LDL Configurator
DICOM contains length-delimited fields. The LDL (Length Delimited Layout) tool specifies a DICOM record layout. Standard DICOM transactions are available in the root and can be edited with the LDL tool.
The LDL Configurator supports explicit length fields, undefined length fields, and sequenced fields.
DICOM is supported as DICOM Router. It receives the DICOM file as DICOM SCP (DICOM Service Class Provider). Then, it routes the DICOM file after transformation to another DICOM SCU (DICOM Service Class User). Conversion from DICOM to other message formats, for example, HL7, is also possible.
Parts of DICOM include:
- DICOM format
A DICOM object is a list of DICOM elements. Each DICOM element is an LDL record of the format (
TAG
LENGTH
,DATA
).TAG is composed of two short integers, indicating (
GROUP
, ,ELEMENT
) and implicitly defines the type for the DATA field. - DICOM element
DICOM elements are one of 28 types, also called VR, or value representation.
DICOM elements are nested under a parent element as the
SEQUENCE
DICOM element (SQ). This organizes DICOM in a hierarchical structure. - DICOM group
A
GROUP
is a logical grouping of data elements, for example, patient identification group or a CT scan group.The
ELEMENT
, is the individual item within that group, for example, patient ID, patient name, or a pixel data element.An even numbered
GROUP
orELEMENT
is DICOM-specified and odd numbered are user-specified. This is similar to Z segments in HL7.An element that defines the
GROUP
always has 0x0000 as itsELEMENT
. - DICOM SOP
DICOM SOP (Service Object Pairs) are DICOM objects that trigger running a service and contain service-specific information.
The DICOM SOP is composed of two parts:
- DIMSE (DIcom Message Service Element) that contains command information.
- IOD (Information Object for Dicom) that contains data for that command.
DIMSE is a list of
ELEMENT
s underGROUP
0x0000 and is indicated by two elements:-
Service Class
(0x0000, 0x0002) Command Code
(0x0000, 0x0100)
A SOP might not have any data, thus it solely consists of DIMSE. If the SOP requires data to be sent, then the presence of data is indicated by setting element (0x0000, 0x0800) to NULL (=0). If set to NULL, then it is expected that there is data following when
GROUP
0x0000 ends.DICOM SOP are service-specific and contain structure and data specific to the service being requested. The DICOM services are also called DIMSE Services, since it is the DIMSE component of SOP that identifies the service.
For more details, see the DICOM dictionary at http://rsb.info.nih.gov/nih-image/download/documents/dicom-dict.txt.
Additional points:
- DICOM fields are always even byte lengths, so fields are padded to make them even. Conversion to and from the DICOM format should be performed in a similar manner.
- Implicit versus explicit DICOM element format should be understood before conversion.
- Groups may have zero lengths. In DICOM, this is available only for groups.
- DICOM
GROUP
andELEMENT
are always in ascending order of their numerical value. - An element can have multiple values. For fixed length elements, such as numerical values, the element length is in multiples to indicate this fact. For variable length elements, for example, text strings, a backslash “\” is used to delimit sub elements.
- PDU numeric data fields are always Big Endian.