DIGITAL PROJECTION RADIOGRAPHY COMPUTED RADIOGRAPHY

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DIGITAL PROJECTION RADIOGRAPHYCOMPUTED
RADIOGRAPHY
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DIGITAL PROJECTION RADIOGRAPHY DEPENDS ON
COMPUTER TECHNOLOGY TO PRODUCE DIGITAL
RADIOGRAPHIC IMAGE
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DIGITAL PROJECTION RADIOGRAPHY
COMPUTED RADIOGRAPHY (CR)
DIGITAL RADIOGRAPHY (DR)
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DIGITAL RADIOGRAPHY vsCOMPUTED RADIOGRAPHY
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DR
X-RAYS
DETECTORS
ADC
11011101
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CR
X-RAYS
CR PLATE
SCANNER
ADC
11011101
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COMPUTED RADIOGRAPHY (CR)USES PHOTOSTIMULABLE
PLATE (IMAGE PLATE) INSTEAD OF FILM, AS THE
IMAGE RECEPTOR.CR USES CASSETTE THAT LOOKS VERY
SIMILAR TO CONVENTIONAL RADIOGRAPHIC CASSETTE.
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CR PLATE !!!!!DOES NOT USE SCREENS OR FILM (
CONVENTIONAL FILM)
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CR PLATE
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CASETTE CONSTRUCTION

• LIGHTWEIGHT ALUMINUM
• PLASTIC
• STEEL FRAME

FRONT PANEL MADE OF LOW ATTENUATION CARBON FIBER
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CR CASSETTES ARE NOT LIGHT-TIGHTIMAGE PLATE
IS NOT SENSITIVE TO LIGHT
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CR CASSETTE IS PROTECTING IMAGE PLATE FROM
DAMAGEIS THE STABLE VEHICLE FOR TRANSPORT AND
PLACEMENT OF THE CASSETTE UNDER THE PATIENT
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BACK PANEL CONTAINS LEAD FOIL TO PROTECT THE
PLATE FROM BACKSCATTER
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BACK PANEL ALSO CONTAINS CHIP TO RECORD PATIENT
DEMOGRAPHIC INFORMATION
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REMOTE OPERATOR PANEL
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IMAGE PLATE
APPROX. 1MM
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CROSS-SECTION OF CR PLATE
PROTECTIVE LAYER
PHOSPHOR LAYER
ANTI-HALO REFLECTIVE LAYER
BASE
BACKING LAYER
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BASE

• PET- POLYETHYLENE TERAPHTALATE

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PHOSPHOR LAYER

• Ba FX Eu 2

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PROTECTIVE LAYER

• FLUORINATED POLYMER MATERIAL

PROTECTS PHOSPHOR LAYER
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ANTI-HALO LAYER REFLECTIVE LAYER

• PREVENTS LASER FROM PASSING THROUGH.
• REFLECTED LIGHT FROM PHOSPHOR IS ALLOWED TO PASS.

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BACKING LAYER

• PROTECTS THE BASE FROM DAMAGE.

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LEAD COATING
SCATTER
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The simplest explanation for luminescence is that
impurities in the crystal lattice are responsible
for luminescence. As the concentration of
impurity ions increase the greater the intensity
of the luminescence. CR screens use barium
fluorohalides doped with europium (europium is
the impurity in the crystal).
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When phosphors are stimulated with x-ray photon
energy electron pair holes are created. In
effect, europium is raised to an excited state
and upon luminescence it is returned to its
ground Eu2 state. This mechanism holds for both
spontaneous luminescence and photostimulated
luminescence
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The shifting of europium from its excited state
back to its ground state for both spontaneous and
photostimulated luminescence is about 0.6 - 0.8
microseconds. With screen-film imaging these
crystals spontaneously luminescence to expose a
film, but with CR imaging the luminescence
occurs, then there is also photoluminescence that
occurs when the screen is stimulated by a narrow
beam of infrared light.
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The holes or vacancies in the lattice are
portions of the lattice normally occupied by
halogens (fluoride, bromide, or iodine). These
vacancies will trap free electrons when
irradiated and are called Farbzentren centers or
F-centers.
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When the photostimulable plate is exposed to high
frequency light, usually from a helium laser, the
electrons in these F-centers are liberated and
cause luminescence at readout.
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THE LATENT IMAGE WILL REMAIN STORED FOR 24
HOURS.IT WILL FADE THROUGH PHOSPHORESCENCE
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FADING

• 25 OF STORED ENERGY

• WITHIN 8 HOURS

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CR AFTER EXPOSURE IS INSERTED INTO CR SCANNER
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CR PLATE
CR SCANNER/READER
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THE SCANNER SCANS THE IMAGE PLATE WITH LASER
LIGHT AND READS THE LATENT IMAGE FROM THE
PHOSPHORREADOUT
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LASER LIGHTHELIUM-NEON (633 nm) LASER BEAM
SWEEPS THE PLATE IN RASTER FASHION
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RASTER
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LASER
PM TUBE
LIGHT GATE
AMPLIFIER
ADC
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SWEEPING OF THE LASER ACROSS THE PLATE

• FAST SCAN DIRECTION
• SCAN DIRECTION
• LASER SCAN DIRECTION

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PLATE MOVEMENT IN THE SCANNER

• SLOW SCAN DIRECTION
• SUB-SCAN DIRECTION
• PLATE SCAN DIRECTION

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THE SPEED OF THE SCANNING LASER BEAM IS ADJUSTED
TO THE LUMINESCENT SIGNAL
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LASER 633 nm
PHOTOSTIMULABLE LUMINESCENCE 390-400 nm
PLATE F-CENTERS
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LASER LASER SPOT SIZE - 100 MICROMETERSPIXEL
SIZE - 100 MICROMETERS
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P.M. TUBE DETECTION SENSITIVITY MATCHED TO
BLUE-PURPLE PSL (390-400 nm)
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AFTER SCANNING THE CR PLATE NEED TO BE CLEARED
FROM RESIDUAL SIGNALPLATE EXPOSED TO HIGH
INTENSITY SODIUM VAPOR OR FLUORESCENT LIGHT
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Typical image plate can be reused thousands of
times
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IMAGE DISPLAY
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IMAGE CHECK-INDEX???
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IMAGE MANIPULATION-WINDOWING
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PICTURE DESTINATION -PACS
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PACS
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CR CHARACTERISTIC CURVE

• VERY WIDE LATITUDE

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CR SYSTEMS

• LESS RADIOGRAPH REPEATS

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CHARACTERISTIC CURVE
LATITTUDE OF FILM
LATITTUDE OF CR
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IMAGE CAN BE SALVAGED WITH CR

• 500 OVEREXPOSURE
• 80 UNDEREXPOSURE

USE ADEQUATE KVP
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HARD COPY GENERATED IN LASER PRINTER
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CR SYSTEM EFFICIENCY CHARACTERISTIC

• QDE- QUANTUM DETECTION EFFICIENCY

NO NEED FOR SCREENS
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QDETHE MEASURE OF THE EFFICIENCY OF CR SYSTEM
TO CONVERT REMNANT X-RAYS TO USEFUL IMAGE SIGNAL
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QDEPATIENT DOSE
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DIGITAL RADIOGRAPHY
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ELECTRONIC DETECTORS

• INDIRECT TECHNIQUE CLASS
• DIRECT TECHNIQUE CLASS

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INDIRECT TECHNIQUE

• INDIRECT CONVERSION FLAT PANEL DETECTORS
• INDIRECT CONVERSION CHARGED COUPLE DEVICE
  DETECTORS

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INDIRECT CONVERSION FLAT PANEL DETECTORS

• USE THIN LAYERS OF SILICON COMBINED WITH THE
  ARRAYS OF PHOTODIODES. P.D. IS COATED WITH CESIUM
  IODIDE OR RARE EARTH MATERIAL- WHEN STRUCK BY
  REMNANT X-RAYS THEY EMIT LIGHT.

ADVANTAGE HIGH QDE DISADVANTAGE LIGHT DIVERGENCE
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PHOTODIODE
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INDIRECT CONVERSION CHARGE COUPLED DEVICE
DETECTORS

• USE CCD ARRAYS TO RECORD THE VISIBLE LIGHT
  EMITTED BY A SCINTILLATION CRYSTAL THAT HAS
  ABSORBED THE ENERGY. AN OPTICAL COUPLING SYSTEM
  DEMAGNIFIES THIS LIGHT AND SENDS IT TO THE CCD
  ARRAY.

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OPTICAL COUPLING
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CCD
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DIRECT TECHNIQUE

• DIRECT CONVERSION FLAT PANEL DETECTORS

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DIRECT CONVERSION FLAT PANEL DETECTORS

• USE AN AMORPHOUS SELENIUM COATED THIN FILM
  TRANSISTOR ARRAY THAT DIRECTLY CONVERTS X-RAY
  ENERGY INTO ELECTRICAL SIGNAL. REMNANT X-RAYS ARE
  ABSORBED IN THE SELENIUM WHERE THEY FORM
  ELECTRON-HOLES. CAPACITORS COLLECT THE CHARGE.

ADVANTAGE NO LIGHT DIVERGENCE
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DR vs CR COMPARISON
DR SYSTEM
ADVANTAGE
DISADVANTAGE

• IMMEDIATE REDOUT
• CASSETTE FREE OPERATION
• GOOD FOR HIGH VOLUME RADIOGRAPHY
• CAN BE USED FOR MAMMOGRAPHY
• DETECTORS CAN BE RE-EXPOSED IMMEDIATELY

• MORE EXPENSIVE
• CAN NOT BE USED IN PORTABLE RADIOGRAPHY??????
• NOT COMPATIBLE WITH EXISTING TABLES

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PORTABLE????
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PORTABLE CT???!!
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MONITORS IN DR

• 1K
• 2K
• 4K

• 1,000 X 1,000 PIXELS
• 2,000 X 2,000 PIXELS
• 4,000 X 4,000 PIXELS

4K MONITORS USED IN MAMMOGRAPHY AND CHEST
RADIOGRAPHY
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DR TERMS TO KNOW

• PIXEL
• VOXEL
• SPATIAL RESOLUTION
• DYNAMIC RANGE
• CONTRAST RESOLUTION
• IMAGE NOISE

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PIXEL
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VOXEL
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The formation