Contour Data Attribute
| Tag | (3006,0050) |
|---|---|
| Type | Required (1) |
| Keyword | ContourData |
| Value Multiplicity | 3-3n |
| Value Representation | Decimal String (DS) |
Sequence of (x,y,z) triplets defining a contour in the Patient-Based Coordinate System described in Section C.7.6.2.1.1 (mm). See Section C.8.8.6.1 and Section C.8.8.6.3.
See Section C.8.8.6.4.
Note
Contour Data may not be properly encoded if Explicit VR Transfer Syntax is used and the VL of this Attribute exceeds 65534 bytes.
Section C.7.6.2.1.1
C.7.6.2.1.1 Image Position and Image Orientation
Image Position (Patient) (0020,0032) specifies the x, y, and z coordinates of the upper left hand corner of the image; it is the center of the first voxel transmitted. Image Orientation (Patient) (0020,0037) specifies the direction cosines of the first row and the first column with respect to the patient. These Attributes shall be provide as a pair. Row value for the x, y, and z axes respectively followed by the Column value for the x, y, and z axes respectively.
The direction of the axes is defined fully by the patient's orientation.
If Anatomical Orientation Type (0010,2210) is absent or has a value of BIPED, the x-axis is increasing to the left hand side of the patient. The y-axis is increasing to the posterior side of the patient. The z-axis is increasing toward the head of the patient.
If Anatomical Orientation Type (0010,2210) has a value of QUADRUPED, the
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x-axis is increasing to the left (as opposed to right) side of the patient
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the y-axis is increasing towards
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the dorsal (as opposed to ventral) side of the patient for the neck, trunk and tail,
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the dorsal (as opposed to ventral) side of the patient for the head,
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the dorsal (as opposed to plantar or palmar) side of the distal limbs,
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the cranial (as opposed caudal) side of the proximal limbs, and
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the z-axis is increasing towards
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the cranial (as opposed to caudal) end of the patient for the neck, trunk and tail,
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the rostral (as opposed to caudal) end of the patient for the head, and
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the proximal (as opposed to distal) end of the limbs
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Note
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The axes for quadrupeds are those defined and illustrated in Smallwood et al for proper anatomic directional terms as they apply to various parts of the body.
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It should be anticipated that when quadrupeds are imaged on human equipment, and particularly when they are position in a manner different from the traditional human prone and supine head or feet first longitudinal position, then the equipment may well not indicate the correct orientation, though it will remain an orthogonal Cartesian right-handed system that could be corrected subsequently.
The Patient-Based Coordinate System is a right handed system, i.e., the vector cross product of a unit vector along the positive x-axis and a unit vector along the positive y-axis is equal to a unit vector along the positive z-axis.
Note
If a patient is positioned parallel to the ground, in dorsal recumbency (i.e., for humans, face-up on the table), with the caudo-cranial (i.e., for humans, feet-to-head) direction the same as the front-to-back direction of the imaging equipment, the direction of the axes of this Patient-Based Coordinate System and the Equipment-Based Coordinate System in previous versions of this Standard will coincide.
The Image Plane Attributes, in conjunction with the Pixel Spacing Attribute, describe the position and orientation of the image slices relative to the Patient-Based Coordinate System. In each image frame Image Position (Patient) (0020,0032) specifies the origin of the image with respect to the Patient-Based Coordinate System. RCS and Image Orientation (Patient) (0020,0037) values specify the orientation of the image frame rows and columns. The mapping of an integer (entire) pixel location (i,j) to the RCS is calculated as follows:
Equation C.7.6.2.1-1.
Where:
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Pxyz The coordinates of the voxel (i,j) in the frame's image plane in units of mm.
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Sxyz The three values of Image Position (Patient) (0020,0032). It is the location in mm from the origin of the RCS.
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Xxyz The values from the row (X) direction cosine of Image Orientation (Patient) (0020,0037).
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Yxyz The values from the column (Y) direction cosine of Image Orientation (Patient) (0020,0037).
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i Column integer index to the image plane. The first (entire) column is index zero.
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Δi Column pixel resolution of Pixel Spacing (0028,0030) in units of mm.
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j Row integer index to the image plane. The first (entire) row index is zero.
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Δj Row pixel resolution of Pixel Spacing (0028,0030) in units of mm.
Note
The integer entire row and column indices (i,j) that are the input to this equation start from zero, which is a common mathematical convention. Many DICOM Attributes define such indices as starting from one, e.g., those affected by Bounding Box Annotation Units (0070,0003) for PIXEL and MATRIX in Section C.10.5 Graphic Annotation Module. This needs to be accounted for when applying this equation literally.
The mapping of a sub-pixel resolution image or total pixel matrix relative location (c,r), such as used in Spatial Coordinates Macro, to the RCS is calculated as follows
Equation C.7.6.2.1-2.
Where:
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Pxyz The coordinates of the voxel (c,r) in the frame's image plane in units of mm.
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Sxyz The three values of Image Position (Patient) (0020,0032). It is the location in mm from the origin of the RCS.
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Xxyz The values from the row (X) direction cosine of Image Orientation (Patient) (0020,0037).
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Yxyz The values from the column (Y) direction cosine of Image Orientation (Patient) (0020,0037).
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c Column sub-pixel resolution index to the image plane. The left pixel edge of the first column of the frame or total pixel matrix is index zero.
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Δc Column pixel resolution of Pixel Spacing (0028,0030) in units of mm.
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r Row sub-pixel resolution index to the image plane. The top pixel edge of the first row of the frame or total pixel matrix index is zero.
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Δr Row pixel resolution of Pixel Spacing (0028,0030) in units of mm.
Additional constraints apply:
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The row and column direction cosine vectors shall be orthogonal, i.e., their dot product shall be zero.
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The row and column direction cosine vectors shall be normal, i.e., the dot product of each direction cosine vector with itself shall be unity.
Section C.8.8.6.1
C.8.8.6.1 Contour Geometric Type
A contour can be one of the following geometric types:
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A Contour Geometric Type (3006,0042) of POINT indicates that the contour is a single point, defining a specific location of significance.
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A Contour Geometric Type (3006,0042) of OPEN_PLANAR indicates that the last vertex shall not be connected to the first point, and that all points in Contour Data (3006,0050) shall be coplanar.
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A Contour Geometric Type (3006,0042) of OPEN_NONPLANAR indicates that the last vertex shall not be connected to the first point, and that the points in Contour Data (3006,0050) may be non-coplanar. Contours having a Geometric Type (3006,0042) of OPEN_NONPLANAR can be used to represent objects best described by a single, possibly non-coplanar curve, such as a brachytherapy applicator.
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A Contour Geometric Type (3006,0042) of CLOSED_PLANAR indicates that the last point shall be connected to the first point, where the first point is not repeated in Contour Data (3006,0050). All points in Contour Data (3006,0050) shall be coplanar.
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A Contour Geometric Type (3006,0042) of CLOSEDPLANAR_XOR indicates that the last point shall be connected to the first point, where the first is not repeated in Contour Data (3006,0050). All points in Contour Data (3006,0050) shall be coplanar. More than one Contour is used to describe an ROI and these Contours are combined by geometric exclusive disjunction, see Section C.8.8.6.3. If any of the Contours within an ROI is of Contour Geometric Type (3006,0042) CLOSEDPLANAR_XOR, all Contours of that ROI shall be of the same type.
Section C.8.8.6.3
C.8.8.6.3 Representing Inner and Outer Contours
Inner and Outer Contours can be represented by two different techniques:
Using the "keyhole" technique, an ROI with an excluded inner part is represented with a single planar Contour. In this method, an arbitrarily narrow channel is used to connect the outer contour to the inner contour, so that it is drawn as a single contour. An example of such a structure is shown in Figure C.8.8.6-1 with the channel at roughly the 12 o'clock position.
Points in space lying along the path defined by the contour are considered to be part of the ROI.
Figure C.8.8.6-1. Example of ROI with excluded inner volume
Using the "XOR" technique, an ROI with an excluded inner part is represented by two planar Contours that are combined by a geometric exclusive disjunction, thus extracting the inner from the outer Contour, see Figure C.8.8.6-2. The contours have the Contour Geometric Type (3006,0042) CLOSEDPLANAR_XOR.
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Figure C.8.8.6-2. Example of ROI with contours exclusively added
Using this technique, it is also possible to create an ROI that includes disjoint parts of the ROI within an interior void. When two or more Contours are present, two Contours are combined using a geometric exclusive disjunction ("XOR"). Then this result is combined by an XOR operation with a third Contour, and so on for all other Contours of this ROI. The order of combination does not matter. An example of the result of an XOR operation of three Contours is visualized in Figure C.8.8.6-3.
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Figure C.8.8.6-3. Example of ROI with disjoint parts
Section C.8.8.6.4
C.8.8.6.4 Source Pixel Planes Characteristics
The Source Pixel Planes Characteristics Sequence (3006,004A) defines a stack of Source Pixel Planes on the originating system from which the Contour data of an ROI was derived. This stack of Source Pixel Planes does not need to correspond to actual Image Storage SOP Instances.
If a receiving system also utilizes a pixel-based representation of Contours, the information in this Sequence may be utilized to define the same pixel grid as the originating system to reduce the magnitude of errors caused by different sampling rates.
If Source Pixel Planes Characteristics Sequence (3006,004A) is present for an ROI in the ROI Contour Sequence (3006,0039) the following apply:
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Contours are specified on Source Pixel Planes defined by the characteristics in the Source Pixel Planes Characteristics Sequence (3006,004A).
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A Source Pixel Plane is not required to coincide with or be parallel to an actual image plane (i.e., Contour Image Sequence (3006,0016) is not required to be present, and if it is present, the referenced images need to not correspond to the characteristics of Source Pixel Planes).
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The x, y, z triplets of Contour Data (3006,0050) shall be defined on the Source Pixel Planes defined by Source Pixel Planes Characteristics Sequence (3006,004A).
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Contour Data (3006,0050) may have a different (e.g., higher) sampling than the Pixel Spacing (0028,0030).
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Source Pixel Planes for all Contours of the ROI will be parallel (since only one Image Orientation (Patient) is specified).
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Source Pixel Planes will be equidistantly spaced (since only one Spacing Between Slices is specified).
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Contours of an ROI shall be specified on every Source Pixel Plane where the ROI is present.
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If no Contour Data is specified for a given Source Pixel Plane of an ROI, the ROI is defined to be absent on that Source Pixel Plane (i.e., a Source Pixel Plane without corresponding Contour Data defines a "gap").