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PRI test 2

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