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RADT 2403 Chapter 16

Digital Radiography

QuestionAnswer
What does SPR stand for? Scanned Projection Radiography
What generation of CT is scanned projection used? 3rd
What is scanned projection used for in CT? positioning of a FOV
What is the capture element? What captures the x-ray photon
What is the capture element in CR? A photostimulable phosphor
What are the capture elements used in DR? Cesium iodide, gadolinium oxysulfide, amorphouse selenium
What is the coupling element? What transfers the x-ray generated signal for collection.
What are types of coupling elements? Lens, fiber optics, contact layer, amorphous selenium
What is the collection element? What collects the signal
What kind of devices can collect the signal? CCD, Photodiode and TFT
How do CDD and Photodiode collect the signal? Light sensitive device that collects photons
How does TFT collect the signal? Charge sensitive device that collects electrons.
What does CDD stand for? Charge-couple device
What does TFT stand for? Thin-film Transistor
What are the two types of Indirect DR? Scintillator and a charge coupled device (CCD) ; Scintillator and amorphouse silicon and thin-film transistor.
What is a scintillator? Phosphor that converts x-rays to light.
What is a commonly used scintillator? Cesium iodide
What is a charge-coupled device? Converts light signal to digital-based signal
What are charge-coupled devices used in place of? Photodiodes
How big are charge-coupled devices? 1-2 cm in size
what material are charge-couple devices based off of? silicon
What is the process for Indirect DR using a scintillator and CCD? X-ray > Phosphor (scintillator > visible light > CCD > Digital signal
What is the process for Indirect DR using a scintillator, and TFT? X-ray > Phosphor (scintillator) > visible light > Photodetector > TFT > digital signal
What is the thin film transistor TFT? Electronic component that includes the readout, charge collector, "Thin film" of an active semiconductor
TFTS act as _______ that allow the pixels to change state rapidly? individual switches
Because TFTs act as individual switches that allow pixels to change state rapidly, what does the allow the pixel to do? Turn on or off much quicker.
What is Direct Radiography (DR)? "Cassette less" type of digital imaging that uses a detector array to record remnant radiation
What are the two types of DR? Indirect Capture and Direct Capture
What is the process of Indirect capture? Converts x-rays > light > electronic/digital signal
What is the process of Direct capture? Converts x-rays directly > electronic/digital signal
What are the 5 types of image receptor materials? Charge coupled device (linear response curve); Cesium iodide/ charge-coupled device ; cesium iodide and amorphous silicone; Amorphous selenium; Barium Fluorhalide with Europium phosphor CR.
What kind of device is a charge coupled device? A device for the movement of an electrical charge
3 Qualities of a charge-coupled device? High sensitivity; Wide dynamic range; Radiation response is linear.
With a charge-coupled device, image contrast is ________ to image receptor x-ray exposure. Unrelated
Charge coupled device can be used in both ____ and _____ capture indirect or direct.
Cesium iodide/Charge coupled device is used in what kind of capture? Indirect
The CsI phosphor absorbs the x-ray photons and transmits scintillation light to the CCD by way of ______? fiber optic bundles
Cesium Iodide/Amorphous Silicone is used in what kind of capture? Indirect
What is amorphous silicone? a fluid which is sprayed on
Cesium Iodide/amorphouse silicone has high ______? photoelectric capture
For CsI/Amoruphous silicone, _______ and ________ are imbedded in each pixel Capacitor and TFT
With CsI/amorphouse silicone, what captures the x-ray photons and transmits scintillation light to the collection element (TFT)? CsI phosphor
What is scintillation? flash of light produced in certain materials when they absorb ionizing radiation
TFT is a type of ______ semiconductor
TFT is a _____ collection electrode charge
TFT is an electronic switch that is _____ during the x-ray exposure allowing a _____ to be stored in a capacitor closed; charge
The captured charge from TFT is _______ to the x-ray exposure received to the "Dexel". proportional
What happens to the switch for TFT once the exposure is complete? It opens and electric charge flows to the charge amplifier.
How is DEXEL arranged? In rows and columns
DEXEL includes what components? the TFT and storage capacitor
Only ____% of the Dexel contributes to the image 80
______% of DEXEL is for the components. Called what? 20 ; The Fill factor
DEXEL is comparable to what? A farm plot. Have to have fields and the barn.
Amorphous selenium is used in what capture? Direct
Amorphous selenium uses no_____ scintillation phosphor.
The a-Se is what both elements? The capture element and the coupling element.
X-ray photons hits the a-Se and is what? directly converted into a charge.
What are some CCD qualities for Indirect DR? high sensitivity and wide dynamic range; responds to a large variety of light energies; allows lower techniques to be used.
What are some imaging challenges in Indirect DR? How is this overcome? Several CCD's must be tiled together to cover the detector array...leaving seams where light cannot be detected...overcome using a software interpolation termed "flat-field correction"
For Indirect DR using a scintillator/a-Si/ and TFT, a-Si is what element? The X-ray collection element?
the a-Si is painted on to supporting material (glass) to create what? "flat panel detector"
What is a TFT: electronic switch that allows a capacitor to collect charge (from freed electrons) until the exposure terminated.
Indirect DR using a scintillator/a-Si and TFT is arranged in what? in a network of dexels (detector elements)
Each dexel contains what? a detector face of a-Si, a charge collection electrode, a capacitor, and a TFT.
How does TFT function in image acquisition? Closes during exposure, opens when exposure ends, sends charge collected by capacitor to charge amplifier.
What does the charge amplifier in TFT do? Located outside the detecter; Converts charge to a digital signal.
What is the DEXEL Fill Factor? the sensitivity and ability of dexels to convert x-ray photons to a digital signal.
How efficient is the fill factor? 80%
What is the effect of high fill factor on image quality? Increased contrast and spatial resolution; high signal-to noise ratios.
Components of DR? TFT and a photoconductor of a-Se
Where is amorphous selenium (a-Se) sandwiched between? charged electrodes.
How is DR Arranged? in rows and columns termed an Active Matrix Array (AMA)
What is Active Matrix Array and what does it do? Network of gatelines and datalines; Allows dexels to be read in sequence.
What is the Image acquistion process for DR? x-rays free electrons in a-Se, creates positively charged holes; free electrons attracted to positively charged electrode; electron holes attracted to negatively charged electrode, builiding on SE layer at bottom of detector; stored capacitor for exposure
X-rays incident upon a layer of a-Se generate electron-hole pair vie what? the internal photoelectric effect.
A bias voltage applied to the depth of the selenium layer does what? Draws the electrons and holes to corresponding electrodes.
The generated current from bias voltage is proportional to what? the intensity of the irradiation
What are more steps to the image acquisition process for DR? 5-10 Volts applied to Se layer; Charge sent to ADC and computer for processing.
What does applying voltage to Se layer do? Opens TFT gates sequentially and dumps the stored charge.
How many dexels can be converted to a visible image in less than 1 second? 1 million
What are the three main steps to digitizing an analog image? Scanning, sampling, and quantization.
What does the scanning step do in digitizing an analog image? process of dividing image up into a matrix...each cell becomes a pixel.
What does the sampling step do in digitizing an analog image? process of detecting and measuring exposure received by the detector.
What does the quantization step of digitizing an analog image do? Assigns a value to each pixel relative to the energy it received.
Digital radiography is more efficient in what? tme, space, and personnel than screen-film radiography.
What are the three elements described in digital imaging? capture element, coupling element, and collection element.
What is the capture element? that in which the x-ray is captured.
What is the capture element for CR? The photostimulable phosphor.
What are the capture elements for DR? sodium iodide (NaI), cesium iodide (CsI), gadolinium oxysulfide (GdOS), or amorphous selenium (a-Se).
What is the coupling element? That which transfers the x-ray generated signal to the collection element.
What are examples of coupling elements? lens, fiber-optic assembly, contact layer or a-Se.
What is the collection element? photodiode, charge-coupled device (CCD) or a thin-film transistor (TFT).
The CCD and photodiode collect what? light photons.
The TFT collects what? electrons
What element is the CCD? light sensing element.
What does sensitivity of the CCD refer to? ability of CCD to detect and respond to low levels of visible light.
What does dynamic range refer to with CCD? ability of the CCD to respond to a wide range of light intensity, from dim to bright.
How is CCD different from screen film? CCD has higher sensitivity for radiation and a much wider dynamic range.
CCD radiation response is _______ linear.
CsI/CCD is an indirect DR process by which x-rays are first converted to _____ and then to an electronic signal. light.
CsI/a-Si is an indrect DR process by which x-rays are first converted first to _____ and then to electronic signal. light.
Spatial resolution in DR is ________ pixel limited.
a-Se is a direct DR process by which x-rays are _______ converted directly into an electronic signal.
X-rays incident on a-Se create what? electron hole pairs through direct ionization of selenium.
Created charge on a-Se is collected by what? a storage capacitor.
What is DM Digital mammography.
What do line spread functions show?
no DR system can match screen-film radiagraphy for... spatial resolution.
___________ is more important than spatial resolution for mammography or soft tissue radiography. contrast resolution.
What is DMT? Digital mammographic tomosynthesis
SPR has better _________ but limited spatial resolution. contrast resolution.
Which is a principal disadvantage of the use of an area beam versus scanned projection radiography? Scatter radiation
In scanned projection digital radiography, which of the following moves to produce an image? The patient
A scanned projection radiograph is... virtually scatter-free
What is part of SPR? detector array
Which of the following has the largest line spread function? screen-film
Advantage of area beam over SPR? short exposure time and reduced motion blur.
What is unique to direct radiography? no cassette is needed.
An x-ray system used for direct radiography has what? a linear H& D curve.
Principal limitation of SPR is what? exam time
What could be used as a radiation detector in direct radiography? BaFlCl
Created by: Cjenki10
 

 



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