Download Chapter 1 Introduction to Digital Radiography and PACS

Chapter 1
Introduction to Digital Radiography
and PACS
Elsevier items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
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Objectives
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Define the term digital imaging.
Explain latent image formation for conventional
radiography.
Describe the latent image formation process for
computed radiography.
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Objectives
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Compare and contrast the latent image formation
process for indirect capture digital radiography and
direct capture digital radiography.
Explain what a PACS (picture archiving and
communication system) is and how it is used.
Define digital imaging and communications in
medicine.
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Key Terms
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Computed radiography
DICOM (digital imaging and communications in
medicine)
Digital imaging
Digital radiography
Direct capture DR
Indirect capture DR
PACS
Teleradiology
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Conventional Radiography
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Method is film-based.
Method uses intensifying screens.
Film is placed between two screens.
Screens emit light when x-rays strike them.
Film is processed chemically.
Processed film is viewed on lightbox.
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Digital Imaging
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Digital imaging is a broad term.
Term was first used medically in 1970s in computed
tomography (CT).
Digital imaging is defined as any image acquisition
process that produces an electronic image that can
be viewed and manipulated on a computer.
In radiology, images can be sent via computer
networks to a variety of locations.
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Historical Development
of Digital Imaging
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CT coupled imaging devices and the computer.
Early CT scanners required hours to produce a single
slice.
Reconstruction images took several days to produce.
First CT scanners imaged the head only.
First scanner was developed by Siemens.
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Historical Development
of Digital Imaging
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Magnetic resonance imaging (MRI) became available
in the early 1980s.
Lauterbur paper in 1973 sparked companies to
research MRI.
Many scientists and researchers were involved.
Advancements in fluoroscopy occurred in the 1970s
as well.
Analog-to-digital converters allowed real-time images
to be viewed on TV monitors.
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Historical Development
of Digital Imaging
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Fluoroscopic images could also be stored on a
computer.
Ultrasound and nuclear medicine used screen
capture to grab the image and convert it digitally.
Eventually, mammography converted to digital
format.
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Digital Radiography Development
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Concept began with Albert Jutras in Canada in the
1950s.
Early PACS systems were developed by the military
to send images between Veterans Administration
hospitals in the 1980s.
Development was encouraged and supported by the
U.S. government.
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Digital Radiography Development
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Early process involved scanning radiographs into the
computer and sending them from computer to
computer.
Images were then stored in PACS.
Computed and digital radiography followed.
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Computed Radiography
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Uses storage phosphor plates
Uses existing equipment
Requires special cassettes
Requires a special cassette
reader
Uses a computer workstation
and viewing station and a printer
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Computed Radiography
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Storage phosphor plates are similar to intensifying
screens.
Imaging plate stores x-ray energy for an extended time.
Process was first introduced in the United States by Fuji
Medical Systems of Japan in 1983.
First system used a phosphor storage plate, a reader,
and a laser printer.
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Computed Radiography
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Method was slow to be accepted by radiologists.
Installation increased in the early 1990s.
More and more hospitals are replacing film/screen
technology with digital systems.
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Digital Radiography
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Cassetteless system
Uses a flat panel detector or charge-coupled device
(CCD) hard-wired to computer
Requires new installation of room or retrofit
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Digital Radiography
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Two types of digital radiography
Indirect capture DR
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Machine absorbs x-rays and converts them to light.
CCD or thin-film transistor (TFT) converts light to electric
signals.
Computer processes electric signals.
Images are viewed on computer monitor.
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Digital Radiography
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Direct capture DR
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Photoconductor absorbs x-rays.
TFT collects signal.
Electrical signal is sent to computer for processing.
Image is viewed on computer screen.
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Digital Radiography
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First clinical application was in 1970s in digital
subtraction.
University of Arizona scientists applied the technique.
Several companies began developing large field
detectors.
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Digital Radiography
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DR used CCD technology developed by the military
and then used TFT arrays shortly after.
CCD and TFT technology developed and continues
to develop in parallel.
No one technology has proved to be better than the
other.
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Comparison of Film to CR and DR
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For conventional x-ray film and computed
radiography (CR), a traditional x-ray room with a
table and wall Bucky is required.
For DR, a detector replaces the Bucky apparatus in
the table and wall stand.
Conventional and CR efficiency ratings are about the
same.
DR is much more efficient, and image is available
immediately.
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Comparison of Film to CR and DR
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Latent image formation is different in CR and DR.
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Conventional film/screen
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Film is placed inside of a cassette that contains an intensifying
screen.
X-rays strike the intensifying screen, and light is produced.
The light and x-ray photons interact with the silver halide grains
in the film emulsion.
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Comparison of Film to CR and DR
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An electron is ejected from the halide.
Ejected electron is attracted to the sensitivity speck.
Speck now has a negative charge, and silver ions will be
attracted to equal out the charge.
Process happens many times within the emulsion to form the
latent image.
After chemical processing, the sensitivity specks will be
processed into black metallic silver and the manifest image
is formed.
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Comparison of Film to CR and DR
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CR
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A storage phosphor plate is
placed inside of CR cassette.
Most storage phosphor plates are
made of a barium fluorohalide.
When x-rays strike the
photosensitive phosphor, some
light is given off.
Some of the photon energy is
deposited within the phosphor
particles to create the latent
image.
The phosphor plate is then fed
through the CR reader.
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Comparison of Film to CR and DR
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CR, continued
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Focused laser light is scanned over the plate, causing the
electrons to return to their original state, emitting light in the
process.
This light is picked up by a photomultiplier tube and
converted into an electrical signal.
The electrical signal is then sent through an analog-to-digital
converter to produce a digital image that can then be sent to
the technologist review station.
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Comparison of Film to CR and DR
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DR
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No cassettes are required.
The image acquisition device is built into the table and/or
wall stand or is enclosed in a portable device.
Two distinct image acquisition methods are indirect capture
and direct capture.
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Comparison of Film to CR and DR
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DR, continued
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Indirect capture is similar to CR in that the x-ray energy
stimulates a scintillator, which gives off light that is detected
and turned into an electrical signal.
With direct capture, the x-ray energy is detected by a
photoconductor that converts it directly to a digital electrical
signal.
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Image Processing
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Conventional radiography
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Image is determined by the film itself and the chemicals.
CR and DR
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Image processing takes place in a computer.
For CR, the computer is located near the readers.
For DR, the computer is located next to x-ray console, or it
may be integrated within the console, and the image is
processed before moving on to the next exposure.
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Exposure Latitude
or Dynamic Range
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Conventional radiography
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Based on the characteristic response of the film, which is
nonlinear.
Radiographic contrast is primarily controlled by kilovoltage
peak.
Optical density on film is primarily controlled by milliamperesecond setting.
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Exposure Latitude
or Dynamic Range
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CR and DR
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Contain a detector that can respond in a linear manner.
Exposure latitude is wide, allowing the single detector to be
sensitive to a wide range of exposures.
Kilovoltage peak still influences subject contrast, but
radiographic contrast is primarily controlled by an image
processing look-up table.
Milliampere-second setting has more control over image noise,
whereas density is controlled by image-processing algorithms.
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Scatter Sensitivity
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It is important to minimize scattered radiation with all
three acquisition systems.
CR and DR can be more sensitive to scatter than
screen/film.
Materials used in the many CR and DR image
acquisition devices are more sensitive to low-energy
photons.
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Picture Archival and
Communication Systems
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Networked group of computers,
servers, and archives to store
digital images
Can accept any image that is in
DICOM format
Serves as the file room, reading
room, duplicator, and courier
Provides image access to multiple
users at the same time, ondemand images, electronic
annotations of images, and
specialty image processing
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Picture Archival and
Communication Systems
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Custom designed for each facility
Components/features can vary based on the following:
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Volume of patients
Number of interpretation areas
Viewing locations
Funding
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Picture Archival and
Communication Systems
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Early systems did not have standardized image
formats.
Matching up systems was difficult.
Vendors kept systems proprietary and did not share
information.
DICOM standards helped change this by allowing
communication between vendors’ products.
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Picture Archival and
Communication Systems
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First full-scale PACS
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Veterans Administration Medical Center in Baltimore used
PACS in 1993.
PACS covered all modalities except mammography.
Shortly after, PACS was interfaced with radiology information
systems, hospital information systems, and electronic
medical records.
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PACS Uses
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Made up of different components
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Reading stations
Physician review stations
Web access
Technologist quality control stations
Administrative stations
Archive systems
Multiple interfaces to other hospital and radiology systems
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PACS Uses
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Early PACS seen only in radiology and some cardiology
departments.
PACS now can be used in multiple departments.
Archive space can be shared among departments.
PACS reading stations may also have image processing
capabilities.
PACS allows radiologists to reconstruct and stitch
images in their offices.
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PACS Uses
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Orthopedic workstations are available for the
following:
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Surgeons can plan joint replacement surgery.
Specialized software allows matching of best replacement
for patient with patient anatomy.
System saves time and provides better fit.
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