The basic unit of information in DICOM files is the data element, which consists of:

The data element tag is a unique identifier for a data element composed of an ordered pair of numbers: a group number followed by an element number. A DICOM file consists of a collection of data elements in ascending order of group number (primary key) and element number (secondary key).

A data element can be standard or private.

Standard data elements are listed in the DICOM data element dictionary, which is defined in Part 6 of the DICOM Standard. Standard data elements always have data element tags with even group numbers. The DICOM Dictionary is indexed by data element tag and specifies for each data element its description (semantics), value multiplicity range, value representation and whether a data element has been retired.

Private data elements are defined by an implementer, to communicate information that is not contained in standard data elements. Private data elements have odd group numbers.

Data elements are organized into data sets. Each data set consists of a series of data elements in ascending order of data element tag. A DICOM file is a data set.

Data sets can be recursively nested. The mechanism employed by DICOM for nesting data sets is by use of the special data elements of value representation sequence of items (SQ). Data elements of value representation SQ may contain zero or more items each of which may contain one data set.

QMedical provides full access to the data elements present in a DICOM file at any level of nesting. QMedical uses reference numbers to address individual data elements within the data hierarchy. To retrieve the reference numbers for all data elements at a given level, use the QMed_GetElements command. Command QMed_FindElement returns the reference number for a particular element at a given level, identified by its group and element number.

Given a particular element reference number, you can get full information about the data element:

To retrieve the content of a data element, more than one commands can be used depending on the type of the data element and the desired 4D type of the returned value(s).

QMed_GetMetaInfo Returns data endianess and pixel representation information
QMed_FindElement Finds a data element by its group and element number
QMed_GetElements Retrieves the reference numbers for all data elements at a given level
QMed_GetDictElementInfo Returns DICOM dictionary information for a data element
QMed_GetElementDataInfo Returns information about a data element instance in a DICOM file
QMed_GetElementData Returns the content of a data element as a BLOB
QMed_GetElementDataAsLong Returns the content of a data element item as a longint
QMed_GetElementDataAsReal Returns the content of a data element item as a real
QMed_GetElementDataAsText Returns the content of a data element item as text

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