Introduction to Radiography Patient Care Chapter 1 Mrs. Nelms

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

Overview of Radiographic Procedure Cassette, alignment of the cassette tray, control booth/panel, what happens during the exposure

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

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

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.

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.

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.

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

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)

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.

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

The X-ray Beam Primary Beam Radiation Field (controlled by a collimator) Central Ray

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.

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 type’s characteristics.

The X-ray Tube

X-ray Tube Housing

X-ray Tube Support

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.

Radiographic Table

Grids and Buckys Bucky: moving grid device below the table Grid: situated between the table top and the film

Upright Cassette Holders

Transformer

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

Fluroscopic Unit

Factors of Radiographic Exposure Exposure time Milliamperage or mA Kilovoltage peak or kVp Distance

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

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

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

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

Image Receptor Systems Cassette Film Film processing Filmless radiography

Image Quality Density Contrast Definition Distortion

Radiation Units Roentgen or C/kg Rad or gray Rem or sievert

Biological Effects of X-Ray Law of Bergonie and Tribondeau Short term effects Long term effects Genetic effects

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