Subject Relative Position in Image Attribute
| Tag | (0010,0028) |
|---|---|
| Type | Optional (3) |
| Keyword | SubjectRelativePositionInImage |
| Value Multiplicity | 3 |
| Value Representation | Unsigned Short (US) |
The position in the image pixel data of the individual subject identified in this Sequence relative to the other subjects. See Section C.7.1.4.1.1.1.
Section C.7.1.4.1.1.1
C.7.1.4.1.1.1 Subject 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):
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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,
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the second value starts at one for the top most subject holder and monotonically increases by one for each successively lower subject holder,
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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
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The order and sign of the machine-relative directions is consistent with the Axis Definition in [ACR-NEMA 300-1985].
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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.
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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).
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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.
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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.
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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.
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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 Figure C.7.1.4-3.
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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
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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.
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For example, a pair of prone non-human organisms arranged head-to-head longitudinally along the bore of the machine would be described as:
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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 Figure C.7.1.4-2.
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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.
Figure C.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
Figure C.7.1.4-2. Example of Subject Relative Position in Image and differing Patient Position for group of 2 mice head-to-head
Figure C.7.1.4-3. Example of Subject Relative Position in Image and overlapping narrow field of view group of 2 mice head-to-head