Introduction to Radiography

1
Introduction to Radiography

• Patient Care
• Chapter 1
• Mrs. Nelms

2
History

• Discovery by Roentgen
• 1st documented medical application
• Snook and his contribution to electricity
• Pupin
• Thomas Edison and Dally
• Eastman Kodak and film
• Training of x-ray technicians

3
Overview of Radiographic Procedure

• Cassette, alignment of the cassette tray, control
  booth/panel, what happens during the exposure

4
X-ray Production

• 4 requirements for the production of x-ray
• Vacuum
• Source of electrons
• Target for the electrons
• High potential difference or voltage between the
  electron source and the target

5
Vacuum

• The x-ray tube itself provides the vacuum
• It is referred to as a glass envelope
• Made of pyrex glass to withstand heat and is
  fitted on both ends for electrical connections
• All of the air is removed (hence the term
  evacuated glass tube this is so that the gas
  molecules will not interfere with the process of
  x-ray production

6
Source of Electrons

• The source of electrons is the wire filament
  (made of tungsten)
• An electric current moves through this wire to
  heat it
• The heat speeds up the movement of electrons and
  moves them away from the nucleus the outer-shell
  electrons get so far away from the nucleus that
  they are flung out of orbit. This forms an
  electron cloud around the filament. These free
  electrons or space charge provide the electrons
  needed for x-ray production.

7
Target for the Electrons

• The target is at the opposite end of the filament
• It is also made of tungsten and is a smooth, hard
  surface where the electrons travel to form x-rays.

8
The Potential Difference or Voltage

• Voltage required for x-ray production is provided
  by a high-voltage transformer
• The two wires coming out of the glass envelope
  (mentioned previously) are connected so that the
  anode side is positive and the cathode end is
  negative.
• The highly positive electrical potential at the
  anode or target end attracts the highly charged
  negative electrons (they move across the tube
  forming an electron stream)
• When these electrons strike the target, the
  kinetic energy of their motion must be converted
  into a different kind of energy. 99 of it is
  converted into heat, but the rest is converted to
  x-rays.

9
Characteristics of Radiation

• X-rays are classified as electromagnetic energy
• They have both electrical and magnetic properties
• They change the field in which they pass through
  both electrically and magnetically
• This change in the field occurs in a repeating
  wave form, a pattern known as a sine wave

10
The Sine Wave

• Amplitude distance between the crest and the
  valley or height of the wave
• Wavelength distance from one crest to another
• Frequency the number of times per second the
  crest passes a given point
• All electromagnetic energy has the same velocity
  (186,000 miles per second)
• When the wavelength is short, crests are close
  together when the wavelength is long, crests are
  further apart. Close crests- high frequency far
  apart crests- low frequency.
• Photon smallest possible unit of
  electromagnetic energy
• Quanta bundles of photons (singular is quantum)
• Electromagnetic spectrum includes x-rays, gamma
  rays, visible light, microwaves and radio waves.
• Ionizing radiation radiation with a wavelength
  shorter than one nanometer. Ionizing radiation
  has sufficient energy to remove an electron from
  an atomic orbit. X-rays are ionizing because
  their wavelength is about 0.1 nanometer (a
  billionth of an inch)

11
(No Transcript)
12
X-rays and Light

• Both are part of the electromagnetic spectrum
• Both travel in straight lines
• Both have an effect on photographic emulsions
• Both have biological effects (they can change
  living organisms)
• X-rays are capable of more harmful effects of
  light because of their greater energy
• X-rays cannot be detected by the human senses we
  can visibly see light- we cannot see x-rays.
  This is an important concept when considering
  radiation safety.

13
X-ray Penetration

• X-rays can penetrate objects that are opaque to
  light
• Differential penetration depending on the object
  thickness and density will determine the
  penetrability of x-rays
• Remnant radiation radiation that is able to
  pass completely through the body and exit. This
  is the radiation that is recorded on an x-ray

14
The X-ray Beam

• Primary Beam
• Radiation Field (controlled by a collimator)
• Central Ray

15
Scatter Radiation

• When the primary beam encounters matter, a
  portion is absorbed within the matter. This
  results in the production of scatter radiation.
  It has less energy than the primary beam, but is
  extremely hard to control. It will bounce from
  the source in all directions causing unwanted
  exposure to the film and unwanted exposure to
  anyone in the room.

16
X-ray Beam Attenuation

• To review, there is the primary beam, scatter
  radiation and remnant radiation. The chart on
  page 9 will help distinguish each types
  characteristics.

17
The X-ray Tube
18
X-ray Tube Housing
19
X-ray Tube Support
20
Collimator

• The collimator allows the radiographer to vary
  the size of the radiation field and to indicate
  with a light beam the size, location and center
  of the field.

21
Radiographic Table
22
Grids and Buckys

• Bucky moving grid device below the table
• Grid situated between the table top and the film

23
Upright Cassette Holders
24
Transformer
25
Control Console

• Locate these items on the control panel of the
  classroom x-ray machine
• Off/on
• mA
• kVp
• Timer
• mAs
• Bucky
• AEC (ours does not have this)
• Meters
• Prep or rotor switch
• Exposure switch
• accessories

26
Fluroscopic Unit
27
Factors of Radiographic Exposure

• Exposure time
• Milliamperage or mA
• Kilovoltage peak or kVp
• Distance

28
Exposure Time

• How long the exposure will continue
• Measured in units of seconds, fractions of
  seconds or milliseconds (thousandths of seconds)
• Longer exposure will produce a darker film
  conversely a shorter exposure will produce a
  lighter film
• Patient dose is directly proportional to exposure
  time
• Discuss AEC

29
Milliamperage

• Measure of the current flow in the x-ray tube
• Determines the amount of electrons available to
  cross the tube, thus the rate at which x-rays are
  produced
• mA is an indication of the number of x-ray
  photons that will be produced per second
• mA setting will determine how much exposure time
  is needed to produce a given amount of exposure
• mAs mA x time (seconds)
• mA can affect the focal spot size in dual focus
  tubes

30
Kilovoltage

• Potential difference across the x-ray tube
• Changes in kV will cause changes to the film
• Typcial kV range in x-ray is between 40 and 150
  in increments of 1 or 2 kilovolts

31
Distance

• Distance between the source and the film is known
  as SID (source-image distance)
• The change in x-ray beam intensity that results
  from changes in SID is expressed as the inverse
  square law

32
Image Receptor Systems

• Cassette
• Film
• Film processing
• Filmless radiography

33
Image Quality

• Density
• Contrast
• Definition
• Distortion

34
Radiation Units

• Roentgen or C/kg
• Rad or gray
• Rem or sievert

35
Biological Effects of X-Ray

• Law of Bergonie and Tribondeau
• Short term effects
• Long term effects
• Genetic effects

36
Radiation Safety

• Personnel safety
• Monitoring devices
• Effective dose equivalent limits- ALARA
• Patient protection
• Gonadal shielding
• Pregnancy and radiation