Transcript Digital Imaging - El Camino College

1
Image Receptors
Image
Receptors
Film Imaging
Film
Construction
Film Handling
Digital
Imaging

Cassette
Digital
Imaging
Direct Digital
Imaging
Cassette
Construction
Darkroom
2
Digital
Radiography
Direct
Capture
Direct-to-Digital
Radiography
(DDR)
Indirect
Capture
Computed
Radiography
(CR)
3
Computed Radiography

Similar to F/S
Uses cassettes as imaging plate (IP)
Imaging plate is termed PSP
4
History of CR

INDUSTRY
• Theory of “filmless radiography” first
introduced in 1970
• 1981 Fuji introduced special cassettes with
PSP plates (replaces film)
• Technology could not support system
• First clinical use in Japan - 1983
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Predictions

 1980 – Bell Labs believed that Unix would be the worlds
dominant operating system
 1982 – Bill Gates thought 640K of main memory would
suffice for workplace operating systems ( This presentation is 80,000
kb)
 1984 – IBM predicted that personal computers would not
amount to anything
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Uses the same general
equipment as F/S
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Computed Radiography

How is it different from F/S?
How the image is captured
How the image is stored
How the image is viewed
How the image is processed after taken
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Computed Radiography

 Review of F/S image production:
 Primary beam
 Exit radiation
 Hits phosphors of intensifying screens, lights helps
form image-latent image
 Some photons hit film directly-latent image
 Film is processed to develop manifest image
 Film stored, duplicated to be seen by others
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Computed Radiography

 Computed Radiography Image Production:
 Primary beam-same as film
 Exit radiation-same as film
 Interacts with CR cassette image plate- latent image -similar to
film
 CR cassette is place in CR reader, laser translates image to
analog signal-different
 Analog signal converted to digital signal
 Image can be viewed on computer monitor-manifest image
 Image can be post-processed-not possible with F/S
 Image is stored in computer system (PACS)
 Image can be viewed by anyone with access to system
 Image can be printed on film with a laser printer
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Cassette with film CR
with PSP

Film Cassette
CR cassette with PSP
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Computed Radiography

Responds to radiation by trapping energy in the
locations where x-rays strike, creating the latent
image
PSP run scanned by a CR reader, converted to
analog image, then to digital image, then image
viewed on monitor.
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
CR Reader- scans the PSP plate
using a RED laser light, releases
trapped electrons which then emit
BLUE light which is converted to
analog image.
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Computed Radiography

Exit radiation exposes CR cassette
Detects the Blue
light emitted
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1.
CR – PSP plate

Stimulated by a RED LIGHT
2. Energy is RELEASED in a form of BLUE
light
3. LIGHT captured by photomultiplier tube
(PMT)
4. Changed to a digital signal
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Computed Radiography
1. X-ray Exposure
Patient
5. Computed
Radiograph
une xposed
2.
PSP
3.
4.
Image
Image
Image
Reader
Scaling
Recorder
detector
X-ray
system
exposed
re-usable
phosphor
plate
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CR Phosphor Plates
ABSORPTION
EMISSION
LASER STIMULATION
X-RAY
ELECTRON
TRAP
ELECTRON
TRAP
LIGHT
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How CR works

1. Blue released light is captured by a PMT
(photo multiplier tube)(laser reader)
2. This light is sent as a digital signal to the
computer
3. The intensity (brightness) of the light –
correlates to the density on the image
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ERASING PLATE

1.
After image is recorded
2.
Plate is erased with high intensity white light
3.
Cassettes are reused
Remember RED, WHITE AND BLUE…..but really it goes Red, Blue White…
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Digital
Radiography
Direct
Capture
Direct-to-Digital
Radiography
(DDR)
Indirect
Capture
Computed
Radiography
(CR)
20
Directed Digital Radiography
(DDR)

Directed digital radiography, a
term used to describe total
electronic imaging capturing.
Eliminates the need for an image
plate altogether.
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Direct Digital Radiography

 Cassette-less imaging
 Uses TFT-Thin Film Transistor
 No film, so no developing,
 No PSP, so CR reader needed
 Immediate image viewing
 Post Processing capabilities
 Multiple viewing stations
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Amorphous Selenium detector technology for
DR Direct Radiography
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Direct Digital Radiography

No cassette used, device similar to Bucky used
Contains thin film transistor
Captures x-ray photons, converts to electron energy,
Electron energy transferred to digital image
Displayed on monitor for IMMEDIATE viewing
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Be able to compare all the different imaging
systems. Compare the advantages,
disadvantages of each system.
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FS - Film inside of cassette
CR – Photostimulable Phosphor Plate (PSP)
DR(DDR) - Thin Film Transistor (TFT)
Don’t forget about Direct Exposure !!
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FS vs. CR
FILM
 Film in cassette
 loaded in a darkroom
 Processed in a
processor
FILM
 Hard copy image –
stores the image
 Viewboxes – view the
images
CR
 PSP in cassette
 Digital image
 Scanned & read- CR
reader
COMPUTER
 Image stored on
computer
 Viewed on a Monitor
 Hard copy (film) can
be made with laser
printer
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CR vs DR
 DR
CR
 Imaging plate
 Processed in a Digital
Reader
 Signal sent to
computer
 Transistor receiver
(like bucky)
 Directly into digital
signal
 Seen immediately on
monitor
 Viewed on a monitor
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COMPUTED RADIOGRAPHY & DIRECT
RADIOGRAPHY
& FILM SCREEN IMAGE CAPTURE
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Image Resolution
(how sharply is the image seen)

CR
 4000 x 4000
 Image only as good a
monitor*
 More pixels = more
memory needed to
store
 CR 2 -5 lp/mm
 RAD 10 lp/mm
 DR ?
 IMAGE APPEARS
SHARPER BECAUSE
CONTRAST CAN BE
ADJUSTED BY THE
COMPUTER –
 (DIFFERENCES IN
DENSITY)
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ADVANTAGE OF
CR/DR

Can optimize image quality
Can manipulate digital data
Improves visualization of anatomy
and pathology
AFTER EXPOSURE TO PATIENT
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CR/DR VS
FILM/SCREEN

1. FILM- these can not be modified
once processed
2. If copied – lose quality
3. DR/CR – print from file – no loss
of quality
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“No fault” TECHNIQUES

F/S: RT must choose technical factors
(mAs & kVp) to optimally visualize anatomic detail
CR: the selection of processing algorithms and
anatomical regions controls how the acquired latent
image is presented for display
 HOW THE IMAGE LOOKS CAN BE ALTERED
BY THE COMPUTER – EVEN WHEN “BAD”
TECHNIQUES ARE SET
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Storage /Archiving
 CR & DR
FILM/SCREEN
1.
Films: bulky
2.
Deteriorates over time
3.
Requires large storage
& expense
4. Environmental
concerns
1. 8000 images stored on
CD-R
2. Jukebox CD storage
3. No deterioration of
images
4. Easy access
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1.
ADVANTAGE OF
CR/DR vs FS

Rapid storage
2. Retrieval of images NO LOST FILMS!
3. PACS- DICOM (storage management)
4. Teleradiology - long distance transmission
of image information
5. Economic advantage - at least in the long
run?
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Transmission of Images

1.
PACS - Picture Archiving & Communications
System
2.
DICOM - Digital Images & Communication in
Medicine
3.
TELERADIOGRAPHY -Remote Transmission of
Images
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Basics of Digital Images
Digital
images are a
(matrix) of
pixel (picture
element)
values
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Analog vs Digital
1. Analog - one value
blends into another
1. like a thermometer
100
80
60
East
2. Digital - distinct
separation
1. 98.6
2. exact
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W est
20
N orth
0
1st
3rd
Q tr
Q tr
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CONTRAST &
DENSITY

1. Most digital systems are capable of 1024
shades of gray –
 but the human eye can see only about 30 shades
of gray
2. The Optical Density and Contrast can be
adjusted after the exposure by the
Radiographer.
3.
This is POST - PROCESSING
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High displayed contrast – narrow window width
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Low displayed contrast (stretched) – wide window width
Basics of Digital Images

1. Pixel values can be any bit depth (values
from 0 to 1023)
2. Image contrast can be manipulated to
stretched or contracted to alter the
displayed contrast.
3. Typically use “window width” and
“window level” to alter displayed contrast
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Danger of Digital

 Then the COMPUTER corrects any exposure errors
 Therefore almost ANY technique can be used on the
patient –
 The computer will fix it
45
DOSE IMPLICATIONS

1.
2.
More exposure to the patient
Techniques established-F/S techniques
3.
4.
5.
Higher kVp = Less mAs
Less patient dose
Goes Contrary to what good techs have been
taught
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80 kvp 200mas
10 mas 80 kvp
Note
Quantum Mottle
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Dose Implications

1. Images nearly always look better at
higher exposures.
2. Huge dynamic range means nearly
impossible to overexpose.
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POST PROCESSING

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TECHNIQUE
CONSIDERATIONS

1. kVp Dependent
2. Now COMPUTER controls
CONTRAST
3. Higher kVp to stimulate
electron traps
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CR – Reader
(replaces Darkroom &
Processor & Chemicals
Diagnostic Viewer
(replaces film, storage & viewboxes)
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EMERGING
PROBLEMS

1. Better – not necessarily faster
2. Learning curve for technologists and
physicians-increase repeat rate?
3. Student applications and issues
4. Pitfalls of CR
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Learning Curve

1. Positioning and proper
collimation are critical to good
imaging outcomes
2. Just like Phototiming, it can
magnify your mistakes
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COLLIMATION
CRITICAL

1.
2.
As the computer reads the density value of each
pixel- it is averaged into the total
Close collimation= Better contrast
3.
Bad collimation= more grays and less detail
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To Produce Quality Images

For Conventional Radiography
or 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 Images

•Accounts for 85% of the total number of repeat exposures.
•Has a direct affect on exposure technique.
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
Towel that was
used to help in
positioning a child
CR/DR is MORE
sensitive to
ARTIFACTS
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