# C.21.2.1 Spatial Fiducials Module Attribute Descriptions

## C.21.2.1.1 Shape Type

For convenient registration, correlated Fiducials exist in each image set of the Registration Sequence. Correlated Fiducials are identified with either Fiducial Identifier (0070,0310) or Fiducial Identifier Code Sequence (0070,0311).

Shape Type (0070,0306) defines the geometric interpretation of the Contour Data (3006,0050) and Graphic Data (0070,0022). A point is defined as a triplet (x,y,z) in the case of spatial data or a pair (x,y) in the case of graphic data.

Defined Terms are:

POINT = a single point designating a single fiducial point.

Note: A point may be the epicenter of a more complex shape such as sphere.

LINE = two points that specify a line or axis such as the inter-orbital line. The point locations have no significance other than identifying the line, i.e. they are not line segment end points.

PLANE = three points that identify a plane such as the laterality plane

SURFACE = three or more points (usually many) that reside on, or near, a region of a curved surface. The surface may be flat or curved, closed or open. The point order has no significance.

RULER = two or more evenly spaced collinear points ordered sequentially along the line, such as a physical ruler placed in the imaging field.

L_SHAPE = three points of two perpendicular line segments, AB and BC, having a common end point B. The order of the points is: ABC. May represent an L-shaped marker placed in the imaging field.

T_SHAPE = three points of two perpendicular line segments AB and CD, such that C bisects AB. The order is ABD.

SHAPE = three or more points that specify the shape of a well-known fiducial type. The term in the Fiducial Identifier Code Sequence (0070,0311) defines the shape and the order of the points that represent it.

## C.21.2.1.2 Contour Data

Contour Data (3006,0050) is an ordered set of triplets that defines a shape. The triplets (x,y,z) denote points in the Reference Coordinate System of the Registration Instance.

Note: Contours may associate observational data with a set of Image features or specify coordinates that are input data for a measurement.

## C.21.2.1.3 Contour Uncertainty Radius

The uncertainty is an estimate of the standard deviation of the fiducial location process.