Radiography Detector Types

Question 1

Two types of Radiography Detectors

Answer 1

Analog and Digital

Question 1

What is Computed Radiography and what is its advantage?

Answer 1

Partially digital radiography detector
Uses special phospor that converts x ray to excited electron states
1. Stores x rays in the phosphor.
2. Electrons approach the conduction band.
3. Electrons are trapped in a high energy state.
4. Red laser excites the electrons which when they drop will result in blue light emission
Consists of laser diode, rotating mirror, imaging plate
1. Good for over/under exposure
2. Greater dynamic range

Question 2

What is CCD and CMOS and what are there advantages?

Answer 2

Silicon devices:
1. Accumulate charge deposited by light
2.Charge Coupled Device:
Great resolution
2.5x2.5 cm
2048 pixels
small and harder to read
Expensive
CMOS:
Noisier, expensive
When charge moves from one spot to the other it provides voltage

Question 3

What is a Thin Film Transistor(TFT)?

Answer 3

Thin film transistors
Hybrid of CCD and Charge coupled devices
Cheaper
Consists of an amplifier
Uses a scintillator for indirect method
Direct
-No scintillator
-Selenium semiconductor
-ion pairs
Dependent on charge, but density does not effect the resolution
lower absortion than scintillator

Question 4

What is a Screen Film Cassette?

Answer 4

Analog, radiography detector.
Conists of a casette, screens an id window, film
The film cannot be reuused
Chemically developing it takes a lot of time

Question 5

What does a screen casette film do?

Answer 5

1.A screen cassette film absorbs incident x rays
2. Emits visible light
3. Thick screen results in more photon absorption but poorer resolution(more light spread)
To make up for the lost resolution with a thick screen we use a two layered thin screen

Question 6

What is an anti scatter grid?

Answer 6

Absorbs scattered radiaton
Aligned with the focal spot
Works only at a fixed distance between focal spot and detector