1. Introduction to x-rays

2. What do these words mean?
Isotope
Radioactivity
Geiger Muller Tube
Atomic mass
Half life
Becquerel

3. Learning objectives
State qualitatively the differential absorption of X-rays by air, fat, other soft tissues and bone and the appearance of X-rays on film after passing through these media.
• Explain techniques for improving quality of X-ray images; use of a grid, narrow beam, filtration.
Describe how the use of image intensifying screens reduces dose rates.

4. Frequency between 1017 – 1020Hz

5. Why are they useful? Fractures Breast cancer Lung cancer Dental
Cardiac units
Airports
Therapeutic

6. How do they work? X-rays can be used because of the
differential absorption (attenuation)
of the x-rays by different body tissues
(such as bone and muscle). To
obtain an image, a uniform beam
of x-rays is transmitted through
the area of interest.
Bone absorbs most of the x-rays
and as such, will appear white on
an x-ray film; soft-tissue (such as
muscle) only absorbs some of
the x-rays and appears grey

7. How are x-rays produced
X-rays are produced when a beam of energy electrons hits a metal target.
When electrons collide they lose KE some of this energy is converted to x-rays but most is converted to heat

8. X ray beam
copper anode
filament
heavy metal target
electron beam
E.H.T
vacuum

9. X-ray attenuation Medium Attenuation Appearance on film Air Negligible
Black
Fat
Small
Dark grey
Other soft tissues
Grey
Bone
High
White

10. Improving image quality
The radiographer aims to produce:
Sharp images by increasing resolution and reducing blur
Good contrast by distinguishing clearly between different body materials.
They can do this by use of a grid, narrow beam, filtration.

11. Use of a grid
A grid of lead strips reduces the blurring of images caused by scattered radiation. If two crossed grids are used at right angles to each other, almost completely eliminate unwanted scatter. To prevent the grid lines appearing on the image the grid is slowly moved across the film during exposure.

13. Narrow beam
The cross section of the x-ray beam can be controlled by the diaphragm, this is usually a pair of lead sheets at right angles to each other. Another type of beam definer is the cone. A narrow bean is preferred as random scatter increases with beam size and blurs the image

15. Filtration
Filters reduce unwanted low-energy scatter. This increases the sharpness of the image and the contrast

16. Intensifying screens
About 97% of the x-rays falling on a photographic film pass straight through without any interaction. The film alone is not a very sensitive method for detecting x-rays.

17. X-rays from patient
Cassette front (plastic)
Front intensifying screen
Double sided film
~ 12mm
Rear intensifying screen
Felt padding
Cassette back metal

18. X-rays from the patient
X-ray absorbed in the fluorescent screen
Visible light
Front fluorescent screen
Double sided film
Rear fluorescent screen
Far fewer a-rays pass straight through
Direct film blackening by x-rays
Indirect film blackening by light

19. Modern screens can intensify the image by up to 250 times
Modern screens can intensify the image by up to 250 times. The increased image intensity then gives shorter exposure times and reduced radiation doses to the patient. However some detail is lost by diffusion of fluorescent light. Typical resolution is mm, whilst direct exposure film can give better than 0.1mm