Transcript digital imaging - El Camino College

DIGITAL IMAGING
DIGITAL IMAGING
TERMINOLOGY
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Film digitizer
Digital radiography
Digital fluoroscopy
Dynamic range
Matrix
Pixel
Imaging plate
Histogram
Algorithms
Window level
Window width
TFT
CCD
 Post-processing image
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enhancement
Latitude
Analog
Digital
Image acquisition
Image processing
Image display
Raster pattern
Laser
Photomultiplier tube
a-Selenium
ADC
ANALOG VS. DIGITAL
ANALOG VS. DIGITAL
SIMILARITIES AND DIFFERENCES
FILM-SCREEN IMAGING
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Need to select exposure factors
Accurate positioning
Use of accessory devices
IR receives radiation after
passing thru patient
Latent image is produced and
enhanced by the use of
phosphorescence
Latent image is chemically
processed
Limited dynamic range (30:1)
No post processing possible
Storage and retrieval issues
DIGITAL & CR IMAGING
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Need to select exposure factors
Accurate positioning
Use of accessory devices
IR receives radiation after
passing thru patient
Latent image is produced (CR)
and enhanced by the use of
phosphorescence
Wide dynamic rage (1000:1)
Post Processing Enhancement is
possible
Processing time reduced
Storage and retrieval easier
COMPUTED RADIOGRAPHY
IMAGING PLATE
Protective layer: Thin clear plastic that protects the phosphor layer
Phosphor layer: this active layer contains the photo-stimuablephosphor (barium fluorohalide phosphors) that react to x-ray
exposure
Reflective layer: reflects light forward when the plate is in the
reader
Conductive layer: absorbs the electrons released during exposure
and 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
information
PSP IMAGING PLATE(CR)
CR Phosphor Plates
ABSORPTION
EMISSION
LASER STIMULATION
X-RAY
ELECTRON
TRAP
ELECTRON
TRAP
LIGHT
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LATENT IMAGE (CR)
Formed by x-ray interaction with PSP
Ionizes phosphors, releasing electrons
Electrons trapped in crystal lattice of phosphor
Latent image is formed
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 and recorded by PMT
Image is sent to monitor for display
PSP plate is exposed to intense white light for erasure
IMAGE PROCESSING
IMAGE DISPLAY
Computed Radiography
1. X-ray Exposure
Patient
5. Computed
Radiograph
une xposed
2.
PSP
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Image
Image
Image
Reader
Scaling
Recorder
detector
X-ray
system
4.
exposed
re-usable
phosphor
plate
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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 (aSelenium). This material absorbs x-rays and converts them to electrons.
These electrons are stored in the TFT
DIRECT DIGITAL IMAGING
TECHNIQUE CONSIDERATIONS
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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
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Histograms are used to plot density of
data, and often for density estimation:
estimating the probability density
function of the underlying variable. The
total area of a histogram used for
probability density is always normalized
to 1. If the length of the intervals on the xaxis 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
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For Film/Screen Radiography
or Digital/CR Radiography:
The same rules, theories, and laws still apply and
can not be overlooked SID, Inverse Square
Law, Beam Alignment, Tube-Part-Film
Alignment, Collimation, Grid, Exposure
Factors: kVp, mAs, Patient Positioning
Quality Images
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•Accounts for 85% of the total number of repeat exposures.
•Has a direct affect on exposure technique.
COLLIMATION CRITICAL
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 As the computer reads the density value of each
pixel- it is averaged into the total
 Close collimation= Better contrast
 Bad collimation= more grays and less detail
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