How to process radiographs

Question 1

Describe the two forms of digital radiography

Answer 1

This is where the digital sensor is exposed to radiation

1. Direct = immediate electronic image produced with solid state sensor
2. Indirect = digital sensor is scanned by laser with a photostimulable phosphur plate

Question 2

What is conventional radiography

Answer 2

Where the photographic film is exposed to radiation and requires chemical processing

Question 3

What is used by a solid state sensor (in direct digital radiography)

Answer 3

1. Thin film transistors

2. Charged-coupled devices

Question 4

Outline the stages in how digital radiographs are processed

Answer 4

1. x-ray photons are converted to light
2. light interacts with silicon due to photoelectric effect
3. there is a charged packet in each pixel
4. a latent image is formed
5. computer converts analogue to digital
6. grey scale value of image is proportional to x-ray energy absorbed by the tissue

Question 5

What do darker pixels represent in digital radiography

Answer 5

Less attenuation to beam thus showing soft tissue

Dense materials therefore show up as white

Question 6

What is the purpose of the phosphur plate (in indirect digital radiography)

Answer 6

• absorbs and stores energy so it isn’t attenuated by patient
• it is then scanned by the laser which releases this energy as light photons
• this is converted into electrical signal by photomultiplier tube in the CR reader
• input into the computer via analogue-digital converter

Question 7

In conventional radiography, describe the states of silver halide crystals

Answer 7

1. Un-exposed = remain unsensitised

2. Exposed = x-ray sensitised crystals

Question 8

Describe the fate of sensitised silver halide crystals

Answer 8

• green colour changes to black metalic silver
• black metalic silver is fixed to plastic base by developer
• fixer is added, washed off plastic base and then dried

Question 9

Describe the fate of unsensitised silver halide crystals

Answer 9

• unexposed so they aren’t affected by developer
• developer removes silver halides into solution leaving the plastic base transparent
• adding fixer washes off the plastic base and then dry it

Question 10

What 3 errors occur in film processing

Answer 10

1. Light fogging
2. Fingernail marks
3. Too high/low temperature