computed radiography and digital radiography

COMPUTED RADIOGRAPHY CR: USES PHOTOSTIMULABLE PLATE IMAGE PLATE INSTEAD OF FILM, AS THE IMAGE RECEPTOR.. CR CASSETTES ARE NOT LIGHT-TIGHT IMAGE PLATE IS NOT SENSITIVE TO LIGHT... CROSS

DIGITAL PROJECTION

RADIOGRAPHY

COMPUTED RADIOGRAPHY

DIGITAL PROJECTION RADIOGRAPHY DEPENDS ON COMPUTER TECHNOLOGY TO

PRODUCE DIGITAL RADIOGRAPHIC IMAGE

DIGITAL PROJECTION RADIOGRAPHY

DIGITAL RADIOGRAPHY

vsCOMPUTED RADIOGRAPHY

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

CR PLATE !!!!!

DOES NOT USE SCREENS OR FILM ( CONVENTIONAL FILM)

CR PLATE

CR CASSETTES ARE NOT

LIGHT-TIGHT

IMAGE PLATE IS NOT

SENSITIVE TO LIGHT

CR CASSETTE IS PROTECTING IMAGE PLATE

FROM DAMAGE

+

IS THE STABLE VEHICLE FOR

TRANSPORT AND PLACEMENT OF THE CASSETTE UNDER THE

PATIENT

BACK PANEL CONTAINS LEAD FOIL TO PROTECT THE PLATE

FROM BACKSCATTER

BACK PANEL ALSO CONTAINS

CHIP TO RECORD PATIENT

DEMOGRAPHIC INFORMATION

REMOTE OPERATOR PANEL

IMAGE PLATE

APPROX 1MM

CROSS-SECTION OF CR

PLATE

PROTECTIVE LAYER PHOSPHOR LAYER ANTI-HALO & REFLECTIVE LAYER

BASE

BACKING LAYER

► PET- POLYETHYLENE TERAPHTALATE

PHOSPHOR LAYER

► Ba FX: Eu +2

PROTECTIVE LAYER

► FLUORINATED POLYMER MATERIAL

PROTECTS PHOSPHOR LAYER

ANTI-HALO LAYER + REFLECTIVE

LAYER

► PREVENTS LASER FROM PASSING THROUGH.

► REFLECTED LIGHT FROM PHOSPHOR IS ALLOWED

TO PASS.

BACKING LAYER

► PROTECTS THE BASE FROM DAMAGE.

LEAD COATING

SCATTER

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).

When phosphors are stimulated with ray photon energy electron pair holes are created In effect, europium is raised

x-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

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.

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.

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.

THE LATENT IMAGE WILL REMAIN STORED FOR 24

HOURS

IT WILL FADE THROUGH

PHOSPHORESCENCE

► 25% OF STORED

ENERGY

► WITHIN 8 HOURS

CR AFTER EXPOSURE IS

INSERTED INTO CR SCANNER

CR PLATE

CR SCANNER/READER

THE SCANNER SCANS THE IMAGE PLATE WITH LASER LIGHT AND READS THE

LATENT IMAGE FROM THE

PHOSPHORREADOUT

LASER LIGHT

HELIUM-NEON (633 nm) LASER BEAM SWEEPS THE PLATE IN RASTER FASHION

RASTER

PM TUBE

AMPLIFIER ADC

LASER

LIGHT GATE

SWEEPING OF THE LASER

ACROSS THE PLATE

► FAST SCAN DIRECTION

► SCAN DIRECTION

► LASER SCAN DIRECTION

PLATE MOVEMENT IN THE

THE SPEED OF THE SCANNING LASER BEAM IS

ADJUSTED TO THE LUMINESCENT SIGNAL

PLATE & F-CENTERS

LASER 633 nm

PHOTOSTIMULABLE LUMINESCENCE

390-400 nm

LASER LASER SPOT SIZE -

100 MICROMETERSPIXEL SIZE - 100 MICROMETERS

P.M TUBE DETECTION

SENSITIVITY MATCHED TO BLUE-PURPLE PSL (390-400

nm)

AFTER SCANNING THE CR

PLATE NEED TO BE CLEARED

FROM RESIDUAL SIGNAL

PLATE EXPOSED TO HIGH

INTENSITY SODIUM VAPOR

OR FLUORESCENT LIGHT

Typical image plate can be reused thousands of times

IMAGE DISPLAY

IMAGE CHECK-INDEX???

IMAGE

MANIPULATION-WINDOWING

PICTURE DESTINATION -PACS

PACS

CR CHARACTERISTIC CURVE

► VERY WIDE LATITUDE

CR SYSTEMS

► LESS RADIOGRAPH REPEATS

CHARACTERISTIC CURVE

LATITTUDE OF CR LATITTUDE OF FILM

IMAGE CAN BE SALVAGED WITH

CR

► 500% OVEREXPOSURE

► 80% UNDEREXPOSURE

USE ADEQUATE KVP

HARD COPY GENERATED IN

LASER PRINTER

CR SYSTEM EFFICIENCY

CHARACTERISTIC

► QDE- QUANTUM DETECTION EFFICIENCY

NO NEED FOR SCREENS

THE MEASURE OF THE EFFICIENCY OF

CR SYSTEM TO CONVERT REMNANT

X-RAYS TO USEFUL IMAGE SIGNAL

PATIENT DOSE

DIGITAL RADIOGRAPHY

ELECTRONIC DETECTORS

► INDIRECT TECHNIQUE CLASS

► DIRECT TECHNIQUE CLASS

INDIRECT TECHNIQUE

► INDIRECT CONVERSION FLAT PANEL DETECTORS

► INDIRECT CONVERSION CHARGED COUPLE DEVICE DETECTORS

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

PHOTODIODE

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.

OPTICAL COUPLING

CCD

DIRECT TECHNIQUE

► DIRECT CONVERSION FLAT PANEL DETECTORS

DIRECT CONVERSION FLAT

ADVANTAGE: NO LIGHT DIVERGENCE

READY - The 17"x17"

amorphous selenium-based

sensor is electrically sensitized

EXPOSE - Incident X-ray photons are

converted into electron-hole pairs A

transverse electric field separates the

electrons and holes and creates a

charge image precisely

corresponding to the X-ray image.

READOUT - The microplasma line

scanner sweeps across the sensor in

less than 2 seconds causing readout

of the charge image and sensor reset.

PORTABLE????

PORTABLE CT???!!

4K MONITORS USED IN MAMMOGRAPHY

AND CHEST RADIOGRAPHY

PIXEL

The formation