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Chapter 2

Chapter 2. Fundamentals of Picture Archiving and Communication Systems （ PACS ）. Outline. Introduction Computer Networks Fundamentals The PACS. Introduction. Picture Archiving and Communication Systems. The history of PACS The components of PACS Image acquisition PACS Displays

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Chapter 2

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  1. Chapter 2 Fundamentals of Picture Archiving and Communication Systems（PACS）

  2. Outline • Introduction • Computer Networks Fundamentals • The PACS

  3. Introduction

  4. Picture Archiving and Communication Systems • The history of PACS • The components of PACS • Image acquisition • PACS Displays • Archive and Database

  5. Image Acquisition • Image sources：Imaging modalities • Radiology Modalities of Nuclear Medicine • X-Ray, CR, MRI, CT,… • Acquisition gateway

  6. PACS Displays • Image Display and Analysis • Image Workstations：Diagnostic, Clinical, Image Processing (3D images, image quality control, ... ) • The Monitor and Display Card • Laser printing devices

  7. PACS Displays Image Viewer Station

  8. PACS Displays Image Viewer Station

  9. Archive and Database • Image Archiving • Image Database Management • Image Compression

  10. MRI X-ray CT PACS NETWORK COT Viewing Station COT Viewing Station Image Storage and Archive PC-based Workstation PC-based Workstation PACS Network

  11. HIS/RIS Image Device Image Acquisition Image Archive Image Display PACS Data Flow

  12. Computer Network Fundamentals

  13. Computer Network Fundamentals • Local Area Networks（LANs） • The Ethernet • The ATM Networks • Wan Area Networks（WANs） • The OSI Reference Model • The TCP/IP Protocols

  14. Local Area Networks（LAN） • Network Topologies • Mesh Topology • Ring Topology • Star Topology • Tree Topology • Bus Topology

  15. A four-node mesh network Mesh Topology

  16. 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

  17. Mesh Topology • Number of links（ L ） L = N(N – 1) / 2 N：Number of nodes (computers)

  18. B A D C Ring Topology

  19. 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.

  20. C D A HUB B D G F H Star Topology

  21. 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.

  22. central hub secondary hub secondary hub C computer C C C C Tree Topology

  23. 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.

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

  25. A B C D Bus Topology

  26. 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.

  27. 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

  28. 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

  29. 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

  30. shared bus A B C N sending computer destination computer Ethernet

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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

  36. ATM Networks • Asynchronous Transfer Mode • Designed for integrated services • Audio message • Video message • Data • Low delay、low jitter、echo cancellation

  37. 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

  38. 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)

  39. 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

  40. 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

  41. 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）

  42. 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

  43. The PACS

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

  45. What is PACS ? • Picture Archiving and Communication Systems • Image and data acquisition, storage, and display subsystems integrated by various digital networks.

  46. History

  47. PACS components • Imaging Devices • Device Interface • Archiving and Database System • Image Displays • System networking

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

  49. HOST a HOST b Send SYM(seq=x) Receive SYM(seq=x) Receive SYM (seq=y, ACK=x+1) Send SYM (seq=x, ACK=x+1) Send ACK(ack=y+1) Receive ACK(ACK=y+1) PPP(Peer-to-Peer Protocol) • The Hand-Shake are illustrated below.

  50. Push HOST a HOST b Pull The PPP in PACS • Peer-to-peer network between an imaging device computer and a PACS acquisition gateway.

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