Basic Principles of Radiation

By the end of the presentation, the individual will be able to:

• Define ionizing radiation

• Correlate wavelength, frequency, and energy

• Differentiate mA and kVp

• Describe how x-rays are generated

• Identify parts of an x-ray tube and Image Intensifier

• Describe Line Focus Principle

• Discuss three reactions of photons when entering a material (patient)

Discovery of X-Ray

First Medical RadiographWilhelm Roentgen

Radiation?

• Electromagnetic Energy

Wavelength

• The shorter the wavelength, the higher the frequency, and therefore the higher the energy

Ionizing Radiation

• When electromagnetic radiation, as it passes through matter, produces ions it is called ionizing radiation

Ionizing and Non-Ionizing Radiation

The Electromagnetic Spectrum

How are x-rays generated?

• Acceleration Collision

X-Ray Tube• Produced, Accelerated, Stopped

Protective housing

• Steel lined with lead

• Window

• Function

• Contain

• Inhibit

• Isolation

• Cooling

X-Ray Imaging

• X-ray tube

• Generator

• High voltage circuit

X-RAY Generator• Power source

• Low voltage High Voltage

• Rectified

X-ray Tube

Negative(-)

Positive(+)

X-ray production

• Focal spot

• Collision + X-ray + Heat

• Smaller spot = better picture, more heat

Line Focus Principle

• Angle anode surface

• X ray beam

X-Ray Beam Production

• Anode + electrons = X ray

• Photons of different energies = primary radiation

Remnant Beam

Primary beam

Remnant

beam

Photons

• Penetrate

• Absorb

• Scatter

Differential absorption

• Density and Thickness

• Picture contrast

• Produce the gray scale in the radiograph

IMAGING EQUIPMENT

• X-Ray tube

• Image intensifier

• C-arm

• Cine camera

• TV monitor

Image Intensifier

Image Intensifier

• X ray Visible light

• Input phosphor –Cesium Iodide

• Converts x-rays to visible light

• Photocathode

• Attached to input phosphor

• Receives light and releases as electrons that travel through the glass envelope

• This is photoemission

Image Intensifier

• Electrostatic lenses

• Positively charged

• Help accelerate the electrons toward the anode

• Output phosphor

• Brightness gain occurs

• Increase in brightness from the input to output phosphor

• Fluorescent image is created much brighter than input phosphor

Magnification of Image

• Input screens of image intensifiers have various diameters

• During magnification the kVp and mAs are automatically increased

mAs = Quantity

• X-ray quantity is directly proportional to the mAs.

mAs - milli-Ampere-seconds

• mAs directly effects

• Radiographic density (blackness of film)

• Patient dose / patient exposure

• mAs does not effect

• Quality of the x-ray beam (penetrating ability)

• Radiographic contrast

• Geometric properties of the beam

kVp - Quality

• The penetrating power of an x-ray beam.

• Higher energy beams can penetrate farther than low energy beams

kV - Kilovoltage

• Higher kV settings provide more electron to x-ray conversion

• Higher kV settings produce shorter wavelength X-rays providing more penetrating ability

• kVp= low contrast (more gray tones)

• kVp= high contrast (more black and white tones)

Radiographic Contrast

• The differences in densities between two adjacent parts of a radiograph

• High contrast – black and white

• Low contrast – mostly grays

• The ideal image contains sufficient information to render a diagnosis, and sufficient contrast to demonstrate structure

Radiographic Contrast

Low contrastHigh contrast

Improvement of Radiographic Quality

• Patient Positioning

• Area of interest as close to film as possible

• Patient instructed to restrain from movement

• Understand anatomy

• Imaging devices

• Collimation, soft shutters, grids

• Selection of technique

Reduction of Scatter Radiation

• Use collimation

• Grids

• Aluminum filters

RADIATION

Hardening of the X-ray beam

• Aluminum filters remove low energy X-rays from beam

• Reduces scatter and patient/staff exposure

By the end of the presentation, the individual will be able to:

• Define ionizing radiation

• Correlate wavelength, frequency, and energy

• Differentiate mA and kVp

• Describe how x-rays are generated

• Identify parts of an x-ray tube and Image Intensifier

• Describe Line Focus Principle

• Discuss three reactions of photons when entering a material (patient)

Bye Bye