How does dynamic range vary for Film versus Digital?
Film: Smaller dynamic range (Curvilinear)
Digital: Larger dynamic range (Linear)
How do pixel density and pixel pitch effect spatial resolution?
- Higher pixel density= better resolution
- Lower pixel pitch= better resolution
What has better spatial resolution? Plain film or Digital?
Plain Film because there are No pixels to limit resolution
What is the AEC?
- Ionization chamber placed between patient and receptor
- Adjust the duration of the exposure depending on thickness/density
- Does not effect KVP
What is Bit Depth?
- Number of shades of gray that you can see in a pixel
- 2^X
- More Pixel depth =more contrast resolution
What are the types of Digital Detectors?
- Storage Phosphors (CR) (indirect)
- Flat panel detector(DR) (direct and indirect)
How does computer radiography/Storage phosphors work?
- Storage phosphor gets hit with X rays and stores latent image
- Laser is used to release trapped electrons as light
- Light is directed towards a Photodetector
- Photodetector converts light to Electrical signal that gets digitized.
How do you reset the plate in Computed Radiography?
Expose it to bright white light
Describe the indirect digital radiography pathway
- X ray hits scintillator (CsI) and creates light
- Light hits the photodiode
- Photodiode converts light to electrical signal which gets transmitted to the TFT
What is lateral dispersion of light?
- Occurs in thicker crystals, light gets dispersed laterally (indirect method only)
- Does not occur with direct method
Describe the direct digital radiography pathway
- X ray hits the photoconductor (Amorphous Selenium)
- X rays are absorbed and electrons are released
- Electrons travel towards the selenium surface and neutralize applied charge
- Electric charge is transmitted to TFT and converted to digital signal
What is fill factor?
Area of the detector that is sensitive to X rays (bigger means more efficient)
How does DQE compare in DR versus CR?
Better in DR (better fill factor= more efficient)
