C.20.2 Spatial Registration Module

Table C.20.2-1 defines the general Attributes of the Spatial Registration Module.

Table C.20.2-1SPATIAL REGISTRATION MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
Content Date (0008,0023) 1 The date the content creation started.
Content Time (0008,0033) 1 The time the content creation started.
Include Content Identification Macro Table 10-12
Registration Sequence (0070,0308) 1 A sequence of registration items. Each item defines a spatial registration of the images referenced in that item to the Registered RCS established by this SOP instance. All referenced images are in the same spatial frame of reference or atlas. One or more Items shall be included in this sequence.
>Frame of Reference UID (0020,0052) 1C Identifies the Frame of Reference of the referenced data, that may or may not be an image set (e.g. atlas or physical space). See C.7.4.1.1.1 for further explanation. Required if Referenced Image Sequence (0008,1140) is absent. May be present otherwise.
>Referenced Image Sequence (0008,1140) 1C Identifies the set of images of the referenced data, registered in this sequence item. One or more Items shall be included in this sequence. Required if Frame of Reference UID (0020,0052) is absent. May be present otherwise.
>>Include 'Image SOP Instance Reference Macro' Table 10-3
>Matrix Registration Sequence (0070,0309) 1 A sequence that specifies one spatial registration. Only a single Item shall be included in this sequence.
>>Frame of Reference Transformation Comment (3006,00C8) 3 User description or comments about the registration.
>>Registration Type Code Sequence (0070,030D) 2 Describes the information input into the registration process. Zero or one Item shall be included in this Sequence.
>>>Include ‘Code Sequence Macro’ Table 8.8-1 Baseline CID 7100
>>Matrix Sequence (0070,030A) 1 Specifies one transformation, that registers the Source RCS/images to the Registered RCS. It is expressible as multiple matrices, each in a separate item of the sequence. One or more Items shall be included in this sequence. The item order is significant and corresponds to matrix multiplication order. See C.20.2.1.1.
>>>Frame of Reference Transformation Matrix (3006,00C6) 1 A 4x4 homogeneous transformation matrix that registers a coordinate system A to B. Matrix elements shall be listed in row-major order. See C.20.2.1.1.
>>>Frame of Reference Transformation Matrix Type (0070,030C) 1 Type of Frame of Reference Transformation Matrix (3006,00C6). Defined terms: RIGID RIGID_SCALE AFFINE See C.20.2.1.2
>Used Fiducials Sequence (0070,0314) 3 The fiducials used to determine the Frame of Reference Transformation Matrix. One or more Items are permitted in this sequence.
>>Include ‘SOP Instance Reference Macro' Table 10-11 Reference to the Spatial Fiducial SOP Instance identifying the Used Fiducial(s)
>>Fiducial UID (0070,031A) 1 The UID that identifies the fiducial used as registration input.

C.20.2.1 Registration Module Attribute Descriptions

C.20.2.1.1 Frame of Reference Transformation Matrix

The Frame of Reference Transformation Matrix (3006,00C6) A M B describes how to transform a point ( B x, B y, B z) with respect to RCS B into ( A x, A y, A z) with respect to RCS A according to the equation below.

[pic]

The Matrix Registration is expressible as multiple matrices, each in a separate item of the Matrix Sequence (0070,030A). The equation below specifies the order of the matrix multiplication where M 1 , M 2 and M 3 are the first, second and third items in the sequence.

[pic]

where [pic] = [pic]

Registration often involves two or more RCS, each with a corresponding Frame of Reference Transformation Matrix. For example, another Frame of Reference Transformation Matrix A M C can describe how to transform a point ( C x, C y, C z ) with respect to RCS C into ( A x, A y, A z ) with respect to RCS A . It is straightforward to find the Frame of Reference Transformation Matrix B M C that describes how to transform the point ( C x, C y, C z ) with respect to RCS C into the point ( B x, B y, B z ) with respect to RCS B. The solution is to invert A M B and multiply by A M C , as shown below:

[pic]

C.20.2.1.2 Frame of Reference Transformation Matrix Type

There are three types of Registration Matrices:

RIGID: This is a registration involving only translations and rotations. Mathematically, the matrix is constrained to be orthonormal and describes six degrees of freedom: three translations, and three rotations.

RIGID_SCALE: This is a registration involving only translations, rotations and scaling. Mathematically, the matrix is constrained to be orthogonal and describes nine degrees of freedom: three translations, three rotations and three scales. This type of transformation is sometimes used in atlas mapping.

AFFINE: This is a registration involving translations, rotations, scaling and shearing. Mathematically, there are no constraints on the elements of the Frame of Reference Transformation Matrix, so it conveys twelve degrees of freedom. This type of transformation is sometimes used in atlas mapping.

See the PS 3.17 Annex on Transforms and Mappings for more detail.