Chapter1 & 9 History of Radiology and X-ray Tube

Timeline of Radiology 1895- Roentgen’s discoveries X-ray or Roentgen rays. 1896-Thomas Edison developed the first fluoroscope 1896- first reported case of biological damage 1921 Potter-Bucky grid was introduced

Timeline 1942 first AEC was demonstrated 1942 first automatic processor developed 1986-1974 calcium tungstate screen cassettes 1970 Intensifying screens 1979 First digital

Timeline 1982 PACS Picture Archiving & Communications Systems ( storage & access of digital images) 1982 Teleradiolgy 1980s CR Computed Radiography (cassette converting images to electronic signal and stored in a computer (filmless)

Timeline 1996 DR direct digital image is directly captured by electronic elements with no intermediate step ( cassettesless)

Important facts Natural Radiation ¾ of all radiation we receive comes from nature rather than technology Minerals in ground ( Terrestrial) Cosmic Internal Radon

Manmade Radiation/Other Medical x-rays Nuclear medicine Consumer products Fallout Occupational

ALARA As Low As Reasonably Achievable X-ray profession is a safe profession

Background of Radiology Discovery of x-ray- November 8, 1895 by Wilhelm Conrad Roentgen in Germany

First x-ray Roentgen’s wife's hand

X-ray Tubes Crooke’s Tube Jackson Focus Tube Coolidge Hot Cathode

Modern x-ray tube

Modern x-ray tube Cathode- negative electrode, source of electrons Consists of the following: Highly evacuated glass tube Two sealed electrodes, Cathode and Anode Cathode- negative electrode, source of electrons Anode - positive electrode, source of radiation (x-rays)

Cathode negatively charged Contains a spiral, incandescent filament of tungsten wire Filament is heated by an electrical current of low amperage from a transformer Temperature of the filament, controlled by the amount of current passing through it, controls the number of electrons emitted

Cathode Filament Source of electrons Coiled tungsten wire Focusing cup Filament current Thermionic emission Coiled tungsten wire Large and small Focusing cup Space charge effect

Thermionic Electron Emission Another reason for the high melting point of tungsten is that the filament gets so hot it actually glows. This glowing is called incandescence. And the process is known as thermionic emission. When the filaments gets that hot it the electrons are “boiled off” or freed from the atoms.

Current Higher the temperature of the filament, the more electrons emitted Direct relationship Stream of electrons from cathode to anode is known as the tube current Current is measured in milliamperes (mA) Stream of electrons are taken from cathode to anode by a transformer (kVp) The speed with which the electrons cross the gap between the cathode and the anode.

Anode Two types Stationary- could be melted from the intense bombardment of electrons. Rotating- composed of metal with a good heat conducting characteristics (molybdenum) Disc shaped anode is coated with an alloy made of tungsten and rhenium

Anode Rotating anode Target Requires a stator and rotor to rotate Tungsten metal High melting point Efficient x-ray production Target Decelerates and stops electrons Energy converted to heat and x-rays Bremsstrahlung and characteristic interactions

Producing X-rays Voltage kicks in, takes electrons across the tube Thermionic Emission is a boiling off effect, electrons move by heat raising the temperature and the electrons boil off the filament Voltage is then responsible for taking the electrons across the tube to the anode (kVp)

Producing X-rays Anode is made of tungsten and rhenium because they have high melting points Anode needs to slow down or stop the electrons Once electrons reach the anode they become photons Each photon accounts for one x-ray

Review Who invented x-rays? What year were x-rays invented? What was the name of the first tube used when x-rays were invented? What was the problem with the first x-ray tube? What was the problem with the second x-ray tube?

What are x-rays? X-ray production is the striking of matter by high speed electrons. X-rays are generated in x-ray tube form of electromagnetic radiation Form of invisible radiant energy Have short wavelengths; gives x-rays ability to penetrate materials that would normally reflect or absorb light

Behaviors of x-rays Two behaviors: Waves and Particles Have shorter wavelengths than regular light Consist of small bundles of energy called photons Wavelength vs. kVp as kVp is increased, the wavelength of x-rays decreases; indirect relationship

X-rays as Energy A form of electromagnetic radiation Behave both like waves and like particles Move in waves that have wavelength and frequency Wavelength and frequency are inversely related X-rays also behave like particles and move as photons

Properties of x-rays Can penetrate materials that normally absorb or reflect light due to short wavelengths Cause certain objects to fluoresce- ability to emit natural light. Ability to penetrate solid and opaque materials to produce an image X-rays are invisible

Properties of x-rays Can produce biological changes that can stimulate or retard growth X-rays travel in straight lines Travel at the speed of light ( 186,000 miles per second) Ionize gases by removing electrons from atoms to form ions ( negatively charged atoms)

Features of X-ray Tube All x-ray tubes are a vacuums, free of air, air impedes the flow of electrons X-rays are produced when energy is changed from one ion to another Cathode is negatively charged source of electrons Anode positively charged source of electrons

Features of X-ray Tube Anode spins 3400 & 10,000 revolutions per minute Spinning the anode, prevents the same spot on the anode from being hit by the stream of electrons Exposure switch- two functions: rotor and exposure Rotor- activates the anode to begin spinning

Features of X-ray Tube Rotor also activates the electrons on the cathode to begin to group and form on the tungsten filament Exposure switch- releases the electrons to be propelled from the cathode to the target of the anode and x-rays are produced

mAs and kVp mAs (milliampere quantity) controls the amount of radiation that will be produced. mAs supplies the current to the cathode kVp (kilovoltage peak)(quality) is the voltage, penetrating ability, power, strength of the electrons traveling across the cathode to the anode.

X-ray Production The production of x-rays requires a rapidly moving stream of electrons that are suddenly decelerated or stopped. The negative electrode (cathode) is heated, and electrons are emitted (thermionic emission). The electrons are attracted to the anode, move rapidly towards the positive electrode, and are stopped or decelerated.