Detectors

Question 1

How does dynamic range vary for Film versus Digital?

Answer 1

Film: Smaller dynamic range (Curvilinear)
Digital: Larger dynamic range (Linear)

Question 2

How do pixel density and pixel pitch effect spatial resolution?

Answer 2

• Higher pixel density= better resolution

- Lower pixel pitch= better resolution

Question 3

What has better spatial resolution? Plain film or Digital?

Answer 3

Plain Film because there are No pixels to limit resolution

Question 4

What is the AEC?

Answer 4

• Ionization chamber placed between patient and receptor
• Adjust the duration of the exposure depending on thickness/density
• Does not effect KVP

Question 5

What is Bit Depth?

Answer 5

• Number of shades of gray that you can see in a pixel
• 2^X
• More Pixel depth =more contrast resolution

Question 6

What are the types of Digital Detectors?

Answer 6

• Storage Phosphors (CR) (indirect)

- Flat panel detector(DR) (direct and indirect)

Question 7

How does computer radiography/Storage phosphors work?

Answer 7

1. Storage phosphor gets hit with X rays and stores latent image
2. Laser is used to release trapped electrons as light
3. Light is directed towards a Photodetector
4. Photodetector converts light to Electrical signal that gets digitized.

Question 8

How do you reset the plate in Computed Radiography?

Answer 8

Expose it to bright white light

Question 9

Describe the indirect digital radiography pathway

Answer 9

1. X ray hits scintillator (CsI) and creates light
2. Light hits the photodiode
3. Photodiode converts light to electrical signal which gets transmitted to the TFT

Question 10

What is lateral dispersion of light?

Answer 10

• Occurs in thicker crystals, light gets dispersed laterally (indirect method only)
• Does not occur with direct method

Question 11

Describe the direct digital radiography pathway

Answer 11

1. X ray hits the photoconductor (Amorphous Selenium)
2. X rays are absorbed and electrons are released
3. Electrons travel towards the selenium surface and neutralize applied charge
4. Electric charge is transmitted to TFT and converted to digital signal

Question 12

What is fill factor?

Answer 12

Area of the detector that is sensitive to X rays (bigger means more efficient)

Question 13

How does DQE compare in DR versus CR?

Answer 13

Better in DR (better fill factor= more efficient)