A framework and toolkit for secure, efficient and standards-based access to remote imaging data has the potential to enhance multi-institutional collaborations in biomedical imaging studies, according to the developers of an open-source application, VirtualPACS.

“In radiology, it is still a challenging task to share data across institutions despite the widespread adoption of the DICOM standard, which enabled digital storage technologies such as PACS,” wrote the authors of an overview of the application in the Feb. issue of the Journal of Digital Imaging. “All too often, the community relies on simple yet inefficient means of sharing data such as burning it on CDs and mailing them.”

The developers, from the department of biomedical informatics at The Ohio State University in Columbus, Ohio, focused on the problem of aggregating multiple image data resources so that clients can interact with them as if they are stored in a centralized PACS.

“VirtualPACS federates multiple remote data sources, including those that do not support DICOM messaging, and presents them to a DICOM client as a single virtual resource, i.e., a virtual PACS,” the authors wrote.

Their framework consists of a presentation, middleware and mediation layer. The presentation layer is simply a gateway between the local DICOM clients and remote image data resources, which converts DICOM requests to grid requests.

“The presentation layer of VirtualPACS is a client-side application that provides DICOM-aware virtualization, i.e., a gateway to other image data resources that are exposed on the grid through the middleware and mediation layers,” the authors noted.

The grid requests are handled by the middleware layer, which executes the requests on the remote resources and feeds the appropriate messages and data back to the presentation layer for conversion back to DICOM. The middleware makes extensive use of the caGrid infrastructure, developed as part of the National Cancer Institute’s cancer Biomedical Informatics Grid (caBIG).

In caGrid, all resources are exposed as Grid services with well-defined interfaces and published data models to ensure semantic and syntactic interoperability,” the authors wrote. “Services and clients interact with each other by communicating over the Grid using standard service invocation protocols.”

According to the developers, the mediation layer implements the tools for mapping various backend image databases to a common set of interfaces and data models so that image data sources can be federated and accessed remotely within the VirtualPACS framework. This is accomplished by wrapping both native and non-native DICOM image databases as caGrid data services; in effect, wrapping heterogeneous data sources with a common interface that allows a common data representation.

“This layer provides support for data source owners to expose their image data resources through a well-defined interface and common image data model so that they can be federated in the VirtualPACS,” the authors wrote.

The team reported that performance of the system in retrieving thoracic CT images of multiple patients in 40-megabyte to 4-gigabyte (GB) groups was satisfactory, with 4 GB DICOM data sets taking approximately 10 minutes to retrieve.

“We are currently working on extensions to this toolkit that target support for other DICOM objects such as structured reports and work lists,” the authors reported. “We are also working on developing security plug-ins that can leverage the DICOM security standard for transactions between a DICOM client and the presentation layer of VirtualPACS. We are also working with NCIA (National Cancer Imaging Archive) and ACRIN (American College of Radiology Imaging Network) to develop grid interfaces for their respective repositories, which will provide authorized users access to these large image archives using their own DICOM workstations.”

The developers have made VirtualPACS and all its software components publicly available, and instructions on how to download and use them can be found on http://www.virtualpacs.org.