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Principles of Radiographic Acquisition (Conventional Radiography…
Principles of Radiographic Acquisition
Conventional Radiography
Cassette
Non-screen
Used direct exposure to x-ray
Screen
Intensifying screens increase the efficiency of radiographic production
Lower mAs values needed
Reduced personnel and patient exposure
Increased contrast
X-ray film
Double-emulsion X-ray Film
Silver Halide Crystals
Sensitivity Speck
Traps electrons
View Box
Archives
Automatic/Manual Processing
Developer
Latent image catalyses reaction which reduces remaining silver halide crystals
Fixer
Prevent further development
Removes undeveloped silver bromide from film
Rinsing/Drying
Removes fixer chemicals that would otherwise discolour film over time
Computed Radiography
Filmless
Image is captured in cassettes containing phosphor storage layer
No chemistry
No darkroom
Laser film reader
Advantages
PACS Archiving system
All images studies are viewable from computers
Central digital archive with remote backup data
Time efficient
Robust
Good quality image
Lower radiation dose possible
Cost effective
Disadvantages
Laser reader sensitive to dust
Maintenance of moving part expensive
Manual labour still required
Digital Radiography
Imaging receptor plate (Se) contains many small detector elements that converts x-rays into electrical signals
Advantages
PACS Archiving system
All images studies are viewable from computers
Central digital archive with remote backup data
Image obtained within seconds
Good quality image
Lower radiation dose possible
Image stitching
X-ray tube takes multiple radiographs and fuses images up to 1.2m length
Dynamic Digital Radiography
Disadvantages
More expensive
More fragile
Types
Direct
X-ray photon strikes a Se plate
Charges are encoded and transmitted to computer for image reconstruction
Indirect
X-ray photons strike a flat panel detector that creates visible light
Grid
Used to absorb scatter radiation to improve radiographic contrast
mAs need to be increased by a factor of 2-3
Recommended when body part thickness is >10cm
Problems
Unfocused grid
Lateral decentering
Does not protect patient or personnel from scatter radiation
DICOM
Unified Standard
Prevent manipulation of image data
PACS
Replaces hard copies and storage
Allows remote access
RIS
Computerised database to store, manipulate and distribute imaging data
HIS