Download computed radiography & direct radiography

COMPUTED
RADIOGRAPHY
Dawn Guzman Charman, M.Ed., R.T.
RAD TECH A
filmless’ radiology
departments
Diagnostic radiographers
have traded their film and chemistry
for a computer mouse
and monitor
advance for Rad Sci Prof, 8/9/99
What Is Digital Imaging?
• Digital imaging is the
acquisition of images
to a computer rather
than directly to film.
3
New Technology
•
•
•
•
•
Has impacted
practicing radiologic technologist
educators
Administrators
students in the radiologic sciences.
• Many local area hospitals
• and medical centers
• have this equipment NOW
Computed
Radiography
Fundamentals
of
Computerized
Radiography
CR SYSTEM
COMPONENTS
• CASSETTES (phosphor plates)
• ID STATION
• IMAGE PREVIEW (QC)
STATION
• DIGITIZER
• VIEWING STATION
COMPUTED RADIOGRAPHY
Medical Imaging is changing
“FILMLESS” Radiology is the future
And the Future is here!
El Camino College
First educational institution in California or across
the country to offer this new technology on a
college campus
Equipment Costs
Don Visintainer successfully
wrote grants, and received
funding from VTEA, P4E, and
private sources
Total
$410,916.00 +
HIDDEN COSTS
*
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
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
History of CR
• By 1998 – over 5000 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
TERMINOLOGY
• F/S -
Film/Screen (currently used method)
• CR -
Computed Radiography
• DR -
Digital Radiography
• DDR - Direct to Digital Radiography
IMAGE CREATION
• SAME RADIOGRAPHY EQUIPMENT
USED
• THE DIFFERENCE IS HOW IT IS
CAPTURED
• STORED
• VIEWED
• And POST -PROCESSED
CONVENTIAL vs DIGITAL
IMAGING
• Currently, most x-ray imaging
systems produce an analog image
(radiographs, & fluoroscopy).
• Using x-ray tube – films in cassettes
CONVENTIAL vs DIGITAL
IMAGING
• Digital radiography systems require
that the electronic signal be
converted to a digital signal –
• Using x-ray tube – cassettes with
phosphor plate OR
• DR systems - transistors
COMPUTED RADIOGRAPHY
& DIRECT RADIOGRAPHY
& FILM SCREEN
IMAGE CAPTURE
FS - Film inside of cassette
CR - PHOTOSTIMULABLE PHOSPHOR PLATE
DR(DDR) - TFT (THIN FILM TRANSISTOR)
Cassette w/ film CR w psp plate
Directed Digital Radiography
(DDR)
Directed digital radiography, a
term used to describe total
electronic imaging capturing.
Eliminates the need for an
image plate altogether.
Amorphous Selenium detector technology for
DR Direct Radiography
IMAGE CAPTURE
CR
– PSP – photostimulable phosphor plate
– REPLACES FILM IN THE CASSETTE
DR – NO CASSETTE – PHOTONS
– CAPTURED DIRECTLY
– ONTO A TRANSISTOR
– SENT DIRECTLY TO A MONITOR
CR vs FS
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
CASSETTES with Intensifying
Screens
• The CASSETTE holds
the film in a light tight
container
• It consist of front and
back intensifying
screens
CR BASICS
• Eliminates the need for film as
a recording, storage & viewing
medium.
• PSP Plate – receiver
• Archive Manager – storage
• Monitor - Viewing
General Overview
CR
• PSP cassette exposed by
conventional X-ray equipment.
• Latent image generated as a
matrix of trapped electrons
in the plate.
CR – PSP plate
• photostimulable phosphor (PSP) plate
• Captures photons
• Stored in traps on plate (latent image)
• PLATE scanned in CR READER
CR Phosphor Plates
ABSORPTION
EMISSION
LASER STIMULATION
X-RAY
ELECTRON
TRAP
ELECTRON
TRAP
LIGHT
CR – PSP plate
• Stimulated by a RED LIGHT
• Energy is RELEASED in a form of BLUE
light
• LIGHT captured by PMT –
• changed to a digiial signal
How CR works
• Released light is captured by a PMT
(photo multiplier tube)
• This light is sent as a digital signal to the
computer
• The intensity (brightness) of the light –
correlates to the density on the image
Densities of the IMAGE
• The light is proportional to
amount of light received
• 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
ERASING PLATE
• After image is recorded
• Plate is erased with high intensity white
light
• and re-used
CR VS DR
– CR -Indirect capture where the image
is first captured on plate and stored =
then converted to digital signal
– DDR -Direct capture where the image is
acquired immediately as a matrix of
pixels – sent to a monitor
DIRECT RADIOGRAPHY
•
•
•
•
•
uses a transistor receiver (like bucky)
that captures and converts x-ray energy
directly into digital signal
seen immediately on monitor
then sent to PACS/ printer/ other
workstations FOR VIEWING
CR vs DR
CR
• imaging plate
DR
• transistor receiver (like
bucky)
• processed in a Digital
Reader
•
directly into digital
signal
• Signal sent to computer
• Viewed on a monitor
• seen immediately on
monitor –
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)
ADVANTAGE OF CR/DR
• Can optimize image quality
• by manipulating digital data
• to improve visualization of
anatomy and pathology
• AFTER EXPOSURE TO PATIENT
ADVANTAGE OF CR/DR
• CHANGES MADE TO IMAGE
• AFTER THE EXPOSURE
• CAN ELIMINATE THE NEED TO
REPEAT THE EXPOSURE
ADVANTAGE OF CR/DR vs FS
•
•
•
•
Rapid storage
retrieval of images NO LOST FILMS!
PAC (storage management)
Teleradiology - long distance transmission
of image information
• Economic advantage - at least in the long
run?
CR/DR VS FILM/SCREEN
• FILM these can not be modified
once processed
• If copied – lose quality
• DR/CR – print from file – no loss
of quality
“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
DR
• Initial expense high
• very low dose to pt –
• image quality of 100s using a 400s
technique
• Therfore ¼ the dose needed to make the
image
Storage /Archiving
FILM/SCREEN
• films: bulky
• deteriorates over time
• requires large storage
& expense
• environmental
concerns
• CR & DR
• 8000 images stored
on CD-R
• Jukebox CD storage
• no deterioration of
images
• easy access
Transmission of Images
• PACS - Picture Archiving &
Communications
System
• DICOM - Digital Images &
Communication
in Medicine
• TELERADIOGRAPHY -Remote
Transmission of Images
Benefits of Computer (web)-based
Viewing Systems
• 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
•
•
•
•
“Film-less” components
CR or DR
CD-ROM or similar output
Email capability
Digitizing capability or
service
Histogram Analysis
• A histogram is a plot of gray scale value
• vs. the frequency of occurrence
• (# pixels) of the gray value in the image
• 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
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
Statistical plots of the
frequency of occurrence of
each pixel's value
Basics of Digital Images
• digital
images are a
(matrix) of
pixel (picture
element)
values
• The algorithm attempts to
distinguish among the parts of the
histogram which represent the
range of densities from bone to
soft tissue
• Histograms set for specific exams (body
parts)
• should produce digital images that are
consistant (regardless of kVp or mAs used
• Correct Algorithm (body part) must be
selected prior to processing imaging plate
Methods to Digitize an Image
• 1. Film Digitizer - Teleradiography system
(PACS, DICOM)
• 2. Video Camera (vidicon or plumbicon)
• 3. Computed Radiography
• 4. Direct Radiography
FILM DIGITIZER
Analog vs Digital
• Analog - one value
blends into another
• (like a thermometer)
100
80
60
• Digital - distinct
separation
• 98.6
• exact
East
40
W est
20
N orth
0
1st
3rd
Q tr
Q tr
ANALOG TO DIGITAL IMAGE
• Conversion of conventional analog
films
• to digital format for PACs and
teleradiology applications
• with scanning laser digitizers
CONTRAST & DENSITY
• Most digital systems are capable of 1024
shades of gray - 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
High displayed contrast – narrow window width
Low displayed contrast (stretched) – wide window width
Basics of Digital Images
• 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
80 KVP
5
5
100
30
15
200
500
• Then the COMPUTER corrects any
exposure errors
• Therefore almost ANY technique can be
used on the patient –
• The computer will fix it
DOSE IMPLICATIONS
• MORE EXPSOURE TO PATIENT
• TECHNIQUES ESTABLISHED
• HIGHER KVP = LESS MAS
• LESS PATIENT DOSE
80 kvp 200mas
10 mas 80 kvp
Note
Quantum Mottle
Dose Implications
• Images nearly always look better at
higher exposures.
• Huge dynamic range means nearly
impossible to overexpose.
POST PROCESSING
TECHNIQUE CONISDERATIONS
• KVP Dependant
• Now COMPUTER controls
CONTRAST
• Higher kVp to stimulate
electron traps
standard image
edge sharpening
•
•
•
•
DEVELOPER
FIXER
WASH
DRY
• WATER - SOLVENT
PROCESSOR PROBLEM
– FIXER RETENTION
scratch
Crimping /cresent mark
REPEAT IMAGES
EMERGING PROBLEMS
• “BETTER” –NOT NECESSARILY
FASTER
• “LEARNING CURVE” FOR
TECHNOLOGIST & PHYSICIANS
• STUDENT APPLICATIONS &
“ISSUES”
• “PITFALLS OF CR”
POSITIONING & PROPER
COLLIMATION ARE CRITICAL
TO GOOD IMAGING
OUTCOMES
Just like Phototiming, it can
magnify your mistakes
COLLIMATION CRITICAL
• 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
Digital imaging is not the end
all, cure all for imaging
problems.
It is still technologist dependent.
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
• towel that was used
to help in
positioning a child
• CR is MORE
sensitive to
• ARTIFACTS
NEW IMAGE
CR image – NEW IMAGE
• Line caused
from dirt
collected in a
CR Reader
Double
exposure
Child
?
Hands over upper
abdomen
High resolution with digital
imaging