Radiology Midterm Review

William Conrad Roentgen

a Bavarian physicist, discovered the x-ray on November 8, 1895

X-Ray (old names)

roentgen rays, roentgenology, and roentgenographs

William Conrad Roentgen (Nobel Prize)

awarded in physics, in 1901.

Crookes Tube

large, partially evacuated glass tube through which cathode rays (electrons) were conducted, developed in 1895

Otto Walkoff

person who made the first dental radiograph

C. Edmund Kells

dentist, is credited with the first practical use of radiographs in dentistry, in 1896.

Nucleus

dense core, of the atom is composed of particles known as protons and neutrons.

Protons

carry positive electrical charges; neutrons carry no electrical charge

Electrons

are tiny negatively charged particles with very little mass; orbit around the nucleus of an atom.

Electron Shell

orbit path of an electron; can contain only a specific number of electrons

Ionization

process by which electrons are removed from the orbital shells of electrically stable atoms through collisions with x-ray photons; occurs when a x-rays have enough energy to push an electron out of its orbit, producing an ion

Ion

an atoms that gains or lose an electron and becomes electrically unbalanced

Photon

a minute bundle of pure energy that has no weight or mass

Ion Pair

are formed when an electron is removed from the atom

Molecule (water)

compound consists of two atoms of hydrogen connected to one atom of oxygen.

X-Ray (characteristics)

form of energy that can penetrate matter and belong to a group called electromagnetic radiation

Electromagnetic Radiation

photons that travel through space at the speed of light in a straight line with a wavelike motion

Electromagnetic Spectrum

shows the various wavelengths of radiation typically used

X-Rays (properties)

short wavelengths, high energy to penetrate matter more easily

Wavelength

distance between the crest (peaka0 of one wave and the crest of the next

Long Wavelength

less energy and less penetration

Short Wavelength

greater energy and penetration

X-Ray Machine (components)

tubehead, extension arm , and control panel

Tubehead

tightly sealed; heavy metal housing contains the x-ray tube that produces dental x-rays.

Metal Housing

metal body of the tubehead that houses the x-ray tube filled with insulating oil

Insulating Oil

fluid surrounds the x-ray tube and prevents overheating by absorbing the heat created in the production of x-rays

Tubehead Seal

made of leaded glass or aluminum. It seals the oil in the tubehead

X-Ray Tube

vacuum environment allows the electrons to flow with minimum resistance between the electrodes (cathode and anode), a glass vacuum tube from which all the air has been removed

Transformer

alters the voltage of incoming electric current.

Aluminum filter

is aluminum sheets (disc) 0.5 mm thick placed in the path of the x-ray beam; filter out the nonpenetrating loner wavelength x-rays

Lead Collimator

metal disc (or plate) with a small opening in the center to control the size and shape of the x-ray beam as it leaves the tubehead

Position-Indicating Device

open-ended, lead-lined cylinder that extends from the opening of the metal housing of the tubehead. It is used to aim the x-ray beam

X-Ray Tube (components)

lead-glass housing ,negative cathode and postive anode

Cathode (components)

tungsten filament in a focusing cup made of molybdenum

Cathode (purpose)

negative electrode that supplies the electrons necessary to generate x-rays

Electrons (production location)

Electrons are generated in the x-ray tube at the cathode

Anode

postive electrode and target for electrons

Tungsten Filament

coiled wire made of tungsten, which produces electrons when heated

Molybdenum Cup

foces the electrons into a narrow beam and directs the beam across the tube toward the tungsten

Anode (purpose)

to convert electrons into x-ray photons

Anode (components)

tungsten target and copper stem

Tungsten Target

plate of tungsten, which serves as a focal spot and converts bombarding electrons into x-ray photons

Copper Stem

dissipates the heat away from the tungsten target

Central Ray

x-rays at the center of beam

PID (safest)

rectangular shape device that limits thesiae ofr the beam to that of a dental film

PID (sizes)

8, 12 or 16" long determined by the technique being used

PID (safest length)

12-16" reduces exposure because there is less divergence (separation) of the beam.

Extension Arm

encloses the wire between the tubehead and the control panel; positions the tubehead; folds up and can be swiveled from side to side.

Extension (drifting cause)

arm is left in an extended position after an exposure and the machine is not in use

Control Panel

x-ray unit contains: master switch

indicator light, exposure button

Indicator light, control devices

Control Panel (control devices)

time, milliamperage [mA] selector, and kilovoltage [kVp] selector

General (braking) radiation

Many electrons that interact with the tungsten atoms undergo not one but many interactions within the target (70% of x-ray energy)

Braking Radiation

Produced when an electron hits the nucleus of a tungsten atom or passes very close to the nucleus of a tungsten atom

Characteristic Radiation

Produced when a high-speed electron dislodges an inner-shell electron from a tungsten atom and causes ionization of that atom

(only at 70 kVp)

Primary Radiation

is the x-rays that come from the target of the x-ray tube

Secondary Radiation

x-radiation that is created when the primary beam interacts with matter.

Scatter Radiation

form of secondary radiation resulting when an x-ray beam has been deflected from its path by interaction with matter.

Radiation (types)

primary, secondary and scattered

X-Radiation Interaction

No interaction; Absorption of energy/photoelectric effect; Compton scatter; Coherent scatter

X-Radiation (no interaction)

x-ray photon passes through the atom unchanged and leaves the atom unchanged; responsible for producing densities on film and make dental radiography possible

X-Radiation (energy absorption)

The total transfer of energy from photon to the atoms of matter

X-Radiation (photoelectric effect)

Ax-ray photon collides with a tightly bound, inner-shell electron, gives up all its energy to eject the electron from its orbit (absorbed by atoms); account for 30% of interactions of matter of x-ray beam)

Compton Scatter

The x-ray photon is deflected from its path during its passage through matter (62% of scattered radiation)

Compton Scatter (ionization)

An x-ray photon collides with a loosely bound, outer-shell electron and gives up part of its energy to eject the electron from its orbit

Compton Scatter (ejected electron name)

Compton electron

Coherent Scatter

An low energy x-ray photon that has its path altered by matter

interacts with outer shell electron and no change in atom occurs producing scattered radiation photon

Voltage

is measured in volts or kilovolts

Volt

A unit of measurement used to describe the potential that drives an electrical current through a circuit

(kilovolt = 1000 volts)

Dental Radiology (kV range)

65 - 100 kV

Dental Radiology (inadequate penetration kV)

<65 kV

Dental Radiology (over penetration kV)

> 100 kV

Kilovoltage Peak (kVp)

Maximum or peak voltage; refers to the peak voltage of an alternating current (AC)

Polychromatic X-Ray Beam

produced as a result of varying kilovoltages in the tube current

Quality

wavelength and energy of the x-ray beam

Quality (control mechnism)

kilovolt peak

Quality (increase kVp by 15 = exposure time effects)

½ exposure time

Quality (decrease kVp by 15 = exposure time effects)

double exposure time

Amperage

Determines the amount of electrons passing through the cathode filament

Amperage (increased effect)

results increased number of electrons traveling from cathode to anode and production of an increased number of x-rays

Quantity

the number of x-rays produced from the the tubehead

Quantity (control mechanism)

milliamperage

Milliamperage (increased effect)

decrease in exposure time to maintain consistent density

Milliamperage

the intensity of the x-ray tube current used udring exposure (mA)

Intensity

The product of the quantity (number of x-ray photons) and quality (energy of each photon) per unit of area per unit of time of exposure

Intensity (formula)

# photons x energy of each photon (divided by) area x exposure rate

Kilovoltage Peak

Regulates the penetrating power of the x-ray beam by controlling the speed of electrons traveling between the cathode and the anode

Kilovoltage Peak (higher setting effect)

produces an x-ray beam with more energy and shorter wavelengths;

Increases intensity of the x-ray beam

Exposure Time

Interval of time during which x-rays are produced; Measured in impulses;

Milliamperage

Controls the penetrating power of the x-ray beam by controlling the number of electrons produced in the x-ray tube and the number of x-rays produced

MIlliamperage (higher setting)

Produces an x-ray beam with more energy, increasing the intensity of the x-ray beam

Exposure time

the interval time in which x-rays are produced

Exposure time (longer)

Produces more x-rays and a more intense x-ray beam

Distance

As x-rays travel from their point of origin, they diverge and spread out to cover a larger surface area

(intensity decreases)

Inverse Square Law

The intensity of radiation is inversely proportional to the square of the distance from the source of radiation

Inverse Square Law (doubled distance)

Beam is one quarter (1/4) as intense

Inverse Square Law (halved distance)

Beam is four times (4x) more intense

Half Value Layer

Aluminum filters are placed in the path of the beam inside the dental x-ray tubehead; thickness reduces the intensity by half

Half Value Layer (purpose)

filters are used to remove the low-energy, less penetrating, longer wavelength x-rays

Half Value Layer (increased effect)

penetrating capability of the x-ray beam while reducing the intensity

Image Characteristics (visual)

contrast, density and image detail (influence quality)