Describe the flat-panel TFT digital detector.
Detector area collects electric charges
What does TFT stand for?
Thin Film Transistor
Distinguish between indirect and direct detectors.
Indirect = photodetector (a-Si) and scintillator to convert x-rays into light
Direct = photoconductor (a-Se)
Understand the important design features of:
fill factor,
dynamic range,
spatial resolution.
Fill factor = how photon sensitive the detector is
Dynamic range = range of signal brightness that can give a good image
Spatial resolutin - line pairs
Explain the concepts of contrast, detail, and resolution.
Contrast = differences in grey shades (brightness)
Detail = spatial resolution - how easily we can resolve pixels
Understand geometric properties of the beam and configuration.
OID, FDD, FSS and penumbra are all properties that we can influence with the beam
Describe methods of reducing x-ray scatter.
- Decrease kVp
- Reduce Field size
-Air gap technique
-Reduce thickness of tissue
-Grids
Active Matrix Readout consists of
- All switches off during x-ray exposure
- 1st row switched on, stored charge amplified & digitised
- Values stored in memory
- Row switched off
- Repeat for each row
Each pixel contains
a TFT/charge switch, a storage (capacitor) and a sensing area (charge)
Fill Factor is the percentage of
pixel area which is sensitive to signal
Low fill factor means
more detector element (white) and loss of x-rays
High fill factor means
more light sensitive area, and not a lot of xrays are lost
