C.8.7.3 X-Ray Collimator
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#### C.8.7.3 X-Ray Collimator

An X-Ray Collimator is a device placed close to the X-Ray Source to restrict the span of the X-Ray beam. It is often made of lead shutters. Figure C.8-9 presents in a graphical form its relationship with the Field Of View Dimensions (0018,1149).

Geometry of the collimator is specified with respect to a row and column coordinate system where the origin is the upper left hand pixel. This origin is specified by the values 1,1 for row/column. A row coordinate represent a number of raw spacing (vertical) and a column coordinate represents a column spacing (horizontal). Up to three different collimator shapes may be used and superimposed.

Figure C.8-9. Relationships of X-Ray Collimator

Table C.8-28. X-Ray Collimator Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Collimator Shape | (0018,1700) | 1 | Shape(s) of the collimator. Enumerated Values: RECTANGULAR CIRCULAR POLYGONAL This multi-valued Attribute shall contain at most one of each Enumerated Value.
Include Table C.8-28b “X-Ray Collimator Dimensions Macro Attributes” |

Table C.8-28b. X-Ray Collimator Dimensions Macro Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Collimator Left Vertical Edge | (0018,1702) | 1C | Required if a value of Collimator Shape (0018,1700) is RECTANGULAR. Location of the left edge of the rectangular collimator with respect to pixels in the image given as column. See Section C.8.7.3.1.1.
Collimator Right Vertical Edge | (0018,1704) | 1C | Required if a value of Collimator Shape (0018,1700) is RECTANGULAR. Location of the right edge of the rectangular collimator with respect to pixels in the image given as column. See Section C.8.7.3.1.1.
Collimator Upper Horizontal Edge | (0018,1706) | 1C | Required if a value of Collimator Shape (0018,1700) is RECTANGULAR. Location of the upper edge of the rectangular collimator with respect to pixels in the image given as row. See Section C.8.7.3.1.1.
Collimator Lower Horizontal Edge | (0018,1708) | 1C | Required if a value of Collimator Shape (0018,1700) is RECTANGULAR. Location of the lower edge of the rectangular collimator with respect to pixels in the image given as row. See Section C.8.7.3.1.1.
Center of Circular Collimator | (0018,1710) | 1C | Required if a value of Collimator Shape (0018,1700) is CIRCULAR. Location of the center of the circular collimator with respect to pixels in the image given as row and column. See Section C.8.7.3.1.1.
Radius of Circular Collimator | (0018,1712) | 1C | Required if a value of Collimator Shape (0018,1700) is CIRCULAR. Radius of the circular collimator with respect to pixels in the image given as a number of pixels along the row direction. See Section C.8.7.3.1.1.
Vertices of the Polygonal Collimator | (0018,1720) | 1C | Required if a value of Collimator Shape (0018,1700) is POLYGONAL. Multiple Values where the first set of two values are: row of the origin vertex; column of the origin vertex. Two or more pairs of values follow and are the row and column coordinates of the other vertices of the polygon collimator. Polygon collimators are implicitly closed from the last vertex to the origin vertex and all edges shall be non-intersecting except at the vertices.

##### C.8.7.3.1 X-Ray Collimator Attribute Descriptions

###### C.8.7.3.1.1 Collimator Vertical and Horizontal Edges

These attributes specify the pixel row or column where the X-Ray beam is fully obscured by a rectangular collimator:

- if the left edge of the collimator is not visible, Collimator Left Vertical Edge (0018,1702) shall have a value of 0;

- if the right edge of the collimator is not visible, Collimator Right Vertical Edge (0018,1704) value shall be 1 greater than the value of Columns (0028,0011) attribute;

- if the top edge of the collimator is not visible, Collimator Upper Horizontal Edge (0018,1706) shall have a value of 0;

- if the bottom edge of the collimator is not visible, Collimator Lower Horizontal Edge (0018,1708) value shall be 1 greater than the value of Rows (0028,0010) attribute.

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