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The SNM 2001 DICOM Demonstration

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  • 1. The SNM 2001 DICOM Demonstration Jerold W. Wallis, MD, President, SNM Computer and Instrumentation Council What is the DICOM demonstration? This project has two parts: (a) A public demonstration is being held at the SNM 2001 meeting to demonstrate recent advancements in DICOM connectivity. Because the goal is to show what we have achieved in recent months, manufacturers are using the latest software versions, some of which may not be available for clinical use yet (but with the expectation that this revised software will become clinically available as soon as possible). This demonstration focuses on image/data compatibility and the ability to process images obtained from other vendors, rather than ability to establish network connections. For this reason, images from other vendors have been pre-loaded on to each vendor’s system. The vendors are showing that they can import these images accurately, and utilize those images in their processing software. Images included in this demonstration are: whole body bone, dynamic renal, ventilation-perfusion, gated blood pool (MUGA), bone SPECT, non-gated myocardial perfusion, gray-scale snapshot, and a color snapshot. Inclusion of a gated myocardial perfusion SPECT study was optional for the 2001 demonstration. These span the DICOM image types of WHOLE BODY, DYNAMIC, STATIC, GATED, TOMO, RECON TOMO, SECONDARY CAPTURE, GATED TOMO, and RECON GATED TOMO. (b) The SNM Computer and Instrumentation Council has worked with manufacturers over the past year to improve DICOM compatibility, an effort which is ongoing. The council has provided a forum for communication and a method for inter-vendor image exchange, for compatibility testing and debugging. The real work of testing and improving software is being performed by the participating vendors. The participating vendors include ADAC (A Philips Medical Systems Company), Areeda Associates Ltd., GE Medical Systems, Marconi Medical Systems, NUMA Inc., Siemens Medical Systems, and Toshiba America Medical Systems. The sections below pertain to the use of DICOM in nuclear medicine, and are not limited to the SNM 2001 demonstration. What is DICOM? DICOM is the standard for Digital Imaging and Communications in Medicine, developed by the National Electrical Manufacturers Association (NEMA) in conjunction with the American College of Radiology (ACR). This standard is intended (Copyright 2001, Society of Nuclear Medicine)
  • 2. to be much wider in scope than a simple nuclear medicine file format, comprising image formats for not only radiology but for all of medicine, with additional specification for messaging and communication between imaging machines, with PACS, and with hospital information systems. Does this mean that DICOM is now guaranteed to work at my site? Although this demonstration is a large step in that direction, there are still many things that can go wrong. Network issues: There must be a functioning network between your two systems, and any security firewalls between them must be configured to allow passage of information between these sites. The SNM 2001 demonstration does not include on-site inter-vendor networking. Communication issues: The first step in sending a DICOM image is for the software to establish a connection between the two machines, where they negotiate the details of the image transmission (e.g., byte mode vs word mode, little-endian vs. big- endian, etc). Only limited connection testing was done as part of this demonstration, as the emphasis is on data compatibility and processing. However, communication problems are relatively uncommon. Component issues: DICOM is specified in terms of many individual components (SOP Classes). If you happen to have two systems that only know how to send DICOM images, but neither knows how to receive and store DICOM images, then these devices will have trouble working together. More information on SOP classes is provided below. Version issues: You may have an older version of the software. In particular, some companies made revisions for this demonstration, which will only reach the consumer later this year. Complex images: The SNM 2001 demonstration includes simple and medium complexity image types. Full testing of the most complex image types (gated SPECT, dual-energy acquisition, raw projection SPECT data without transaxial data, etc.) still needs to be performed. Display and processing issues: The image may arrive, but may not be automatically recognized to be of a type to allow processing using a specific software package. Additionally specific display tools that you are used to on one system may not be available on another vendors system. Can’t I just specify that products I purchase are “DICOM compatible”? As you are no doubt starting to realize, this will not work. At a minimum you will need to specify what broad types of images you will be dealing with (DICOM objects), and what you want to be able to do with them (DICOM services). There are several types of objects relevant to nuclear medicine.
  • 3. Nuclear medicine (old version, retired): This was an early version of the nuclear medicine format, which did not adequately allow for multiple images in a single file. It is no longer in use, but still may be present on some systems Nuclear medicine (current): This is the current version of the nuclear medicine specification. PET: This is a separate DICOM specification for PET images. Some PACS systems are not yet able to receive or work with PET DICOM objects. PET systems may therefore include the ability to send data as standard nuclear medicine objects (which is adequate for most purposes) rather than (or in addition to) using PET objects. Secondary Capture objects. These are screen snapshots, frequently used for sending of complex processing screens (e.g., bullseye plots, lasix renal curves, etc). If you wish your nuclear medicine system to be able to receive images from the remainder of radiology (e.g., MRI, CT, CR, or US), you will need to make sure your system can handle these object types as well. What DICOM services are relevant to Nuclear Medicine? DICOM services include: Verification: Check to see if another system is on-line and available Storage: Ability to accept images for storage. Query/retrieve: Ability to inquire as to existence of a study (or types of studies based on transmitted specifications), and retrieve those studies from the remote system. This might be used for moving data from a remote system to a local one, or to pull data from an archiving node. Print management: Ability to print an image, including maintaining a print queue. Modality Worklist: Ability to query the local radiology information system (RIS) for a list of patients to be done that day, and use that information to automatically fill in fields in the image study header on the acquisition system. This will make sure that names, birth-dates, and other patient identifiers are consistent throughout the system (especially needed if images are to be forwarded to a PACS archive). Each of these services is linked to a broad study type, to create a “service-object pair” or SOP. For example, one such pair might be the ability to Store Nuclear Medicine images, where storing is the service, and nuclear medicine is the object type. Other DICOM components include Performed Procedure Step, Storage Commitment, Softcopy Presentation State, Print Consistency, and Structured Reporting. Information about how these work together in the clinical setting can be found at the web site “Integrating the Health Care Enterprise” (IHE). http://www.rsna.org/IHE/index.shtml
  • 4. What is a DICOM conformance statement, and how should I use it? For the most part, a DICOM conformance statement is a list of the service object pairs, or SOPs (see above), that are supported by that system. The conformance statement can be used as a preliminary screen to see if the system you are considering buying supports the types of things you wish to do with it. For example, if it does not support Storing of Nuclear Medicine images, you will not be able to send such images to it. If the DICOM conformance statement matches my needs, is image inter- operability via DICOM guaranteed to work? Unfortunately, no. There are still many other things that can go wrong, as illustrated in the section above entitled “Does this mean that DICOM is now guaranteed to work at my site?”. When specifying DICOM compliance for a purchase, in addition to specifying the needed SOP classes, it is best to also detail what you want the end result to be in terms of functionality. For example, in addition to specifying that you want a PACS system to support the Nuclear Medicine store and query/retrieve functions, you might detail the specific camera types that you have for which the system needs to work, and include a requirement that you will be able to display and process the data upon retrieval. Will I be able to read my Nuclear Medicine studies from a DICOM-based PACS system? Perhaps. While many PACS are able to receive and display nuclear medicine data, the flexibility and versatility of that display will likely be markedly limited compared to a dedicated nuclear medicine review station. For example, you might not be able to view pulmonary perfusion and ventilation images side-by-side. And, you may not be able to do any processing such as reframing a dynamic series, nor are you likely to be able to view sagittal and coronal slices from transaxial data. You will almost certainly be unable to display gated SPECT images correctly at the current time. What else are the SNM and other organizations doing to promote DICOM interoperability? The SNM 2001 demonstration is just the first phase of our efforts. The second phase will address more complex data types, such as gated SPECT studies, and the third phase will look more closely at communication outside of nuclear medicine, to PACS systems. More importantly, we are part of a multi-organizational task force that is working with manufacturers to address global priorities and directions in making DICOM work for nuclear medicine. Though we did not develop the standard nor have direct control over its implementation, the SNM is working hard to make DICOM a useful tool in nuclear medicine.
  • 5. Where can I learn more about DICOM? Good places to start are http://www.rsna.org/practice/dicom.html and http://www.dclunie.com/ . Additional information can be found at http://www.nema.org/standards/ and http://www.rsna.org/IHE/index.shtml .