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Unit IIICreating the Image
Chapter 26Digital Image Management
Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 4
Objectives
• Discuss advantages of using PACS in a medical imaging department
• Explain why a PACS network may require a separate computer network from the one used throughout an institution
Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 5
Objectives
• Describe laser printers that can be used for digital images
• Explain soft-copy monitor display parameters
Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 6
Objectives
• Identify types of storage available for digital images
• Discuss necessity for Digital Imaging and Communication in Medicine (DICOM) in medical imaging
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Introduction
• Filmless environment has become possible today due to:– Faster data handling– High resolution monitors– Efficient storage options– Communication standardization
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Introduction
• PACS– Hardware and software
• HIS/RIS
• Integration of the electronic medical record (EMR)
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Digital Imaging Formats
• CR/DR
• Digital fluoro/angiography
• Computed tomography
• MRI
• Sonography
• Others
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Image Acquisition
• Mini PACS
• Teleradiology
• Film digitizers– Laser digitizer– CCD digitizer
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Laser Digitizer
• Laser scans film in raster pattern
• Light transmitted through film detected
• Converted into electronic signal and digitized
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CCD Digitizer
• Light focused into a line shines through film
• Strikes linear array CCD detector
• A signal proportional to the amount of light striking the detector is sent to the computer
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Image Distribution
• Network infrastructure and file management– Large impact on data distribution
• Images need to be distributed to radiologists and clinicians
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Image File Size
• Dependent upon:– Matrix size– Bit depth
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Gray Scale Bit Depth
• 8 – 32 bits– 1 byte = 8 bits
• File size of pixel– Multiplied by bit depth and divided by 8
• 8 – 32 bit depth• 1 – 4 bytes of storage
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Bandwidth
• Controls the speed at which data can be sent over a network
• Bits per second– bps
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PACS network
• Separate network allows for large data files to be moved quickly– LAN (local area network)– Ethernet
• Bandwidth 10 Mbps
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Teleradiology
• WAN (wide area network)– Much slower
• Wireless networks– Currently even slower
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PACS Difficulties
• Large files
• Limited bandwidth
• Special language
• Problems interfacing with HIS
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HIS/RIS
• Hospital information systems– Database containing all patient medical
record information except for radiology
• Radiology information systems– Radiology specific database
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HIS/RIS
• Ideally want interconnected HIS/RIS– RIS then sends needed patient information
to PACS
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Filmless/Paperless Environment
• HIS registers patients and sends orders to RIS
• RIS generates worklist for the day
• PACS sends image and patient data to radiologist/clinician
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Image Display
• Hard-copy display
• Soft-copy display
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Hard-Copy Display
• Laser printers
• Dry processors
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Laser Printer Components
• Laser source
• Collimator lens or beam shaping optics
• Beam modulator
• Deflecting mirror-shaping lenses
• Cylindrical deflection mirror
• Unexposed film storage
• Mechanical transport
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Laser Printers
• 8 bit gray scale
• Light sources– Infrared (780-820 nm)– Solid-state diode (~670-680 nm)– Helium-neon (633nm)
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Laser Printers
• Film exposed line by line in raster pattern
• Exposed film processed by dry or wet processor
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Laser Printer Calibration
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Wet Laser Film
• Contains silver halides
• Spectrally sensitive to red or infrared wavelengths– Will be fogged by red safelights
• Processed through developer, fixer, wash and dried
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Dry Processors
• Thermally processed– Heat-sensitive film
• Silver-based emulsion• Dye microcapsules• Carbon-based adherographic printing
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Silver-Based Emulsion Dry Processor Film
• Silver Benhate– Laser light creates latent image centers– Heat develops latent image centers
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Dye Microcapsule DryProcessor Film
• Become permeable when exposed to laser
• Heat activates chemical processing
• Cooling causes processing to stop
• If stored in high heat film density can increase over time
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Carbon-Based Adherographic Printing
• Film exposed to gallium arsenide laser
• Carbon particles adhere to areas exposed by laser
• Cover sheet sealed or laminated onto finished film
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Dry Processor Film
• Shorter shelf life
• More sensitive to heat and humidity
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Soft-Copy Display
• Monitors– CRT– Flat panel
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CRT
• Components– Electron gun– Phosphor screen
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CRT
• Electron stream– Raster pattern
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Flat Panel LCD Monitors
• Light source shines on individual pixels
• Liquid crystal and hydrogenated amorphous silicon TFTs– Located between glass plates
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Storage
• Typical large radiology department– 150,000 examinations– 3.2 Terabytes of memory
• 3-5 years of storage• 16 Terabytes
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Storage
• Short-term– Local hard drive– PACS server and RAID
• Long-term– Jukebox of disks or tapes
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Storage
• Off-site– Ensures integrity if there is a catastrophic
event
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DICOM
• Standards-based protocol created by joint efforts of ACR and the National Electrical Manufacturers Association (NEMA)
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