DIGITAL IMAGING CR Phosphor Plates Computed Radiography TECHNIQUE CONSIDERATIONS 80 kVp 200mAs
Jones, Paul, News Director/On-Air Personality has reference to this Academic Journal, PHwiki organized this Journal DIGITAL IMAGING DIGITAL IMAGING TERMINOLOGY Film digitizer Digital radiography Digital fluoroscopy Dynamic range Matrix Pixel Imaging plate Histogram Algorithms Window level Window width TFT CCD Post-processing image enhancement Latitude Analog Digital Image acquisition Image processing Image display Raster pattern Laser Photomultiplier tube a-Selenium ADC
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ANALOG VS. DIGITAL ANALOG VS. DIGITAL FILM-SCREEN IMAGING DIGITAL & CR IMAGING Need to select exposure factors Accurate positioning Use of accessory devices IR receives radiation after passing thru patient Latent image is produced in addition to enhanced by the use of phosphorescence Latent image is chemically processed Limited dynamic range (30:1) No post processing possible Storage in addition to retrieval issues Need to select exposure factors Accurate positioning Use of accessory devices IR receives radiation after passing thru patient Latent image is produced (CR) in addition to enhanced by the use of phosphorescence Wide dynamic rage (1000:1) Post Processing Enhancement is possible Processing time reduced Storage in addition to retrieval easier SIMILARITIES AND DIFFERENCES
COMPUTED RADIOGRAPHY IMAGING PLATE Protective layer: Thin clear plastic that protects the phosphor layer Phosphor layer: this active layer contains the photo-stimuable-phosphor (barium fluorohalide phosphors) that react to x-ray exposure Reflective layer: reflects light as long as ward when the plate is in the reader Conductive layer: absorbs the electrons released during exposure in addition to reduces static electricity Color layer: absorbs stimulating light but reflects emitted light Support layer: semi- rigid layer that provides support Barcode label: allows technologist to use patient/exam identifying in as long as mation PSP IMAGING PLATE(CR)
CR Phosphor Plates ABSORPTION EMISSION X-RAY LIGHT LASER STIMULATION ELECTRON TRAP ELECTRON TRAP LATENT IMAGE (CR) Formed by x-ray interaction with PSP Ionizes phosphors, releasing electrons Electrons trapped in crystal lattice of phosphor Latent image is as long as med Remains until processed by a reader But does begin to decay so must be read in a timely fashion IMAGE PROCESSING
IMAGE PROCESSING PSP plate exposed to radiation Electrons are trapped in phosphor layer Plate is exposed to a red laser light As electrons are released, a blue light is emitted Blue light is captured in addition to recorded by PMT Image is sent to monitor as long as display PSP plate is exposed to intense white light as long as erasure IMAGE PROCESSING IMAGE DISPLAY
CR Imaging-Image Acquisition DIRECT DIGITAL IMAGING TYPES OF DIRECT DIGITAL IMAGING
DIRECT DIGITAL IMAGING DIRECT DIGITAL IMAGING Flat panel detector consists of plate covered with amorphous selenium (a-Selenium). This material absorbs x-rays in addition to converts them to electrons. These electrons are stored in the TFT DIRECT DIGITAL IMAGING
TECHNIQUE CONSIDERATIONS kVp Dependent, need mAs to saturate optimally Now COMPUTER controls CONTRAST Higher kVp to stimulate electron traps 80 kVp 200mAs 10 mAs 80 kVp Note Quantum Mottle Histograms are used to plot density of data, in addition to often as long as density estimation: estimating the probability density function of the underlying variable. The total area of a histogram used as long as probability density is always normalized to 1. If the length of the intervals on the x-axis are all 1, then a histogram is identical to a relative frequency plot. For x-ray purposes, a histogram tells how often a certain degree of gray is seen in the image.
To Produce Quality Images For Film/Screen Radiography or Digital/CR Radiography: The same rules, theories, in addition to laws still apply in addition to can not be overlooked SID, Inverse Square Law, Beam Alignment, Tube-Part-Film Alignment, Collimation, Grid, Exposure Factors: kVp, mAs, Patient Positioning Quality Images
COLLIMATION CRITICAL As the computer reads the density value of each pixel- it is averaged into the total Close collimation= Better contrast Bad collimation= more grays in addition to less detail NEXT WEEK .
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