DIGITAL IMAGING

DIGITAL IMAGING

TERMINOLOGY

Film digitizerDigital radiographyDigital fluoroscopyDynamic rangeMatrixPixelImaging plateHistogramAlgorithmsWindow levelWindow widthTFTCCD

Post-processing image enhancement

LatitudeAnalogDigitalImage acquisitionImage processingImage displayRaster patternLaserPhotomultiplier tubea-SeleniumADC

ANALOG VS. DIGITAL

ANALOG VS. DIGITAL

FILM-SCREEN IMAGINGFILM-SCREEN IMAGING DIGITAL & CR IMAGINGDIGITAL & CR IMAGING

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

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

SIMILARITIES AND DIFFERENCES

COMPUTED RADIOGRAPHY

IMAGING PLATE

Protective layerProtective layer: Thin clear plastic that protects the phosphor layer

Phosphor layerPhosphor layer: this active layer contains the photo-stimuable-phosphor (barium fluorohalide phosphors) that react to x-ray exposure

Reflective layerReflective layer: reflects light forward when the plate is in the readerConductive layerConductive layer: absorbs the electrons released during exposure and reduces static electricityColor layerColor layer: absorbs stimulating light but reflects emitted lightSupport layer: semi- rigid layer that provides support

Barcode labelBarcode label: allows technologist to use patient/exam identifying information

PSP IMAGING PLATE(CR)

CR Phosphor PlatesCR Phosphor Plates

ABSORPTION EMISSION

X-RAY

LIGHT

LASER STIMULATION

ELECTRONTRAP

ELECTRONTRAP

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LATENT IMAGE (CR)

Formed by x-ray interaction with PSPIonizes phosphors, releasing electronsElectrons trapped in crystal lattice of

phosphorLatent image is formedRemains until processed by a readerBut 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 redred laser light

As electrons are released, a blue light is emitted

BlueBlue light is captured and recorded by PMT

Image is sent to monitor for display

PSP plate is exposed to intense whitewhite light for erasure

IMAGE PROCESSING

IMAGE DISPLAY

X-rayX-raysystemsystem

PatientPatient

PSPPSPdetector detector

ComputedComputedRadiographRadiograph

1. X-ray Exposure1. X-ray Exposure

ImageImageReaderReader

2.2.

ImageImageScalingScaling

3.3.

ImageImageRecorderRecorder

4.4.

une xposedune xposed

exposedexposed

5.5.

re-usablere-usablephosphorphosphor

plateplate

Computed Radiography

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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 (a-Selenium). This material absorbs x-rays and 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

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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 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, 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

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Quality Images30

COLLIMATION CRITICAL

As the computer reads the density value of each pixel- it is averaged into the total

Close collimation= Better contrastBad collimation= more grays and less

detail

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NEXT WEEK……….