Fundamentals of Picture Archiving and Communication SystemsPACS

1
Chapter 2

• Fundamentals of Picture Archiving and
  Communication Systems(PACS)

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Outline

• Introduction
• Computer Networks Fundamentals
• The PACS

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Introduction
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Picture Archiving and Communication Systems

• The history of PACS
• The components of PACS
• Image acquisition
• PACS Displays
• Archive and Database

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Image Acquisition

• Image sourcesImaging modalities
• Radiology Modalities of Nuclear Medicine
• X-Ray, CR, MRI, CT,
• Acquisition gateway

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PACS Displays

• Image Display and Analysis
• Image WorkstationsDiagnostic, Clinical, Image
  Processing (3D images, image quality control, ...
  )
• The Monitor and Display Card
• Laser printing devices

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PACS Displays
Image Viewer Station
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PACS Displays
Image Viewer Station
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Archive and Database

• Image Archiving
• Image Database Management
• Image Compression

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PACS Network
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PACS Data Flow
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Computer Network Fundamentals
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Computer Network Fundamentals

• Local Area Networks(LANs)
• The Ethernet
• The ATM Networks
• Wan Area Networks(WANs)
• The OSI Reference Model
• The TCP/IP Protocols

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Local Area Networks(LAN)

• Network Topologies
• Mesh Topology
• Ring Topology
• Star Topology
• Tree Topology
• Bus Topology

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Mesh Topology
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Mesh Topology

• Point-to-point network
• Every two communication nodes has a dedicated
  connection
• Each pair of computer performs communications
  independent of others
• The number of links increases fast as the number
  of nodes increases

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Mesh Topology

• Number of links( L )
• L N(N 1) / 2
• NNumber of nodes (computers)

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Ring Topology
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Ring Topology

• The computers are connected as a ring.
• Each computer links to its two neighbors in a
  circular arrangement.
• The last computer connects to the first.
• The message travels along the ring and is
  transferred by each computer until it reaches the
  destination.
• One link fails causes the network down.

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Star Topology
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Star Topology

• The network connection is arranged as a star.
• All computers links to a hub.
• The hub directs the message from the sender to
  its destination.
• Each computer does not directly connect to others.

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Tree Topology
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Tree Topology

• An alternative form of star topology
• All the nodes connect to the central hub, an
  active hub.
• A node may be a computer or a secondary hub.
• Each secondary hub has a group of computers
  connecting to it.

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Tree Topology

• The secondary hub may be an active or a passive
  hub.
• Can assign priority to each link.

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Bus Topology
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Bus Topology

• All nodes link to a transmission cable, a shared
  bus.
• Any computer can send messages to any other nodes
  through the bus.
• All the nodes receive the messages from the
  sender.

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Ethernet

• First Designed in 1973
• at Xerox Palo Alto Research Center
• Operates at 2.94 Mbps
• DIX Ethernet
• Developed by DEC, Intel, and Xerox in1980
• 10 Mbps Standard

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Ethernet

• 10 Base T
• By SynOptics in 1987
• Speed 10 Mbps
• Fast Ethernet
• By Grand Junction in 1992
• Speed 100 Mbps
• Standard(IEEE 802.3u) defined by IEEE in 1995

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Ethernet

• Gigabit Ethernet
• IEEE 802.3z in 1998
• Speed 1G Bps
• Uses Bus Topology
• All computers connect to a shared bus
• One computer sends message at a time
• Message travels along the bus to each connected
  computer

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Ethernet
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CSMA/CD

• CSMA/CD
• Carrier Sense with Multiple Access / Collision
  Detection
• Media Access Control for Ethernet
• Coordinates the access of transmission media(bus)
  among connected computers

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CSMA/CD

• Carrier Sense
• Listen before transmit
• Sense the media for carrier before sending
  message
• Multiple Access
• All connected computers can transmit data
• Transmission can be performed when the shared bus
  is idle

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CSMA/CD

• Collision occurs when two computers send message
  at the same time
• Two senders sense the media at the same time and
  find no carrier on it
• Both send data
• Data corrupted(Signal Quality Error)
• Receiver receives incorrect data

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CSMA/CD

• Collision Detection(CD)
• Detecting collision after transmission
• Transmission stopped when collision is detected
• Transmission Recovery(The backoff)
• Both sending nodes wait for different lengths of
  time to send data again

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CSMA/CD

• Transmission Recovery(The backoff)
• The length of time is randomly selected less than
  a specified maximum delay
• Collision may still occurs after waiting a random
  delay.
• If collision occurs again, the maximum delay for
  each computer increases

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ATM Networks

• Asynchronous Transfer Mode
• Designed for integrated services
• Audio message
• Video message
• Data
• Low delay?low jitter?echo cancellation

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ATM Networks

• ATM cells
• Small and fixed-size packets
• 53 bytes long
• 5 bytes for header(overhead)
• 48 bytes for data(payload)
• 10 cell tax, but the small size cells provide
  a low delay and jitter communication

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ATM Networks

• Uses connection-oriented service
• A connection is established before transmission
• Connection remains until the communication ends
• The connection is called the virtual channel (VC)

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ATM Networks

• Uses a connection identifier(VPI/VCI) to specify
  a virtual channel, instead of destination address
• A cell is assigned a VPI/VCI when a connection is
  established
• A cell is directed to the destination by label
  switching mechanism

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Quality of Service(QoS)

• ATM provides quality of service(QoS)specified by
  users.
• QoS specifications are provided and remain in
  effect throughout the communication
• ATM QoS specifications
• CBR?VBR?ABR?UBR

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Quality of Service(QoS)

• Constant Bit Rate(CBR)
• Handles the transmission for time-sensitive
  message such as uncompressed audio and video
• Set up a constant bandwidth
• Variable Bit Rate(VBR)
• For compressed data transmission
• Real-time VBR( VBR-rt )
• Non-real-time VBR(VBR-nrt)

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Quality of Service(QoS)

• Available Bit Rate(ABR)
• Transmission uses the available bandwidth
• Application for bursty transmission
• Unspecified Bit Rate(UBR)
• Uses the highest transmission rate at at given
  time
• Packets may be lost at heavy trafficy

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The PACS
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Advantages of PACS

• Improves the quality of diagnosis.
• Speeds up health care.
• Reduces operation cost.
• Promotes a more efficient operating environment

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What is PACS ?

• Picture Archiving and Communication Systems
• Image and data acquisition, storage, and display
  subsystems integrated by various digital
  networks.

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History
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PACS components

• Imaging Devices
• Device Interface
• Archiving and Database System
• Image Displays
• System networking

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Imaging Devices and Interfaces

• Imaging Modalities
• Acquisition Gateway
• Peer-to-peer network interfaces.
• Master/slave device-level interfaces.

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PPP(Peer-to-Peer Protocol)

• The Hand-Shake are illustrated below.

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The PPP in PACS

• Peer-to-peer network between an imaging device
  computer and a PACS acquisition gateway.

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The Peer-to-Peer of two modes

• Push mode and pull mode
• Push mode, from the modality computer.
• Pull mode, from the gateway computer.

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Master/Slave
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Archive and Database

• Operation of a PACS controller

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Display Workstations

• Major function of a PACS workstation.

Function
Description Case prepartion
Accumulation of relevant images and information
patient
examination. Case selection
Selection of cases for a given subpopulation. Imag
e arrangement Tools for arranging and
grouping images for easy
review. Interpretation
Measurement tools for facilitating the
diagnosis. Documentation Tools for
image annotation, text, and voice reports. Case
presentation Tools for a comprehensive
case presentation.
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System Networking

• OSI and TCP/IP mode