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149 Cards in this Set
- Front
- Back
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Computed radiography screens respond to radiation with
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photostimulable luminescence
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A photostimulable phosphor in a metastable state will emit light
I. immediately II. when stimulated by light III. over time |
I, II & III
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Europium is the _____ of the photostimulable phosphor
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activator
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The photostimulable phosphor screen is processed in a
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reader
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The computed radiography reader is made up of _____, _____, and _____ modules.
I. mechanical II. chemical III. optical IV. computer |
mechanical
optical computer (I,III, IV) |
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The four steps of creating an image with computed radiography are
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metastable state, stimulate, read, and erase
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Following the laser stimulation of the photostimulable phosphor, the excited electrons are _____
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still excited
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The laser is one of the _____ features of the computed radiography reader.
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optical
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Optical filters are used to filter out the _____ light and allow the _____ light to reach the photodetector.
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stimulating, emitted
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What are examples of photo detectors?
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CCD, photo diode,photo multiplier tube
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The larger the laser beam will it increase or decrease spatial resolution?
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Will decrease
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types of devices that can record the emitted light by the PSP?
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CCD, PD, PMD
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Purpose of the photo detectors?
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Converts light emitted to electrically signal
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What does the ADC do?
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Converts analog to digital to be read or seen on monitor.
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The output signal from the photostimulable phosphor plate is converted from analog to digital by the _____
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photodetector
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Computed radiography and screen-film imaging both have a(n)
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latent image
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The principal source of noise in computed radiography is _____.
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scatter radiation
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With computed radiography the contrast is _____.
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constant regardless of radiation exposure
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The laser beam must be less than 100 nm in order to maintain _____.
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high spatial resolution
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_____ is prevented by flooding the erased imaging plate with bright light
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Ghosting
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Computed radiography imaging produces _____ gray levels
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10,000
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In digital radiography, the latent image is formed on the _____.
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radiation detector
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Pixel size, FOV, matrix size, pixel pitch, pixel depth (pixel density, or p/mm), FSS, OID, SID determine?
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Spatial resolution
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window level, bit rate (shades of gray = 2^n in each pixel), window width, dynamic range
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Contrast resolution
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What is the most recent development in digital radiography image receptors?
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direct capture solid-state devices
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Exposure index is?
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Manufacturer's index
Digital calculation for correct amount of radiation. |
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Digital radiography first began to be used in clinical settings in the _____.
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1980s
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In digital radiography, spatial resolution is improved with increased
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matrix size
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The number of visible shades of gray in a digital image is determined by _____.
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bit depth
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_____ requires the largest matrix size
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Computed radiography
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primary effect under exposure is called?
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noise
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does noise increase or decrease contrast?
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decrease
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noise for CR
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quantum mottle (not enough radiation), electrical signal noise, electrical component
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film/screen noise is only called
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quantum mottle
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effect of over exposure in DR
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nothing
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Mechanical features of the CR reader are ?
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the drive mechanism (fast scan, slow scan and IP transport)
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Optical features are?
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Rotating oscillating mirror or rotating polygon mirror
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optical filter will filter out ?
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stimulating light and allow emitting light (AKA the signal)
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sampling and quantization are
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the process of analog-to-digital conversion (ADC)
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sampling is ?
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matrix size
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quantization is
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bit rate
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The typical matrix size for digital radiography is _____.
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1024 Ã- 1024
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Spatial resolution is determined by the ratio of _____ to _____.
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field of view, matrix size
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Computed radiography uses (a) _____ for latent image formation
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photostimulable phosphor
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Recognize the meaning of the acronyms PSL, PSP, SPS, IP, PMT, and PD
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PSL-photostimulable luminescence; PSP-photostimulable phosphor; SPS-storage phosphor screens, IP-imaging plate; PMT-photomultiplier tube; PD-photodiodes
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purpose of the capture element?
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capture the x-ray
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Explain what a photostimulable phosphor is
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Substance that fluoresces instantly when struck by x-rays or other types of electromagnetic radiation (Ex. Phosphors in intensifying screens)
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Explain what is meant by photostimulable luminescence
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The process when some substances emit some light when struck by x-rays, but again emit light when exposed to another light source, delayed light
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In DR the capture element
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cesium iodide (CsI)
gadolinium oxysulfide(GdOS) Amorphus silium (a-Se) |
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capture element for CR
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PSP - photostimulable phosphor
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Give the purpose of a capture element for digital radiography
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It captures the x-ray
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State the three substances used as for the capture element for digital radiography
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Cesium iodide, gadolinium oxysulfide, or amorphous selenium
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Explain the purpose of the coupling element for digital radiography
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It is the way the x-ray generated signal is transferred to the collection element
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List the objects or methods use for coupling in DR
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Fiber optics, optical lenses, contact layer, or amorphous selenium
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Explain the purpose of the collection element for digital radiography.
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It produces the electronic signal that is recorded as the image file
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List the objects or methods use for collection in DR
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Photodiode, charged coupled device, thin film transistor
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Explain the purpose of a CCD.
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It receives the light emitted by a scintillation phosphor and emits an electric signal
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Explain the purpose of a CMOS
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It uses specialized pixel censors when struck with x-ray photons convert x-rays into light and store them in capacitors
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SPR in DR is?
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Scanned Projection Radiography (mostly for CT)
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What is the principle advantage of scanned projection radiography?
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Collimation to a fan x-ray w/ associated scatter radiation rejection and improvement in image contrast
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Scintillation phosphor in SPR is?
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Cesium Iodide
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What is cesium iodide used with in scanned projection radiography?
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CCD - charged coupling device
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State the purpose of CsI for DR.
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In indirect DR they use CsI phosphors as a scintillator and is married to a linear array of CCD’s through a fiber optic light path; it captures x-rays and emits light
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Explain the purpose of CCD for DR
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It receives the light emitted by a scintillation phosphor and emits an electric signal
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Explain the function of amorphous silicon in DR
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Amorphous silicon converts the light emitted by CsI is converted to an electric signal
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CsI/CCD is what kind of system
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Indirect Dr (x-rays are converted 1st to light then to electrical signal)
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Interpolation
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Estimation of value b/t two known values
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TFT is
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thin film transistor
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Spatial resolution in DR is limited by?
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Pixel size!!!!
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Explain what is meant by a DEL.
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Detector element, the pixel in a solid state device is referred to as this
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Name the primary substance used for direct digital radiography.
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Amorphous selenium
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Compare direct and indirect digital radiography
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Direct digital radiography provides better spatial resolution because there is no spreading of light, but there is higher patient dose
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Explain the purpose of Dicom
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Digital imaging communications In medicine, the standard method used to allow interoperability and interconnection between medical imaging devices as well as a standard format used to transfer images, it allows different practices to use equipment from different manufacturers
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List the four components of a PACS
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Picture viewing at diagnostic, reporting, consulting, and remote workstations; archiving images using short or long-term storage devices; communications using local or wide area networks or public communication services; and systems that include modality interfaces and gateways to the practice and department information systems, offering one integrated system to the user
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How is digital radiography used?
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It uses a receiver that captures and converts x-ray energy (in) directly into a digital signal, the image is seen immediately on a monitor and then sent to PACS/ printer/ or other workstations for viewing
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What is an obscure way of producing a digital image?
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Scanned projection radiography
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What is a CCD
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A silicon-based semiconductor
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Is a CCD smaller or larger than a typical iR?
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Smaller, and it has very small pixels
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What does CMOS stand for?
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Complementary metal oxide silicon
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How do the CMOS systems work
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Each pixel has its own amplifier which is switched on and off by the circuitry and converts the light photons into electric charges, an analog-to-digital converter also located in the pixel converts voltage from the amplifier, the system is highly efficient and takes up less fill space than CCD’s
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What can be a coupling element?
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lens, fiber optic assembly, a contact layer or amorphous selenium
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What does the coupling element do?
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Transfers the x-ray-generated signal to the collection element.
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what can the collection element be?
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photodiode, a charge-couple device (CCD) or thin film transistor(TFT)
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Photodiode and CCD are light sensitive devices that ?
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collect light photons
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TFT (thin film transistors) is a charge-sensitive device that?
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Collects electrons
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How do the CMOS systems work
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Each pixel has its own amplifier which is switched on and off by the circuitry and converts the light photons into electric charges, an analog-to-digital converter also located in the pixel converts voltage from the amplifier, the system is highly efficient and takes up less fill space than CCD’s
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What are the three methods indirect DR is used?
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Light emitted is transferred by fiber optics to an array of CCD’s; a solid state IR is built using CsI and an amorphous silicon, the CsI captures x-rays and emits light, the light is converted into an electric signal by the amorphous silicon, and GdOS is used to capture, and an a-SI is used for coupling
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What are advantages of DR
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Fast throughout, low patient radiation dose, equipment can be updated, less noise, and powerful post processing
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What is the major cause of noise in digital radiography and also the main factor limiting quality?
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Electronic noise
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What makes more precise pixel values
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The more time allowed for signal conversion
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What causes inaccuracies in pixel values in subsequent exposures reducing image quality?
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Incomplete charge transfer
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What is it when exposures are taken in too rapid sequences and there might not be enough time for each previous exposure to transfer the entire signal?
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Electronic memory artifact
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How is the solid state device constructed
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In an active matrix array of thin film transistors, each pixel in the array has its own capacitor and circuitry
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What is the percentage of the pixel that will record x-rays
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Fill factor
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How is true direct digital radiography used
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The image forming x-ray interacts with amorphous selenium which produces the electric signal
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How do digital mammography and film-screen mammography compare
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Digital offer less spatial resolution than film-screen, digital has better contrast resolution so digital is equal if not better than film screen
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What matrix size is required for reading digital radiographic images
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2048 X 2048
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What type of monitor and what size matrix is used for mammo
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4K, 4096 X 4096
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What are the three principle advantageous imaging characteristics of CCD?
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Sensitivity, dynamic range, and size
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What is sensitivity
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The ability of a CCD to detect and respond to very low levels of visible light
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What is dynamic range
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The ability of the CCD to respond to a wide range of light intensity from very dim to very bright
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Explain what is meant by photostimulable luminescence
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The process when some substances emit some light when struck by x-rays, but again emit light when exposed to another light source, delayed light
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Name two common compounds that function as PSP’s
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Barium fluorobromide doped with europium, barium fluorohalide doped w/ europium
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State the substance in the PSP’s used in radiography that functions as the activator
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Europium
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Explain how light is given off when PSL occurs
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X-rays stimulate electrons to electron trap and electrons that have been stored in traps are stimulated by light and sent home
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Recognize the layers and purpose of each in a SPS.
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PSP crystal, protective overcoat, binder (active layer where PSP attaches), reflective layer, antistatic layer, lead, base
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Explain what TDL is, how it works, and where it is used.
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Thermoluminescent dosimeter, light is emitted when a TDL crystal is heated and made with lithium fluoride, nuc med techs and fluoro radiologists
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Explain what OSL is, how it works, and where it is used
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Optically stimulated luminescence, light is emitted when an OSL crystal is illuminated, current day film badge
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Compare immediate fluorescence and delayed fluorescence in PSP’s
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50% given off immediately, 50% stored
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State approximately how long the latent CR image will remain stable
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8 hours is the upper limit
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Explain how the latent CR image becomes manifest
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It’s read by a laser, emits light, light is converted to electric signal, and converted to computer
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Give the size range for the laser beam used in computed radiography
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A diameter of 50-100 nm
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Recognize the types of devices that can record the light emitted by the PSP.
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Photomultiplier tubes, photodiodes, and CCD’s
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State the purpose of these devices
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They all convert light into an electric signal
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Name the device that digitizes the analog image emitted from a PSP
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ADC
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State the purpose of the ADC, and what ADC stands for
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To digitalize the analog image emitted from a PSP, Analog to digital converter
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Name the step in the process where the CR image goes from being analog to digital.
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Analog to digital conversion step
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Explain how and why and IP is erased
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The plate is exposed to intense white light, after the plate has been read, there are still some electrons in the metastable state, these could appear in subsequent images causing ghosting or even double exposures
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Explain what may cause an IP to be over saturated and what steps should be taken when it occurs
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Way too much radiation
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State what types of radiation can fog an IP
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Background radiation from ionizing radiation such as x-rays, ultraviolet, gamma, and particulate
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Compare the dynamic range of CR to conventional radiography
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Computed Radiography has a very wide range while conventional has a narrow range
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Explain what is meant by exposure latitude
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Range of x-ray exposures over which radiograph is acceptable, margin of error
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Compare large and small laser beams when scanning an IP.
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A small laser allows greater resolution, but takes longer to scan plate, and has a lower signal to noise ratio as a large laser allows smaller resolution, but takes shorter time to scan plate, and a higher signal to noise ratio
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Compare the spatial resolution of a CR image to spatial resolution of a film-screen image.
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Conventional radiography has greater spatial resolution
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Compare the contrast resolution of a CR image to the contrast resolution of a film-screen image
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Computed radiography has greater contrast resolution
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Compare the latitude of a CR imaging system to the latitude of a film-screen imaging system
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Computed radiography has much wider latitude than conventional
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Explain the purpose of an exposure index
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To give numeric value of the amount of radiation that reaches the IP
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State the primary effect of under exposure on a CR image
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It results in noise, quantum mottle and insufficient contrast
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State the primary effect of over exposure on a CR image
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Creates excess scatter and the scatter reduces contrast
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What do some compare europium to
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The sensitivity speck
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What is the SPS housed in and what is it called together?
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A cassette, the imaging plate
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What will happen to the latent image if the plate is not processed
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It will eventually fade
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What is removed from the cassette when it is inserted into the reader
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The SPS (storage phosphor screen)
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What is the laser made out of
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Helium-neon
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What do the laser stimulated phosphors emit as they return to ground state
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Violet light
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What happens if the plate does not move in a smooth, precise manner
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There will be artifacts in the image
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What is inside the reader?
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Complex arrangement of the laser, beam shaping optics, light collecting optics, filters, and a photodetector
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What is the purpose of the beam shaping optics
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As the laser moves across the plate, it needs to be focused and a constant size and shape must be maintained
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What does filtering do to the signal to noise ratio
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Increases it
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What must be done in order to create a record or file of this image
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The amount of light given off by the PSP must be collected and recorded
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What breaks the continuous light signal into image pixels and assigns them a gray value
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The ADC
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What determines matrix and pixel size
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Sampling frequency
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What determines the gray values?
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Bit rate
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How long must over saturated plates need to be set aside for before they are erased
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24 hours
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What should be done to an IP if it hasn’t been used in 48 hours?
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Needs to be erased
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What type of relationship does computed radiography have between exposure and resulting luminescence?
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Linear
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What is the comparison between spatial resolution and contrast resolution
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Spatial resolution shows smaller objects better while contrast resolution shows difference in grays better
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What is conventional radiography determined by?
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Sampling frequency
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What has better quality conventional or computed radiography?
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They are both the same
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