Building a DICOM Library in C

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Building a DICOM Library in C

• Victor Derks
• GE Healthcare

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Contents

• Introduction
• Design Goals
• Inception
• Approach and Effort
• Design Challenges
• Character Encoding
• DICOM C-STORE on a Wide Area Network (WAN)
• DICOM Operations on a Wide Area Network
• Conclusions
• Recommendations

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Introduction

• Microsoft .NET Platform Group within GE
  Healthcare
• Provide Microsoft .NET components to applications
  teams
• Internal DICOM library is a one of these
  components
• The preferred programming language of our group
  is C

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Design Goals

• Requirements
• DICOM File I/O
• DICOM Communication
• Focus Areas
• Internationalization
• Service Oriented Architecture
• Easy to use for C programmers

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Inception

• Started in 2007 building prototypes
• Wrap existing C internal implementation in .NET
  layer?
• Create new C implementation?
• Findings
• .NET \ C Memory Management Models are
  conflicting
• Mixed solution doesnt work well due to high
  interaction between the layers
• No option to leverage new .NET patterns
• Asynchronous Programming Model
• Thread pool

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Approach and Effort

• Test Driven Development (TDD)
• DICOM Standard defines expected behavior
• 50 of these unit tests check for bad cases
• About 2000 unit tests
• Note Lines Of Code counted with CLOC 1.52.
  Average is 60 K Lines.

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• Design Challenge 1
• Character Encoding

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DICOM Character Sets

• Originally only support for ASCII (IR-6)
• 1993 Latin 1\2\3\4\5, Arabic, Hebrew, Cyrillic,
  Greek, Japanese,..
• 1999 \ 2000 Thai, Korean
• 2003 UTF8 (ISO_IR 192), but this is an option
• Most modern applications use internally UTF16
  Unicode strings (C \ .NET \ Java)
• .NET provides standard text encoders
• UTF8
• Many code page based encoders

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Text Conversions

• Input (decoding)
• Read and convert DICOM text values to .NET
  strings.
• Output (encode)
• Many use cases require text updates to the DICOM
  data. For example Patient Information
  Reconciliation.
• Output would be easy if all DICOM systems would
  support UTF8

.NET Strings
encode
DICOM values
DICOM values
decode
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LegacyCharacter Set Encoding

• Steps needed to serialize DICOM text data to an
  output device that doesnt support UTF8
• Application needs to define encoding method
• Application needs to define allowed character
  sets and preferred order
• Library needs to scan all characters
• Library computes required character sets and
  serialize data
• Recommendation design / use systems that support
  UTF8

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• Design Challenge 2
• DICOM C-STORE on a Wide Area Network

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C-STORE on a WAN Intro

• Historically most DICOM communicationis on a
  local network
• Trend is to store images in regional and national
  DICOM data centers
• Wide Area Network (WAN)
• Bandwidth 1 Mbit/s up to 1 Gbit/s
• Round Trip Time (RTT) 10 ms up to 1 s for
  satellite connections

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C-STORE Example

• Example
• Sending a study of 2000 compressed instances of
  125 Kbyte on a local network
• Bandwidth 100 Mbit/s, Round Trip Time 1 ms,
• N (Tx Trtt) 27 seconds
• Sending same study on a Wide Area Network
• Bandwidth 100 Mbit/s, Round Trip Time 200 ms,
  
• N (Tx Trtt) 425 seconds
• 425 seconds vs 27 seconds 15 times slower!

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C-STORE on a WANRoot Cause

• Local
  92
• WAN
  6
• Solutions (within the Standard)
• Open more connections
• Supports DICOM Asynchronous Operations (PS 3.7
  Annex D.3.3.3)

1
1
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C-STORE on a WAN Solution

• 
  99
• Transmission time (N Tx) Trtt 25 seconds
• Both DICOM systems need to support asynchronous
  operations
• Maximum number of pending requests is 65536
• Responses can arrive out of order

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6
5
4
8
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9
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2
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• Design Challenge 3
• DICOM Operations on aWide Area Network

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DICOM Operationson a WAN

• Same WAN sample configuration
• Round Trip Time 200 ms
• Secure DICOM (TLS)
• Connection Establishment is slow
• TCP / IP Protocol slow start algorithm

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DICOM Association pool

• Pooling is automatic
• Pool will reuse a suitable open association
• If no association available, pool will open a new
  association
• Auto learning which presentation contexts are
  required
• Number of open associations is managed
• Associations are closed after idle timeout
• Compatible with Asynchronous Operations
• CP-948 C-STORE sub operations (Std 2008)

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Conclusions

• Conclusions
• Having a GE DICOM library in .NET allows us to
  quickly adapt to changes in the Standard.
• We have seen good performance
• .NET provides a rich set of libraries which makes
  it relatively easy to develop DICOM applications

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Recommendations

• Recommendations
• Use the Microsoft .NET Guidelines to ensure a
  library is consistent with .NET (FxCop)
• Use UTF8 as the default character encoding
• Great if DICOM Standard would make this required
  in the future (roadmap)
• To be Internet / Wide Area Network ready
• Support Asynchronous Operations
• Support re-use of open DICOM associations

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Questions \ Perguntas

• Questions ?
• Contact
• victor.derks_at_ge.com
• http//groups.google.com/group/comp.protocols.dico
  m