KEYWORDS: Visualization, Diagnostics, Medical imaging, Structural dynamics, Computer aided diagnosis and therapy, Detection and tracking algorithms, Algorithm development, Information visualization, Visual analytics, Digital imaging
DICOM Structured Reporting (SR) allows for the exchange of structured data and coded information in a standardized
way. Although SR documents cannot be viewed directly, the DICOM standard does not specify how an application
should render them. As a consequence, the interoperability of SR documents which are intended to be displayed to a
medical user is restricted to those structures that are known to the visualizing application. In order to avoid this
limitation, we have developed a unified process for the adequate visualization of arbitrary structured medical reports.
The basic idea of this new approach is to map well-known sub-structures of the document tree (e. g. templates) to
appropriate display components. For this purpose, the generic processing part is strictly separated from an extensible
knowledge base which includes a machine-readable description of the template structures and display components.
During our work we found out that the template detection is a crucial part of the whole visualization process. On the one
hand, the existing template identification method in the DICOM standard covers only a limited number of cases. On the
other hand, the complexity and dynamic structure of SR templates make the detection difficult or even impossible in
certain cases. Therefore, we propose to enhance this identification method and to revise the corresponding part of the
standard. In conclusion, we hope that the presented approach will assist vendors in developing general purpose reporting
workstations and thereby promote the use of DICOM Structured Reporting.
In 2003, the DICOM standard celebrated its 10th anniversary. Aside from the standard itself, also OFFIS’ open source DICOM toolkit DCMTK, which has continuously followed the development of DICOM, turns 10 years old. On this occasion, this article looks back at the main standardization efforts in DICOM and illustrates related developments in DCMTK. Considering the development of the DICOM standard, it is possible to distinguish several phases of progress. Within the first phase at the beginning of the 1990s, basic network services for image transfer and retrieval were being introduced. The second phase, in the mid 1990s, was characterized by advances in the specification of a file format and of regulations for media interchange. In the later but partly parallel third phase, DICOM predominantly dealt with the problem of optimizing the workflow within imaging departments. As a result of the fact that it was now possible to exchange images between different systems, efforts concerning image display consistency followed in a fourth phase at the end of the 1990s. In the current fifth phase, security enhancements are being integrated into the standard. In another phase of progress, which took place over a relatively long time period concurrently to the other mentioned phases, DICOM Structured Reporting was developed.
KEYWORDS: Medicine, Standards development, Information technology, Telecommunications, Radiology, Information fusion, Imaging systems, System integration, Data storage, Databases
The IHE (Integrating the Healthcare Enterprise) initiative has recently developed into a multi-national effort that addresses the specific needs of healthcare systems in North America, many European countries as well as Japan. The introduction of IHE in Europe is a particular challenge because the structure of the healthcare sector deviates significantly from country to country, with different legislation, language, medical and organizational procedures and, not the least, different vendors: HIS/RIS systems are typically tailored towards a specific market, and the majority of vendors is only present in one or a few countries.
The first multi-national "European Connect-a-thon" was performed in April, 2002 with 57 participating systems from 33 companies, in preparation of four different public demonstrations in three countries. The systems were grouped into a French, German and Italian section (according to the national extensions supported by each system), with certain overlaps, i. e. systems participating in multiple sections in parallel. In conclusion, experiences in Europe show that IHE cannot simply be copied, but has to be adapted to the specificities of national healthcare systems. The good news is, however, that the specifics are only of minor nature compared to the overall complexity of the transactions involved.
Jorg Riesmeier, Marco Eichelberg, Joachim Kieschke, Hans-Peter Hellemann, Birgit Gruschka-Hellemann, Roman Sokiranski, Axel Munte, Wilfried Thoben, Peter Jensch
In January 2002, the Bavarian Statutory Health Care Administration ("Kassenarztliche Vereinigung Bayerns", KVB) started a recertification programme for quality assurance and quality improvement in mammography reading. All accredited radiologists and gynaecologists are asked to prove their qualification every 1-2 years. The recertification programme requires the physicians to read 50 cases randomly selected from a larger collection of high-quality test cases. The portion of malignant and benign cases corresponds to the requirements of the German National Association of Statutory Health Insurance Physicians ("Kassenarztliche Bundesvereinigung", KBV). In order to read the mammograms on a softcopy device the images are digitised with a high-quality scanner and converted to DICOM Digital Mammography format. The workstation software has been implemented according to the particular requirements of this programme. To verify the applicability of digitised mammograms for recertification purposes, a comparative study with 32 trained radiologists and gynaecologists has been performed. As a result the study showed that there was no significant difference in the error rate of the reported findings between conventional film and softcopy reading. The first intermediate results of this quality initiative are promising. The introduction of a corresponding federal German recertification programme is intended.
With the release of 'DICOM Structured Reporting' (SR) as an official extension of the standard about two years ago, DICOM has entered a new domain that is only indirectly related to medical imaging. Basically, DICOM SR is a general model allowing to encode medical reports in a structured manner in DICOM's tag-based format. Therefore, the existing DICOM infrastructure can be used to archive and communicate structured reports, with only relatively small changes to existing systems. As a consequence of the introduction of medical reports in a digital form, the relevance of security measures increases significantly. We have developed a prototype implementation of DICOM structured reporting together with the new security extensions for secure transport connections and digital signatures. The application allows to create, read and modify any SR document, to digitally sign an SR document in whole or part and to transmit such documents over a network. While the secure transport connection protects data from modifications or unauthorized access only during transmission, digital signatures provide a lifetime integrity check and, therefore, maintain the legal document status of structured reports. The application has been successfully demonstrated at RSNA 2000 and ECR 2001, and is freely available on the Internet.
KEYWORDS: Data modeling, Receivers, RGB color model, Systems modeling, Image processing, Picture Archiving and Communication System, Data communications, Chromium, Medical imaging, Printing
The DICOM standard has established itself successfully in the PACS world. Practice has shown, however, that interoperability of DICOM devices cannot be taken for granted. Many devices only support a subset of the capabilities and options of the DICOM services they claim to support - and even that sometimes in a non-conforming manner. This issue is only partly addressed by the concept of the DICOM conformance statement which describes the services, options and features supported by an implementation and allows an expert to assess whether two DICOM implementations are likely to interoperate. We propose a new approach that can be understood as a step towards an 'automated' conformance statement. The 'Description Notation' for Interoperability Assessment' (DeNIA) allows to formally describe the data structures sent or received by a DICOM implementation. An evaluation tool reads two of these models and automatically derives a conclusion whether or not the two systems can successfully exchange messages and whether all messages created by the sender can be understood by the receiver. DeNIA allows to explicitly describe the capability of a receiver to 'gracefully' accept certain deviations from the standard -- a capability which accounts for much of the interoperability found in DICOM systems today.
The DICOM standard has been used successfully to exchange medical images for some time. However, the important aspect of image display consistency has mostly been disregarded in the past, which led to inconsistent implementations. This situation is changing now since DICOM has defined a set of services which guarantee the consistency of grayscale images for both hardcopy and softcopy. We have developed a test environment that helps to evaluate the conformance of an implementation of these new services. This environment consists of a set of test images and presentation states for softcopy displays as well as a number of test cases for hardcopy devices. The purpose of each test as well as the expected output are documented. Images and presentation states can also be visualized by means of a reference implementation, a DICOM presentation state and an image viewer that also allows to visualize print jobs. In our experience the services for image display consistency are implementable and work very well, however, there are some small details that can be subject to different interpretations. The test environment does not cover all possible cases but definitely helps making an implementation more conformant with the DICOM standard. The test suite is made available on the Internet as Open Source.
The DICOM standard defines in detail how medical images can be transmitted and stored. However, there have been no precise rules on how to interpret the parameters contained in a DICOM image which deal with the image presentation. As a result, the same image frequently looks different when displayed on different workstations or printed on a film from various printers. Three new DICOM extensions attempt to close this gap by defining a comprehensive model for the display of images on softcopy and hardcopy devices: Grayscale Standard Display Function, Grayscale Softcopy Presentation State and Presentation Look Up Table. A prototype implementation of these extensions has been shown at the 1999 annual tradeshow of the Radiological Society of North America (RSNA) as part of the scientific exhibit (infoRAD). This demonstrated a simulated radiological workflow in which images were created, interpreted at a diagnostic workstation and later reviewed on a clinical workstation. Images could also be printed using DICOM Print. The prototype shows a proof of concept, i.e. that image integrity and consistency over a variety of display and print devices can be achieved and in addition, that the new DICOM extensions can be implemented relatively easily, without a significant performance penalty. The extensions allow to store all parameters defining how an image is displayed or printed in a separate DICOM object that can be managed with the existing DICOM database services. In particular, this satisfies the user's need to view images at different locations in a consistent manner, and to document the image appearance on which a diagnosis is made in softcopy environments.
KEYWORDS: Image compression, Binary data, Medical imaging, Data compression, Data storage, Cardiology, X-ray computed tomography, Image segmentation, Telemedicine, Data transmission
DICOM is today's de-facto standard for exchanging medical images. Since new image acquisition devices produce more and more image and non-image data, image compression has become an important part of the standard. However, the compression of non-pixel data also stored in DICOM data sets has been disregarded up to now. In the scope of an EU research project we have examined a large amount of real-world DICOM images to test whether or not there is a potential for compressing the non-pixel attributes. As a result we have found out that it is indeed possible to reduce the size of header information in DICOM data sets significantly. However, the contribution to the overall compression ratio is very small. We conclude that compression of DICOM header information is only interesting for data sets which mainly consist of non-pixel data. Since new DICOM modalities introduce more and more of such data, the importance of this issue is likely to increase. Also many DICOM network services are based on more or less large 'textual' data structures. Especially for use with narrow-band networks extensions as proposed in this paper could be a solution to save valuable bandwidth.
The exchange of medical images over networks or storage media is usually done in DICOM format today. In addition to uncompressed image storage, DICOM supports both lossless and lossy image compression techniques. Whereas lossless compression is popular for some applications, lossy compression in DICOM has never gained intensive usage. However, the quickly rising data volumes produced by the latest generation of modalities indicate that compression will remain an important issue although network bandwidth and storage capacities are increasing as well. The study presented in this contribution examines the conditions under which existing uncompressed DICOM images can be compressed with lossless and lossy JPEG resulting in valid DICOM images. The aim of the study was to enhance an existing open-source DICOM toolkit with JPEG support such that a wide range of DICOM images can be processed. Since image compression is not an integral part of the DICOM data model, its introduction can lead to surprising conflicts, e.g. because the special requirements of certain modalities do not match the JPEG model or because ambiguities in the standard are interpreted differently by different implementers. The resolution of the existing ambiguities could help to make DICOM image compression more robust in the future.
DICOM is widely accepted today as the standard protocol for medical image interchange. DICOM offers very flexible data structures allowing to easily encode a wide variety of modality specific image formats. This flexibility, however, causes problems in image display: most DICOM viewers are limited to the 'most usual' subset of the standard's specification which makes up the vast majority of images but covers only a very small part of DICOM's capabilities. Our approach was to design a toolkit which attempts to overcome the common restrictions of existing DICOM implementations. Apart from completeness, i.e. the support for all image formats defined in DICOM, the main objectives were: efficiency, extensibility and portability. The resulting toolkit is built on a well-designed C++ class hierarchy which makes extensive use of template classes and inline methods for best performance. Two applications based on this toolkit have been developed: a conversion and manipulation tool and a small DICOM viewer. In addition to the freely available DICOM test images distributed by vendors of medical equipment we used artificially created images covering all aspects and options of the DICOM image models for testing. Our implementation demonstrates that it is both possible and practicable to support the entire DICOM image format without sacrificing efficiency. Nevertheless the question remains whether DICOM's present complexity is really necessary. An introduction of useful restrictions would make it much easier for DICOM implementers to support the standard's image format in its entirety and thus increase the software's robustness.
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