In-Stack Position Number Attribute
| Tag | (0020,9057) |
|---|---|
| Type | Conditionally Required (1C) |
| Keyword | InStackPositionNumber |
| Value Multiplicity | 1 |
| Value Representation | Unsigned Long (UL) |
| Example Values |
|
The ordinal number of a frame in a group of frames, with the same Stack ID (0020,9056).
Required if Stack ID (0020,9056) or Functional MR Sequence (0018,9621) is present.
See Section C.7.6.16.2.2.4 and Section C.7.6.16.2.2.8 for further explanation.
Note
Part of the Frame Content Functional Group Macro with usage: U
Section C.7.6.16.2.2.4
C.7.6.16.2.2.4 Concatenations and Stacks
Due to implementation specific reasons (such as maximum object size) the information of a multi-frame image may be split into more than one SOP Instance. These SOP Instances form together a Concatenation. This is a group of SOP Instances within a Series that is uniquely identified by Concatenation UID (0020,9161).
The Dimension Index Sequence (0020,9222) for each SOP Instance with the same Concatenation UID (0020,9161) shall contain exactly the same Attributes and values.
In a Concatenation the Dimension Index Sequence (0020,9222) Items of the Shared Functional Groups (5200,9229) shall be identical and have the same values for all individual SOP Instances. The Items of the Per-Frame Functional Groups Sequence (5200,9230) shall be identical for all individual SOP Instances but the values may change per frame. For all other Attributes of all the Modules of the IOD, the same Attributes shall be present and the values shall be identical, with the exception of the following Attributes:
-
Number of Frames (0028,0008)
-
Concatenation Frame Offset Number (0020,9228)
-
In-concatenation Number (0020,9162)
-
SOP Instance UID (0008,0018)
-
Instance Creation Time (0008,0013)
Note
The intent of Concatenations is to split what might have been encoded in a single SOP Instance into smaller fragments for more convenient storage or transmission. All the multiple SOP Instances of a Concatenation should be able to be assembled into a valid single SOP Instance. Hence it is not permitted to change such Attributes as Photometric Interpretation (0028,0004), Rows (0028,0010), Columns (0028,0011), etc.
Stacks describe application-specific groups of frames that have a geometric relationship. Stacks have a Stack ID (0020,9056) that contains a descriptive name that identifies the stack. A Stack ID (0020,9056) may be re-used in another SOP Instance even outside a concatenation. The value of Stack ID (0020,9056) is unique within the scope of a particular Dimension Organization UID (0020,9164) if present, otherwise it is unique within the scope of a particular Concatenation UID (0020,9161). See Figure C.7.6.16-3 for an example.
Figure C.7.6.16-3. Identifying Attributes for Concatenation, SOP Instances, Frames and Stacks
Each frame in a stack has an In-Stack Position Number (0020,9057) that is the ordinal number (starting from 1) of the frame within the set of frames with the same Stack ID (0020,9056), see Figure C.7.6.16-4 for an example.
Figure C.7.6.16-4. Example of multiple stacks
In order to allow interoperable operations on stacks, 2 different frames with the same Stack ID (0020,9056) can only have the same In-Stack Position Number (0020,9057) if they have the same values for the following Attributes:
-
Dimension Organization UID (0020,9164) to qualify the Stack ID
-
Image Position (Patient) (0020,0032)
-
Image Orientation (Patient) (0020,0037)
-
Rows (0028,0010) * first value of Pixel Spacing (0028,0030) (= field of view in the row direction)
-
Columns (0028,0011) * second value of Pixel Spacing (0028,0030) (= field of view in the column direction)
-
Slice Thickness (0018,0050)
Section C.7.6.16.2.2.8
C.7.6.16.2.2.8 Usage of Temporal Position Index, Stack ID and In-Stack Position Number in fMRI Volumes
For fMRI volumes the Temporal Position Index is used to distinguish between the multiple volumes acquired in time (phases of a volume) for the same Stack ID. Each frame in the volume has an In-Stack Position Number that is the ordinal number in space of each volume. See Figure C.7.6.16-4c for an example.
Figure C.7.6.16-4c. Example of Functional MRI volumes