Features > Streaming Support

Introduction

In a traditional PACS installation, images are auto-routed via DICOM to all the workstations that radiologists may read at. Intelligent rules may be created to attempt to reduce the network load, although invariably the studies must be sent to more than just the workstation that the study ends up being read at. Many times this ends up putting stress on a hospital's network.

An alternative approach has been developed by various vendors in recent years, which is often called "streaming". In this case, a non-DICOM transport mechanism is developed, often using compression, where the images can be requested on demand from a server and retrieved to the client Workstation at a speed that meets a radiologists expectations for performance. This design reduces the overall network traffic, because images are only sent where they're needed.

The ImageServer has developed a streaming method for accessing imaging studies on demand. The following sections describe the ImageServer implementation.

How it Works

The ImageServer streaming server-side implementation uses two Web Services. One web service supplies study information to client systems. The ImageServer maintains an XML file on the server which contains DICOM header information about all the DICOM files within a study. The web service returns a compressed version of this XML file to clients upon request.

The second web service is a modified DICOM WADO server. It uses the MIME types "application/clearcanvas" and "application/clearcanvas-header". Requests for the "application/clearcanvas" MIME type will return compressed or uncompressed pixel data by frame to the client. Requests for the "application/clearcanvas-header" MIME type will return a requested subset of the original DICOM file without the pixel data.

The header streaming service is implemented using WCF while the image streaming service is implemented using “HTTP/1.1” protocol as specified in the DICOM WADO specifications.

Image streaming service in ImageServer extends the Uri syntax specified in DICOM WADO by incorporating the notion of server partitions. For example, to retrieve an image from the CLEARCANVAS server partition, the web client (Workstation or internet browser) will send a GET request to the following address (default port is 1000):

http://serverip:1000/wado/CLEARCANVAS?requestType=WADO&contentType=application%2Fdicom

&studyUid=<STUDY_ID>&seriesUid=<SERIES_ID>&objectUid=<OBJECT_ID>