Section 6

Question 1

Describe the flat-panel TFT digital detector.

Answer 1

Detector area collects electric charges

Question 2

What does TFT stand for?

Answer 2

Thin Film Transistor

Question 3

Distinguish between indirect and direct detectors.

Answer 3

Indirect = photodetector (a-Si) and scintillator to convert x-rays into light
Direct = photoconductor (a-Se)

Question 4

Understand the important design features of:
fill factor,
dynamic range,
spatial resolution.

Answer 4

Fill factor = how photon sensitive the detector is
Dynamic range = range of signal brightness that can give a good image
Spatial resolutin - line pairs

Question 5

Explain the concepts of contrast, detail, and resolution.

Answer 5

Contrast = differences in grey shades (brightness)
Detail = spatial resolution - how easily we can resolve pixels

Question 6

Understand geometric properties of the beam and configuration.

Answer 6

OID, FDD, FSS and penumbra are all properties that we can influence with the beam

Question 7

Describe methods of reducing x-ray scatter.

Answer 7

• Decrease kVp
• Reduce Field size
  -Air gap technique
  -Reduce thickness of tissue
  -Grids

Question 8

Active Matrix Readout consists of

Answer 8

1. All switches off during x-ray exposure
2. 1st row switched on, stored charge amplified & digitised
3. Values stored in memory
4. Row switched off
5. Repeat for each row

Question 9

Each pixel contains

Answer 9

a TFT/charge switch, a storage (capacitor) and a sensing area (charge)

Question 10

Fill Factor is the percentage of

Answer 10

pixel area which is sensitive to signal

Question 11

Low fill factor means

Answer 11

more detector element (white) and loss of x-rays

Question 12

High fill factor means

Answer 12

more light sensitive area, and not a lot of xrays are lost