Introduction to digital radiography and pacs

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Introduction to Digital Radiography Introduction to Digital Radiography and PACSand PACS


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ObjectivesObjectives

Define the term Define the term digital imagingdigital imaging. . Explain latent image formation for conventional Explain latent image formation for conventional

radiography.radiography. Describe the latent image formation process for Describe the latent image formation process for

computed radiography.computed radiography.


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Compare and contrast the latent image formation Compare and contrast the latent image formation process for indirect capture digital radiography and process for indirect capture digital radiography and direct capture digital radiography.direct capture digital radiography.

Explain what a PACS (picture archiving and Explain what a PACS (picture archiving and communication system) is and how it is used.communication system) is and how it is used.

Define digital imaging and communications in Define digital imaging and communications in medicine.medicine.

ObjectivesObjectives


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Key TermsKey Terms

Computed radiographyComputed radiography DICOM (digital imaging and communications in DICOM (digital imaging and communications in

medicine)medicine) Digital imagingDigital imaging Digital radiographyDigital radiography Direct capture DRDirect capture DR Indirect capture DRIndirect capture DR PACSPACS TeleradiologyTeleradiology


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Conventional RadiographyConventional Radiography

Method is film-based.Method is film-based. Method uses intensifying screens.Method uses intensifying screens. Film is placed between two screens.Film is placed between two screens. Screens emit light when x-rays strike them.Screens emit light when x-rays strike them. Film is processed chemically.Film is processed chemically. Processed film is viewed on lightbox.Processed film is viewed on lightbox.


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Digital ImagingDigital Imaging

Digital imagingDigital imaging is a broad term. is a broad term. Term was first used medically in 1970s in computed Term was first used medically in 1970s in computed

tomography (CT).tomography (CT). Digital imaging is defined as any image acquisition Digital imaging is defined as any image acquisition

process that produces an electronic image that can process that produces an electronic image that can be viewed and manipulated on a computer.be viewed and manipulated on a computer.

In radiology, images can be sent via computer In radiology, images can be sent via computer networks to a variety of locations.networks to a variety of locations.


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Historical DevelopmentHistorical Developmentof Digital Imagingof Digital Imaging

CT coupled imaging devices and the computer.CT coupled imaging devices and the computer. Early CT scanners required hours to produce a single Early CT scanners required hours to produce a single

slice.slice. Reconstruction images took several days to produce.Reconstruction images took several days to produce. First CT scanners imaged the head only.First CT scanners imaged the head only. First scanner was developed by Siemens.First scanner was developed by Siemens.


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Magnetic resonance imaging (MRI) became available Magnetic resonance imaging (MRI) became available in the early 1980s.in the early 1980s.

Lauterbur paper in 1973 sparked companies to Lauterbur paper in 1973 sparked companies to research MRI.research MRI.

Many scientists and researchers were involved.Many scientists and researchers were involved. Advancements in fluoroscopy occurred in the 1970s Advancements in fluoroscopy occurred in the 1970s

as well.as well. Analog-to-digital converters allowed real-time images Analog-to-digital converters allowed real-time images

to be viewed on TV monitors.to be viewed on TV monitors.



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Fluoroscopic images could also be stored on a Fluoroscopic images could also be stored on a computer.computer.

Ultrasound and nuclear medicine used screen Ultrasound and nuclear medicine used screen capture to grab the image and convert it digitally.capture to grab the image and convert it digitally.

Eventually, mammography converted to digital Eventually, mammography converted to digital format.format.



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Digital Radiography DevelopmentDigital Radiography Development

Concept began with Albert Jutras in Canada in the Concept began with Albert Jutras in Canada in the 1950s.1950s.

Early Early PACSPACS systems were developed by the military systems were developed by the military to send images between Veterans Administration to send images between Veterans Administration hospitals in the 1980s.hospitals in the 1980s.

Development was encouraged and supported by the Development was encouraged and supported by the U.S. government.U.S. government.


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Digital Radiography DevelopmentDigital Radiography Development

Early process involved scanning radiographs into the Early process involved scanning radiographs into the computer and sending them from computer to computer and sending them from computer to computer.computer.

Images were then stored in PACS.Images were then stored in PACS. Computed and Computed and digital radiographydigital radiography followed. followed.


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Computed RadiographyComputed Radiography

Uses storage phosphor platesUses storage phosphor plates Uses existing equipmentUses existing equipment Requires special cassettesRequires special cassettes Requires a special cassette Requires a special cassette

readerreader Uses a computer workstation Uses a computer workstation

and viewing station and a printerand viewing station and a printer


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Computed RadiographyComputed Radiography Storage phosphor plates are similar to intensifying Storage phosphor plates are similar to intensifying

screens.screens. Imaging plate stores x-ray energy for an extended time.Imaging plate stores x-ray energy for an extended time. Process was first introduced in the United States by Fuji Process was first introduced in the United States by Fuji

Medical Systems of Japan in 1983. Medical Systems of Japan in 1983. First system used a phosphor storage plate, a reader, First system used a phosphor storage plate, a reader,

and a laser printer. and a laser printer.


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Computed RadiographyComputed Radiography

Method was slow to be accepted by radiologists.Method was slow to be accepted by radiologists. Installation increased in the early 1990s.Installation increased in the early 1990s. More and more hospitals are replacing film/screen More and more hospitals are replacing film/screen

technology with digital systems.technology with digital systems.


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Digital RadiographyDigital Radiography

Cassetteless systemCassetteless system Uses a flat panel detector or charge-coupled device Uses a flat panel detector or charge-coupled device

(CCD) hard-wired to computer(CCD) hard-wired to computer Requires new installation of room or retrofitRequires new installation of room or retrofit


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Two types of digital radiographyTwo types of digital radiography Indirect capture DRIndirect capture DR

• Machine absorbs x-rays and converts them to light.Machine absorbs x-rays and converts them to light.• CCD or thin-film transistor (TFT) converts light to electric CCD or thin-film transistor (TFT) converts light to electric

signals.signals.• Computer processes electric signals.Computer processes electric signals.• Images are viewed on computer monitor. Images are viewed on computer monitor.



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Direct capture DRDirect capture DR• Photoconductor absorbs x-rays.Photoconductor absorbs x-rays.• TFT collects signal.TFT collects signal.• Electrical signal is sent to computer for processing.Electrical signal is sent to computer for processing.• Image is viewed on computer screen. Image is viewed on computer screen.



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First clinical application was in 1970s in digital First clinical application was in 1970s in digital subtraction.subtraction.

University of Arizona scientists applied the technique.University of Arizona scientists applied the technique. Several companies began developing large field Several companies began developing large field

detectors.detectors.



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DR used CCD technology developed by the military DR used CCD technology developed by the military and then used TFT arrays shortly after.and then used TFT arrays shortly after.

CCD and TFT technology developed and continues CCD and TFT technology developed and continues to develop in parallel.to develop in parallel.

No one technology has proved to be better than the No one technology has proved to be better than the other.other.



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Comparison of Film to CR and DRComparison of Film to CR and DR

For conventional x-ray film and For conventional x-ray film and computed computed radiographyradiography (CR), a traditional x-ray room with a (CR), a traditional x-ray room with a table and wall Bucky is required.table and wall Bucky is required.

For DR, a detector replaces the Bucky apparatus in For DR, a detector replaces the Bucky apparatus in the table and wall stand.the table and wall stand.

Conventional and CR efficiency ratings are about the Conventional and CR efficiency ratings are about the same.same.

DR is much more efficient, and image is available DR is much more efficient, and image is available immediately.immediately.


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Latent image formation is different in CR and DR. Latent image formation is different in CR and DR.

Conventional film/screenConventional film/screen• Film is placed inside of a cassette that contains an intensifying Film is placed inside of a cassette that contains an intensifying

screen.screen.• X-rays strike the intensifying screen, and light is produced.X-rays strike the intensifying screen, and light is produced.• The light and x-ray photons interact with the silver halide grains The light and x-ray photons interact with the silver halide grains

in the film emulsion.in the film emulsion.



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• An electron is ejected from the halide.An electron is ejected from the halide.• Ejected electron is attracted to the sensitivity speck.Ejected electron is attracted to the sensitivity speck.• Speck now has a negative charge, and silver ions will be Speck now has a negative charge, and silver ions will be

attracted to equal out the charge. attracted to equal out the charge. • Process happens many times within the emulsion to form Process happens many times within the emulsion to form

the latent image.the latent image.• After chemical processing, the sensitivity specks will be After chemical processing, the sensitivity specks will be

processed into black metallic silver and the manifest image processed into black metallic silver and the manifest image is formed.is formed.


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CRCR• A storage phosphor plate is A storage phosphor plate is

placed inside of CR cassette.placed inside of CR cassette.• Most storage phosphor plates are Most storage phosphor plates are

made of a barium fluorohalide.made of a barium fluorohalide.• When x-rays strike the When x-rays strike the

photosensitive phosphor, some photosensitive phosphor, some light is given off.light is given off.

• Some of the photon energy is Some of the photon energy is deposited within the phosphor deposited within the phosphor particles to create the latent particles to create the latent image. image.

• The phosphor plate is then fed The phosphor plate is then fed through the CR reader.through the CR reader.


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CR, continuedCR, continued• Focused laser light is scanned over the plate, causing the Focused laser light is scanned over the plate, causing the

electrons to return to their original state, emitting light in the electrons to return to their original state, emitting light in the process.process.

• This light is picked up by a photomultiplier tube and This light is picked up by a photomultiplier tube and converted into an electrical signal. converted into an electrical signal.

• The electrical signal is then sent through an analog-to-digital The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to converter to produce a digital image that can then be sent to the technologist review station. the technologist review station.


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DRDR• No cassettes are required. No cassettes are required. • The image acquisition device is built into the table and/or The image acquisition device is built into the table and/or

wall stand or is enclosed in a portable device. wall stand or is enclosed in a portable device. • Two distinct image acquisition methods are indirect capture Two distinct image acquisition methods are indirect capture

and direct capture. and direct capture.


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DR, continuedDR, continued• Indirect capture is similar to CR in that the x-ray energy Indirect capture is similar to CR in that the x-ray energy

stimulates a scintillator, which gives off light that is detected stimulates a scintillator, which gives off light that is detected and turned into an electrical signal. and turned into an electrical signal.

• With direct capture, the x-ray energy is detected by a With direct capture, the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical photoconductor that converts it directly to a digital electrical signal. signal.


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Image Processing Image Processing

Conventional radiographyConventional radiography• Image is determined by the film itself and the chemicals. Image is determined by the film itself and the chemicals.

CR and DRCR and DR• Image processing takes place in a computer. Image processing takes place in a computer. • For CR, the computer is located near the readers.For CR, the computer is located near the readers.• For DR, the computer is located next to x-ray console, or it For DR, the computer is located next to x-ray console, or it

may be integrated within the console, and the image is may be integrated within the console, and the image is processed before moving on to the next exposure.processed before moving on to the next exposure.


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Exposure Latitude Exposure Latitude or Dynamic Rangeor Dynamic Range

Conventional radiographyConventional radiography• Based on the characteristic response of the film, which is Based on the characteristic response of the film, which is

nonlinear. nonlinear. • Radiographic contrast is primarily controlled by kilovoltage Radiographic contrast is primarily controlled by kilovoltage

peak.peak.• Optical density on film is primarily controlled by milliampere-Optical density on film is primarily controlled by milliampere-

second setting.second setting.


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Exposure LatitudeExposure Latitudeor Dynamic Rangeor Dynamic Range

CR and DRCR and DR• Contain a detector that can respond in a linear manner.Contain a detector that can respond in a linear manner.• Exposure latitude is wide, allowing the single detector to be Exposure latitude is wide, allowing the single detector to be

sensitive to a wide range of exposures.sensitive to a wide range of exposures.• Kilovoltage peak still influences subject contrast, but Kilovoltage peak still influences subject contrast, but

radiographic contrast is primarily controlled by an image radiographic contrast is primarily controlled by an image processing look-up table.processing look-up table.

• Milliampere-second setting has more control over image noise, Milliampere-second setting has more control over image noise, whereas density is controlled by image-processing algorithms.whereas density is controlled by image-processing algorithms.


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Scatter SensitivityScatter Sensitivity

It is important to minimize scattered radiation with all It is important to minimize scattered radiation with all three acquisition systems.three acquisition systems.

CR and DR can be more sensitive to scatter than CR and DR can be more sensitive to scatter than screen/film.screen/film.

Materials used in the many CR and DR image Materials used in the many CR and DR image acquisition devices are more sensitive to low-energy acquisition devices are more sensitive to low-energy photons. photons.


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Picture Archival andPicture Archival andCommunication SystemsCommunication Systems

Networked group of computers, Networked group of computers, servers, and archives to store servers, and archives to store digital imagesdigital images

Can accept any image that is in Can accept any image that is in DICOMDICOM format format

Serves as the file room, reading Serves as the file room, reading room, duplicator, and courierroom, duplicator, and courier

Provides image access to multiple Provides image access to multiple users at the same time, on-users at the same time, on-demand images, electronic demand images, electronic annotations of images, and annotations of images, and specialty image processingspecialty image processing


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Custom designed for each facilityCustom designed for each facility Components/features can vary based on the following:Components/features can vary based on the following:

• Volume of patientsVolume of patients• Number of interpretation areasNumber of interpretation areas• Viewing locationsViewing locations• FundingFunding



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Early systems did not have standardized image Early systems did not have standardized image formats.formats.

Matching up systems was difficult.Matching up systems was difficult. Vendors kept systems proprietary and did not share Vendors kept systems proprietary and did not share

information.information. DICOM standards helped change this by allowing DICOM standards helped change this by allowing

communication between vendors’ products.communication between vendors’ products.



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First full-scale PACSFirst full-scale PACS• Veterans Administration Medical Center in Baltimore used Veterans Administration Medical Center in Baltimore used

PACS in 1993.PACS in 1993.• PACS covered all modalities except mammography.PACS covered all modalities except mammography.• Shortly after, PACS was interfaced with radiology Shortly after, PACS was interfaced with radiology

information systems, hospital information systems, and information systems, hospital information systems, and electronic medical records.electronic medical records.



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PACS UsesPACS Uses

Made up of different componentsMade up of different components• Reading stationsReading stations• Physician review stationsPhysician review stations• Web accessWeb access• Technologist quality control stationsTechnologist quality control stations• Administrative stationsAdministrative stations• Archive systemsArchive systems• Multiple interfaces to other hospital and radiology systemsMultiple interfaces to other hospital and radiology systems


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Early PACS seen only in radiology and some cardiology Early PACS seen only in radiology and some cardiology departments.departments.

PACS now can be used in multiple departments.PACS now can be used in multiple departments. Archive space can be shared among departments.Archive space can be shared among departments. PACS reading stations may also have image processing PACS reading stations may also have image processing

capabilities.capabilities. PACS allows radiologists to reconstruct and stitch PACS allows radiologists to reconstruct and stitch

images in their offices.images in their offices.

PACS UsesPACS Uses


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Orthopedic workstations are available for the Orthopedic workstations are available for the following:following:• Surgeons can plan joint replacement surgery.Surgeons can plan joint replacement surgery.• Specialized software allows matching of best replacement Specialized software allows matching of best replacement

for patient with patient anatomy.for patient with patient anatomy.• System saves time and provides better fit.System saves time and provides better fit.

PACS UsesPACS Uses

Introduction to digital radiography and pacs

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