Imaging 2 - digital
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| Physical basis for the CR image is the IP detector, which is made of a photostimulable phosphor (PSP) (3 steps): | show 🗑
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| show | Indirect TFT and direct TFT.
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| show | indirect uses phosphor, direct uses a photoconductor.
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| show | phosphor (indirect)- convert x-ray energy into electrical through an intermediate stage of light photons, photoconductors (direct) convert energy energy directly into electrical charge without the intermediate stage.
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| 2 types of indirect digital detectors? | show 🗑
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| show | indirect, CCD chip
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| Which detector is not classified as a flat-panel digital detector but is available commercially? | show 🗑
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| show | x-ray absorber, scintillator, light optics, the CCD. (which is a sensor chip.. or many...)
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| What does the CCD (sensor chips) do? | show 🗑
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| Scintillator screen does what in CCD detectors? **** | show 🗑
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| show | x-ray scintillator (conversion layer usually cesium iodide or gradolinium), an amorphous silicon (a-Si) photodiode flat panel layer, with a thin-film transistor (TFT) (for reader of the electrical charges by the photodiode)
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| Scintillator layer used in indirect flat-panel (TFT) is usually either ___________ or ________. | show 🗑
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| show | cesium iodide (Csi) crystals are deposited in needle like fashion, (structured phosphors)
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| show | gradolinium oxysulfide crystals, (turbid phosphors)
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| show | Csi- structured, Gradolinium- turbid
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| show | X-ray detection of CR is inefficient and this affects image quality and dose, Spatial resolution of CR is less than FS radiography. CR IPs can easily be damaged. CR IPs must be transported to a separate image processor for image data extraction
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| (flat panel DR) Selenium drum technology developed specifically for: | show 🗑
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| CCD indirect digital detector order: | show 🗑
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| show | scintillator, produce electron-hole pairs.
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| show | During readout, system electronics provide systematic collection of changes on each chip in a manner referred to as a “bucket brigade”. (the charge pattern from the readout of pixels is sent to the ADC for digitization)
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| show | The charge pattern from the readout of pixels (from the light of the scintillator falling on each pixel that produced electron-hole pairs...) is sent to the ADC for digitization. Then sent to computer for processing.
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| show | powdered. (this is why structured phosphor like Csi crystals are better)
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| show | thin-film transistor
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| Indirect flat panel TFT detectors: following the x-ray scintillator (x-ray detection medium) is what? | show 🗑
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| Indirect flat panel TFT detectors: a-Si photodiode layer is for what? | show 🗑
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| Indirect flat panel TFT detectors: purpose of the capacitor? | show 🗑
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| show | scintillator phosphor such as CsI, a-Se photoconductor to convert x-rays directly
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| Indirect TFT: the purpose of the a-Si photodiode layer is ? | show 🗑
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| Indirect TFT: the purpose of the capacitator is ? | show 🗑
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| Direct TFT: the photoconductor is usually what substance? | show 🗑
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| Direct TFT: the photoconductor (a-Se) does what? | show 🗑
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| show | consists of rows and columns that play a role in addressing and readout of the signal from each pixel.
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| Flat panel TFT: each pixel contains what 3 things? | show 🗑
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| The sensing area (in each pixel of a TFT) will detect the light from the CsI scintillator in the indirect TFT detector, or in the case of a direct TFT, ______________. | show 🗑
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| show | photodiode, storage capacitor.
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| The ______________ of the pixel receives the data from the layer above it that captures x-rays that are converted to light (indirect) or electrical charges (direct). | show 🗑
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| Fill factor is what? | show 🗑
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| Fill factor is expressed how? | show 🗑
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| show | spatial resolution and contrast resolution (detail and signal-to-noise)
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| Detectors with ____ fill factors (____ sensing areas) will provide better spatial and contrast resolution. | show 🗑
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| Indirect TFT detectors use a light sensitive ___________ to capture light from the scintillator phophor (such as CsI) to produce _________. Direct TFT detectors use an a-Se ___________ to convert the x-rays _________. | show 🗑
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| show | atomic number (Z#), density, and thickness of attenuating material.
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| X-ray scintillators are what for indirect flat panel TFTs? | show 🗑
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| General operating principles/steps of indirect TFT? | show 🗑
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| show | photons fall upon the a-Se photoconductor layered on top of a matrix of a a-Si TFT array. As xrays strike the a-Se, electral charges are created and the electrical field causes them to move towards the TFT elements where they are collected and stored.
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| show | initialization.
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| What is exposure latitude? | show 🗑
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| show | does not
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| Raw digital data is first subject to pre-processing and presented as _______________ image. | show 🗑
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| After the image is presented as "for processing" image, it then undergoes digital image _____________, and the resultant image is labeled a _________________ image. | show 🗑
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| show | post
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| show | flat-field image.
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| You base scaling the histogram on what? | show 🗑
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| Third step in image processing is ___________, where the adjusted or scaled raw data values are mapped to the "for presentation" values to display an optimum image. | show 🗑
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| "processing optimization rules" are what | show 🗑
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| the ability of the imaging system to resolve fine details present in an object is called | show 🗑
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| 3 tests to measure spatial resolution? | show 🗑
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| What is the modulation transfer function? *** | show 🗑
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| An MTF of ____ represents a perfect detector. | show 🗑
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| show | fine details, contrast.
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| show | better
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| High MTF value at lower spatial frequencies means that the detector provides better _____. | show 🗑
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| show | the response of the detector to different levels of radiation exosure
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| show | Detective quantum efficiency. "the efficiency of a detector to convert the x-radiation signal at its entrance window into useful image signal.
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| It is important to have low or high SNR? | show 🗑
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| show | DQE= SNR 2out / SNR 2in
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| A perfect digital detector would have a DQE of __. | show 🗑
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| As the spatial frequencies increase, the DQE ______ | show 🗑
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| show | memory effect
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| show | the persistance of the image, that is, charge is still being produced after the radiation beam from the tube has been turned off.
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