C.7.1.4.1.1Groups of Subjects
It is common to image multiple small non-human organisms for pre-clinical research as a group at the same time.
In such cases, the single value of Patient ID (0010,0020) corresponds to the identification of the entire group. The same applies to related Attributes, if present, such as Issuer of Patient ID (0010,0021). Other Attributes of the Patient Module that are present shall be those shared by the entire group of non-human organisms, otherwise they shall be absent or empty (e.g., Patient's Sex (0010,0040)). Any acquisition-related Attributes that are Patient-specific (e.g., injected contrast or radiopharmaceutical dose) shall also be absent or empty (and the information may be communicated in separate acquisition context Instances).
The Group of Patients Identification Sequence (0010,0027) provides a means of describing the identifiers and locations of the individual subjects, if known at the time of acquisition, regardless of whether or not the group images are later segmented into individual images.
It is also common to segment the acquired images of the group of non-human organisms and extract the image pixel data for each non-human organism into separate images.
The Source Patient Group Identification Sequence (0010,0026) provides a "backward reference" within the segmented (individual subject) images to the Patient ID (0010,0020) used to identify the whole group.
Note
Individual derived SOP Instances may reference the source image explicitly by its SOP Instance UID. Additional objects, such as Segmentations, may be created to encode the regions segmented for individual non-human organisms, and referenced from the derived images. See also Annex VVV “Segmentation of Images of Groups of Animals (Informative)” in PS3.17.
For example, an image of a group of 6 mice in a 3 column, 2 row single longitudinal plane array might be described as:
Patient ID (0010,0020) = "Inv234_Exp_56_Group78"
Issuer of Patient ID (0010,0021) = "MyMouseLab"
Group of Patients Identification Sequence (0010,0027)
>Patient ID (0010,0020) = "Inv234_Exp_56_Group78_Mouse01"
>Issuer of Patient ID (0010,0021) = "MyMouseLab"
>Subject Relative Position in Image (0010,0028) = 1\1\1
...
>Patient ID (0010,0020) = "Inv234_Exp_56_Group78_Mouse06"
>Issuer of Patient ID (0010,0021) = "MyMouseLab"
>Subject Relative Position in Image (0010,0028) = 3\2\1
In this example, the optional Issuer of Patient ID (0010,0021) is shown to emphasize that if it is needed, it should be repeated; i.e., there is no "inheritance" of the issuer from the Data Set enclosing the Sequence.
The naming of the group and the individual non-human organisms in the identifier is purely illustrative; it is not meant to imply preference for one local convention or another, or for using a discrete identifier for the group as opposed to, say, a concatenated list of individual non-human organism identifiers used as the group identifier.
See FigureC.7.1.4-1.
For example, segmented images of an individual non-human organism derived from the group image might be described as:
Patient ID (0010,0020) = "Inv234_Exp_56_Group78_Mouse04"
Issuer of Patient ID (0010,0021) = "MyMouseLab"
Source Patient Group Identification Sequence (0010,0026)
>Patient ID (0010,0020) = "Inv234_Exp_56_Group78"
>Issuer of Patient ID (0010,0021) = "MyMouseLab"
C.7.1.4.1.1.1Subject Relative Position in Image and Patient Position
Subject Relative Position in Image (0010,0028) shall be encoded as a 3D ordinal position in machine-relative orthogonal dimensions, such that when facing the front of the machine (gantry):
the first value starts at one for the left most subject holder and monotonically increases by one for each successive subject holder towards the right,
the second value starts at one for the top most subject holder and monotonically increases by one for each successively lower subject holder,
the third value starts at one for the outer most subject holder and monotonically increases by one for each successive subject holder inwards (i.e., increasing values from the front to the back of the gantry along the direction orthogonal to the first two dimensions, usually the long axis of the table).
Note
The order and sign of the machine-relative directions is consistent with the Axis Definition in [ACR-NEMA 300-1985].
Image-relative positions are not used, since there may be multiple acquisitions in different orientations. The machine-relative positions are applicable regardless of whether acquired images are cross-sections or projections.
Patient-relative positions are not used, since the non-human organisms may not be arranged in the same direction (e.g., a pair of non-human organisms may be arranged head-to-head).
There is no requirement that there be the same number of non-human organisms in each dimension. E.g., one in the top "row"and two below, in one longitudinal plane, would be represented as 1\1\1, 1\2\1, 2\1\1.
The goal is to describe only the relative locations of non-human organisms in any form of multiple non-human organism holder ("mouse hotel"), without attempting to specify the exact physical dimensions or absolute locations, regardless of whether the holder is regular or symmetric in any particular dimension or not (e.g., to include "revolver-like" and hexagonal arrangements). Nor is the "distance" between each non-human organism described.
The position is defined in terms of subject holders rather than subjects, since some holders may be empty or unused but still partially or completely visible in some of the images. In such cases the relative positions need to be consistently encoded by the acquisition device and recognized by automated segmentation algorithms. E.g., if the top row of in a two row holder is unoccupied, then the non-human organisms in the bottom row will be identified with a row position of 2, not 1.
Due to field of view and anatomical region of interest considerations, adjacent non-human organisms may sometimes be partially overlapped (e.g., Cheng TE et al. A rat head holder for simultaneous scanning of two rats in small animal PET scanners: Design, construction, feasibility testing and kinetic validation. Journal of Neuroscience Methods. 2009 Jan 15;176(1):24–33. http://dx.doi.org/10.1016/j.jneumeth.2008.08.031 and Xu S et al. In vivo multiple-mouse imaging at 1.5 T. Magnetic Resonance in Medicine. 2003;49(3):551–7. http://dx.doi.org/10.1002/mrm.10397); such cases may be described as a either a single plane or two planes of non-human organisms, as long as there is sufficient information to identify which non-human organism is which.
See FigureC.7.1.4-3.
The description of the physical relative locations of the non-human organisms does not account for any spatial distortion that may occur in the images due to the acquisition technique used (e.g., aliasing in MRI).
Patient Position (0018,5100) may be used to describe the machine-relative position of each non-human organism when the non-human organisms are not all arranged in the same direction.
Note
Patient Position (0018,5100) is used rather than Patient Orientation Code Sequence (0054,0410) because Patient Position (0018,5100) is present in the IODs for those modalities most commonly used for small animal imaging in preclinical research.
For example, a pair of prone non-human organisms arranged head-to-head longitudinally along the bore of the machine would be described as:
Subject Relative Position in Image = 1\1\1 and Patient Position = HFP
Subject Relative Position in Image = 1\1\2 and Patient Position = FFP
See FigureC.7.1.4-2.
The presence of Subject Relative Position in Image (0010,0028) and Patient Position (0018,5100) within Group of Patients Identification Sequence (0010,0027) within the Patient Module implies that the relative locations and orientations of multiple non-human organisms within a group cannot change over time. I.e., a "group", identified by a particular Patient ID (0010,0020) (the unique key of the Patient entity in the Information Model), is defined not only by the non-human organisms that comprise it but also their relative locations and positioning. If the same non-human organisms are imaged together but in a different arrangement, a different Patient ID (0010,0020) for the group shall be used.
FigureC.7.1.4-1.Example of Subject Relative Position in Image for group of 6 mice in a 3 column, 2 row single longitudinal plane array, all feet first prone
FigureC.7.1.4-2.Example of Subject Relative Position in Image and differing Patient Position for group of 2 mice head-to-head
FigureC.7.1.4-3.Example of Subject Relative Position in Image and overlapping narrow field of view group of 2 mice head-to-head
