be relatively still to minimize distortion
- Bite block is there to position dental arches in correct spot when machine takes radiograph (central incisors bite on this)
- special chin rest for edentulous patient
How will structures appear when placed closer to film during panoramic radiograph?
Smaller and more clear
How structures appear when placed farther from the film during panoramic radiograph?
Projected image gets magnified
Correct way to position the aprons during a panoramic radiograph
High in front, low in back
Position of tongue while panoramic radiograph is being taken
Tongue has to be kept against the hard palate to reduce the glossopharyngeal airspace.
Proper appearance of occlusal plane on a panoramic radiograph.
Should look like a smile line.
What happened during panoramic x-ray: anterior teeth look big and wide?
Patient was positioned too far back.
What happened during panoramic x-ray: anterior teeth look small and narrow?
Patient was positioned too far forward.
Position of anterior midline/midsagital plane in panoramic radiograph…
Centered and perpendicular to the floor
Position of posterior midline in panoramic radiograph…
Combination of the two ends of the radiograph.
What are real/true images?
- Single images
- Double images
Formed when the object is radiographed between the COR and the film.
Common double images
hyoid, hard palate, epiglottis
What is a double image?
- 1 structure scanned twice
- between COR and receptor
- not extremely blurred
What are ghost images?
Reflected images of a structure located between the x-ray source and the COR.
Common ghost images
- L and R markers form machine
- Mandibular rami
- Earrings
- Cervical vertebrae
- Hyoid bone
Characteristics of ghost images
1) Appears on opposite side of real image.
2) Appears superior to or above real image.
3) Appears magnified.
4) Appears fuzzy or distorted.
5) Vertical dimension appears larger/blurred out, horizontal component may or may not be magnified.
Source of horizontal component of panoramic radiograph magnification…
COR
Source of vertical component of magnification for panoramic radiograph…
tubehead –> distance is constant –> less vertical magnification
Position of Frankfort horizontal plane during panoramic radiograph…
Parallel to the floor (auriculo-orbitale)
Position of spinal column during panoramic radiograph…
Straightened, especially cervical portion
Observed when patient is too far forward while taking panoramic radiograph…
- blurred and narrow anterior teeth
- double image of cervical spine, superimposed over rami (different from gazebo effect)
Observed when patient is too far back while taking panoramic radiograph…
- blurring and widening of anterior teeth
- ghosting of rami and spine
Observed when chin is too far down while taking panoramic radiograph…
- accentuated smile line
- “V” mandible
- double image of spine, “gazebo effect”
- blurred mandibular anterior roots
Observed when chin is too far up while taking panoramic radiograph…
- flat/inverted occlusal plane
- blurred maxillary anterior roots
- hard palate superimposed on roots
- broad and flat mandible
Observed when head twisted while taking panoramic radiograph…
Midline asymmetry:
- Uneven width of rami
- Uneven magnification of teeth
- Uneven blurring
(BMW)
Observed when head tipped sideways during panoramic radiograph…
- Unequal condylar height
- Distorted nasal structures
Observed when un-straightened neck while taking panoramic radiograph…
- Accentuated cervical spine ghosting
Observed when tongue not against palate while taking panoramic radiograph…
(palato-glossal or glossopharyngeal airspace)
Airspace shadow over maxillary roots and rami
Observed when patient moved while taking panoramic radiograph…
- Blurred areas
- Large step defects in inferior border of mandible
Suggested order of interpreting panoramic radiographs…
Cortical borders of bone –> medullary bone –> internal structures (foramina and canals) –> airspaces –> shadows –> teeth
Generally speaking: bone –> airspace –> soft tissue –> teeth
Difference between fracture and movement artifacts on a panoramic radiograph…
Radiolucent lines indicate (mandibular) fracture
What is ectodermal dysplasia?
Group of syndromes deriving form abnormalities of the ectodermal structures: hair, nails, skin, sweat glands, etc.
Dental anomalies:
- Peg-shaped or pointed teeth
- Congenitally absent teeth
- Defective enamel
What is cherubism?
- genetic disorder
- prominent inferior 1/3 of face
- loss of mandibular bone replaced by fibrous tissue
- premature loss of primary teeth and uneruption of permanent
- Large radiolucent areas within the ramus, body, angle, coronoid process, and maxilla
What is dentin dysplasia I?
- Genetic disorder
- Enamel is normal, but dentin is atypical
- Abnormal pulpal morphology
- Type 1 (coronal) and type II (radicular)
What is Gardner’s syndrome?
- AKA familial colorectal polyposis
- Oral manifestation is multiple unerupted supernumerary teeth, odontomas, and osteomas.
What is florid cemento-osseous dysplasia?
- Benign condition of the jaw
What is a large ameloblastoma?
- Benign, slow-growing aggressive tumor of the odontogenic epithelium
- More common in mandible
- Rarely malignant or metastatic
- Invades adjacent structures
- May cause severe facial asymmetry
Biological interactions of ionizing radiation:
- Direct
- Indirect
What is direct action of radiation?
- When energy of a photon or secondary electron ionizes biologic macromolecules (radiation affects macromolecule directly) –> produces free radical
- Accounts for 1/3 of the radio-chemical effects
What is indirect action of radiation?
- Radiation (photon) absorbed by water which then causes radiolysis of water (ionizes water) –> produces a free radical
- Free radical can then go on to affect other molecules
- Accounts for 2/3 of the radio-chemical effects
- makes sense since most of the body is comprised of water
What is the principle radiation interaction with the body?
Indirect (about 2/3)
What are free radicals?
- uncharged molecule containing a single unpaired electron in the outer shell
- highly reactive and unstable
- capable of diffusion through the cell and interaction at a distant site
- excess energy can be transferred to other molecules to disrupt bonds and produce point lesions
What can OH radicals form?
Hydrogen peroxide, which is poisonous to the cell and therefore acts as a toxic agent.
What can H free radicals form?
Can react with O2 to form hydroperoxyl.
Principle damaging products following radiolysis of water?
- Hydroperoxyl
- Hydrogen peroxide
What can hydroperoxyl free radicals form?
Hydrogen peroxide
Trickle down effect of radiation injury:
Radiation affects the body on an atomic level –> ionizes atoms into free radicals –> affects the function of molecules –> affects function of cell –> affects function of tissue –> affects organ –> ultimately affects the body as a whole of the individual
Define deterministic effect of radiation
Radiation injury that results in killing of large number of cells.
Define stochastic effect of radiation.
Sublethal damage to individual cells that result in cancer formation or heritable mutations
Characteristics of stochastic effect of radiation injury.
- Risk is proportional to dose
- Implies no threshold
- Severity of the effect is independent of the dose
Characteristics of deterministic effects of radiation injury
- Severity is proportional to the dose
- There is a threshold
- Do not occur as a result of normal dental radiologic examinations
- EX: harmful tissue effects, in-utero birth defects, cataracts, radiation burns on skin
Radiation is especially damaging on what type of cells…
- Rapidly dividing cells
- Irradiation of such cells cause reduction in size of tissue, mitotic delay, reproductive death, or loss of capacity for mitotic division
Effects on cell replication (deterministic effect)
- DNA Damage: chromosome abberations
- Apoptosis: programmed cell death
- By-stander effect: un-radiated cells exhibit irradiated effects as a result of signals received from irradiated cells
Types of DNA damage (deterministic effect)
- Single stranded DNA break: of little consequence, can be repaired using intact strand
- Double stranded DNA break: disrupt H-bonds between strands, cause unwanted cross-linking within helix, and change or loss of base
- cause majority of the damage
Mild mitotic delay induced by….
low dose of radiation
G2 block in cell cycle and some cellular death caused by…
moderate dose of radiation
Effect of radiation on oral mucous membranes
- Mucositis: inflammation of mucous membranes
- Can result in pseudo membrane formation: loosely adherent necrotic epithelium
- Pain and discomfort may be present
- Changes in oral flora –> candida infection
- Fibrotic reparative reaction
Effects of radiation on teeth
- Growth retardation
- Destroys tooth buds if irradiation proceeds calcification
- Agenesis of teeth/retarded root development
- Adults less prone to direct effects
What are radiation caries?
Type 1. widespread and superficial caries
Type 2. caries of the cementum and dentin at cervical region
Type 3. dark pigmentation of entire crown
** may exist in combinations
Effects of radiation on taste buds:
- extensive degeneration of taste acuity, decreases by a factor of 1K - 10K
- higher than normal concentrations needed to elicit taste response after being subjected to three weeks of radiotherapy
Effects of radiation on salivary glands
- Parenchyma becomes more sensitive
- Parotid glands > submandibular and sublingual
- Decreases salivary flow or completely inhibit it due to loss of acini –> increase in strep mutans and lactobacillus –> increase in caries
- Can return to normal in 6-12 months
Indications for hyperbaric oxygen
- Carbon monoxide poisoning
- Decompression sickness (for divers)
- Air or gas embolism (HB Oxygen reduces size of air)
- Adjunctive therapy for radiation tissue damage –> soft tissue osteoradionecrosis
- Clostridial myonecrosis (bacterial infection gas in tissues gangrene or necrosis)
Purpose of hyperbaric oxygen
Helps restore O2
What is osteoradionecrosis?
- Soft tissue and bone necrosis due radiation making the area hypocellular, hypovascular, and hypoxic
- Mandible more susceptible
- Can become infected
- Appears similar to osteomyelitis
Radiation effects on skin…
Redness, dryness, itchy, peeliing, or blistering
What is radiation dermatitis?
- Radiation induced dermatitis
- Generally manifests itself within a few days to weeks after the start of radiotherapy
- Onset depends on radiation dose intensity, sensitivity of individual to radiation
4 modifying factors…
1) dose: damage increases with dose; there is a minimum dosage required to see deterministic effects
2) dose rate: rate of the exposure; high dose rate causes more damage
3) oxygen content: damage goes up with oxygen content because of indirect radiation through free radicals
4) linear energy transfer: how much energy the particle releases per distance
______ linear energy transfer (LET) is bad
high
X-rays are considered _______ linear energy transfer (LET)
Low
Relative biologic effectiveness (RBE)
- quantification of the ability to produce biologic damage
- As LET increases, RBE increases
- Maximum level of RBE can be reached due to overkill
Oxygen enhancement ratio (OER)
- Inverse relationship with LET: OER is high for low LET, decreases as LET increases
- Tissue is more sensitive to radiation the more O2 it has
Sensitivity to radiation vs age
- highest while still developing (most sensitive before birth)
- lowest as adults
- in old age, sensitivity increases again
What is doubling dose?
- A way to measure the risk from genetic mutations from exposures
- the amount of radiation a population requires to produce in the next generation as many additional mutations that may arise spontaneously
Type of radiation matters…
- If applying same dose of alpha and beta particles, alpha particles will do more damage.
- If applying the “dose equivalent” of each, same damage will be done.
Dose equivalent
- standard of comparison based on the amount of damage that type of radiation does
- a scaling unit multiplied by the absorbed dosage to compare the RBE of two different means of radiation
Damage factors
- Part of the body that’s exposed: extremities can handle more radiation
- Age of the individual
- Biological differences: sensitivity of individual to radiation
Types of radiation
- Particulate: alpha and beta particles
- Electromagnetic: combination of electric and magnetic waves, photons, gamma radiation
What are alpha particles?
- Helium nucleu
- High LET
What are beta particles?
- high energy electrons
- Low LET
Penetration abilities of alpha particles
- travel an inch in air
- stopped by a sheet of paper
- not an external hazard, but can cause tissue damage if they get into the body
- more damaging than beta particles
Penetration abilities of beta particles
- travels anywhere from inches to many feet in the air
- stopped by a layer of clothing or less than an inch of a substance
- can cause skin injury, but alpha particles are much more dangerous
Penetration abilities of gamma particles
- Travels many feet in the air, many inches in human tissue
- Stopped by inches to feet of concrete or less than an inch of lead
- Damaging to tissues externally and internally
- Most damaging
- Emitted from nucleus of some unstable radioactive atoms
_________ radiation = high LET
Particulate, high
- direct action
- damages DNA directly by breaking bonds
_________ radiation = low LET
Electromagnetic
- indirect action (2/3 of the time)
- damages DNA indirectly via radicals and reactive molecules
What’s radiosensitivity?
- Relative susceptibility of cells, tissues, organs, organisms, or other substances to injury via radiation.
- Directly proportional to rate of cell division, and inversely proportional to the degree of cell differentiation
- Actively dividing cells, or those not fully mature are most at risk
The following are more radiosensitive…
- high division rate
- high metabolic rate
- non-specialized (undeveloped)
- cells that are well nourished
Effective dose
- allows the risk from exposure from one body region to be compared to risk to another region
- estimates the risk in humans; measures equivalent whole body dose
How to reduce patient exposure…
- use rectangular collimators
- use a 16” position indicating device (PID)
- film selection
- ALARA: as low as reasonably achieved
Radiation projection goals
- Prevent deterministic effects
- Minimize stochastic effects
Caries formation requires…
- bio-film (plaque)
- fermentable carbohydrates
- tooth surface
Bacteria believed to be responsible for the majority of cavities in teeth.
Streptococcus mutans
Stephan Curve
When fermentable carbohydrates are present - lead to the dissolution or demineralization of hard tissues and lactic acid is produced by bacteria and diet. pH is lowered to 5.5
Disease indicators for caries progression
The following lead to low pH -> caries progression:
- white spots
- restorations < 3 years
- enamel lesions
- cavities/dentin
Risk factors for caries
- bad bacteria
- absence of saliva
- dietary habits (poor)
Protective factors against caries
The following contribute to health pH -> no caries:
- saliva & sealants
- antibacterials
- fluoride
- effective diet
Prevalence
the total number of cases at point in time divided by the population at
Incidence
number of new cases of a disease or condition in a specified time period usually a year divided by the persons at risk
Steps to caries progression:
- Precavitated lesion (white spot) - demineralization (may be seen radiographically)
- Cavitation of enamel
- Decay reaches DEJ
- As decay progresses through dentin, we see a “double arrow” radiolucency
- Decay reaches pulp
- Decay progresses apically
Radiology of dental caries
Caries –> demineralization –> less attenuation of x-ray beam –> more photons hit the film –> dark area on film
Frequency of bitewing examination depends on:
- Age
- Medical condition
- Medications
- Diet
- Oral hygiene
- Prior caries history (most common predictor of current caries
Optimal viewing conditions for (bitewing) radiographs:
- Masking borders with a dark mount
- Bright, even illumination
- Dim, indirect room light
- Bitewings should have proper contrast and clear non-overlapped interproximal contacts
Timeline of caries progression
- Microscopic –> no radiographic evidence
18 months (+/-6) - “White spot” –> may be seen radiographically
~ 24 months - Cavitation –> clearly evident
White spot lesions can progress in one of two ways:
1) undergo partial remineralization (will appear less white and smoother)
2) in-tact surface can break and become a cavity
A minimum of __% demineralization must occur before the lesion can be seen on a film-based radiograph. Digital radiographs are in the __-__% range.
60, 50-55
Carious lesions usually form a ______ shape.
Triangular/cone
Note: tip does not show up that well; radiographs underestimate lesions; triangular shape with the broad base at the tooth surface
Technical note: geometry of the lesion changes the signal to noise ratio across the mesio-distal dimention of the lesion
Which radiographs are best for caries detection?
Bitewings = ???
Periapicals = ???
Panoramic = ???
Bitewings –> proximal and occlusal caries in the posterior teeth
Periapicals –> proximal caries of anterior teeth
Panoramics –> occlusal caries
Define:
- True positive
- True negative
- False positive
- False negative
True positive (TP): diagnosed as having disease, and the patient does indeed have the disease True negative (TN): diagnosed as not having disease, and the patient indeed does not have disease False positive (FP): diagnosed as having disease, when patient does not have disease False negative (FN): diagnosed as not having disease, when patient does have disease
Sensitivity
Percentage of people who are correctly diagnosed with the disease with respect to the total number of people who actually have the disease in the population
TP/(TP+FN)
Specificity
Percentage of people who were correctly diagnosed as NOT having the disease with respect to all individuals without disease
TN/(FP+TN)
Purpose of receiver-operating characteristic (ROC) curves
- help decide where to draw the line between “disease” and “no disease”
- Graph:
- overlap indicates where test cannot distinguish normal from disease
- below cutoff we consider test to be normal
- above cutoff we consider test to be abnormal
Film speed is controlled by…
- Size of the silver halide crystals
- bigger crystals = faster speed
Note: F speed film is fastest since larger halide 1/2 exposure needed
Note: PSP or digital intraoral receptors require less radiation than film; current PSP allows for 50% dose reduction in comparison to F speed film
Progression of caries into dentin
- At DEJ, lesion broadens along junction
- Apex points toward the pulp
- Lesion progresses toward the pulp along dentinal tubules
Zone of necrosis decomposed dentin –> zone of bacterial invasion –> zone of dimineralized dentin –> hypermineralized sclerotic dentin –> tertiary dentin inside original pulp space
Occlusal caries
- common in children and adolescents
- starts in pits and fissures
- enamel portion of occlusal lesion may not be seen on a radiograph
- dentinal portion usually below a fissue
- buccal pit or buccal pit caries may be superimposed and be mistaken for occlusal caries <– clinical exam will help to differentiate
Root caries
- Occurs on exposed root surface –> associated with gingival recession
- Can be confused with cervical burnout
- Cervical burnout extends from height of bone to CEJ
- Caries will efface the proximal surface of the root and have more diffuse inner borders - Can be very difficult to treat
Proximal lesions
- located between contact area and gingival margin
- important to distingish between caries and cervical burnout
Cervical burnout & Mach Band effect
- Extends from height of bone to CEJ
- Mach band effect: optical illusion –> area appears more radiolucent because there’s a sharp contrast between enamel and dentin
- Can contribute to a false positive reading and unnecessary restoration of sound tooth structure
Caries detector devices
- Logicon: computer aided radiology
- Transillumination & Kavo Diagnocam: enhanced visual examination
- Diagnodent: Ultrasound surface analysis
- Spectra caries detector
What does the logicon caries detector do?
- Takes a picture –> analyzes contours of the tooth –> extracts density and spatial information to produce a tracing of radiolucent sites
What does the DIAGNOdent laser do?
- laser light excites fluorescence in bacterial pigments such as porphyrins
- specifically designed for occlusal caries
- does not read demineralization itself
What types of caries can be detected clinically?
Buccal, lingual, occlusal
Only __% of lesions actually progress beyond the enamel.
50
What are spectra-air techniques?
- Takes picture of occlusal surface
- Enables precise localization of caries using a numerical and color scale
- Uses PC to display and analyze images
What is KavoCam?
Produces image that is generated without x-ray.
Shows coronal tooth structures above gingiva in detail.
