DH 112: Radiography Exam 1

Type of radiation

Particulate and Electromagnetic

Particulate radiation

-Many natural source...radium

-Subatomic particles, protons, neutrons, electrons, alpha and beta particles

- Occupy space

- Have mass and weight

- Except for neutrons, they are electrically charged

- Can't reach speed of light

- Not used in dentistry

Electromagnetic radiation

- No mass or weight

- No electrical charge

- Pass through space with wavy motion straight path

- Travel speed of light

- Have different measurable energies

Wavelength

Distance between the crest of one wave to the next (oscillation)

Frequency

# of wavelength per sec

X-ray with shorter waves...

higher frequency

X-ray with longer waves...

lower frequency (lazy)

When wavelength and frequency change...

the characteristics of radiation change

X-rays are produced when...

high speed electrons are stopped or slowed down suddenly

The kinetic energy of these high-speed electrons is transferred into...

heat (99.8%) and X-rays (0.2%)

Digital imaging

Modernize film, through computer

Analog

Old, traditional film

Conditions necessary to produce x-ray

- Source of high speed electrons

- Method of stopping these high speed electrons

- X-ray tube

Source of electrons

1. Cathode (-): Located at one end of the xray tube, there is filament (a small coil of tungsten wire), and tungsten can withstand great deal of heat w/o melting

2. Boiling off electrons: Electric passed through filament wire and heats up/ boils off electrons and they clusters around the filament.

- When high volt is passed through the x-ray tube, electrons are forced across to the other end of of the tube at high speed.

- Then these high speed of electrons slowed down/ stopped when they strike the anode (target) (Bremsstrahlung/ braking radiation)

3. Anode (+): Where x-ray are produced, have "target" (where electrons strike), it made of tungsten encased in copper, which copper conducts heat away from the target

- Focal spot: area on target where electrons are focused.

Production of x-rays

1. Sources of electrons (heated filament)

2. High speed electrons (high volt)

3. Sudden stop of electrons (anode-copper)

Why is production of X-ray occurs in a vacuum (sealed lead glass envelope)?

- If molecules were present, the electrons would interact w them and change wavelengths, slowing down speed

- X-ray then exit the envelope through the window

Exposure variables

- Millamperage (mA)

- Kilovoltage (kVp)

- Exposure time

Controlling X-ray Production

- Electricity is the energy used to produce X-rays

- Electrical energy consists of a flow electrons through a conductor

- Amperage: The measurement of the # of electrons moving thru conductor

Thermionic emission

- Releasing charged particle when its heated

- As the _____ increased, more electrons are boiled off

- Control ________ =. Control amount of current

Control Amperage

- Below mA(5) and high mA(15)

- Increase in mA = increase the # of boiled off electrons = increase the # electrons striking the target = increase # of x-ray produced

Milliamp Adjustment

Controls the quantity or # of X-rays emitted

Amperage

Measurement of the # of electrons pass thru the conductor

Voltage

- Measurement of the electrical force.

- High volt = greater energy

Step down transformer

- Household volt = 110

- Volt needed to boil off electrons is 3-5 volts

________ is activated when you TURN ON the machine, only need 3-5 volts

Step up transformer

- High volt needed to moved the electrons from cathode to anode at high speed

- 110 house volt is increased to 100,000 (100kV)

- Step up is activated when you PUSH EXPOSURE BUTTON

Electrons cross the tube gap at a_______speed

high rate of speed. If this forced increased, electorns would strike the target with GREATER energy of force

Kilovoltage (kVp) controls....

- Controls the wavelength of the emitted x-ray

kVp adjustment

Controls the penetrating power of the X-ray

Exposure Time

- Length of time electrons are pushed across the tube gap from the cathode to anode

- Length of time x-ray are emitted from the target

Impulse timer

- Alternating current, which means the current travels first in 1 direction and builds up to a peak, then goes down to 0

- Each peak of this cycle is called _____ and x-ray machine have 1 ____/ peak every 1/60 of a sec

- X-ray are emitted in quick spurts not steady stream

X-ray measures the relative...

density (shades of gray) of an object

Dental radiograph is a....

recorded image on film or sensor receptor

Different absorption

- Diff tissues = differ amounts of absorption/ attenuation of x-rays

What determines the amount of absorption?

Density of tissue

Latent image (invisible) is formed....

on the photographic film as x-rays pass thru these structures/tissues and expose the film

Radiolucent

Dark area on film where x-ray PASS THRU and REACH the film

Radiopaque

White area are where few x-ray are able to reach the film b/c they're absorbed by the tissue

4 types of radiation

- Primary

- Leakage

- Secondary

- Remnant

Primary radiation

- Short wavelength

- High energy

- Usable x-ray

Leakage radiation

- Radiation passed thu shielding of x-ray tube

- Newer x-ray has less leakage

Secondary radiation (scatter)

- When x-ray strike or pass through matter, bounce back

- Long wavelength

Remnant radiation

- Primary rays have passed completely thru pt

- Continue until they absorbed by other objects (lead wall)

T or F: X-ray linger in the room after exposure

False, b/c they travel speed of light