3 - Digital Imaging Flashcards
is film or digital less expensive initially
film: less espensive initially
digital: expensive initially
does film or digital have quick acquisition
film: slow
digital: quick
how do process film vs. digital
film: chemical processing
digital: no darkroom and no chemicals
radiation dose of film vs digital
film: more radiation dose
digital: 80% less radiation dose
security of film vs. digital
film: physical security
digital: cyber security
what is smallest element of digital picture
pixel
what is spatial distribution of pixels in rows and columns with different shades of grey in each pixel
matrix
what is a digital image with an approximation of real scene
digitization
what is used for sensor construction
- scintillation screen
- fiber optic faceplate
- active semiconductor layer
- charge-coupled device (CCD)
- complementary metal oxide semiconductor (CMOS)
what protects semiconductor layer and provides a sharper image to reduce scatter
fiber optic faceplate
what is active semiconductor layer made of
silicon
what happens to active semiconductor layer when exposed to radiation
- Electrons are released from valence band into the conduction band, generating an electron hole charge pair
- Electrons are then attracted towards the most positive potential in the device where they create “charge packets”
- Each packet corresponds to one pixel
- Amount of electron hole pairs is proportional to the amount of exposure an area receives
what is this called:
each pixel is like a tiny battery with its charge equal to the number of electrons trapped inside; the computer records the charge in each pixel and converts it into a gray value
Simplified Sensor Concept
what move photogenerated charge from pixel to pixel and convert it to voltage at an output node
charge-coupled device (CCD)
what has each pixel individually read
complementary metal oxide semiconconductor (CMOS)
a small range of voltage values are grouped together as a single value
sampling (Analog to digital conversion)
poor representation of original image, less storage space
wide sampling
better representation of original image, more storage space
narrow sampling
every sampled signal is assigned a numeric value
quantization
the emission by a substance of stored energy as light
luminescence
main advantage of PSP
flexible (fits in patient’s mouth better)
what consists of reusable imaging plate coated with phosphor instead of the sensory
PSP
key characteristics of PSP
1) Made of europium-doped barium Fluoro halide
2) X-ray exposure - energy is stored (latent image)
3) Plate processing
4) Image is read with a scanning laser
5) Photomultiplier tube amplifies the signal
6) Light energy is converted to electrical energy
7) Analog to digital converter (ADC) - converts electrical energy to digital image
8) Plate is exposed to bright white light to erase any residual trapped energy to
reuse the PSP
what is PSP made of
europium-doped barium Fluoro halide
