DICOM PS3.3 2021b - Information Object Definitions

10.39 Patient to Equipment Relationship Macro (Current)
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## 10.39 Patient to Equipment Relationship Macro

The Patient to Equipment Relationship Macro describes a position of the patient with respect to a device. The position is defined by means of a transformation matrix between a Patient Frame of Reference and an Equipment Frame of Reference.

Table 10.39-1. Patient to Equipment Relationship Macro Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Image to Equipment Mapping Matrix | (0028,9520) | 1 | A rigid, homogeneous 4x4 transformation matrix that maps the patient coordinate space in the Frame of Reference used for the patient model to the coordinate system defined by the equipment. Matrix elements shall be listed in row-major order. See Section 10.39.1.1, Section 10.39.1.2 and Section C.7.6.21.1.
Frame of Reference Transformation Comment | (3006,00C8) | 3 | Comments entered by a human operator about the relationship between the patient frame of reference and the equipment. For display purposes only, shall not be used for other purposes.
Patient Location Coordinates Sequence | (3006,00C9) | 2 | Specific points in the patient coordinate system which further characterize the position of the patient with respect to the equipment. Zero or more Items shall be included in this Sequence.
>3D Point Coordinate | (0068,6590) | 1 | Coordinate (x,y,z) in mm describing the location in the patient Frame of Reference that will be transformed to the Equipment Frame of Reference by using the Image to Equipment Mapping Matrix (0028,9520).
>Patient Location Coordinates Code Sequence | (3006,00CA) | 1 | Identifies the type of Patient Location Coordinate. One or more Items shall be included in this Sequence.
>>Include Table 8.8-1 “Code Sequence Macro Attributes”. | CID is specified at invocation.
Patient Support Position Sequence | (3006,00CB) | 2 | Actual Patient Support Position parameters. Shall be consistent with the Image to Equipment Mapping Matrix (0028,9520). See Section 10.39.1.2. Zero or one Item shall be included in this Sequence.
>Include Table 10.40-1 “Patient Support Position Macro Attributes”.

### 10.39.1 Patient to Equipment Relationship Macro Attributes Description

#### 10.39.1.1 Equipment Coordinate System

A piece of equipment has an Equipment Coordinate System which can be used for expressing geometric concepts such as locations and orientations. The coordinate system is characterized by the location of the origin and the orientation of coordinate axes with respect to the equipment. The Equipment Coordinate System is a right-handed coordinate system.

Equipment Coordinate Systems are typically based on a standardized definition of axes. The choice of origin is often device-specific or device-type-specific. It may be any significant location on the machine such as the manufacturer-dependent machine isocenter.

The Equipment Coordinate System can be used as the parent for derived coordinate systems.

#### 10.39.1.2 Image to Equipment Mapping Matrix and Patient Support Position Macro

The Image to Equipment Mapping Matrix (0028,9520) describes the relationship between the Patient-oriented coordinate system and an Equipment Coordinate System. This matrix AM Bdescribes a rigid transformation of a point ( Bx, By, Bz) with respect to the Patient coordinate system into ( Ax, Ay, Az) with respect to the Equipment Coordinate System as defined in Section C.7.6.21.1.

The Equipment Coordinate System is identified by the Equipment Frame of Reference UID (300A,0675). For further information on the definition of the Equipment Frame of Reference, see Section 10.39.1.1. The patient-oriented coordinate system is identified by the Frame of Reference UID (0020,0052) of the SOP Instance it is used within. Both coordinate systems are expressed in millimeters.

The Patient Support Position Macro invoked by Patient Support Position Sequence (3006,00CB) allows the exchange of device-specific parameters for the patient support device. Applications designed to guide a specific patient support device will be able to de-compose the transformation into device-specific parameters or derive a transformation matrix out of these parameters. Applications that are unable to know the decomposition of the transformation to those parameters and vice versa will still be able to display the native labels and numerical values of those parameters to human readers.

The Patient Support Position Sequence (3006,00CB) may be present to annotate the matrix and display the decomposed matrix contents. The content of the Patient Support Position Macro shall be used for display purposes only. It shall not be used for other purposes. The content of this Macro shall not be used as a substitute for the Image to Equipment Mapping Matrix (0028,9520). In general, there is more than one way to reach the point in space that is described by the Image to Equipment Mapping Matrix (0028,9520). Hence it is explicitly not implied how this position is reached.

In some cases (e.g., emergency treatments in Radiotherapy), the Patient Frame of Reference is not defined by an image series. In this case an arbitrary Frame of Reference is used for the patient coordinate system in the Frame of Reference Module of the SOP Instance. The Image to Equipment Mapping Matrix (0028,9520) has the same meaning as in the case of image-based Patient Frame of Reference.

If the Image to Equipment Mapping Matrix (0028,9520) and the Patient Support Position Sequence (3006,00CB) are both present, the information in both locations shall be consistent.

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DICOM PS3.3 2021b - Information Object Definitions