RTE 1000 X-Ray production

Exposure

produced by a radiographer using two switches(deadman) located on the control panel of the x-ray unit (sometimes there is a single switch that has two levels of operation vs a separate button for each operation)

deadman switches

require pressure to be applied during the entire x-ray exposure process, otherwise the exposure stops immediately upon release

The two switches

The rotor (or prep) button • The exposure (or x-ray) button

rotor (or prep) button

Causes an electrical current to be induced across the filament in the cathode (like turning on a light

current

the rate at which electrons flow past a point in a complete electrical circuit; the flow of negatively charged electrons that go from a negative to positive area

Filament current

~ 3 to 5 amps (A operates at ~ 10 V

amount of current flowing through the filament depends on

the mA set at the control panel

heating of the filament causes

thermionic emission

thermionic emission

– the boiling off (emission) of electrons from the filament

When the filament produces enough heat

the outer-shell electrons of the filament atoms are boiled off, or emitted, from the filament

space charge

The electrons that are emitted from the filament during thermionic emission form a cloud around the filament(This cloud is an actual negative charge from these electrons that exists in the space around the filament)

space charge effect

the tendency of the space charge to prevent more electrons from being boiled off the filament surface (this is based on the mA technique that was set)

Due to its negative charge, the focusing cup forces the electrons

in the space charge to remain together

In addition to the boiling off electrons, pushing the rotor button

activates the stator (on the anode side of the tube

stator then starts to turn the anode (via the rotor) which

accelerates it to top speed in preparation for x-ray production

kVp selected is applied across the tube from cathode to anode, which creates

potential difference

cathode becomes highly negatively charged, strongly repelling the

negatively charged electrons

anode becomes highly positively charged, thus creating

a strong attraction from the negatively charged electrons

Electrons travels within tube at half speed of light in tube

speed of light out of tube

Tube current refers to

the flow of electrons from cathode to anode and is measured in units called milliamperes (mA) (aka electron/electric current)

As electrons strike the anode target, their kinetic energy (energy of motion) is converted to either

electromagnetic energy (x-rays) or thermal energy (heat)

99% of the electron kinetic energy is converted to heat; less than 1% is

converted to x-rays

The primary exposure factors are

kVp • mA • Exposure time

Kilovoltage Peak (kVp) determines

the speed at which the electrons in the tube current move

Selecting a higher voltage results in greater repulsion of

electrons from the cathode and greater attraction of electrons toward the anode

The speed at which the electrons in the tube current move determines

the quality or energy of the x-rays that are produced

In addition to kVp affecting the quality of x-ray photons produced, it affects the

quantity or number of x-ray photons produced

Increased kVp results in more x-rays being produced because it increases the

efficiency of x-ray production

Tube current is the number of

electrons flowing per unit time between the cathode and the anode

Exposure time determines

the length of time over which the x-ray tube produces x-rays(length of time the tube current is allowed to flow from cathode to anode)(longer the exposure time, the greater the quantity of electrons that flow from the cathode to the anode and the greater the quantity of x-rays produced)

mAs is expressed as

mA x s = mAs

Tungsten

used cause high melting point

two main sources of ionizing radiation(going out in sun is electromagnetic radiation)

Natural background environmental radiation/Man-made radiation

Natural background environmental radiation

Consists of: • cosmic rays , terrestrial radiation, internally deposited radionuclides, and radon

Man-made radiation

Diagnostic x-rays constitute the largest man-made source of ionizing radiation • Natural background radiation results in an annual dose of approximately 3.1 mSv; a U.S. citizen is exposed to an average radiation dose of of 6.2

Radon

the largest source of natural environmental radiation; it is a radioactive gas that is produced by the natural radioactive decay of uranium, which is present in trace quantities in the Earth; all earth-based materials, such as concrete, bricks, and gypsum wallboard contain radon. Radon emits alpha particles, which are not penetrating, and contribute a radiation dose only to the lungs “Radioactive decay” (emission)

Alpha radiation

has a very short-energy range, thus is nearly harmless because the radiation energy is deposited in the superficial layers of the skin only

Internally deposited radionuclides are

natural metabolites, specifically potassium-40; they have always been with us and contribute an equal dose to each of us

Terrestrial radiation results from

deposits of uranium, thorium, and other radionuclides (excess nuclear energy that is unstable) in the Earth

Cosmic rays are

particulate (particles) and electromagnetic radiation emitted by the Sun and star

Sources of ionizing radiation

natural background environmental radiation and man-made radiation.

Natural background environmental radiation

Consists of cosmic rays, terrestrial radiation, internally deposited radionuclides, and radon.

Man-made radiation

Diagnostic x-rays constitute the largest man-made source of ionizing radiation.

Natural background radiation annual dose

Approximately 3.1 mSv.

Average radiation dose for a U.S. citizen

Approximately 6.2 mSv.

Cosmic rays

Particulate and electromagnetic radiation emitted by the Sun and stars.

Terrestrial radiation

Results from deposits of uranium, thorium, and other radionuclides in the Earth.

Internally deposited radionuclides

Natural metabolites, specifically potassium-40, that contribute an equal dose to each of us.

Radon

The largest source of natural environmental radiation; a radioactive gas produced by the natural radioactive decay of uranium.

Where is radon found?

All earth-based materials, such as concrete, bricks, and gypsum wallboard, contain radon.

What type of radiation does radon emit?

Alpha particles.

Effect of radon alpha particles

They are not penetrating and contribute a radiation dose only to the lungs.

Alpha radiation

Has a very short energy range and deposits radiation energy in the superficial layers of the skin.

Most significant source of human-made radiation

Diagnostic and interventional medical radiation.

U.S. medical radiation dose in the 1980s

Approximately 0.53 mSv annually.

U.S. medical radiation dose in 2006

Approximately 3.0 mSv annually.

Reason for increased medical radiation dose in 2006

Increased use of computed tomography (CT).

NCRP update in 2019

Updated diagnostic and interventional medical radiation exposure in the U.S. from 2006 to 2016.

U.S. medical radiation dose from 2006 to 2016

Decreased approximately 15–20% to about 2.3 mSv annually.

Reasons for the decrease in medical radiation dose

Technical advances in imaging equipment and awareness campaigns such as Image Gently and Image Wisely.

Reducing unnecessary radiation exposure

Radiologic technologists have primary responsibility because they usually control x-ray imaging systems.

Currently accepted approximate annual medical radiation dose

3.0 mSv.

Other sources of man-made radiation

Nuclear power generation, research applications, industrial sources, and consumer items.

Consumer items that contribute radiation

Watch dials, exit signs, smoke detectors, and airport surveillance systems.

Radiation dose from consumer items

Approximately 0.1 mSv annually.

Nuclear power stations and industrial applications

Contribute very little to our radiation dose.

Two categories of ionizing radiation

Particulate radiation and electromagnetic radiation.

Five physical characteristics of ionizing radiation

Mass, energy, velocity, charge, and origin.

Particulate radiation

Subatomic particles capable of ionization.

Examples of particulate radiation

Electrons, protons, and rare nuclear fragments.

Requirement for particulate radiation to ionize

Must be in motion and possess sufficient kinetic energy.

Alpha particle

Has 4 atomic mass units, 2 protons, 2 neutrons, and 2 units of positive charge.

Origin of alpha particles

The nucleus of heavy elements.

Alpha particle compared to an electron

It is large and exerts a great electrostatic force.

Alpha particle energy

Travels fast but loses energy quickly and transfers kinetic energy easily because of its mass and charge.

Beta particle

Has an atomic mass number of zero and one unit of negative or positive charge.

Origin of beta particles

The nuclei of radioactive atoms.

Difference between electrons and negative beta particles

Negative beta particles originate in radioactive nuclei; electrons exist in shells outside atomic nuclei.

Electromagnetic radiation

Includes x-rays and gamma rays.

Photons

Electromagnetic rays with no mass or charge that travel at the speed of light.

Speed of electromagnetic radiation

Exists at the speed of light or not at all.

Range of electromagnetic radiation

Has unlimited range in matter.

X-rays

Produced outside the nucleus in the electron shells of atoms.

Gamma rays

Emitted from the nucleus of a radioisotope and usually associated with alpha or beta emission.

Alpha particles and ionization

Highly ionizing radiation with a very short range in matter.

Beta particles and ionization

Do not ionize as easily and have a longer range.

X-rays and ionization have

a low ionization rate and a very long range.

Most important radiation in nuclear medicine

Beta and gamma radiation.