Exam 1 (1-4) Flashcards
Dental radiographs:
Images or pictures produced by x-rays
Remain the basis for many diagnostic procedures
Play an essential role in oral health care
What is Radiography?
Making of radiographs by exposing an image receptor,
either film or digital sensor
Dental radiography
The purpose is to provide oral health care team radiographs of the best possible diagnostic quality.
The goal is to obtain the highest quality radiographs while maintaining the lowest possible radiation exposure risk for the patient.
Oral radiology:
Study of x-rays and techniques used to produce radiographic images
X-Ray discovered by Professor Wilhelm Conrad Roentgen 1895
X-ray:
Initially, X represented the unknown.
Radiograph:
Photo negative and x-ray film are similar.
X-rays resemble radio waves.
Prefix “radio” and suffix “graph” combined.
Panoramic radiography
Capable of exposing the entire dentition and surrounding structures on a single image
Computed tomography scan (CT)
Imaging a single selected plane of tissues
Delivers high dosage of radiation
Cone-beam computed tomography (CBCT)
Lower doses of radiation
* Purported to become the gold standard
Early dental x-ray film packets
Glass photographic plates wrapped in black paper and rubber
Machine-wrapped dental x-ray film packet
First available in 1919 from Kodak
Emulsion coating:
One-sided coating
Required long exposure times
Both sides coated now
Exposure times much shorter
Who introduced digital radiography and what does it do?
Digital imaging systems replace film as the image receptor with a sensor.
French dentist- Frances Mouyen, 1987
RadioVisioGraphy
What are the advantages of digital radiography?
Advantages:
Reduction in radiation dosage
Elimination in film and processing chemistry
Elimination of film packaging disposal
Bisecting technique:
First and earliest method
A. Cieszyński, 1907
Applied the rule of isometry to dental radiology
Paralleling technique:
Franklin McCormack, 1920
Less-complicated; more practical
Uses of Dental Radiographs:
Detect, confirm, and classify oral diseases and lesions
Detect and evaluate trauma
Evaluate growth and development
Detect missing and supernumerary (extra) teeth
Document the oral condition of a patient
Educate patients about their oral health
Matter:
Anything that occupies space and has mass.
Energy:
The ability to do work and overcome resistance
Examples:
Heat
Light
Electricity
X-radiation
Atom:
The smallest particle of an element that still retains the properties of the element
Molecule:
The smallest particle of a substance that retains the properties of that substance
Atoms + Atoms = molecule
Atoms are composed of:
Electrons (-)
Negative charge
Protons (+)
Positive charge
Neutrons (neutral)
No charge
Atoms:
Electrons revolve around a nucleus in paths called shells or energy levels.
Protons and neutrons form the nucleus (center)
In the neutral atom, the number of positively charged protons in the nucleus is equal to the number of negatively charged orbiting electrons. The innermost orbit or energy level is the K shell, the next is the L shell, and so on.
Binding energy:
Electrons are maintained in orbits by positive attraction of protons.
Ion:
is an atom with extra (+) or missing (-) electrons
Charged particle
Positive ion:
Atom from which an electron (-) has been removed
(more protons than electrons)
Negative ion:
Negatively charged electron (-) separated from the atom
(-e itself)
Ion pair:
Positively charged atom ion and negatively charged electron ion
Ionization:
Formation of ion pairs
What’s going on in this picture?
Ionization is the formation of ion pairs. When an atom is struck by an x-ray, an electron may be dislodged and an ion pair results.
Radiation:
Emission and movement of energy through space
Electromagnetic radiation (x and gamma rays)
Particulate radiation (alpha and beta particles)
Ionizing radiation:
Any radiation that produces ions
Radioactivity:
The process whereby certain unstable elements undergo spontaneous disintegration (decay) in an effort to attain a stable nuclear state.
Dental x-rays do not involve the use of radioactivity.
Electromagnetic Radiation:
Movement of wave-like energy through space as a combination of electric and magnetic fields.
Electromagnetic spectrum:
Consists of an orderly arrangement of all known radiant energies.
X-radiation includes:
Gamma rays
Ultraviolet rays
Visible light
Infrared
Microwave
Radio waves
All energies of the electromagnetic spectrum share the following properties:
Travel at the speed of light
Have no electrical charge
Have no mass or weight
Pass through space as particles and in a wave-like motion
Give off an electrical field at right angles to their path of travel and a magnetic field at right angles to the electric field
Have energies that are measurable and different
Electromagnetic radiation display two contradictory properties:
Believed to move through space as both a particle and a wave.
Particle or quantum theory:
Assumes electromagnetic radiations are particles, or quanta called photons
Photons are bundles of energy that travel through space at the speed of light
Wave theory:
Assumes electromagnetic radiation is propagated (spread) in the form of waves:
Wavelength
Frequency
Velocity
Wavelength:
Distance between two similar points on two successive waves
May be measured in the metric system or in angstrom (Å) units
Wavelength is determined by distances between crests.
Frequency:
The measure of the number of waves that pass a given point per unit of time
Hertz (Hz)
Special unit of frequency
One hertz equals one cycle per second.
Velocity:
Speed of the wave
Soft radiation:
Grenz rays
Limited penetrating power
Unsuitable for exposing dental radiographs
(long wavelength)
Hard radiation:
Wavelengths used in diagnostic dental radiography range from about
0.1 to 0.5 Å
Great penetrating power
(Short wavelengths)
Properties of X-rays
X-rays are believed to consist of minute bundles (or quanta) of pure electromagnetic energy called photons.
Photons:
Photons have no mass or weight, are invisible, and cannot be sensed.
X-ray photons are often referred to as “bullets of energy.”
X-rays:
Are invisible
Travel in straight lines
Travel at speed of light
Have no mass or weight
Have no charge
X-ray photons have the ability to penetrate
materials or tissues depends on:
The wavelength of the x-ray
and
thickness and density of the object.
Materials that are extremely dense and have a high atomic weight will absorb more x-rays than thin materials with low atomic numbers.
Dense materials such as bones appear radiopaque (white/light gray) (bones/teeth = white/gray)
Less dense materials such as the pulp chamber appear radiolucent (black/dark gray) (spaces/foramen = black)
In a dental x-ray tube, the kinetic energy of electrons is converted to electromagnetic energy by the formation of:
General or bremsstrahlung radiation
German for “braking”
Characteristic radiation
General/bremsstrahlung radiation:
Produced when high-speed electrons are stopped or slowed down by the tungsten atoms of the dental x-ray tube.
Characteristic radiation:
(C)
Produced when a high-speed electron from the tube filament collides with an orbiting K-shell electron of the tungsten target.
Primary radiation:
General and/or characteristic radiation generated at a target inside x-ray tube head
Refers to the useful beam, or those x-rays generated for the
purpose of making a radiographic image
Secondary radiation:
Formed as a result of primary radiation striking and interacting with matter
Not as penetrating as primary radiation
Not useful in the production of a radiographic image
Can contribute to a lowered contrast, poor quality image
Scatter radiation:
Form of secondary radiation
Results when x-rays are deflected in all directions as a result of interaction with matter
Not useful
Can cause unnecessary additional exposure to patient tissues and to the careless operator who does not follow safety protocols
Lead apron + lead wall = no scatter radiation
Absorption:
Process of transferring energy of x-rays to atoms of material through which the x-ray beam passes
The beam of x-rays passing through matter is
weakened and gradually disappears.
(tooth absorbs energy = turns white)
Interaction of X-rays with Matter:
Four possibilities:
- No interaction
- Coherent scattering
- Photoelectric effect
- Compton effect
No interaction:
(A)
X-ray photon can pass through an atom unchanged and no interaction occurs.
In dental radiography, about 9% of the x-rays pass through the patient’s tissues without interaction.
Coherent scattering:
(B)
Incoming x-ray photon interacts with the electron by causing the electron to vibrate at the same frequency as the incoming x-ray photon.
Accounts for about 8% of the interactions of matter with the dental x-ray beam
Photoelectric effect:
Incoming x-ray photon collides with an orbital electron and imparts electromagnetic energy to the electron in the form of kinetic energy causing electron to fly from its orbit, creating an ion pair.
All-or-nothing energy loss
High-speed electron (called a photoelectron)
knocks other electrons from the orbits of other atoms (forming secondary ion pairs) until all its energy is used up.
Accounts for about 30% of the interactions of matter with the dental x-ray beam
Compton scattering:
Similar to the photoelectric effect
Incoming x-ray photon collides with an orbital electron and ejects it. But, only a part of the x-ray energy is transferred to the electron, and a new, weaker x-ray photon is formed and scattered in a new direction.
Accounts for about 60% of the interactions of matter with the dental x-ray beam.
The International Commission on Radiation Units and Measurements
(ICRU)
has established standards that clearly define radiation units and radiation quantities. The most widely accepted terms used for radiation units of measurement come from the Système Internationale (SI), a modern version of the metric system.
The SI units are:
Coulombs per kilogram (C/kg)
Gray (Gy)
Sievert (Sv)
Radiation Measurement Terminology:
Quantity SI Unit
Exposure coulombs per kilogram (C/kg)
Absorbed dose gray (Gy)
Dose equivalent Sievert (Sv)
Effective dose equivalent microsievert (µSv)
Exposure:
Measurement of ionization in air produced by x- or gamma rays
Unit for measuring exposure is coulombs per kilogram (C/kg)
Does not measure the radiation absorbed by body tissues or other materials.
Exposure does not become a dose until the radiation is absorbed.
Absorbed dose:
Amount of energy deposited in any form of matter, such as the tissues of the head and neck of a patient, by any type of radiation (alpha or beta particles, x- or gamma rays)
Unit for measuring absorbed dose is the gray (Gy)
Dose equivalent:
Used to compare the biological effects of the various types of radiations
Product of the absorbed dose times a biological-effect qualifying or weighting factor determined by quantum physicists
Unit for measuring dose equivalent is the sievert (Sv)
weighing factor for X-ray = 1
absorbed dose and dose equivalent are equal
Effective dose equivalent:
Used to compare the risk of radiation exposure producing a biological response
Expressed using the term microsievert (μSv)
Compensates for the differences in area exposed and tissues, critical or less critical, that may be in the path of the x-ray beam
Background radiation:
The ionizing radiation that is always present in our environment
Dental x-rays and other man-made medical applications account for 48% of total radiation exposure to U.S. population.
Who is responsible for the radiation dose the patient occurs at the time of exposure?
the radiographer
Which part of the dental x-ray machine contains the master switch and other exposure buttons?
the control panel
What enables the tube head to be positioned?
the extension arm or bracket
Which part of the dental x-ray machine contains the x-ray tube from which x-rays are generated?
the tube head
What do dental x-ray machines require in order to produce x-rays?
an electrical source.
What are the different options available for control panel placement?
- It may be integrated with the extension arm
- It may be remote from the unit or mounted on a shelf or the wall.
What are the five major controls that will be present on dental x-ray machines?
- the line switch to an electrical outlet
- the milliampere (mA) selector
- the kilovolt peak (kVp) selector
- the timer
- the exposure button
This switch, located on the control panel, maybe flicked ON or OFF. It features an indicator light that turns on indicating when the machine is operational.
What is it called? Do this first!
Line Switch
What measures the amount of current passing through the wires of the circuit?
The milliampere selector; mA
determines #free electrodes at cathode (-) → # X-rays produced
How is the mA set?
it is set by turning a selector knob or by pressing the marked push button of touching a keypad.
What enables the operator to change the peak kilovoltage?
a kilovolt peak (kVp) selector
(penetrating)
kVp determines the speed of electrons traveling toward the target on the anode (+) and, therefore, the penetrating ability of the x-rays produced.
What determines the speed of electrons traveling toward the target on the anode and, therefore, is the penetrating ability of the x-ray produced?
kVp (penetrating)
What sets the timer?
What is the purpose of the timer?
How many impulses are there in a second?
- the selector knob, button or keypad
- it serves to regulate the duration of the interval that the current will pass through the x-ray tube.
60/sec
What is the “dead man” exposure switch?
it is an exposure switch that automatically terminates the exposure when the operator’s finger ceases to press on the timer button.
X-ray machines with digital electronic timers are accurate to the ______ of a second?
1/100-second intervals
How far should the area of protection be from the source of the x-ray beam?
Why is it important to firmly press the timer button for the full duration of an exposure?
6 feet
letting go of the results in the formation of an insufficient number of x-rays to properly expose the image receptor. There is a beep that sounds when this is done. The beep is required by law.
Why is the extension arm hollow?
to permit the passage of electrical wires from the control panel to the tube head from one or both sides at a point where the tube head attaches to a yoke.
The tube head is attached to the extension arm by means of a _____ that can revolve 360 degrees horizontally where it is connected?
Yoke
What does the tube head’s heavy metal, lead-lined housing contain?
x-ray dental tube
insulating oil
step-up and step-down transformers
What functions are performed by the tube head metal housing?
- it protects the x-ray tube from accidental damage.
- it increases the safety of the x-ray machine by grounding its high voltage components to prevent electrical shock.
- it prevents overheating of the x-ray tube by providing a space filled with oil, gas, or air to absorb the heat created during the production of x-rays.
- it is lined with lead to absorb any x-rays produced that do not contribute to the primary beam that exits through the port in the direction of the position indicating device (PID)
Identify #1
Tube head
Identify #2
Low voltage transformer
Identify #3
Primary beam
Identify #4
High voltage transformer
Identify #5
Window
Identify #6
Collimator
Identify #7
Central ray
Identify #8
Filter
Identify #9
PID
Identify # 10
X-Rays
Identify # 11
Port
Identify # 12
Oil
Identify #13
Copper stem
Identify # 14
Cathode (-)
Identify # 15
Focusing cup
Identify # 16
Anode (+)
Identify # 17
Electron cloud
Identify # 18
Filament
Identify # 19
Glass envelope
Identify # 20
Radiator
Identify # 21
Tungsten target
Identify # 22
Vacuum
How can electricity be defined?
it can be defined as electrons in motion.
Two electrical circuits are used in producing dental x-rays, what are they?
- a filament circuit
- a high voltage circuit
What does the filament circuit do?
it provides a low voltage (3-8 V) to the filament of the x-ray tube to generate a source of electrons needed for the production of x-rays
What does a high-voltage circuit provide?
it provides the high voltage (50-100 kV) necessary to accelerate the electrons from the cathode filament to the anode target.
What is required to decrease (step down) or increase (step-up) ordinary
110-V or 220-V current that enters the x-ray machine.
a transformer
What is the purpose of a step-down transformer?
it decreases the voltage from the wall outlet to approximately 5V, just enough to heat the filament and form an electron cloud.
What is the purpose of a step-up transformer?
it increases the voltage from the wall outlet to approximately 50-100 kV to propel the electrons toward the target.
What measures the number of electrons that move through conductor?
the amperage
What is the unit of quantity of electric current?
ampere
What does an increase in amperage result in?
it results in an increase in the number of electrons available to travel from the cathode to the anode when the tube is activated; thus producing more x-rays.
True or False
A small current is required to generate the number of electrons necessary to produce dental x-rays.
True
What does the term milliampere (mA) denote?
it denotes that 1/1,000 ampere is used.
What mA is typically used in dental x-ray machines?
4-15 mA
Define voltage?
it is the electrical pressure between two electrical charges. It determines the speed of the electrons traveling from cathode to anode.
What happens when voltage is increased?
.
the electrons travel faster and produce a harder type of radiation
What is a polychromatic beam?
X-rays of different energies; containing high-energy rays and also containing soft rays that have barely enough energy to escape from the tube.
What is the kV range that dental x-ray machines can operate within?
50 kV- 100 kV
What types of current may be used by dental x-ray machines?
alternating current (AC) or direct current (DC)
What is alternating current (AC)?
A flow of electric charge that alternates between positive and negative phases. There are 60 direction changes per second. X-rays are only produced when the current is in the positive direction (up).
What does alternating current causes the dental x-ray machine to produce?
it causes it to produce x-rays in a series of bursts, or pulses, rather than in a continuous flow
What is direct current (DC)?
this current flows continuously in one direction, eliminating the alternating cycles; resulting in a more constant and even flow of x-rays.
This is similar to the current produced by battery power.
What causes a dental x-ray machine to produce x-rays at a more consistent wavelength?
Direct current flow
What is a key difference between AC and DC x-ray machines?
Direct current dental x-ray machines produce more consistent exposures at very short exposure times and may slightly reduce patient radiation exposure.
When are x-rays produced?
they are produced when a stream of high-speed electrons is stopped or slowed down and diverted off course.
What three conditions must exist for x-rays to be produced?
- An available source of free electrons.
- High voltage to impart speed to the electrons (kVp)
- A target that is capable of stopping/slowing the electrons.
What is located inside the tube head, is a glass bulb from which the air has been pumped to create a vacuum?
the x-ray tube
Define cathode:
a negative (-) electrode
Define anode:
a positive electrode
What is the purpose of the cathode?
To supply the electrons necessary to produce x-rays. It contains the tungsten filament wire
Explain the process of thermionic emission.
The tungsten filament wire, when heated to incandescence, produces electrons.
True or False
The cathode consists of a thin spiral filament of tungsten wire.
True
What is the benefit of Tungsten?
Its high atomic number makes it possible to liberate electrons, through thermionic emission, from their orbital shells when the metal is heated. These released electrons then form an electron cloud around the wire.
What is the purpose of the focusing cup?
it directs (focuses) the electrons toward the target on the anode.
What accurately controls the thermionic emission and therefore controls the quantity of free electrons available?
mA
What is the purpose of the anode?
the purpose is to provide a target that stops or significantly slows the high-velocity electrons, converting their kinetic energy into x-rays (electromagnetic energy).
What does the anode consist of?
a copper bar with a tungsten plate imbedded in the end that faces the focusing cup of the cathode
What is set into the copper at an angle of 20 degrees to the cathode?
the tungsten plate (called the target)
What does the 20-degree angle of the target (tungsten plate) direct?
it directs most of the x-rays produced in one direction to become the primary beam.
What is the focal spot?
it is a small rectangular area on the target of the anode to which the focusing cup directs the electron beam.
Why is the focal spot size important?
it plays an important role in determining the radiographic image sharpness
Why is the tungsten plate embedded in the core of a copper bar?
because copper is highly conductive and carries the heat generated off to the radiator which is just outside the tube.
If the tube head is properly sealed, ____ is the only place through which x-rays can escape.
the port
Why is the collimator useful?
it is useful because it further reduces (funnels) the x-ray beam to the desired size after it exits through the port.
How do x-rays travel?
in diverging straight lines as they radiate from the focal spot. This beam of x-rays is called a useful beam or primary beam.
What is a filter?
it is a thin sheet of aluminum placed in the path of the x-ray beam.
What does the intensity of the x-ray beam refer to?
it refers to the quantity and quality of the x-rays.
Define quantity.
this is the number of x-rays in the beam = (mA)
Define quality.
this refers to the energy strength or penetrating ability of the x-ray beam. (kVp)
Define intensity
the product of the number of x-rays and the energy strength of the x-rays per unit of area per unit of time. The intensity of the x-ray beam is affected by milliamperage, kilovoltage, exposure time, and distance.
What happens if you increase the mA?
there will be an increase in the number of electrons.
What is the ethical responsibility of the radiographer?
to produce the highest diagnostic-quality radiographs for patient who have given consent.
What are the three basic requirements for an acceptable diagnostic radiograph?
- All parts of the structures recorded must be imaged as close to their natural shapes and sizes as a patient’s oral anatomy will permit.
- The area examined must be imaged completely with enough surrounding tissue to distinguish between the structures.
- The radiograph should be free of errors and show proper density, contrast, and definition
Define radiolucent.
It is the portion of the image that is dark or black.
Structures that appear radiolucent permit the passage of x-rays with little or no resistance.
transparent to X-rays
Ex: pulp chamber, PDL
Define radiopaque.
The portion of the image that is light or white. The structures that appear this way are dense and absorb or resist the passage of x-rays.
Not transparent
Ex: enamel, dentin and bone
Define density.
The degree of darkness or image blackening.
An image that appears light is said to have little density; whereas an image that appears dark is said to have more density.
______ is increased when the milliamperage (mA) of the exposure time is increased and more x-rays are produced to reach the film emulsion or digital sensor.
The degree of darkening of a radiograph
Increased mA = dark X-rays
Define contrast.
many shades of gray that separate the dark and light areas.
An area with good contrast will contain black, white, and enough shades of gray to differentiate between structures and their conditions.
What type of contrast describes a radiograph in which the density differences between adjacent areas are small?
Low contrast or Long Scale
Hard to distinguish between colors
Higher kVp = low contrast
Define sharpness
It is a geometric factor that refers to the detail and clarity of the outline of the structures shown on a radiograph
What generally causes unsharpness?
movement of the patient, image receptor, or the tube head during the exposure.
