Материал: part03

Figure C.8.31.6-3. Isocenter Coordinate System​

C.8.31.6.1.2 X-Ray Source Coordinate System​

The X-Ray Source coordinate system (Os, Xs, Ys, Zs) is defined as follows (see Figure C.8.31.6-4):​

•​Origin Os is identical to the origin of the Isocenter coordinate system O.​

•​Xs axis is in the plane normal to the axis of rotation of the X-Ray source through Os and is perpendicular to the X-Ray source.​ Positive direction is from GANTRY LEFT to GANTRY RIGHT when the X-Ray source is overhead (As1 equals 0°).​

•​Ys axis is the axis of rotation of the X-Ray source. Positive direction is from GANTRY FRONT to GANTRY REAR.​

•​Zs axis is normal to the Xs Ys plane. The +Zs direction is generally toward the X-Ray source, defined by the right-hand rule from​ +Xs and +Ys.​

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Figure C.8.31.6-4. X-Ray Source Coordinate System​

The X-Ray Source coordinate system (Os, Xs, Ys, Zs) is characterized with respect to the Isocenter coordinate system (O, X, Y, Z),​ by two angles describing the X-Ray center beam. These angles are relative to the Isocenter reference system, and independent from​ the patient position on the equipment.​

X-Ray Source Isocenter Primary Angle (0018,9543) (so-called As1 in Figure C.8.31.6-5) is defined as the angle between the YZ plane​ and the YZs plane. The angle from +Zs toward +Xs is positive.​

X-Ray Source Isocenter Secondary Angle (0018,9544) (so-called As2 in Figure C.8.31.6-5) is defined as the angle between the XZ​ plane and the XZs plane. The angle from +Zs toward +Ys is positive.​

Figure C.8.31.6-5. X-Ray Source Isocenter Angles​

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C.8.31.6.1.3 Breast Support Coordinate System​

The Breast Support (see Figure C.8.31.6-6) is the housing over the detector onto which the breast is placed before imaging. For the​ purpose of this description, Breast Support top surface refers to the patient contact surface of the Breast Support, closest to the X-​ Ray source.​

Figure C.8.31.6-6. Breast Support Orientation​

The Breast Support coordinate system (Ob, Xb, Yb, Zb) is defined as follows (see Figure C.8.31.6-7):​

•​Origin Ob, the so-called Breast Support Reference Point, is an arbitary point, as defined by the equipment manufacturer, on the​ axis of the center of rotation of the Breast Support.​

•​Xb axis lies parallel to the Breast Support top surface, passes through Ob, and is parallel to X when the Breast Support top surface​ is normal to gravity. The +Xb direction is toward BREAST SUPPORT RIGHT.​

•​Yb axis lies parallel to the Breast Support top surface, passes through Ob, and is perpendicular to the Xb axis. The +Yb direction is​ toward BREAST SUPPORT ANTERIOR.​

•​Zb axis is normal to the Breast Support top surface and passes through Ob. The +Zb direction is toward BREAST SUPPORT HEAD.​

The Breast Support coordinate system (Ob, Xb, Yb, Zb) is characterized, with respect to the Isocenter coordinate system (O, X, Y, Z),​ by two rotations that describe the Breast Support tilt and a 3D translation (see Figure C.8.31.6-7). It is the most common convention​ in breast projection X-Ray system design to have the Breast Support rotate identically and in synchronization with the system C-arm​ (they are most often rigidly integrated):​

Breast Support Isocenter Primary Angle (0018,9545) (so-called Ab1) is defined as the angle between the YZ plane and the YZb plane.​ The angle is positive when the Breast Support Right end of the Breast Support is lower than the Breast Support Left end of the Breast​ Support, and is 0° when the Breast Support surface is normal to the +Z direction. In digital breast tomosynthesis, because the X-Ray​ sourcemovesindependentlyoftheBreastSupport,theBreastSupportIsocenterPrimaryAngleistheprincipalplacewheretheuser's​ perception of the C-arm angle is encoded.​

Breast Support Isocenter Secondary Angle (0018,9546) (so-called Ab2) is defined as the angle between the XY plane and the XYb​ plane. The angle is positive when the Breast Support Anterior side of the Breast Support is lower than the Breast Support Posterior​ endoftheBreastSupport,andis0°whentheBreastSupportsurfaceisnormaltothe+Zaxis.InmostbreastprojectionX-Rayimaging​ equipment the value of Ab2 is 0°.​

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Ab1

+Zb

Ob

+Xb

Ab2

+Zb

Ob

+Yb

Figure C.8.31.6-7. Breast Support Angles with respect to the Isocenter Reference System​

Breast Support X Position to Isocenter (0018,9547) (so-called BX) is defined as the translation of the Breast Support Reference Point​ Ob with respect to the Isocenter coordinate system in the +X axis direction. Breast support translation toward +X is positive.​

Breast Support Y Position to Isocenter (0018,9548) (so-called BY) is defined as the translation of the Breast Support Reference Point​ Ob with respect to the Isocenter coordinate system in the +Y axis direction. Breast support translation toward +Y is positive.​

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Breast Support Z Position to Isocenter (0018,9459) (so-called BZ) is defined as the translation of the Breast Support Reference Point​ Ob with respect to the Isocenter coordinate system in the +Z axis direction. Breast support translation toward +Z is positive.​

Note​

A translation of (BX, BY, BZ) = (0, 0, 0) means that the Breast Support Reference Point Ob is at the System Isocenter.​

Figure C.8.31.6-8. Breast Support Translation with respect to the Isocenter Reference System​

C.8.31.6.1.4 Detector Coordinate System​

A detector coordinate system is defined that allows the detector to be either stationary or in motion. For clarity of understanding and​ interoperability, detector motion terms that may be used during image acquisition are defined, as indicated in Type of Detector Motion​ (0054,0202):​

•​Stationary Detector​

•​Rotating Detector​

•​Translating Detector​

•​Complex Detector​

An infinite variation of detector motions is possible through timeand angledependent combinations of detector rotation and detector​ translation.​

At any given point in time during image acquisition the detector origin Od may be translated with respect to the system isocenter​ and/or the detector coordinate system rotated with respect to the isocenter coordinate system. The detector coordinate system (Od,​ Xd, Yd, Zd) is defined as follows (see Figure C.8.31.6-9):​

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