AGR 324 Quiz 1 Study Guide

Who discovered the x-ray?

Roentgen in 1895

What does the “x” stand for in x-ray?

unknown

What are the 12 unique properties of x-rays?

1. Invisible

2. electrically neutral

3. have no mass

4. travel at the speed of light in a vacuum

5. cannot be focused by a lens

6. form a polyenergetic beam

7. can be produced in a range of energies

8. travel in straight lines

9. cause fluorescence in certain substances

10. can cause chemical change to occur in radiographic and photographic film

11. can be absorbed or scattered by tissues in the body; can produce scattered and secondary radiation

12. can cause chemical and biological damage to living tissue

Photons can have what?

Many different energy levels

Element

Smallest particle of a substance

Atom

The smallest part of an element

Positively charged

protons

no charge

neutrons

negatively charged

electrons

Types of energy

mechanical, chemical, thermal, nuclear, electromagnetic, electrical

The two types of energy used to produce x-rays

electrical energy and electromagnetism

A continuous range of all types of electromagnetic radiation, organized by wavelength and frequency

Electromagnetic spectrum

X-rays have a what frequency and what wavelength than visible light?

higher, shorter

The number of waves passing a given point per unit of time

Frequency

The total distance from crest to crest or trough to trough

Wavelength

Photons

Smallest quantity of electromagnetic radiation

they have no mass

they have no electrical charge

You have to efficiently dissipate heat because what % of what you produce is heat and how much is actually x-rays?

99, 1

speed that the electrons in the current transfer energy along the circuit

Voltage

Short wave-length and high frequency = high penetrating

High voltage

Amperage, measures electric current that activates the tube

current

what slows the current as it travels through a wire

Resistance

larger diameter

lower resistance

a timer controls length of time x-rays are being produced

time

kV

kilovoltage

mA

milliamperes

seconds

time

The number of electrons used to produce x-ray photons

Current: mA

controls the penetration of x-ray beam; regulating photon frequency and energy

Voltage: kVp

time over which x-rays are produced. Listed as milliseconds: 1/60 or .16

Time (sec)

mAs

milliamperes per second

wire that provides another way for the electricity to travel if the circuit is broken

ground

mechanically interrupt flow of electricity; safety mechanism

fuses

power supply to x-ray machine should not go to anything else

amperage

examples of direct current

flashlight

batteries in a specific orientation

power source must be close to the end user

one positive and one negative pulse

120 cycles per second

transmits a low current with high voltage

alternating current

Within the x-ray circuit provides the current and voltage determined by setting kV on the control panel

Autotransformer

Increases the current and voltage determined by setting mA on the control panel

High-voltage transformer

Reduces the current and voltage to the correct amount to heat the cathode filament and produce the electron cloud

Filament Transformer

Keep the electricity flowing in one direction like a direct current

Rectifiers

What are the parts of the x-ray machine

1. high-voltage transformer

2. x-ray generator (control panel)

3. X-ray tube

Connects to hospital power lines

probably located under the x-ray table

high-voltage transformer

gets power from the transformer and sends it to the x-ray tube via rectifiers

may be mounted on the x-ray tube stand or be a separate unit

x-ray generator (control panel)

where x-rays are produced

x-ray tube

large focus

large filament

details, small focus (detailed extremity or pocket pet)

small filament

electron cloud

space charge

thin, coiled tungsten wire inside a focusing cup

cathode

the BLANK has a beveled edge and carries a slightly negative charge to aim the electrons towards the anode

focusing cup

The target where the photons of energy, traveling at tremendous speed, are directed

tungsten plate

very small area upon which photons are focused

focal spot

Mounted on a stem, the entire thing moves when the circuit is closed

fixed angle of 11-15 degrees

keeps heat from building up on a single focal spot

rotating anode

portable unit, dental units

the heat has to dissipate between exposures

stationary anode

why do we use a copper shield around the anode?

to help dissipate heat

the intensity of radiation is greater on the BLANK side of the beam

cathode

the image will lose resolution as the focal spot gets larger

focal spot bloom

may occur if photons bounce off the anode and then are attracted back to an area outside the focal point

off-focus radiation

ideal distance from patient for portable units?

30 inches

two steps for the exposure switch

1. activates the rotating anode, you should be able to hear it

2. activates the exposure; some units have a beep or other signal

radiation doses should be kept

as low as reasonably achievable (ALARA)

Stochastic (somatic)

occurs by chance, no minimum dose

late term effects that may occur years later after exposure

cumulative dose over years of exposures

usually cancer; cataracts; thyroid issues

Deterministic (nonstochastic)

appears immediately

very rare in diagnostic imaging

sunburn

accidental exposure can cause

hematopoietic effects; blood cell disturbances

gastrointestinal effects

central nervous system affects

what appears white on x-rays

bones

what appears less dense, radiolucent

fat and air

Measures the light intensity emitted by a crystal in the detector, when the crystal is heated. The intensity of light is dependent on radiation exposure

Thermoluminescent (TLD)

Contains sensitive elements that absorb and store some of the energy. The dosimeter is read by stimulating the elements and releasing energy as light. The amount of light is used to determine exposure

Optically stimulated (OSL)

persons under what age are not allowed to work in radiographic areas

18 years old

amount of radiation absorbed per unit mass of matter

radiation absorbed dose (RAD)

unit measured by dosimeters worn be vet clinic staff

Radiation equivalent man/mammal (REM) or sievert (Sv)

dose measured by dosimeters worn by service personnel calibrating the x-ray machine

Roentgen or air kerma (Gya)

3 cardinal rules for reducing x-ray exposure

1. decrease time of exposure

2. increase the distance between source and subject

3. shielding between the operator and the source

what should never be placed in the primary beam

gloved hands

immobilization equipment

troughs

sandbags

foam wedges

soft velcro straps

patient comfort and safety is key