DICOM INTERNATIONALCONFERENCE & SEMINAR

Oct 9-11, 2010 Rio de Janeiro, Brazil

Building a DICOM Library in C#

Victor Derks

GE Healthcare

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

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#

Design Goals

Requirements:– DICOM File I/O– DICOM Communication

Focus Areas:– Internationalization– Service Oriented Architecture– Easy to use for C# programmers

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 doesn’t work well due to high interaction

between the layers– No option to leverage new .NET patterns:

• Asynchronous Programming Model• Thread pool

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.

Name Lines Of Code Lines Of Test Code

GE DICOM Library (C#) 34,637 33,707

Comparable Open Source:

ClearCanvas (C#) 87,738

Dcm4che 2.0.24 (Java) 40,954

PixelMed 20100912 (Java) 86,864

Design Challenge 1:

Character Encoding

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

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…

DICOMvalues

.NET Strings

DICOMvalues

decode encode

LegacyCharacter Set Encoding

Steps needed to serialize DICOM text data to an output device that doesn’t 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

Design Challenge 2:

DICOM C-STORE on a Wide Area Network

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

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!

C-STORE on a WAN:Root 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

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

3

1

6 5 48 79

2

Design Challenge 3:

DICOM Operations on aWide Area Network

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

Name Time

TCP / IP Handshake 200 ms

TLS / SSL Handshake 400 ms

DICOM Handshake 200 ms

DICOM Request \ Response 200 ms

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)

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

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

Questions \ Perguntas

Questions ?

Contactvictor.derks@ge.com

http://groups.google.com/group/comp.protocols.dicom