DR Digital Imaging Flashcards
(50 cards)
Digital
A device or system that represents information as continuously variable numerical values.
Example - digital watch
CR and DR are digital
Analog
A device or system that represents information as continuously variable physical quantities.
Example - mechanical watch
X-ray film
FPD Flat Panel Detector (DR Imaging Plate)
Takes the place of cassettes and readers; 3 different types:
Tethered (w/cord)
Fixed (mounted in Bucky)
Wireless (uses radio signal sent from FPD to base)
Capture element
Remnant X-ray energy is captured.
Indirect DR - amorphous Sillicon
- converts X-ray to visible light
Direct DR - amorphous selenium
- converts X-ray directly to electrons
Coupling element
Transfers X-ray generated signal to collection element
Indirect DR - amorphous silicon
- light sent to photoconductive material
Direct DR - amorphous selenium
-electrons sent to TFT
Collection element
Collects photons or electrons to be quantified - assigned a digital value
Indirect DR -TFT - electrons from photoconductive material collected by TFT
Direct DR - TFT - electrons from amorphous selenium collected by TFT
Algorithm
A finite sequence of instructions, an explicit step by step procedure for solving a problem, often used for calculation and data processing. A computers mathematical “recipe”, not one size fits all
Sampling
The process used to digitize the spatial information in an image, typically achieved by dividing an image into a square or rectanglar array of sampling points.
Spatial resolution
The ability to see really small structures, the field of view, matrix size
Pixel size
Measured from side to side of the pixel, a less accurate measure, does not account for dead zones
Pixel pitch
Measures center of pixel to center of other; takes into consideration dead zones, a more accurate assessment.
Pixel density
/mm
the number of pixels per given area
Amorphous
having no shape or organization
Indirect Conversion Flat Panel Detectors
Detector that uses thin layers of amorphous silicon with an array of photodiodes - coated w/Photostimulable phosphor that emits light - converted to an electrical charge, signal sent to ADC to convert to digital signal. High QDE - lower patient dose; loss of resolution due to divergence of light emitted.
Amorphous Silicon (a-Si)
Phosphor material - emits light when stimulated
Direct Conversion Flat Panel Detectors
Uses a amorphous selenium coated TFT that directly converts X-ray to electrical signals. Absorbs remnant radiation in the selenium layers that are collected by capacitors, then sent to the ADC to convert to digital.
No light conversion = no light divergence
Amorphous Selenium (a-Se)
Absorbs X-ray - converts directly to electrons (no light divergence)
TFT - Thin Film Transistor
Collect electric charges, positioned in a matrix, detects charges on a pixel by pixel basis.
Capable of very high spatial resolution (greater than 20lp/mm)
AMA - Active Matrix Array
Amorphous silicon, capacitor, and TFT assembly
DEL - Detector Element
Small square capable of recording a certain number of electrons.
The smallest possible dot of information.
Capacitor
Temporarily collects electrical signal
Matrix
The layout of cells in rows and columns containing pixels/voxels. The larger the matrix, the better the resolution.
Hounsfeld Units/CT Numbers
a quantitive scale for describing radio density calculated by comparing the linear attenuation coefficient of each pixel
Dot/matrix image
A 2 dimensional patterned array, used to represent characters, symbols and images
