RAD: Principles of Physics 3

Matter

anything that occupies space and has mass

Atoms

fundamental building blocks

Mass

quantity of matter contained in any physical object as described by its energy equivalence

Weight

term used to describe the mass of an object

What is mass measured in?

kilograms (kg)

Potential energy

ability to do work by virtue of position

Energy

ability to do work

Kinetic energy

energy of motion

Chemical energy

energy released by a chemical reaction

Electrical energy

the work that can be done when an electron moves through an electrical potential difference (voltage)

Thermal energy (heat)

energy of motion as the molecular level

Nuclear energy

energy that is contained within the nucleus of an atom

Electromagnetic energy

energy that is a combination of electric and magnetic fields

Does electromagnetic energy include sound or diagnostic ultrasound?

No

Radiation

energy emitted and transferred through space

Mass-energy equivalence

E = mc²

Irradiated

term used to describe matter that intercepts radiation and absorbs part of all of it

Ionizing radiation

special type of radiation that includes x-rays

Ionization

when an x-ray passes close to an orbital electron of an atom and transfers sufficient energy to the electron to remove it from the atom

Ion pair

the orbital electron and the atom from which it was separated

Electromagnetic radiation with sufficient energy to ionize

X-rays, gamma rays, and ultraviolet light

Are alpha and beta particles rays?

No

Natural environmental radiation

results in ~3 millisieverts (mSv) annually

Man-made radiation

results in 3.1 mSv annually

Natural environment radiation components

cosmic rays, terrestrial radiation, internally deposited radionuclides, and radon

Cosimic rays

increases with altitude and latitude

Terrestrial radiation

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

Radon

radioactive gas that is produced by the natural radioactive decay of uranium, which is present in trace quantities in the Earth

What does radon emit?

alpha particles, which are not penetrating, and therefore contributes a radiation dose only to the lung

Natural environmental radiation result

~300 to 1000 microsievert (μSv)/h at waist level in the United States

Diagnostic x-rays

constitute the largest man-made source of ionizing radiation (3.0 mSv/yr)

Accepted approximate annual dose resulting from medical applications of ionizing radiation

3.0 mSv

What percentage of our annual average radiation dose is attributable to medical imaging?

48%

November 8, 1895

Discovery of X-rays by Wilhelm Röntgen through the use of cathode rays and Crookes tube

General types of x-ray examination

radiography, fluoroscopy, and computed tomography (CT)

What are x-ray voltages measured in?

Kilovolt peak (kVp)

What are x-ray currents measured in?

milliampere (mA)

ampere (A)

measure of electric current

Intensifying screen

used to reduce exposure time

Double-emulsion file

two glass x-ray plates with the emulsion surfaces together, exposure time was halved, and the image was considerably enhanced

Cellulose nitrate

substitute for the glass plate

Fluoroscope

developed in 1898 by the American inventor Thomas A. Edison

1904

Clarence Dally, assistant and friend of Thomas A. Edison, who experienced a severe x-ray burn that eventually required amputation of both arms

1910

acute injuries began to be controlled as the biologic effects of x-rays were scientifically investigated and reported

Diaphragm

inserting a leather or aluminum filter that improved the diagnostic quality of radiographs

1907

The Snook interrupterless transformer is introduced

1913

The Coolidge hot-filament x-ray tube is developed

Gonadal shield

should be used with all persons of childbearing age or younger when the gonads are in or near the useful x-ray beam and when use of such shielding will not interfere with the diagnostic value of the examination

Filtration

usually aluminum or copper, are inserted into the x-ray tube housing so that low-energy x-rays are absorbed before they reach the patient

Collimation

restricts the useful x-ray beam to that part of the body to be imaged and thereby spares adjacent tissue from unnecessary radiation exposure

Air kerma

the unit of radiation exposure

What is air kerma measured in?

joules per kilogram (J/kg)

gray

unit of radiation absorbed dose

Sievert (Sv)

unit of occupational radiation exposure and effective dose

Becquerel (Bq)

unit of radioactivity