For the other Explicit Data Elements or Implicit Data Elements, see section 7.1 of Part 5 of the DICOM Standard. With Explicit Value Representation (VR) Data Elements, for VRs that are not OB, OW, OF, SQ, UT, or UN, the format for each Data Element is: GROUP (2 bytes) ELEMENT (2 bytes) VR (2 bytes) LengthInByte (2 bytes) Data (variable length). LZW (zip) compression can be used for the whole data set (not just the pixel data), but this has rarely been implemented.ĭICOM uses three different Data Element encoding schemes. Pixel data can be compressed using a variety of Standards, including JPEG, Lossless JPEG, JPEG 2000, and Run-length encoding (RLE). In these cases, three- or four-dimensional data can be encapsulated in a single DICOM object. Another example is NM data, where an NM image, by definition, is a multi-dimensional multi-frame image. However, the attribute may contain multiple "frames", allowing storage of cine loops or other multi-frame data.
For many modalities, this corresponds to a single image.
A single DICOM object can have only one attribute containing pixel data. logically, the main object has no "header" as such, being merely a list of attributes, including the pixel data). This is similar to the way that image formats such as JPEG can also have embedded tags to identify and otherwise describe the image.Ī DICOM data object consists of a number of attributes, including items such as name, ID, etc., and also one special attribute containing the image pixel data (i.e. That means that a file of a chest x-ray image, for example, actually contains the patient ID within the file, so that the image can never be separated from this information by mistake.
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