Radiology

Chapter’s 2, 3. & 4

Electromagnetic spectrum Unique abilities

Some rays visible some are not

Penetrates matter Produces latent image

Produces fluorescence Light bulb

Produces ionization of matter Change matter

Matter

Anything that occupies space and has mass

Matter can be altered by energy

Fundamental unit of matter is the Atom

Desk Chair Computer Tissue Muscle Teeth Bone Your Patient

Atom

An atom is the smallest unit of an element, it consist of a positively charged protons found in the nucleus. Negatively charge electrons that orbit around the nucleus.

Neutron

Proton

Electron

Electrons

Nucleus(Dense core that occupies very little space)

Protons Subatomic particles and

positively charged

Neutrons Subatomic particles and

has no charge

Nuclear Composition

Equal number of protons and electrons form a stable atom.

The number of protons and neutrons equals the atomic weight.

Force will knock an electron out of their orbit. X-radiation Electromagnetic energy

Is this Atom stable or unstable?

Ionization(production of ions)

Converting atoms into ions. To produce ions a force or a collision

such as x-radiation or electromagnetic energy must eject an electron out from its orbit. Thus making the atom unstable.

Spontaneous release excess energy in the form of wave or particles.

ION

Electrostatic ForceBinding energy holds electrons in their orbits(Example: sun and the planets)

There are seven shells an atom can have they are k, l, m, n, o, p, and q.

K-shell has the highest energy and the strongest binding energy

Nucleus

q

p

o

nm

l

k

Atoms into ions

Positive ions are ionized atoms.

An ionized atom has been interrupted by some force: X-radiation Electromagnetic energy

Negative ions are electrons out of orbit or unstable structures.

This ejected ion will speed off to interact with other atoms.

When they interact or collide it sets off a chain reaction and in turn will eject other electrons until the energy dissipates.

Elements Elements

Substances made up of only one type of Atom

Molecule

Molecule Two or more Atoms

make up a molecule

Two Hydrogen and one Oxygen = Water

Bonded together by electrons on the outer most shells

Ionizing Radiation(all radiation cause biological changes)

Particulate Responsible for

radioactivity

Radioactivity is when atoms spontaneously disintegrate or decay. Power plant Atomic bomb

Electromagnetic Series of wave like

energies with no mass some high energy some low energy

Visible and invisible Man made or natural

occurring

Electromagnetic Energy Made up of both wave and particle that

travel in a straight line X-ray = bundle of energy, is termed, x-ray

photon which has no mass no charge and travels at the speed of light (186,000 MPS)

X-ray photon is what interacts with matter (your patient)

Examples of electromagnetic radiation and there wave like patterns

Less energy

More energy

Electromagnetic Energy

Wavelength Distance between the

crest of the wave to the next wave

Frequency Refers to the number of

wavelength that pass a given point in a certain amount of time. We can adjust the frequency by kilovoltage

Voltage

Measurement of electrical force that cause electrons to move from a negative pole to a positive one (Strength)

Dental x-ray units require a high level of electrical potential

Kilo-Voltage Peak(KVp)

Kilovoltage controls the level of penetration Shorter wavelength =

more penetrating High frequency = more penetrating Longer wavelength =

less penetrating Low frequency the =

penetrating

Kilovoltage Kilo = 1000 Volatage = volts 110 or 220 Higher voltage means

greater energies Dental radiographs require

65 to 100 kilovolts Higher KVp should be used

when area is dense or thick Adjust KVp on individual

diagnostic needs Overall QUALITY of

primary beam

Amperage

Measurement of electrons moving through a conductor

Current is measured in amperes

Milliamperes (mA) Milliampere

Milli = 1/1000 Ampere = Electrical

current NOT voltage mA settings

7, 10, and 15 Thermionic emissions

Higher the setting increases temperature resulting in some electrons being ejected out of their orbit.

Ampere allows electrical current to flow thru a filament which results in a cloud of electrons

Depending on mA setting will depend on the QUANTITY of x-rays produced

Milliamperes-Seconds

Exposure time Interval of time in which

photons are being produced (.117 secs)

Longer time = more photons

High mA = more photons

Both mA and exposure time both have a direct influence on the number of electrons produced

If we produce to many photons our dental film will be dark or black

Radiographic Density(Degree of darkness or blackness of an x-ray.)

Density Amount of radiation

reaching the film KV or mA

Distance from the x-ray tube to the patient

Patient thickness (Density)

Developing conditions

The more photons that strike the film the more dense (black) the radiograph will appear

Tubehead

Cathode Negative electrode

consist of tungsten filament held in a cup shaped holder made of molybdenum

Negative = electrons, therefore electrons are created to produce photons

*

Electrons held in place

Tubehead

Anode Positive electrode consist

of a wafer thin tungsten plate embedded in a solid copper rod

Positive = collision = photons

*

Collision produced photons (indicated in red)

TransformersThree types are used in production of x-rays

Step down decreases the voltage from the incoming 110 or

220 to three to five volts required Step up

Increases the voltage to 65,000 to 100,000 volts required

Autotransformer Compensator

Inside the Tubehead

This is What Happens Electricity excites the filament at 3-5 volts, creating thermionic

emissions, a release of electrons from the tungsten filament when heated, this cloud of electrons stay in place until the exposure button is pushed. The high voltage circuit is activated. The electrons produce are accelerated across the x-ray tube to the anode. The molybdenum cup helps to direct the electrons to the tungsten target. When the electrons strike the tungsten target their energy of motion or kinetic energy is converted to x-ray energy and heat. More heat is created that x-rays and is dissipated through the copper stem and absorbed by the insulating oil. X-rays are produce in all direction only a few will escape through the unleaded portion of the tube. Those x-rays will be directed to the aluminum filter, which will remove the long waves. The collimator will focus the remaining short waves and travel down the lead lined PID and exit the tubehead

Production of radiation(not all produce the same in the tube head)

General radiation AKA braking radiation

An electron passes near the nucleus and is deflected by the positively charge nucleus

Once deflected this kinetic energy is converted into photons

Bremsstrahlung German

(braking radiation)

Production of radiation(not all produce the same in the tube head)

Characteristic radiation

Electron that has been deflected continues to travel ejecting other electrons out of orbit until they loose their kinetic energy Energy in motion

Important Terms

kVp = Kilovoltage peak=quality of beam kVp = density = low contrast = lots of

shades of gray Low kVp = low density = high contrast = lighter

film = black & white film Contrast – varying shades of gray Density – overall blackness or darkness of

film

Important Terms

mA=Milliamperage=quantity of x-rays produced=density To many mA’s=darker film=higher density To little mA’s=light film=lower density # of electrons from cathode to anode # of x-ray photons in beam mA regulates temperature of cathode

Important Terms

Exposure time – refers to interval of time x-rays are produced-measured in impulses Longer time=longer time x-rays emitted=darker

film=greater film density Less time=less time x-rays emitted=lighter films=

less film density Subject Thickness effects quality and

quantity of penetrating power

Important Terms

Kilovoltage peak rule – RHS – when kVp is increased by 15 – exposure time should be decreased by ½

When kVp is decreased by 15 – exposure time should be doubled

Milliampere-seconds (mAs) = combination of milliamperes and exposure time Milliampers X exposure time (seconds) =

milliampere-seconds (increase mAs-decrease time)

Important Terms

Attenuation aka Dose When matter absorbs radiation (only during

secondary) Primary Radiation aka Primary Beam

Penetrating beam – Roentgen Units = R Secondary Radiation

Created when Primary beam hits matter (soft tissues, head , skull, teeth) less penetrating power

Radiation pt receives – RAD = radiation absorbed

Important Terms

Scatter Radiation A type of secondary radiation Has been deflected off of path Travels to all parts of the body & operatory

REM = Roentgen equivalent to man MPD = maximum permissible dose

Dental radiographer = 5.0 REM per year Non health care worker = .1 REM per year .08 RAD’s in FMX

Radiation Biology

Radiation Biology-the study of effects of ionizing radiation on living tissue

Absorption Ionization page 39 – all x-rays harmful to

living tissue When x-rays strike patient tissues ionization

results Free Radical Formation-causes cell damage

Sequence of Radiation Injury page 41

Latent Period=the time that elapses between exposure to ionizing radiation and the appearance of visible clinical signs. Example: Sitting in the sun – hours later skin

redness appears

Sequence of Radiation Injury

Period of injury After the latent period Cell injury can result as:

cell death changes in cell function – ex: endometriosis breaking or clumping of Chromosomes – ex: (cell)

reproduction problems many more cell specific

Cell injury is the desired result in cancer tx

Sequence of Radiation Injury

Recovery period Not all cell radiation damage is permanent Damage caused by low-level radiation is repaired

within cells of body. Ex: skin was burned – it has repaired itself

Sequence of Radiation Injury

Cumulative effects – overtime Radiation damage accumulates in tissue of entire

body Can lead to:

Poor health Cancer – Thyroid/Skin Cataract formation Birth defects

Dental x-rays do not cause cancer – falls under MPD

Sequence of Radiation injury cont.

Recovery period=Not all cellular radiation injuries are permanent. With each radiation exposure, cellular damage is followed by repair.

Cumulative effects=The effects of radiation exposure are additive, and unrepaired damage accumulates in the tissues, cumulative effects of repeated radiation exposure can lead to health problems.

Determining Factors for Radiation Injury

Total dose – RAD – measurement of attentuation – absorbable dose

Dose rate – rate @ which exposure to radiation occurs & absorption takes place Cells need time to recover

Amount of tissue irradiated – area exposed Cell sensitivity Age

Short-Term and Long-Term Effects

Short-term page 42 Short-term effects are

associated with large mounts of radiation absorbed in a short time. Includes nausea, vomiting, diarrhea, hair loss and hemorrhage.

Long-term page 42 Effects that appear after

years, decades or generations. Long-term effects are associated with small amounts of radiation absorbed repeatedly over a long period.

Somatic and Genetic Effects

Somatic effects Somatic cells are all the

cells except reproductive cells. Major somatic effects of radiation exposure include the induction of cancer, leukemia and cataracts. These are not transmitted to future generations.

Genetic effects Genetic effects are not

seen in the person irradiated but are passed on to future generations. The radiation-induced mutations affect the health of the off-spring. Genetic damage cannot be repaired.

Radiation Measurements MPD, Maximum Permissible dose

The dental radiographer must know radiation measurements to discuss exposure and dose concepts with the dental patient.

Traditional or standard system R-roentgen=measurement of radiation REM (Me)=5.0 year or .01 weekly Pregnant operator=0.1 per year RAD (pt.)=0.1 per year

Risk Estimates

Radiosensitive parts Lymphoid tissue Blood forming tissues Reproductive cells Formative cells Embryo cells

Radioresistant parts Salivary glands Kidney Liver Cells of mature bones Muscle Nerves

Critical Organs

Thyroid Gland Use Thyroid collar

Bone Marrow Skin

Very sensitive to radiation Eyes

Cataract

Patient Exposure and Dose pg. 46

Film- Using F-speed film instead of D reduces absorbed dose by 60%. Using

F-speed instead of E reduces absorbed dose by an additional 20%

Collimation-Radiation exposure can be limited by using rectangular collimation, reduces absorbed dose by 60%-70% rather the round collimation (PID).

Patient Exposure and Dose

Technique-Radiation exposure can be limited by using a longer source-to-film distance. XCP for example

Exposure factors-Radiation exposure can be limited by using a higher Kilovoltage peak, the use of higher kilovoltage peak reduces skin dose.

Surface exposure-intensity of radiation @ pt skin surface

REDUCING EXPOSURE RISKS Dental radiation risks – estimated 3

to1,000,000 30 PA’s to equal one chest x-ray’s worth of

radiation Film speed Collimation – PID use of Rectangular best –

most common is round – pointed not used Technique – use film holding devices Exposure – higher kVp less time

Risk versus Benefit

X-radiation is harmful to living tissues Benefit of disease detection outweighs risk of

biological exposure Properly prescribed & exposed – only when

needed ALARA Principle – as low as reasonably

achievable – minimize risk to pt and operator FMX – full mouth survey – taken no more than

once every 3-5 yrs – 14 PA’s & 4 BW’s