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Chap 1, 3, 4

Imaging 2 - digital

Discovery of X-ray was made by who in what year? W, C. Roentgen in 1895
5 other terms synonymous with CR? photostimuable luminescence (PSL)* Storage phosphor radiography (SPR) Digital luminescence radiography (DLR) Photostimuable storage phosphor (PSP)* Digital storage phosphor (DSP)
CR is linked to _________ and the phenomenon of _______. photostimuable phosphors (PSP), photostimuable luminescence (PSL)
What year was CR commercialized in diagnostic radiology? What manufacturer first introduced it? 1983, fuji
*What (5) characteristics must the phosphors have to be useful in radiology? good x-ray absorption efficiency, capable of being stimulated by a helium-neon laser. Luminescence light must be compatible with the photomultiplier tube (PMT) phosphor,& the luminescence must be shorter than 1 usec. Must store latent image for hours.
*The phosphors (that meet the characteristics) are usually what? barium fluoro halide, with europium activators added/doped.
*The halide can be: ____, _____, ______, or _____. chlorine, bromine, iodine, or a mixture of them.
How are the mechanics of how PSPs thought to work? X-rays fall on PSP, europium atoms r ionized & e- more from valence band to conduction band. e- travel to +charged F-center (where they create the latent image). PSP scanned by a red laser beam, trapped e- more up to conduction band, free to return to va
***In the f-center, the number of trapped e- is ___________? proportional to the absorbed radiation.
*What happens to e- in the F-center? Spatially distributed to form the latent image
To render the latent image visible, the PSP is scanned by a laser beam. This process referred to as what? photostimuable excitation.
***The laser light used must be capable of being _________.. absorbed by the f-centers. (Absorption causes trapped e- to move up c-band, where they are free to return to the v-band.)
What results in the emission of bluish purple light? Transition of e- from higher energy to lower energy state. (from c-band to v-band). Called photostimuable luminescence (PSL).
*What is photostimuable luminescence (PSL)? Emission of blue/purple light from e- going from high energy to lower energy state from c-band to v- band.
Final step in making the latent image visible? (after photostimuable luminescence PSL) PSL is collected by a light collection device and sent to a photomultiplier tube, is digitized by the ADC (analog digital converter) and then sent to computer for processing.
What is fading? time it takes for the latent image to disappear.
F-centers store latent images for how long? Then they loose what % of the image? 8 hours, then they loose 25%. (after 8 hrs you only have 75% of your image left...)
The digital detector used in CR imaging is the what? Imaging plate (IP)
*The IP consists of what layers? PSP layer on a base. 2 protective layers, elctroconductive layer, and a light-shielding layer. (protective, PSP, electroconductive, support, light-shield, protective)
What are the 2 types of IPs? Standard resolution and high resolution.
Standard IPs have _____ phosphor layers and do what? High resolution IPs ave ____ phosphor layers and do what? thick, absorb more radiation thinner, provide sharper images.
Thick phosphor IPs (standard) have faster or slower speeds than high res? faster.
Imaging cycle has 3 steps that are: exposure of IP, readout of exposed IP, erasure of IP.
Current CR readers use _____ that emit a red laser beam? solid state diodes
The emitted light from the IP is optically filtered and collected by the what? light channeling guide
After the light is filtered and collected by the light channeling guide, the light/PSL (photostimuable luminescence) is sent to the photodetector. What does the photodetector do? converts PSL into an electrical signal that is first amplified, then digitized by the ADC.
A photodetector is called what for a point scan reader? and what for a line scan reader? point scan= photomultiplier line scan=charge-couple device (CCD)
Current CR readers employ what scan principles? Line scan.
The movement of the IP is the _______ direction, and the laser beam movement across the IP is called the _____ direction. slow scan, fast scan
Over or under exposure causes high noise? under
exposure indicator for fuji? Kodak? Agfa? Konica? fuji- S-number kodak- EI Agfa- LgM (log of median values) Konica- S-value
Fuji, agfa, kodak acceptable ranges? *** fuji= 100-300 Agfa= 2.05-2.35 Kodak= 1850-2150
For Kodak; if the exposure is doubled, what happens to the EI? increase by 300. (if you decrease by exposure by .5, you reduce the EI by 300) proportional.
What is spatial resolution? related to the size of the pixels in the image matrix.. detail.
The smaller the pixel size, the better or worse the spatial resolution? (detail) better
pixel size can be calculated how? PS= field of view (FOV)/matrix size
The greater the matrix size, the smaller the pixels and the better _________. image sharpness.
Density resolution of a digital image is linked to the bit depth, which is what? the range of gray levels per pixel
The greater the ______, the better the density resolution. bit depth
two kinds of noise? electronic (system) and quantum noise.
quantum noise is determined by the what? number of x-ray photons falling upon the detector.
Low exposure factors will create ____ signal and ___ noise, and higher exposure factors will create ____ signal and _____ noise. low is less signal and more noise, high is more signal and less noise. (noise increases as the detector exposure decreases) (...high has more photons at the detector...)
The noise ______ as the detector exposure decreases. increases
DQE. what does it stand for and what is it? Detective quantum efficiency. The digital detector takes an input exposure and converts it into useful output image. The DQE is a measure of the efficiency with which the detector performs that task.
What is the Moire pattern? Artifact, due to using the wrong grid frequency. (bunch of lines)
what is QA? quality assurance. Systems/procedures for assuring quality patient care. (administrative)
What is QC? Quality control. Component of QA, but QC deals with the technical aspects (instead of administrative) of equipment performance.
If the exposure field (collimation margins) is not correctly located, what is likely to occur? The histogram analysis will be performed on all the exposure data, so if there is substantial extraneous exposure on the plate, a histogram analysis could occur. Then the exposure index will be improperly determined.
Increased dynamic range allows what? more data to be captured during acquisition.
why can one no longer use image density (brightness) to evaluate the accuracy of the IR exposure? digital image acquisition decouples
fixed speed class No histogram analysis No rescaling Operates like Film/screen Brightness depends on the selected technique Brightness can be manipulated and adjusted at the Control monitor
Over and under exposure are now represented in what? mR.
3 important factors that contribute to high image clarity: selection of technical exposure factors, correct part positioning, precise alignment of part, beam, and receptor.
The SID is essentially limited by what? Grids focal range.
One can reduce the patient exposure by __-___% by doing routine radiography at a ___" rather than at 40" SID. 12-15%, 48" instead.
What way should a portable grid be placed? Why? crosswise. Off level cut-off is less likely to occur
When would you see a moire effect? IF the scan frequency and the grid frequency are similar and oriented in the same direction.
grid frequency is what? why is it important? lines per inch, important because the image is scanned line by line.
Universally recommended grid frequency? 178 Ip/i or 70 lines/cm
As the frequency increases, the lead content ____. decreases
kVp still controls what? differential attenuation, signal difference or subject contrast
What has more effect on image contrast than the kVp? processing algorithm
Most common reason for histogram analysis errors? exposure field recognition failure. (the inclusion of the off-focus radiation/scatter outside the collimation will widen/skew the histogram)
What is pixel pitch? the distance between adjacent pixels. (center of one to center of the one next to it)
Pixel pitch determines what? the maximum spatial resolution. (spatial res. is related to the size of the pixels in the image matrix.. detail.)
With CR systems, spatial resolution is determined by _____, which is determined by the _________ as the laser scans the plate. pixel pitch, sampling frequency (AKA pixel density).
The higher the sampling frequency and the smaller the pizel pitch, the ____ pixels/mm and the ____ the spatial resolution. smaller, higher
Preprocessing: histogram and field recognition
post processing: contrast enhancement (..contrast scaling) and edge enhancement (..spatial frequency)
ADC does what? converts analog to binary
Modern readers have a red laser beam with a wavelength of what? 670-690 nm.
Phosphorescence is? delayed emission of light
Luminescence is? light in general. (not heat)
Fluorescence is? immediate light emission from being stimulated
Stimulated phosphorescence? delayed stimulation of light by using a PSP
How to render a latent image visable in CR? PSP must be scanned by a laser beam with a specific wavelength, reffered to as photostimulated excitation.
Uses light channeling guides and photmultiplier tube? Point scan reader
Uses linear lasers and CCD? line scan reader
kVp is _____ contrast, not _____ contrast. subject, not image.
What is a matrix? series of boxes laid out in rows and columns that give form to the image, (box filled with boxes.. called pixels)
What are pixels? The individual matrix boxes (little boxes in big box)
In medical imaging, each pixel represents a 3D volume of tissue known as what? a voxel
In DR, what is the FOV and what is it determined by? the overall dimension of the image matrix is called the Field of view. Determined by the size of the receptor
Direct detectors use what 2 things? amorphous selenium (a-Se)(as an active layer), and a thin film transistor (TFT)
Two types of indirect detectors? Flat panel TFT, charged coupling device (CCD)
Is the entire image receptor read in DR? No, only the exposed detector elements are used for the image data.
Major components of CR reader? (5) laser source, IP transport mechanism, light channel guide, photodetector, ADC
Why is DR D log E curve dangerous? The linear line is dangerous because the IR will continue to record over exposure even though the computer brings down the density to an acceptable range. Has a wide acceptable range.
Basic steps of how a CR reader works? IP placed on transport mechanism for laser light scanning, blue/purple light emitted, that PSL is collected by light channeling guide and sent to photodetector which changes it to electrical signal. That signal is sent to ADC and converted to digital.
Created by: Zoest35