PACS Controller and Image Archive

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PACS Controller and Image Archive
Picture Archiving and Comunication System
May 13, 2003 Dr. Tsi-chain Chao Dr. Ing-Tsung
Hsiao
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PACS Networks
Image Acquisition Gateway Computer
CT
SPECT
PET
X-ray
PACS Controller
MRI
Ultrasound
Display Workstation
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PACS Central Node
PACS Controller
Image Archive

• Data Integrity
• Efficiency

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1. Image Management

• Backup, backup, backup
• Local storage management retains at least two
  copies of an image on separate storage devices
  until it has been archived successfully to the
  long-term storage devices

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PACS Controller System

• Four major components an archive server, a
  database system, an optical disk library, and a
  network
• Fig. 10-2

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Archive Server

• Consists of multiple CPUs, SCSI buses, and
  Ethernet/ATM network interface.
• Acts as a PACS controller for data flow within
  the entire PACS network.
• Uses data cache (large RAID/Mag disks for at
  least 2-week storage? high data thru-put/for
  faster read-operation
• example 13.6Gb storage 500 CT (11.68Mb) 1000
  MR (3.47Mb) 500 CR (7.46 Mb) studies.

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Database System

• Redundant database servers
• Reliable database system (Oracle)
• Structured query language (SQL)
• Mirror database for duplicating the data to
  ensure no data loss
• Also used to interface with RIS/HIS

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Archive library

• Permanent storage
• Optical disk
• Tape
• CD-ROM
• WORM (write once/read many)
• Redundant power supply or UPS
• Storage capacity at least terabytes

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Backup Archive

• Two identical archive libraries for
  fault-tolerance
• Two different locations to protect from natural
  disaster.
• Two different media fast/expensive and
  cheap/slow

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Network

• Connected to WAN (T1/ATM)
• Connected to LAN (ethernet/ATM)
• high-speed
• conventional for backup

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PACS controller system software

• Image receiving from acq. computer to server
• Image stacking cached images in the local disks
  of the server
• Image routing routed to destination (display
  workstation) using pre-defined routing table.
• Image archiving from temporary to long-term
  storage
• Studies grouping multiple studies for the same
  patient are archived contiguously

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PACS controller system software-cont.

• Platter management reserve space for patient
  revisiting.
• RIS/HIS interfacing ADT info is needed for
  prefetch, studies grouping, and platter
  management.
• PACS database updating
• Image retrieving retrieving requested by the
  display workstation
• Image prefetching automatic historical data
  retrieving when patient arrives.

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PACS controller system software

• Fig. 10-3

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3. Storage Media

• Immediately accessible RAID
• Fast accessible Regular hard drive
• Temporary long term MO
• Permanently storage CD-Rom, WORM, DVD-ROM
• Backup Tape

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3.1 RAID 0

• RAID 0 implements a striped disk array, the data
  is broken down into blocks and each block is
  written to a separate disk drive

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Advantages

• I/O performance is greatly improved by spreading
  the I/O load across many channels and drives
• Best performance is achieved when data is striped
  across multiple controllers with only one drive
  per controller
• No parity calculation overhead is involved
• Very simple design
• Easy to implement

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Disadvantages

• Not a "True" RAID because it is NOT
  fault-tolerant
• The failure of just one drive will result in all
  data in an array being lost
• Should never be used in mission critical
  environments

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Applications

• Video Production and Editing
• Image Editing
• Pre-Press Applications
• Any application requiring high bandwidth

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3.2 RAID 1

• One Write or two Reads possible per mirrored pair
• Twice the Read transaction rate of single disks,
  same Write transaction rate as single disks

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Advantages

• 100 redundancy of data means no rebuild is
  necessary in case of a disk failure, just a copy
  to the replacement disk
• Transfer rate per block is equal to that of a
  single disk
• Under certain circumstances, RAID 1 can sustain
  multiple simultaneous drive failures
• Simplest RAID storage subsystem design

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Disadvantages

• Highest disk overhead of all RAID types (100)
  inefficient
• Typically the RAID function is done by system
  software, loading the CPU/Server and possibly
  degrading throughput at high activity levels.
  Hardware implementation is strongly recommended
• May not support hot swap of failed disk when
  implemented in "software"

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Applications

• Accounting
• Payroll
• Financial
• Any application requiring very high availability

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3.3 RAID 2

• Each bit of data word is written to a data disk
  drive (4 in this example 0 to 3). Each data word
  has its Hamming Code ECC word recorded on the ECC
  disks. On Read, the ECC code verifies correct
  data or corrects single disk errors.

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Hamming Code

• 0 ? 0 ? 1 ? 0 ? 1 ? 0 ? 0 0
• Differences between any two code are at least 3.
• Can detect where is the error for single/double
  error.

• 0 0 0 0, 0 0 0
• 0 0 0 1, 1 1 1
• 0 0 1 0, 1 1 0
• 0 0 1 1, 0 0 1
• 0 1 0 0, 1 0 1
• 0 1 0 1, 0 1 0
• 0 1 1 0, 0 1 1
• 0 1 1 1, 1 0 0

• 1 0 0 0, 0 1 1
• 1 0 0 1, 1 0 0
• 1 0 1 0, 1 0 1
• 1 0 1 1, 0 0 1
• 1 1 0 0, 0 1 0
• 1 1 0 1, 1 1 0
• 1 1 1 0, 0 0 0
• 1 1 1 1, 1 1 1

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Advantages

• "On the fly" data error correction
• Extremely high data transfer rates possible
• The higher the data transfer rate required, the
  better the ratio of data disks to ECC disks
• Relatively simple controller design compared to
  RAID levels 3,4 5

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Disadvantages

• Very high ratio of ECC disks to data disks with
  smaller word sizes inefficient
• Entry level cost very high - requires very high
  transfer rate requirement to justify
• Transaction rate is equal to that of a single
  disk at best (with spindle synchronization)

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3.4 RAID 3

• The data block is subdivided ("striped") and
  written on the data disks. Stripe parity is
  generated on Writes, recorded on the parity disk
  and checked on Reads.

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Advantages

• Very high Read data transfer rate
• Very high Write data transfer rate
• Disk failure has an insignificant impact on
  throughput
• Low ratio of ECC (Parity) disks to data disks
  means high efficiency

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Disadvantages

• Transaction rate equal to that of a single disk
  drive at best (if spindles are synchronized)
• Controller design is fairly complex
• Very difficult and resource intensive to do as a
  "software" RAID

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Applications

• Video Production and live streaming
• Image Editing
• Video Editing
• Prepress Applications
• Any application requiring high throughput

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3.5 RAID 5

• Each entire data block is written on a data disk
  parity for blocks in the same rank is generated
  on Writes, recorded in a distributed location and
  checked on Reads.

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Advantages

• Highest Read data transaction rate
• Medium Write data transaction rate
• Low ratio of ECC (Parity) disks to data disks
  means high efficiency
• Good aggregate transfer rate

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Disadvantages

• Disk failure has a medium impact on throughput
• Most complex controller design
• Difficult to rebuild in the event of a disk
  failure (as compared to RAID level 1)
• Individual block data transfer rate same as
  single disk

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Applications

• File and Application servers
• Database servers
• WWW, E-mail, and News servers
• Intranet servers
• Most versatile RAID level

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4. PACS Server System Operations

• Automatic system which can exchange data disk
  automatically except optical disks.
• Fault-tolerant system supported by UPS, mirror
  database, central monitoring system, redundant
  spare parts, and a fast manufacturers service

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5. DICOM-Compliant PACS Server
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Communication using DICOM
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DICOM Compliant IAG
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DICOM Compliant PACS Controller