5. 5
Byte
The basic unit of binary coded information
Kilobyte—210 – 1024 bites
Megabyte—1024 times1024bites
6. Performance parameters
Pixel: Smallest complete sample of an image. Has a
varied set of tones in shades of white/ black/grey.
Expressed in binary codes (bits).
Size of the pixel : Smaller the size , better
resolution.
CR- 50 to 200 microns, DR- 100 to 200 microns, DM- 50
to 100 microns.
Gray Scale: Shades of Gray in between pure black and
pure white.
Bit Depth: No of shades to define each pixel ,measured
as no of bits. Larger the depth, incr gray scale and large
file size.
7. Spatial Resolution: finer details, diff objects in an
image. Depends on sampling frequency and no of
pixels.
expressed in lp/mm.
Contrast Resolution: Color or gray scale
differentiation. Indicate the no of shades of grey that
a detector can capture.
File Size.
Performance Parameters(contd..)
12. Computed Radiography (CR)
Been around since 1980-81
Uses same radiographic equipment
No change in X-ray machine
Uses an imaging plate
Contains a photostimulator phosphor
Need a cassette reader
Images can be sent to a PACS
13. 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.
14. Computed Radiography (CR)
Re-usable metal imaging plates replace
film & cassette
Uses conventional bucky & x-ray
equipment
15. CR SYSTEM COMPONENTS
CASSETTES (phosphor plates)
ID STATION
IMAGE PREVIEW STATION
DIGITIZER
VIEWING STATION
19. CROSS-SECTION OF CR PLATE
PROTECTIVE LAYER
PHOSPHOR LAYER
ANTI-HALO & REFLECTIVE LAYER
BASE
BACKING LAYER
20. PHOSPHOR LAYER BASE
Ba FX: Eu +2 PET- POLYETHYLENE
TERAPHTALATE
PROTECTIVE LAYER
FLUORINATED POLYMER MATERIAL
PROTECTS PHOSPHOR LAYER
21. 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.
29. Add module code number and lesson title 29
(Europium Activated Barium FluoroHalide) BaFX:Eu , (X= Cl,
Br, or I)
30. Add module code number and lesson title 30
The principle of PSP
Excitation Storage Emission
CB
Trap
ADC
PMT
31. 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).
LUMINESCENCE
32. 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
LUMINESCENCE
34. 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.
LUMINESCENCE
35. 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.
LUMINESCENCE
36. Add module code number and lesson title 36
(Images courtesy of AFGA)
PSP digitizer Casette and PSP
Workstation
37. Reading Imaging Plate
Reader scans plate with
laser
Laser releases
electrons trapped in
high energy
states
Electrons fall to low
energy states
Electrons give up
energy as visible light
Laser Beam
Higher Energy
Elect ron
St at e
Lower Energy
Elect ron
St at e
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-
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-
-
-
-
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-
-
-
-
-
-
-
-
-
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Lower Energy
Electron State
38. Reader scans plate
with laser light using
rotating mirror
Film pulled through
scanner by rollers
Light given off by
plate measured by
PM tube &
recorded by
computer
Reading Imaging Plate
50. AFTER SCANNING THE CR
PLATE NEED TO BE CLEARED
FROM RESIDUAL SIGNAL
PLATE EXPOSED TO HIGH
INTENSITY SODIUM VAPOR OR
FLUORESCENT LIGHT
51.
52. After read-out, plate erased using a bright
light
Plate can be erased virtually without limit
Plate life defined not by erasure cycles but by
physical wear
60. Much greater latitude
than screen/film
Plate responds to many
decades of input
exposure
under / overexposures unlikely
Computer scale inputs
exposure to viewable
densities
Unlike film, receptor separate
from viewer
64. CR SYSTEM EFFICIENCY CHARACTERISTIC
QDE- QUANTUM DETECTION EFFICIENCY
NO NEED FOR SCREENS
QDE:
THE MEASURE OF THE EFFICIENCY OF CR SYSTEM TO
CONVERT REMNANT X-RAYS TO USEFUL IMAGE
SIGNAL
QDE PATIENT DOSE
65.
66. Receptor provides direct digital output
No processor / reader required
Images available in < 15 seconds
Much less work for technologist
77. PACS and DICOM
THE ROLE OF PACS :
A Picture Archiving and Communication System (PACS) aims to replace
conventional analogue film and paper clinical request forms and reports with
a completely computerized electronic network whereby digital images are
viewed on monitors in conjunction with the clinical details of the patient and
the associated radiological report displayed in electronic format.
The ROLE OF DICOM:
Digital Imaging and Communications in Medicine (DICOM) is a standard for
handling, storing, printing, and transmitting information in medical imaging. It
includes a file format definition and a network communications protocol.
DICOM enables the integration of scanners, servers, workstations, printers,
and network hardware from multiple manufacturers into a picture archiving
and communication system (PACS). The different devices come with DICOM
conformance statements which clearly state the DICOM classes they
support. DICOM has been widely adopted by hospitals .
