In the Netherlands, an increasing number of hospitals is operating filmless. This does not only affect the internal workflow, but also the external workflow. In increasing amounts, data will be transferred between hospitals on CD-R. This data can concern patients that transfer from one hospital to another or patients that require a second opinion. However, because every hospital in the Netherlands uses its own patient ID conventions, the interchange of data is difficult.1
Fortunately, the DICOM standard defines a standardized approach to exchange DICOM data on a storage medium. In the DICOM standard, medium normalization is dedicated only to data exchange, not to inner storage format. DICOM Part 10 deals with media storage and file format for media interchange.2 This document covers DICOM models for media storage which define access to storage media independently from specific physical media storage formats and file structures. One of the tools used to standardize the storage is the use of a DICOMDIR for each file set. This file includes a description of the DICOM Media Storage Directory, which contains general information of the complete file-set. A DICOMDIR file, which may be seen as a table of content of one medium, should be present at the root level of that medium to comply to PS 3.10 of the DICOM standard. Besides the DICOMDIR, other media formats and restrictions are defined in DICOM Part 123—for example, the usage of different media (e.g., CD-R, MOD, and DVD-RAM) and the requirement of storing only one fileset per medium.3 Since synchronous and online negotiation is not possible between the media provider and the media user on image format and encoding, and on media structure, DICOM defines in its Part 114 some guidelines, called Application Profiles, which may help to anticipate compatibility issues between different equipment. For example, a file-set reader that complies to the STD-GEN-CD profile (all types of images, only uncompressed) should be able to read data from any CD containing information compatible with this profile.
The application of the DICOM standards can be evaluated within the IHE (Integrating the Healthcare Enterprise) initiative. This initiative focuses on real use-cases to define rules to improve operability between functional actors for a set of use-cases. These use-cases are always based on standards such as DICOM and HL-7 and often lead to the definition of restrictions to DICOM and HL-7 services. In the IHE/PDI 2004 experimental test of portable media use at the RSNA of 2004, the following restrictions or suggestions were given:
Only use STD-GEN-CD profile for this experiment,
A strict convention for naming of CD files and subdirectories
Restricted rules for CD labeling,
No windows autorun on the CD.
Media creators could also insert web content, but only when they conformed to strict rules.
Although many of the media (CD-R discs) delivered to our hospital have their own viewers installed, this is not optimal, especially in view of the fact that every hospital has its own vendor promoting his own viewer with a variety of different user interfaces and capabilities. Furthermore, some of the software packages need to be installed onto the hard drive of the computer, which is not always allowed on general workstations. In order to include all these CD-Rs in the normal radiology workflow, the data have to be available in the picture archive and communication system (PACS). However, they should not be transferred into the PACS without adaptation to the institution’s standards.
Within the Netherlands, as in most countries, every hospital uses its own patient identification number; no nation wide number is available. Therefore, the risk exists that when patient data are transferred into the PACS without adapting the patient number, they might overwrite an existing patient and/or be lost. Furthermore, all interaction between components such as PACS, RIS, HIS, Speech recognition is based on the accession number of a study. These accession numbers are also hospital-specific. For this reason, the patient has to be known in our hospital and our identification information has to be entered into the data retrieved from the CD-R. To achieve this, a new work process had to be designed and software had to be sought for.
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Methods
As a first step in the adaptation of the work process, a request form was designed for the requesting physician. On this form, patient information has to be added including a new, locally generated, patient identification number. Besides this, the physician can describe the reason for which the CD-R has to be read into the PACS. Priority handling and whether or not to destroy the CD-R can also be marked. The filled out form is then shipped to the radiology department together with the CD-R, where a new (virtual) radiological procedure is planned in the RIS. This new procedure is then automatically placed into the DICOM modality worklist. When reading a CD, the data on this CD can be linked to the data in the DICOM modality worklist for the conciliation as required by the IHE initiative and described in the proposed Portable Data for Imaging (PDI) profile.5 Possible procedure descriptions for CD-Rs are: “EXTERNAL IMAGES” or “SECOND OPINION.” By defining these two specific procedures, data from CD-R can be easily distinguished from locally acquired data since these descriptions also show up on the PACS.
To transfer the data to the PACS and to perform the reconciliation, a software package named Open LiteBox (ETIAM, Rennes, France) was evaluated. It reads DICOM data from the CD-R and has the ability to transfer this data to the PACS. Before this transfer is carried out, patient identification information can be changed (Fig 1). This change of identification information is not manual, but a DICOM Modality Work List (DMWL) server can be queried to find the appropriate entry. Hereafter, a selection can be made to perform Patient Information Reconciliation, in which certain fields of the data on the CD-R are replaced by the information retrieved using the DMWL service. The reconciliation is performed “on the fly” during DICOM transfer to the PACS, i.e., the original data are left unchanged.