Transcript images - El Camino College

Computed
Radiography
and
Digital Radiography
1
filmless’ radiology
departments
Diagnostic radiographers
have traded their ______ and
_________
for a __________ and __________
advance for Rad Sci Prof, 8/9/99
2
What Is Digital Imaging?
Digital imaging is the
acquisition of images to
a computer rather than
directly to film.
3
New Technology

Has impacted everyone:
1.
Practicing radiologic technologist
2.
Educators
3.
Administrators
4.
Students in the radiologic sciences.
4
Computed
Radiography
Fundamentals
of
Computerized
Radiography
5
Radiology 1895
Radiology 2001
6
CR SYSTEM COMPONENTS
1.
CASSETTES (phosphor plates)
2.
ID STATION
3.
IMAGE PREVIEW (QC) STATION
4.
DIGITIZER
5.
VIEWING STATION
7
8
History of CR
INDUSTRY
• Theory of “filmless radiography” first
introduced in 1970
• 1981 Fugi introduced special cassettes with
PSP plates (replaces film)
• Technology could not support system
• First clinical use in Japan - 1983
9
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
10
History of CR



By 1998 – over 5,000 CR systems in use
nationwide
1998 – Local area hospitals begin to
incorporate CR systems in their departments
(Riverside Co. Hosp builds new hospital in
Moreno Valley) – completely CR system – 1st
generation equipment
11
TERMINOLOGY
1.
F/S -
______________________
2.
CR -
_____________________
3.
DR -
_____________________
4.
DDR - _____________________
12
IMAGE CREATION


SAME RADIOGRAPHY EQUIPMENT
USED
THE DIFFERENCE IS HOW IT IS
1.
2.
3.
4.
___________
___________
___________
___________
13
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Conventional vs. Digital Imaging

Conventional X-ray imaging
systems
Produce an analog image
(radiographs, & fluoroscopy).
 Using x-ray tube with films & cassettes

15
Conventional vs. Digital Imaging


Digital radiography systems require
that the electronic signal be
converted to a digital signal –
Using x-ray tube –


CR cassettes with phosphor plate (PSP)
DR systems with transistors (TFT)
16
COMPUTED RADIOGRAPHY &
DIRECT RADIOGRAPHY
& FILM SCREEN
IMAGE CAPTURE
FS - Film inside of cassette
CR – Photostimuable Phosphor Plate (PSP)
DR(DDR) - Thin Film Transitor (TFT)
17
Cassette with film CR with PSP
18
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Directed Digital Radiography
(DDR)
Directed digital radiography, a
term used to describe total
electronic imaging capturing.
Eliminates the need for an image
plate altogether.
20
21
Amorphous Selenium detector technology for
DR Direct Radiography
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IMAGE CAPTURE
_____________
1.


PSP – photostimulable phosphor plate
Replaces film in the cassette
_____________ – No cassette-
2.


Photons captured directly onto TFT
Sent directly to a monitor
25
CR vs. FS
FILM
 Film in cassette
 loaded in a darkroom
 Processed in a
processor
CR
 PSP in cassette
 Digital image
 Scanned & read- CR
reader
FILM
 Hard copy image –
stores the image
 Viewboxes – view
the images
COMPUTER
 Image stored on
computer
 Viewed on a Monitor
 Hard copy (film) can
be made with laser
26
printer
CR BASICS
• Eliminates the need for film as a
recording, storage & viewing medium.
• PSP Plate – receiver
• Archive Manager – storage
• Monitor - Viewing
27
General Overview
CR
PSP cassette exposed by
conventional X-ray equipment.


Latent image generated as a
matrix of trapped electrons
in the plate.
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CR – PSP plate
1.
Photostimulable phosphor (PSP) plate
2.
Captures photons
3.
Stored in traps on plate (latent image)
4.
PLATE scanned in CR READER
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CR Phosphor Plates
ABSORPTION
EMISSION
LASER STIMULATION
X-RAY
ELECTRON
TRAP
ELECTRON
TRAP
LIGHT
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CR – PSP plate
1.
Stimulated by a ________________ LIGHT
2.
Energy is ________ in a form of _____ light
3.
4.
LIGHT captured by photomultiplier tube
(PMT)
Changed to a __________________ signal
31
How CR works
1.
2.
3.
Blue released light is captured by a
PMT (photo multiplier tube)
This light is sent as a digital signal to
the computer
The intensity _________ of the light –
correlates to the ______ on the image
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Reference detector
f-theta
lens
Cylindrical mirror
Beam splitter
Light channeling guide
Laser
Output Signal
Source
Beam deflector
ADC
Laser beam:
Scan direction
PMT
Amplifier
To image
processor
Plate translation:
Sub-scan direction
33
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
34
35
CR “PROCESSORS”
36
Densities of the IMAGE
1. The light is proportional to
amount of light received
2. Digital values are then
equivalent (not exactly the
same) to a value of optical
density (OD) from a film, at that
location of the image
37
38
39
ERASING PLATE
1.
2.
3.
After image is recorded
Plate is erased with high intensity
_______________________ light
Cassettes are reused
40
CR VS. DR


CR -______________ where the
image is first captured on plate and
stored = then converted to digital
signal
DDR -____________ where the image
is acquired immediately as a matrix of
pixels – sent to a monitor
41
Digital
Radiography
Direct
Capture
Direct-to-Digital
Radiography
(DDR)
Indirect
Capture
Computed
Radiography
(CR)
42
DIRECT RADIOGRAPHY

Uses a transistor receiver (like bucky)



Captures and converts x-ray energy
directly into digital signal
Images seen immediately on monitor
Sent to PACS/ printer/ other
workstations FOR VIEWING
43
CR vs DR
CR
 Imaging plate



DR
 Transistor receiver
(like bucky)
Processed in a
Digital Reader

Signal sent to
computer

Directly into digital
signal
Seen immediately on
monitor
Viewed on a monitor
44
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Image Resolution –
(how sharply is the image seen)
CR
• 4000 x 4000
• Image only as good a
monitor*
• 525 vs 1000 line
• More pixels = more
memory needed to
store
• CR 2 -5 lp/mm
• RAD 3-6 lp/mm
• DR ?
• IMAGE APPEARS
SHARPER BECAUSE
CONTRAST CAN BE
ADJUSTED BY THE
COMPUTER –
• (DIFFERENCES IN
DENSITY)
46
ADVANTAGE OF CR/DR

Can optimize image quality

Can manipulate digital data

Improves visualization of anatomy
and pathology

AFTER EXPOSURE TO PATIENT
47
ADVANTAGE OF CR/DR


Changes made to image after the
exposure
Can eliminate the need to repeat
the exposure
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ADVANTAGE OF CR/DR vs FS
1.
Rapid storage
2.
Retrieval of images NO LOST FILMS!
3.
PAC (storage management)
4.
5.
Teleradiology - long distance transmission
of image information
Economic advantage - at least in the long
run?
49
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
50
“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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DR
1.
Initial expense high
2.
Very low dose to pt –
3.
4.
Image quality of 100s using a 400s
technique
Therefore ¼ the dose needed to
make the image
52
Storage /Archiving
FILM/SCREEN
1.
Films: bulky
2.
Deteriorates over time
CR & DR
1.
2.
3.
4.
Requires large storage
& expense
3.
Environmental
concerns
4.
8000 images stored on
CD-R
Jukebox CD storage
No deterioration of
images
Easy access
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Transmission of Images
1.
2.
3.
___________ - Picture Archiving &
Communications System
____________- Digital Images &
Communication in Medicine
__________ -Remote Transmission
of Images
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Benefits of Computer (web)-based
Viewing Systems
1.
2.
3.
Hardcopy studies are no longer
misplaced or lost- eliminates films
Multiple physicians may access same
patient films
Patients do not have to wait in Radiology
for films once study is completed
57
“Film-less” components
1.
2.
3.
4.
CR or DR
CD-ROM or similar
output
Email capability
Digitizing capability or
service
58
PACS
Digital Images Archive
Database
and Workflow
Engine
Remote Facilities
Internet VPN
Workstations
Remote
Workstations
59
Histogram Analysis
1.
2.
3.
A histogram is a plot of gray scale
value
vs. the frequency of occurrence
(# pixels) of the gray value in the
image
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

HISTOGRAM – a bar graph depicting
the density distribution (in numerical
values) of the imaging plate
ALGORITHM – a set of mathematical
values used to solve a problem or find
an average
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Histogram
Low attenuation
(e.g., lungs)
High attenuation
(e.g., mediastinum)
12,000
Frequency
10,000
8,000
6,000
4,000
2,000
0
0
200
400
600
800
1,000
Digital number
Adapted
from AAPM
TG10
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Statistical plots of the
frequency of occurrence of
each pixel's value
65
Basics of Digital Images

Digital
images are a
(matrix) of
pixel (picture
element)
values
66
67

The algorithm attempts to
distinguish among the parts of
the histogram which represent
the range of densities from
bone to soft tissue
68



Histograms set for specific exams (body
parts)
Should produce digital images that are
consistent (regardless of kVp or mAs used)
Correct Algorithm (body part) must be
selected prior to processing imaging plate
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Methods to Digitize an Image
1. _________ - Teleradiography system
(PACS, DICOM)
2. ________ (vidicon or plumbicon)
3. _____________ _______________
4. _____________ _______________
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FILM DIGITIZER
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Analog vs Digital
1.
______________ one value blends
into another
1.
like a thermometer
100
80
60
East
40
2.
______________ distinct separation
1.
2.
98.6
exact
W est
20
N orth
0
1st
3rd
Q tr
Q tr
73
ANALOG TO DIGITAL IMAGE
1.
2.
3.
Conversion of conventional analog
films
To digital format for PACs and
teleradiology applications
With scanning laser digitizers
74
CONTRAST & DENSITY
Most digital systems are capable of 1024
shades of gray –
1.

2.
3.
but the human eye can see only about 30
shades of gray
The Optical Density and Contrast can be
adjusted after the exposure by the
Radiographer.
This is POST - PROCESSING
75
High displayed contrast – narrow window width
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Low displayed contrast (stretched) – wide window width
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Basics of Digital Images
1.
2.
3.
Pixel values can be any bit depth (values
from 0 to 1023)
Image contrast can be manipulated to
stretched or contracted to alter the
displayed contrast.
Typically use “window width” and “window
level” to alter displayed contrast
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80
80 KVP
5
5
100
30
15
200
500
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


Then the COMPUTER corrects any
exposure errors
Therefore almost ANY technique can be
used on the patient –
The computer will fix it
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DOSE IMPLICATIONS
1.
2.
3.
4.
More exposure to the patient
Techniques established
Higher kVp = Less mAs
Less patient dose
83
80 kvp 200mas
10 mas 80 kvp
Note
Quantum Mottle
84
Dose Implications
1.
2.
Images nearly always look better
at higher exposures.
Huge dynamic range means nearly
impossible to overexpose.
85
POST PROCESSING
86
TECHNIQUE CONISDERATIONS
1.
2.
3.
KVP Dependant
Now COMPUTER controls
CONTRAST
Higher kVp to stimulate
electron traps
87
standard image
edge sharpening
88
REPROCESSED
NO GRID
HAND ALGO
89
QC – Reader
(replaces Darkroom &
Processor & Chemicals
Diagnostic Viewer
(replaces film, storage & viewboxes)
90
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FILM SCREEN PROCESSOR
92
REPEAT IMAGES
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EMERGING PROBLEMS
1.
2.
Better – not necessarily faster
Learning curve for technologists and
physicians
3.
Student applications and issues
4.
Pitfalls of CR
95
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1. _____ and proper __________
are critical to good imaging
outcomes
2. Just like Phototiming, it can
magnify your mistakes
97
COLLIMATION CRITICAL
1.
2.
3.
As the computer reads the density
value of each pixel- it is averaged into
the total
Close collimation= Better contrast
Bad collimation= more grays and less
detail
98
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A
B
100
101
102
103
104
1. Digital imaging is not the
end all, cure all for imaging
problems
2. It is still technologist
dependent
105
To Produce Quality Images
For Conventional Projection
or CR Radiography:
The same rules, theories, and laws still
apply and can not be overlooked
FFD/OFD (SID/SOD)
Inverse Square Law
Beam Alignment Tube-Part-Film Alignment
Collimation
Grids
Exposure Factors: KVP, MaS
Patient Positioning
106
107
108
CONVENTIONAL RADIOGRAPHY
VIEWING OF “X-RAY FILM” IMAGES
109
• Towel that was
used to help in
positioning a child
NEW IMAGE
• CR is MORE
sensitive to
• ARTIFACTS
110
CR image –

NEW IMAGE
Line caused
from dirt
collected in a
CR Reader
111
High resolution with digital
imaging
112