DR Flashcards
TFT
Thin film transistor
CCD
Charge coupled device
AMA
Active matrix array
ADC
Analog digital conversion
DEL
Detector element
What are some advantage of DR?
Faster
No physical storage space required
Post processing allows for post acquisition alterations
Reduce patient radiation dose
What are the 3 elements of digital radiography?
Capture element
Coupling element
Collection element
What are possible materials for the capture element in DR?
Sodium iodide (NaI)
Cesium iodide (CsI)
Gadolinium oxysulfide (GdOS)
Amorphous selenium (a-Se)
Transfers the xray generated signal to the collection element
Coupling element
What are typical detector dimensions for DR?
43x43cm
43x35cm
What is the typical pixel dimension in a digital detector?
139-200 um
Micrometers
What are possible coupling elements?
Lens or fibre optic assembly
A contact layer
a-Se
What are possible collection elements?
Photodiode
Charge coupled device (CCD)
Thin film transistor (TFT)
Which collection elements are light sensitive devices that collect light photons?
Photodiode and CCD
Which collection element is a charge sensitive device that collects electrons?
TFT
What is the capture element in CR?
Photostimuable phosphor (PSP)
What causes exit radiation to create an electric charge?
Interaction with the detector
The pattern of the electric charge constitutes the latent image
Array of CCDs or TFTs with an xray absorption material
Active matrix array (AMA)
Converts xray photons to an electrical charge
Photoconductors
Converts xray energy to light photons
Scintillators
What are the two main types of xray absorption materials
Photoconductors and scintillators
What is the absorption material attached?
To the surface of the AMA
*array measures xray absorption rather than counting/measuring the actual X-rays
The conversion of X-rays, either direct or indirect is based on what?
The xray absorption material
What are the 3 elements of a DR detector?
Capture element
Coupling element
Collection element
The way in which X-rays are captured
Capture element
(CsI, GdOS, a-se)
Transfers cray generated signal to the collection element
Coupling element
(Lens or fibre optics, contact layer, a-se)
What material can act as a capturing or coupling element?
a-se
Collects light photons or electrons?
Collection element
(Photodiode, charged coupling device, thin film transistor)
What two collection elements are light sensitive devices that collect light photons?
Photodiode, charged coupled device
Which collection element is a charge sensitive device that collects electrons?
Thin film transistor
What is the capture element for indirect (CCD)?
CsI
What form of indirect DR uses fiber optics for a coupling element?
Indirect (CCD)
Deposited as powdered particles
Turbid/unstructured phosphor
GdOS
(Reduces spatial resolution)
Crystals are deposited in a needle like fashion perpendicular to detector surface
Structures phosphor
CsI
Higher DQE and spatial resolution
Collects and stores electrical charge
Thin film transistor (TFT)
*charge produced as a matrix of detector elements(DEL)
T/F
The term thin film transistor and flat panel detector are interchangeable
True
T/F
The maximum possible surface area is wanted for capture element to increase effectiveness
True
T/F
Detectors use about 2.5km of electrical bias, control, and data lines in the TFT
True
Each row of pixels is connected to what line?
The same horizontal control line
Each column is connected to which line?
The same vertical data line
The ratio of sensing area of the pixel to the area of the pixel itself
Fill factor
What are the 3 components that the pixel contains
TFT
Storage capacitor
Sensing area
T/F
As pixel size is reduced, spatial resolution increases, but fill factor decreases
True
T/F
A smaller fill factor decreases efficiency and effectiveness
True
Requires scintillating screen to convert X-rays to light
Indirect (CCD)
What is used to focus light onto the CCD chip in indirect DR?
Lenses or fibre optics
*optics in a CCD a critical contributors to the quality of a digital image
What does the CCD chip consist of, and what does it represent?
A series of semiconductor capacitors. Each capacitor represents a pixel
T/F
Spatial resolution in DR is pixel limited
True
Information is read out row by row by via the changing of the _______
Control line voltage
