Networking with Silverlight mdcm

As recently announced, I am adapting the C# DICOM library mdcm to Silverlight. Due to the compactness and security limitations of Silverlight, I have had to make several workarounds. However, I have now reached a stage where a large degree of the original library's functionality is in place. The only large part missing now is codec handling, which is highly dependent upon native support libraries in the original mdcm library.

Most recently, I have included network support in the Silverlight library. The client functionality is definitely in place; with the latest commit in the Github repository there is a working example of a storage SCU (service class user).

There are a few restrictions: Silverlight only supports the TCP protocol; there is currently no support for TLS or SSL. The only available port range is 4502-4534, and the port access has to be granted through a separate policy access server. As far as I have been able to find out, the server that the Silverlight client application is communicating with also has to be located on the same system. The supported DNS name of the computer should be obtained as follows:

string DnsHostName = Application.Current.Host.Source.DnsSafeHost;

(I should state that I have not yet learned all the windings of the Silverlight network support, so there may be more flexibility to this than I yet know.)

To test the functionality, I created a new Silverlight hosting web application in my mdcm fork at Github, denoted SL.DicomToXml.Web. When running this web application via Visual Studio, it is possible to open DICOM files on the regular file system. The DICOM file dump is displayed on screen, together with the contained image if any.

In the background, the application is also trying to send the DICOM object to a storage SCP server on port 4502. For this to work, a storage SCP application has to be running on the same computer (I used the storescp application from the OFFIS DCMTK library).

Furthermore, an access policy server has to be running, granting the Silverlight application access to ports 4502 through 4534. Based on code that I obtained from Stackoverflow user luke here, I also included a very simple policy server application, SilverlightPolicyServer, in the mdcm tree. Before any DICOM object sending can take place, the policy server must also be running; double-click the executable or start it from the command prompt.

Getting this to work in Silverlight was a little bit of a challenge. In particular, the Socket class in Silverlight is extremely stripped compared to its vanilla .NET counterpart. The regular mdcm library also makes extensive use of the NetworkStream class for sending and receiving network data. NetworkStream is not included at all in the core Silverlight library. Fortunately Alexander Wieser has developed a replacement in his Crystalbyte Networking project at Codeplex, and this support class was easily included in the Silverlight mdcm library.

While discussing the workarounds I have had to take in the Silverlight mdcm library, I should also mention that file access has been limited to the isolated storage assigned per user and application. This means that DICOM file access is limited to this isolated storage, and it is only practically available when running the Silverlight application. To access files on the regular file system, the most efficient solution is probably to open the file stream directly through an open-file dialog, pretty much like it is done in the demo application.

Silverlight and a converter for multiple values

Once again I have hit an annoying limitation in Silverlight, and once again the problem has been recognized and mitigated by other developers...

In XAML databinding in WPF, it is possible to do simultaneous data binding conversion for multiple values using the IMultiValueConverter interface. In the Silverlight core libraries there is however only support for single value conversion using IValueConverter.

In one example Silverlight application I developed, I wanted to compute the resulting amount in a specified physical unit, given the amount in another physical unit. A Silverlight multi-value converter would have come in handy, and gladly enough the job had already been done.

Colin Eberhardt has provided an extensive solution together with detailed usage instructions in his blog. I have applied Colin's implementation and it works flawlessly.

Apparently Silverlight 5 Beta is due at the upcoming MIX 2011 meeting. It will be interesting to see whether multi-value conversion will also be included in the SL5 libraries. If not, I still have something to fall back on, thanks to Colin.

DeflateStream in Silverlight

Another circumvented area in the Silverlight core libraries is compression and decompression of streams. The entire System.IO.Compression namespace that can be found in the regular .NET Framework is missing in Silverlight.

But of course, this limitation has been recognized. In the dotnetzip project on Codeplex, there is a Silverlight branch that among other things provide a DeflateStream replacement. This was a very welcome finding in my efforts of adapting as much as possible of the mdcm C# DICOM library to Silverlight.

My thanks go to the Codeplex user cheeso for this contribution!

WriteableBitmap extensions in Silverlight

The Silverlight WriteableBitmap class, intended for user-defined bitmap design, has very limited functionality by itself. It really only provides the Pixels property for direct modification of the editable bitmap.

Fortunately, this limitation has been recognized and mitigated by René Schule. René has initiated WriteableBitmapEx, which is a library of extension methods for the WriteableBitmap class. The entire project is open source (Microsoft Public License) and can be found on Codeplex.

I most urgently needed methods for rotation and flipping of the bitmap image, but there are also various methods for cropping, resizing, individual pixel editing, drawing shapes on the bitmap etc. All in all some very helpful extension methods for this specific need.

Parallel operations in Silverlight

As far as I have been able to find out, Silverlight is fairly limited with respect to parallel and/or multithreaded computation support. The Parallel framework from .NET 4.0 is for example not present at all. However, it seems like the ThreadPool is a reasonable candidate for doing at least some work in parallel.

Based on the MSDN documentation for Silverlight, I have composed a very simple code snippet for separating larger computational work onto for example all available CPU cores.

int threads = Environment.ProcessorCount;

WaitHandle[] handles = new WaitHandle[threads];

for (int i = 0; i < threads; ++i)

{

handles[i] = new ManualResetEvent(false);

ThreadPool.QueueUserWorkItem(

delegate(object state)

{

...some long-running thread-able process...

((ManualResetEvent)state).Set();

}, handles[i]);

}

WaitHandle.WaitAll(handles);

I tested the above snippet on my eight CPU core computer, and repeated the same process throughout all iterations. The above parallel approach was then 2.5 times faster than the purely sequential one. Not a very impressive result, of course. There is certainly room for improvements, hopefully I will be able to implement more impressive speed-ups in due time.

DICOM and WPF

I have recently taken up the effort of adapting the C# DICOM class library mdcm to Silverlight, as can be seen on the forked project website at Github.

Initially, I excluded all imaging, codec, HL7 and network functionality in order to make the library build at all in Silverlight.

Just now I have begun looking at porting the mdcm image handling to Silverlight. The mdcm library uses the .NET System.Drawing library for image handling, which is not available in Silverlight. However, I have modified the source code so that when it compiles for Silverlight, it instead uses the BitmapSource and WriteableBitmap classes from the System.Windows.Media.Imaging namespace.

The added benefit of these modifications are that they are equally applicable to WPF, i.e. it would be a simple task to switch from Windows Forms (which the original mdcm library depends upon) to WPF, given these Silverlight motivated modifications.

I have not explicitly made any WPF adaptation yet, but this is clearly worth future exploration.

UPDATE AUG 21: WPF support is now implemented! Please have a look in the Github repository and this blog post.

Advanced calculations for the web!

In my efforts to bring further functionality to the web, I have today explored the possibility of porting the versatile Meta.Numerics class library to Silverlight. Luckily enough, this was quite an easy task.

I only had to omit serialization support via the Serializable attribute, and the ADO.NET coupling of the various statistical Sample classes, otherwise the Silverlight class library built without issues.

The Meta.Numerics class library is distributed under the Microsoft Public License. I soon hope to find a suitable way for making the Silverlight library modifications public, either via Github or CodePlex.