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
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.
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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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
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 .