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# Value Representations

The following Value Representations describe the data type and format of each DICOM attribute. These are defined in Section 6.2 of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding.

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VR | Definition | Details
--- | --- | ---
AE | Application Entity A string of characters with leading and trailing spaces (20H) being non-significant. The value made of 16 spaces, meaning “no application name specified”, shall not be used. | Character Repertoire Default Character Repertoire excluding control characters LF, FF, CR and ESC. Length 16 bytes maximum IDL Data Type STRING
AS | Age String A string of characters with one of the following formats -- nnnD, nnnW, nnnM, nnnY; where nnn shall contain the number of days for D, weeks for W, months for M, or years for Y. For example, “018M” would represent an age of 18 months. | Character Repertoire “0”-”9”, “D”, “W”, “M”, “Y” of Default Character Repertoire Length 4 bytes fixed IDL Data Type STRING
AT | Attribute Tag Ordered pair of 16-bit unsigned integers that is the value of a Data Element Tag. Example A Data Element Tag of (0018,00FF) would be encoded as a series of 4 bytes in a Little-Endian Transfer Syntax as 18H,00H,FFH,00H and in a Big-Endian Transfer Syntax as 00H,18H,00H,FFH. The encoding of an AT value is exactly the same as the encoding of a Data Element Tag as defined in Section 7. | Character Repertoire Not applicable Length 4 bytes fixed IDL Data Type ULONG
CS | Code String A string of characters with leading or trailing spaces (20H) being non-significant. | Character Repertoire Uppercase characters, “0”-”9”, the SPACE character, and underscore “_”, of the Default Character Repertoire Length 16 byte maximum IDL Data Type STRING
DA | Date A string of characters of the format yyyymmdd; where yyyy shall contain year, mm shall contain the month, and dd shall contain the day. This conforms to the ANSI HISPP MSDS Date common data type. Example “19930822” would represent August 22, 1993. For reasons of backward compatibility with versions of this standard prior to V3.0, it is recommended that implementations also support a string of characters of the format yyyy.mm.dd for this VR. See also DT VR in this table. For reasons specified in the previous column, implementations may wish to support the “.” character as well. | Character Repertoire “0”-”9” of Default Character Repertoire Length 8 bytes fixed For reasons specified in the previous columns, implementations may also wish to support a 10 byte fixed length as well. IDL Data Type STRING
DL | Delimitation |
DS | Decimal String A string of characters representing either a fixed point number or a floating point number. A fixed point number shall contain only the characters 0-9 with an optional leading “+” or “-” and an optional “.” to mark the decimal point. A floating point number shall be conveyed as defined in ANSI X3.9, with an “E” or “e” to indicate the start of the exponent. Decimal Strings may be padded with leading or trailing spaces. Embedded spaces are not allowed. | Character Repertoire “0” - “9”, “+”, “-”, “E”, “e”, “." of Default Character Repertoire Length 16 bytes maximum IDL Data Type STRING
DT | DATE TIME The Date Time common data type. Indicates a concatenated date-time ASCII string in the format: YYYYMMDDHHMMSS.FFFFFF&ZZZZ The components of this string, from left to right, are YYYY = Year, MM = Month, DD = Day, HH = Hour, MM = Minute, SS = Second, FFFFFF = Fractional Second, & = “+” or “-”, and ZZZZ = Hours and Minutes of offset. &ZZZZ is an optional suffix for plus/minus offset from Coordinated Universal Time. A component that is omitted from the string is termed a null component. Trailing null components of Date Time are ignored. Non-trailing null components are prohibited, given that the optional suffix is not considered as a component. For reasons of backward compatibility with versions of this standard prior to V3.0, many existing DICOM Data Elements use the separate DA and TM VRs. Standard and Private Data Elements defined in the future should use DT, when appropriate, to be more compliant with ANSI HISPP MSDS. | Character Repertoire “0” - “9”, “+”, “-”, “.” of Default Character Repertoire Length 26 bytes maximum IDL Data Type STRING
FL | Floating Point Single Single precision binary floating point number represented in IEEE 754:1985 32-bit Floating Point Number Format. | Character Repertoire Not applicable Length 4 bytes fixed IDL Data Type FLOAT
FD | Floating Point Double Double precision binary floating point number represented in IEEE 754:1985 64-bit Floating Point Number Format. | Character Repertoire Not applicable Length 8 bytes fixed IDL Data Type DOUBLE
IS | Integer String A string of characters representing an Integer in base-10 (decimal), shall contain only the characters 0 - 9, with an optional leading “+” or “-”. It may be padded with leading and/or trailing spaces. Embedded spaces are not allowed. The integer, n, represented shall be in the range: -2 31 <= n <= (2 31 - 1). | Character Repertoire “0”-”9”, “+”, “-” of Default Character Repertoire Length 12 bytes maximum IDL Data Type STRING
LO | Long String A character string that may be padded with leading and/or trailing spaces. The character code 5CH (the BACKSLASH “\” in ISO-IR 6) shall not be present, as it is used as the delimiter between values in multiple valued Default Character Repertoire and/or as defined by (0008,0005). | Character Repertoire 64 chars Length 64 chars maximum The length of the VRs for which the Character Repertoire can be extended or replaced are expressly specified in characters rather than bytes because the mapping from a character to the number of bytes used for that character’s encoding may be dependent on the character set used. IDL Data Type STRING
LT | Long Text A character string that may contain one or more paragraphs. It may contain the Graphic Character set and the Control Characters, CR, LF, FF, and ESC. It may be padded with trailing spaces, which may be ignored, but leading spaces are considered to be significant. Data Elements with this VR shall not be multi-valued and therefore character code 5CH (the BACKSLASH “\” in ISO-IR 6) may be used. Default Character Repertoire and/or as defined by (0008,0005). | Character Repertoire 10240 chars Length 10240 chars maximum The length of the VRs for which the Character Repertoire can be extended or replaced are expressly specified in characters rather than bytes because the mapping from a character to the number of bytes used for that character’s encoding may be dependent on the character set used. IDL Data Type STRING
OB | Other Byte String A string of bytes where the encoding of the contents is specified by the negotiated Transfer Syntax. OB is a VR which is insensitive to Little/Big Endian byte ordering (see Section 7.3 of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding). The string of bytes shall be padded with a single trailing NULL byte value (00H) when necessary to achieve even length. | Character Repertoire Not applicable Length See Transfer Syntax definition IDL Data Type BYTE
OF | Other Float String A string of 32-bit IEEE 754:1985 floating point words. OF is a VR which requires byte swapping within each 32-bit word when changing between Little Endian and Big Endian byte ordering (see Section 7.3 of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding). | Character Repertoire Not applicable Length See Transfer Syntax definition IDL Data Type INT
OW | Other Word String A string of 16-bit words where the encoding of the contents is specified by the negotiated Transfer Syntax. OW is a VR which requires byte swapping within each word when changing between Little Endian and Big Endian byte ordering (see Section 7.3 of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding). | Character Repertoire Not applicable Length See Transfer Syntax definition IDL Data Type INT
PN | Person Name A character string encoded using a 5 component convention. The character code 5CH (the BACKSLASH “\” in ISO-IR 6) shall not be present, as it is used as the delimiter between values in multiple valued data elements. The string may be padded with trailing spaces. The five components in their order of occurrence are: family name complex, given name complex, middle name, name prefix, name suffix. Any of the five components may be an empty string. The component delimiter shall be the caret “^” character (5EH). Delimiters are required for interior null components. Trailing null components and their delimiters may be omitted. Multiple entries are permitted in each component and are encoded as natural text strings, in the format preferred by the named person. This conforms to the ANSI HISPP MSDS Person Name common data type. This group of five components is referred to as a Person Name component group. For the purpose of writing names in ideographic characters and in phonetic characters, up to 3 groups of components (see Annex H examples 1 and 2) may be used. The delimiter for component groups shall be the equals character “=” (3DH). The three component groups of components in their order of occurrence are: a single-byte character representation, an ideographic representation, and a phonetic representation. Any component group may be absent, including the first component group. In this case, the person name may start with one or more “=” delimiters. Delimiters are required for interior null component groups. Trailing null component groups and their delimiters may be omitted. Precise semantics are defined for each component group. See section 6.2.1 of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding. Examples: Rev. John Robert Quincy Adams, B.A. M.Div. “Adams^John Robert Quincy^^Rev.^B.A. M.Div.” [One family name; three given names; no middle name; one prefix; two suffixes.] Susan Morrison-Jones, Ph.D., Chief Executive Officer “Morrison-Jones^Susan^^^Ph.D., Chief Executive Officer” [Two family names; one given name; no middle name; no prefix; two suffixes.] John Doe “Doe^John” [One family name; one given name; no middle name, prefix, or suffix. Delimiters have been omitted for the three trailing null components.] (for examples of the encoding of Person Names using multi-byte character sets see Annex H of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding) This five component convention is also used by HL7 as defined in ASTM E-1238-91 and further specialized by the ANSI MSDS. In typical American and European usage the first occurrence of “given name” would represent the “first name”. The second and subsequent occurrences of the “given name” would typically be treated as a middle name(s). The “middle name” component is retained for the purpose of backward compatibility with existing standards. The “Degree” component present in ASTM E-1238-91 is absorbed into the “Suffix” component. | Character Repertoire Default Character Repertoire and/or as defined by (0008,0005) excluding Control Characters LF, FF, and CR but allowing Control Character ESC. Length 64 chars maximum per component group The length of VRs for which the Character Repertoire can be extended or replaced are expressly specified in characters rather than bytes because the mapping from a character to the number of bytes used for that character’s encoding may be dependent on the character set used. IDL Data Type STRING
SH | Short String A character string that may be padded with leading and/or trailing spaces. The character code 05CH (the BACKSLASH “\” in ISO-IR 6) shall not be present, as it is used as the delimiter between values for multiple data elements. The string shall not have Control Characters except ESC. Default Character Repertoire and/or as defined by (0008,0005). | Character Repertoire 16 chars Length 16 chars maximum The length of VRs for which the Character Repertoire can be extended or replaced are expressly specified in characters rather than bytes because the mapping from a character to the number of bytes used for that character’s encoding may be dependent on the character set used. IDL Data Type STRING
SL | Signed Long Signed binary integer 32 bits long in 2's complement form. Represents an integer, n, in the range: - 2 31 <= n <= (2 31 - 1) | Character Repertoire Not applicable Length 4 bytes fixed IDL Data Type LONG
SQ | Sequence of Items Value is a Sequence of zero or more Items, as defined in Section 7.5 of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding). | Character Repertoire Not applicable Length Not applicable IDL Data Type LONG
SS | Signed Short Signed binary integer 16 bits long in 2's complement form. Represents an integer n in the range: -2 15 <= n <= (2 15 - 1) | Character Repertoire Not applicable Length 2 bytes fixed IDL Data Type INT
ST | Short Text A character string that may contain one or more paragraphs. It may contain the Graphic Character set and the Control Characters, CR, LF, FF, and ESC. It may be padded with trailing spaces, which may be ignored, but leading spaces are considered to be significant. Data Elements with this VR shall not be multi-valued and therefore character code 5CH (the BACKSLASH “\” in ISO-IR 6) may be used. Default Character Repertoire and/or as defined by (0008,0005). | Character Repertoire 1024 chars Length 1024 chars maximum The length of Value Representations for which the Character Repertoire can be extended or replaced are expressly specified in characters rather than bytes because the mapping from a character to the number of bytes used for that character’s encoding may be dependent on the character set used. IDL Data Type STRING
TM | Time A string of characters of the format hhmmss.frac; where hh contains hours (range “00” - “23”), mm contains minutes (range “00” - “59”), ss contains seconds (range “00” - “59”), and frac contains a fractional part of a second as small as 1 millionth of a second (range “000000” - “999999”). A 24 hour clock is assumed. Midnight can be represented by only “0000” since “2400” would violate the hour range. The string may be padded with trailing spaces. Leading and embedded spaces are not allowed. One or more of the components mm, ss, or frac may be unspecified as long as every component to the right of an unspecified component is also unspecified. If frac is unspecified the preceding “.” may not be included. Frac shall be held to six decimal places or less to ensure its format conforms to the ANSI HISPP MSDS Time common data type. Examples “070907.0705” represents a time of 7 hours, 9 minutes and 7.0705 seconds. “1010” represents a time of 10 hours, and 10 minutes. “021” is an invalid value. For reasons of backward compatibility with versions of this standard prior to V3.0, it is recommended that implementations also support a string of characters of the format hh:mm:ss.frac for this VR. See also DT VR in this table. | Character Repertoire “0” - “9”, “.” of Default Character Repertoire Length 16 bytes maximum IDL Data Type STRING
UI | Unique Identifier A character string containing a UID that is used to uniquely identify a wide variety of items. The UID is a series of numeric components separated by the period “.” character. If a Value Field containing one or more UIDs is an odd number of bytes in length, the Value Field shall be padded with a single trailing NULL (00H) character to ensure that the Value Field is an even number of bytes in length. See Section 9 and Annex B of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding for a complete specification and examples. | Character Repertoire “0” - “9”, “.” of Default Character Repertoire Length 64 bytes maximum IDL Data Type STRING
UL | Unsigned Long Unsigned binary integer 32 bits long. Represents an integer n in the range: 0 <= n < 2 32 | Character Repertoire Not applicable Length 4 bytes fixed IDL Data Type ULONG
UN | Unknown A string of bytes where the encoding of the contents is unknown (see Section 6.2.2 of Digital Imaging and Communications in Medicine (DICOM) - Part 5: Data Structures and Encoding). | Character Repertoire Not applicable Length Any length valid for any of the other DICOM VRs IDL Data Type BYTE
US | Unsigned Short Unsigned binary integer 16 bits long. Represents integer n in the range: 0 <= n < 2 16 | Character Repertoire Not applicable Length 2 bytes fixed IDL Data Type UINT
UT | Unlimited Text A character string that may contain one or more paragraphs. It may contain the Graphic Character set and the Control Characters, CR, LF, FF, and ESC. It may be padded with trailing spaces, which may be ignored, but leading spaces are considered to be significant. Data Elements with this VR shall not be multi-valued and therefore character code 5CH (the BACKSLASH “\” in ISO-IR 6) may be used. The text will be interpreted as specified by Specific Character Set (0008,0005). | Character Repertoire Default Character Repertoire and/or as defined by (0008,0005). Length 2 32 -2 Limited only by the size of the maximum unsigned integer representable in a 32 bit VL field minus one, since FFFFFFFFH is reserved. IDL Data Type STRING