Stochastic effects
Cell DNA injury
No threshold
-All or non response
In stochastic effects the greater the does
Increases the probability of occurrence
Any amount of radiation
Deterministic effect
High amount of radiation
- Increased cell death
- Threshold does
Threshold dose
(Deterministic effect)
Clinical symptoms apparent at any dose above threshold
Severity is PROPORTIONAL to dose
2 types of effects from formation of free radicals
Direct effects
Indirect Effects
Law of Bergonie and Tribondeau
Radiosensitivity of different tissues
- Amount of undifferentiated cells
- Mitosis activity
- Length of active proliferation
Oocytes and lymphocytes
What cells have the highest radiosensitivity
Lymphoid tissues Bone marrow Testes Ovaries Small intestines
The more undifferentiated the more
Mitosis and more radiosensitive tissue that is
Oocytes and lymphocytes are highly _______ but very _____
Differentiated
Sensitive
Linear Energy Transfer
The rate at which energy from photons is imparted as they travel through matter
High LET
Densely ionizing
Low LET
Sparsely ionizing
As energy is given off
Different damage is done
Absorbed Dose
Measure of the total energy transferred from any type of radiation to matter
rad or Gy
100 rads =
1 Gy
Equivalent Dose
Measure of how different types of radiation affect various tissues
-Sv
Radiation sighting factor (Wr)
1 Sv=
1 Gy
Effective Dose
Measure of estimated risk in humans
-Sv
Tissue weighting factor (Wt)
Acute Radiation Syndrome
Whole Body irradiation
Onset is ore rapid and severity increases with greater dose
Management depends on stage
Mucositis
Second week of therapy
Erythematous mucosa Sloughing of the irradiated tissue Painful Secondary infection Difficulty consuming food Heals within 2 months after completion of radiotherapy
Xerostomia
Parenchuymal cells of salivary glands are radiosensitive
Reduced salivary flow
Pain/tenderness
Difficulty chewing and swallowing
May resolve in 6-12 months
Taste Loss
Second/third week of therapy
Reduced salivary flow my a contributing factor
Reversible
Trips us
Inflammation and fibrosis of musculature
Limited opening 2 months after completion of radiation therapy
PT
MOM affected
Radiation Caries
Rampant tooth decay
-mostly due to salivary gland changes
Maintenance and compliance
-daily fluoride varnish
Impeded Tooth Development
Children receiving radiotherapy -Incompletely formed teeth —root development -Malformed teeth -Tooth bud destruction -Microdontia
Restorative procedures
Osteoradionecrosis
50-60 Gy
Reduction of blood supply bone remolding capacity and mineralization
breakdown of oral mucosa
Mandible>maxilla
Debridemtn
Resection
Restorative procedures
Pre-Radiotherapy clearance when possible
Is radiation induced cancer a stochastic effect of radiation?
True; even one does of radiation can cause cancer. More doses increase risk but the end result does not change
All electromagnetic radiation can cause carcinogneis
False
The closer to the nucleus the higher the
Bonding energy
Highest bonding energy shell
K
Lowest bonding energy shell layer
P
Z number
(Atomic number)
of protons
Same number of electrons in a neutral atom
A number (Atomic mass #)
of P+N
The binding energy of electrons in a specific end shell is higher in an element with
A high Z number
T/F Radaiton induced cancer is a stochastic effect of radiation
True
No threshold increase amount increases risk
T/F All electromagnetic radiation can cause carcinogenesis
False
Not all is the same
Which electrons have highest bonding energy
Closer to nucleus
Which shell is closet to nucleus
K shell
Klmnopq
Z number
The number of neutrons protons in a neutral atom
Higher atomic number (z number)
Higher the bonding energy
Z number is the same as # of
Electrons in a neutral atom
A number:
of Protons + neutrons
Radiation is energy in
Motion
Radiation moves
In a straight line from a central point
It diverges
If the radiation beam is further away
More face face would be exposed because it is divergent
Radiation can be ___ or ___
Electromagnetic (waves) or particulate (particles )
Radiation can be _____ or ____ radiation
Ionizing
Nonionizing
Ionization
Reaction that has sufficient energy to remove electrons from atoms it encounters in its path
Wave theory
Radiation is propagated as waves
Electric and magnetic fields are in planes at right angles
Travel at speed low light
How far from source do you have to be away
6 feet
_____ wavelength has higher energy
Shorter
Frequency and wavelength are _____related
Inversely
Wavelengths
Distance between 2 succcesive crests or troughs
Measured in meters or angstroms (X-rays)
Frequency
of oscillations vibrations or cycles per second
Electromagnetic radiation
Transfers of energy through space as a combination of electrical and magnetic fields
Quantum theory
Electromagnetic radiation is considered as bundles of energy called photons
Higher frequency _______ energy
Higher
Longer wavelength
Lower energy
Lower frequency
Ionization
Gaining or losing an electron
y
Ionization occurs when
Occurs when particulate or electromagnetic radiation energy is greater than binding energ
Threshold for ionization
10e
Types of ionizing good radiation
Gamma rays x rays and some UV rays
In ionization the ejected particle
Is a negative ion
The remainder of atom is positive
X rays are produced when
velocity electrons are suddenly declarations when they pass close to the nuclei of high Z# absorbing material
3 requirements for X-ray production
Electrons
High velocity of electrons
High Z number absorbing material (tungsten )
2 mechanism of X ray production
Electron to nucleus
Electron to electron interaction
Electron to nucleus interaction
Bermesstrahlung radiation
-the fast voting electrons either slow down or stop when they come close to the nucleus of the atoms and part of their energy is transferred as X rays
Electron to Electron interaction
Characteristic radiation
Few electrons interact with tungsten target originated electrons imparting enough energy to ionize the tungsten target
When electrons displace inner shell electrons, characteristic radiation is produced
Electrons have different kinetic energies
True
Homogenous radiation
AC converted to DC
All cathode electrons will have similar KE and the resulting radiation is more homogenous
Which is less radiation to patient homogenous or heterogenous radiation
Homogenous
Long wavelength radiation have more energy compared to short wavelength T/F
False
Which shell of an atom has the greatest binding energy
K shell
X rays are produced when high velocity atoms are suddenly decelerated when they pass close to the nuclei of high Z # absorbing material
False
ELECTRONS not atoms
PID
Position indicating device
In the tube head
4 conditions to produce X-rays
1) Production of high speed electrons
2) Separation of electrons from tungsten filament at cathode
3) concentration of electrons: electrons are negatively charged and repel each other. We need to focus them on a small region on the anode known as the target
4) Sudden stoppage of electron stream
How to form electron cloud
The cathode is the source for electrons made of tungsten filament. The filament is heated at low volatile and electrons are separated from the filament
-thermionic emission
Focusing cap
Focuses the negative electrons to the positive anode which then results in characteristic bremstahlngasads radiation
Anode
Tungsten target covered in copper
Tungsten target
High atomic number
High melting point
Low vapor pressure
Good thermal conductivity
X ray tube
A glass bulb with vacuum inside it. A metal housing surrounds the tube and protects the tube from accidental damage and prevents overheating of the tube by providing a space filled with oil
Filtering the beam
Beam exiting the tube has different wavelengths
Removes lower energy X ray photons
Inherent filtration
The glass covering and oil in the tube contribute to stopping low energy
Total filtration
Aluminum + inherent filtration
At 50-70 kVP
At least 1.5 mm total filtration must be used
Above 70 kVP
At least 2.5 mm total filtration is required
X ray machines rated below 60kVp should not be used
Filtration reduces patient skin exposure
TRUE
Factors controlling X-ray beam
Tube voltage Exposure time Tube current Filtration Collimating Distance
KVP affects
Both quality and quantity of radiation
Higher kVP
1) Increase amount of radiation
2) determine the maximum energy of x rays produced
An increase of 15% kVP should be accompanied by
A reduction of on half in mAs
An increase of 15 kVP
Would require having the exposure time
Decrease of 15kVp doubling the exposure time
Low kVp leas to X-rays with
Longer wavelength and lower energy and so they do not penetrate much in matter
Higher kVp
Increases the energy of the X-ray photons which can now travel deep in tissues/matter
The mA or tube current of an X-ray tube affects
Quantity of the X-rays produced
Exposure time of an X-ray tube affects the
Quantity of X-rays produced
____ and ____ both control the quantity of X-rays produced
Exposure time, mA
MAs determine
The total number of X-ray photons produced in the beam
Most effective beam limiting devices
Collimating
Lead
Collimating
To minimize the amount of radiation to patients and reduce scatter radiation
Collimating should restrict the beam diameter to no more than
7 cm (2.75 in)
The intensity of radiation varies
Inversely as the square of the source film distance
X-rays that pass all the way through
Dark or radioluscent
X rays that are absorbed completely
Radiopaque or white
Three means of beam attentuation
Coherent scattering
Photoelectric absorption
Comptons scattering
Scattering interaction
Photons interact with absorber atoms but then are scattered in another direction
This allows us to see the different between enamel dentin bone and soft tissues
Coherent scattering
Low energy photons interact with outer electrons
The incident photons interacts with he electron in the outer shell causing it to vibrate momentarily at the same frequency as the incoming photon
Photoelectric absorption
Incident photon interacts with inner e usually k
Overcomes binding energy and ejects electron
Ejected electron acquires the remainer KE
The empty spot is usually filled
Photoelctron/recoil electron
Overcomes binding energy and ejects electron
The frequency of photoelectric interaction is inversely proportional to
Cube of photon energy
Higher energy photons are less likely to undergo absorption
The frequency of photoelectric interaction varies directly with the third power of
The atomic number of the absorber more likely with inner shells
As z number increases there is more photoelectric absorption
The probability that a photon will be absorbed by a photoelectric interaction in bone is approximately
6.5 times greater than in an equal thickness of soft tissue
Comptons scattering
Incident photon interacts with an outer electron
Overcomes binding energy ejects election; ejected electron acquires part of KE
Remainder of energy given off as scattered photon
Major source of scatter radiation
Compton probability greater in
Bone than soft tissue
Secondary electrons give up energy by 2 processes
Collisional interaction
-resulting in ionization of atom
Radiatiavie interactions
-Bremsstrahlung
% of scattering
Coherent 7%
Photoelectric 27%
Compton 57%
HVL
Half value layer
Thickness of an absorber such as aluminum required to reduce by one half the number of x ray photons passing through it
Beam Attenuation: Monochromatic beam
A constant fraction of the beam in attenuated as the beam moves through each unit thickness of an absorber
The absorption of the beam depends primarily on the
Thickness and mass of the absorber and energy of beam
In reality beams are
Polychromatic beams not monochromatic
Polychromatic beams
Absorption of individual photons depends on their energy
Low energy photons are much more likely to be absorbed than high energy photons
Beam hardening
As an X-ray beam passes through matter the intensity of the beam decreases as quantity decreases but the mean energy of the resultant beam increases
Collimator size
Round 2.75
Retrunagler 2 inches
Best collimator
Rectangular collimator
A digital image
Is a representation of two dimensional image as a finite set of digital values called picture elements or pixels
Pixel values
Typically represent gray levels colors heights opacities etc
Do digital save from radiation
Reduction compared with current standard of F speed film
Increase in number of radiographs made
Increase in the number and ease of remakes
Digital Imaging Chain
Image Acquistion
Image processing
Image Dispaly
Why go digital
Efficient work flow
Image enhancement
Better case acceptance
Co-diagnosis
Wired systems
CCD
CMOS
(Phosphors uses plates)
Sensors are made of
Silicone
CMOS each pixel
Has its own transistor does not go from one well to another
Phosphor wireless sensor
Sensor is made from a plastic plate coated with a phosphor material sensitive to X-ray
PSP sensor is exposed to X-ray
The image is then digitized with a special scanner
Plate must be cleared by light exposure
Digital Detector characteristics
Contrast resolution
Spatial resolution
Detector latitude
Detector sensitivity
Contrast resolution
Ability to distinguish different desensities in the image
8 bit
2^8=256
Spatial resolution
Capacity to distinguish fine detail
Detector latitude
Ability of a receptor to capture a range of exposure
Full range of human tissues from Gingiva to enamel
Detector sensitivity
Ability to respond to small amts of radiation
No classification standards for dental detectors yet
Detector Quantum effeciency
DQE is the measure of noise and contrast expressed as a function of object detail
Bit depth at least
12
Image processing
To restor enhance or analyze
-image restoration
-image enhancement
—brightness contrast
—sharpening and smoothing
—-color
—Digital subtraction
Digital subtraction
Two radiographs are taken with identical exposure geometry over a timer interval and superimposed
Monitor contrast
1000:1
Maxillary central incisor
Receptor selection:
Size 1
Sensor vertical
Entire length of bite block should be used to position the sensor back in the palate
Mandibular anterior
Place the sensor flat on top of the tongue. Insert hero tally to the lower first molar region
Root he sensor into an upright position making sure the bend in the metal bar is even with the center of the nostrils
Maxillary Posteriors
Retract the cheek and guide the sensor into the mouth between teeth 8 9 this is where the vault is in the palate and will give you plenty of room
Push sensor back until it is level with the desired teeth
Mandibular Posterior
Retract place sensor into mouth between tongue and teeth at a 45 degree downward angle for comfort
Slide sensor back toward themolar area centering the premolar/second molar on the center of the bite tab
Mandibular molar receptor
Size 2
Sensor horizontal
Premolar or molar Bitewing
Size 2
Horizontal or vertical
Overlap erro
Incorrect horizontal angulation
Incisal edge not visible
Incorrect sensor placement
Elongation error
Decreased vertical angulation
Foreshortening error
Increased vertical angulation
Cone cut error
X ray beam not centered on the receptor
Blooming
Each pixel cell of a ccd device converts photons to electrons during exposure
Electrons oversaturate the wells
Auto firing
White blank images
Caused by static
T/F photoelectric absorption is the primary contributor to the formation of a radiopgraphic image
True
It is recommend that na indivula operating a handheld x ray deveined wear a lead apron T/F
True
X ray tube length
Increasing the X-ray source to skin distance leads to a dose reduction of 10-25%
Reducing personal exposure
6 feet away at an angle of 90-135
Inverse square law
Effective dose
Occupational: 20 mSv
Public: 1 mSv
Effective dose: lens of eye
20 mSV
15 mSv
Effective dose skin hands and feet
500 mSv
50 mSv
Which image best visualizes periodontal bone levels
Bitewing
The greater the object receptor distance, the less magnification there will be
False
Because the beam is diverging the further away you are the larger the image will be
Broad radiographic examinations of the maxillofacial region
Images lack fine detail
Less invasive
Rapid scan time
Relatively low radiation dose
Panoramic indications
Osseous components of TMJs Impacted teeth Eruption abnormalities Pathology Trauma
Focal trough
Where beam is centered (mandible)
Closer to the panoramic beam means the image projects
Higher due to slight tilt
Ghost images
Always on opposite side and blurry
Head rotation
Whatever side the patient head is turned toward is more magnified
The focal trough goes to the left
If too far forward
Anteriors blurred
Too far back
Too much mandible
Overexposed
KVP to high black image
Underexposed
KVP too low brigh white
Lateral cephalmoteric skull projection
Evaluations of craniofacial skeletal morphology developmental growth occlusal relationships and treatment progress
PA cephalometric
Evaluation of facial asymmetry and orthographic surgery
Tongue not on palate
Radiolucent cant see
Too forward
Blurring of anterior teeth
A lot more spine
To far back
Anterior look too large
No spine
Huge mandible
Chin tilted down
Exaggerated smile line
Mandibular anterior teeth look too small
Chin elevated
Flat smile line
