Although since 1992 DICOM 3.0 has become accepted worldwide, in clinical procedures, equipment as well as databases typically still comply with the ACR-NEMA 2.0 standard. Thus, in most cases an ACR-NEMA 2.0 to DICOM 3.0 conversion is required. The DICOM 3.0 standard provides several major enhancements to the earlier ACR-NEMA version.
Two fundamental components of DICOM, described in detail in Chapter 47, are information object class and service class. The information objects define the contents of a set of images and their relationship (e.g., patients, modalities, studies). They consist of normalized objects, including attributes inherent in the real-world entity, and composite objects, which combine normalized object classes. On the other hand, ACR-NEMA describes images obtained from different modalities based on a composite information concept.
The service class describes the action performed on the objects (e.g., image storage, query, retrieval, print). These commands are backward compatible with the earlier ACR-NEMA version. The composite commands are generalized, whereas the normalized commands are more specific.
For image transmission, DICOM uses existing network communication standards based on the International Standards Organization Open Systems Interconnection. If an imaging device transmits an image object with a DICOM 3.0 command, the receiver must use a DICOM 3.0 command to receive the information. However, if a DICOM object is transmitted with a TCP/IP communication protocol (without invoking the DICOM communication), any device connected to the network can receive the data with the TCP/IP protocol.
An ACR-NEMA to DICOM conversion also becomes a preprocessing function. Usually vendors provide the users with a DICOM interface that generates a new file format and permits the acquisition station (or workstation) to work in a DICOM environment. If users prefer to deal with the conversion problem themselves, the preprocessing function should be installed at the acquisition station or the acquisition gateway.
FIGURE 15 Angiograms. (a) Original image. (b) Processed image shrunk toward its center to perform the blood-vessel size correction and to sharpen the edges (examples are indicated by arrows).
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