DICOM and virtual microscopy
Clinical use of virtual microscopy must be compatible with existing imaging standards, such as JPEG2000 and Digital Imaging and Communications in Medicine (DICOM). Although a DICOM Object definition for visible light microscopy exists, virtual slides are too large (both pixel and byte size) to be used directly as these objects. In addition, the access characteristics of virtual slides differ from conventional DICOM images. Panning and zooming within a huge specimen area and decoding fractions of the image on demand, are both mandatory in virtual microscopy.
By using JPEG2000 and JPIP, virtual slides can be used within DICOM without needing to alter the standard specification. Currently, the DICOM standard includes the basic parts of the JPEG2000 standard in Supplements 61 and 105. Supplement 106 (JPEG 2000 Interactive Protocol) describes two JPIP-based Transfer Syntaxes as methods of delivering image pixel data apart from patient data: the non-compressed JPIP Referenced Transfer Syntax and the Deflate-compressed JPIP Referenced Deflate Transfer Syntax.
With the JPIP Transfer Syntaxes, the DICOM-based Picture Archiving and Communication System (PACS) server gives its client a Uniform Resource Locator (URL) string that refers to the virtual slide pixel data provider (i.e., a JPIP server), together with the image name, which can be arbitrary and unrelated to patient data (as shown in Figure 1). Upon receiving the pixel data provider reference, the PACS workstation either uses a built-in JPIP viewer or invokes an external one for retrieving the virtual slide from the specified JPIP server.
Figure 1. Using virtual slides within a DICOM-based PACS over JPIP.