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PRI test 2
| Term | Definition |
|---|---|
| White part inside of cassette is the? | Image intesnsifying screens |
| Dynamic range | range of exposure intensities that an IR can accurately detect |
| Film screen dynamic range | very limited, narrow latitude, not much margin for error |
| What is Latitude? (dynamic range chart) | range of exposure producing densities over which a radiograph is acceptable. ie margin for error |
| Digital systems dynamic range | wide range, wide latitude, more room for error |
| Limitations to Film screen (8) | narrow latitude, very sensitive, cannot be exposed to light, limited dynamic range, cost of film, chemical processing, no post-processing, film arcives occupy space |
| Radiographic film | medium for image acquisition, processing, and display. More sensitive to light and less sensitive to xrays. |
| Film types (2) | single-emulsion coating film, double-emulsion coating film. Need to be used with proper cassette with 1 or 2 intensifying screen. |
| The emulsion layer | crystal layer, most important layer for image formation, active layer for xrays to interact with and transfer information. Mixture of Silver halide crystals (silver bromide & silver iodide) |
| What is the mixture in the emulsion layer that is photosensitive on a film? | Silver halide crystals (silver bromide & silver iodide) |
| What are intensifying screens? | Used to help reduce patient exposure to ionizing radiation. They are placed into the cassettes. contain 'rare earth' phosphors. purpose: intensify the action of the xrays to permit lower patient radiation exposure. |
| 'Rare earth' phosphors in intensifying screens? (3) | Gadolinium, Lanthanum, Yittrium |
| How does the itensifying screen work? | it takes the xray energy then converts it into visable light to expose the film |
| spectral matching | light absorption characteristics of the film MUST match to light emitted from the screens. ie. blue ilm= blue intensifying screen cassette |
| better resolution= | more radiation |
| faster speed= | more light= less exposure (advantage) less resolution (disadvantage) |
| Resolution/recorded detail | measure of the ability of a system to image 2 separate objects and visually distinguish one from the other. |
| contrast resolution | ability of the IR to distinguish (resolve) between objects having similar subject contrast (tissues) |
| small crystal size/thinner emulsion layer= | slower (decreased) system speed, increases resolution, decreases density |
| larger crystal size | |
| review last slides of film screen imaging | |
| Pixel (Picture Element) | smallest component (picture element) of an image |
| pixel size | measured in microns 100 microns= 0.1 mm |
| Bits (Binary Digits) | Eah pixel is represented by a series of bits. Bits represent different shades of gray on an image. |
| Byte (Binary Term) | 8 bits= 1 byte. Each byte=256 shades of gray can be represented. |
| Matrix | combination of rows and columns of pixels that form the image |
| digital image characteristics? slide | |
| matrix size | digital image quality is improved when a large matrix size can contain a greater number of smaller pixels |
| smaller pixels= | better resolution |
| Field of View (FOV) | --->dimensions of the anatomic area!!<--- Pixel size and number can be affected by changes in either FOV or matrix size |
| Pixel size= | FOV/matrix size |
| Decreasing matrix size = | less pixels, less resolution |
| Increasing matrix size | more # of pixels, better resolution |
| review matrix size slides | |
| pixel bit depth (number of bits) | number value assigned to a pixel. Controlled by the attenuation of xrays passing through the volume of tissue. ex, thicker patient has more volume |
| spatial resolution | is limited by the size of the pixel. Smaller pixel size= better spatial resolution |
| spatial frequency | measure of resolution. small objects have higher spatial frequency. Increasing number of lp/mm= improved spatial resolution |
| ADC | Analog to Digital converter |
| IP | Imaging plate |
| PD | Photodiode |
| PMT | Photomultiplier Tube |
| PSL | Photostimulable luminescence |
| PSP | Photostimulable Phosphor |
| SP | Storage Phosphor |
| SPS | Storage Phosphor Screen |
| What is a digital receptor? | device which intercepts image-formation radiation and produces image in digital form. |
| know CR uses barium flourohalide phosphor layer | |
| 2-step process for image formation for CR | 1. Image capture 2. image readout |
| put details . like Laser scans in zig zag | |
| CR. What is sampling? | The analog signal from the PMT must be sampled. ex, if you choose abdomen on computer and do a chest it will not readout correctly |
| Nyquist Theorem | sampling for each pixel must be done at least 2 times to achieve the desired level of spatial resolution. |
| What is Quantization? | Each pixel represents a brightness value (in numberical value) which controls the shades of gray |
| Flat-Panel Detectors !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! | Only DR. |
| What is a DEL? | "Detector Element" in the matrix. Used for DR systems. Collects electrons and converts them into a digital value by an analog digital converter (ADC). Similar to pixels in CR, smaller DEL size is better recorded detail. 1 DEL= 1 pixel |
| 2 types of DR receptors | 1. Indirect Conversion/Capture 2. Direct Conversion/Capture |
| Indirect Capture (Conversion) Detector. What are the 2 steps? | 1. Scintillator (Cesium Iodide) receives & converts exit radiation into visible light. 2. Light is converted into an electric charge by photodetector (amorphous silicon photodiode) |
| Direct Capture (Conversion) Detector. What is the 1 step? | |
| Exposure Index | Numeric value to represent exposure received by the IR. Dependent on intensity of radiation striking the detector. NOT a measure of patients exposure. |
| 2 methods of displays for EI numbers | Direct & Indirect |
| Indirect Method (Sensitivity or 'S' Number) | Indirectly proportional. Higher S Number than range= underexposure. |
| Direct Method | |
| How to prevent scatter radiation for Digital systems? | 1. Collimation 2. Grids. Digital systems are more sensitive to scatter radiation. |
| Close collimation in DR= | Better contrast |
| Bad collimation in DR= | more grays and less detail |
| In CR/DR mAs is used to | saturate body part optimally, and density. |
| In CR/DR kVp |
Created by:
jveliz91
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