Detector Isocenter Secondary Angle Attribute
| Tag | (0018,9551) |
|---|---|
| Type | Required (1) |
| Keyword | DetectorIsocenterSecondaryAngle |
| Value Multiplicity | 1 |
| Value Representation | Double (FD) |
Secondary angle of the Detector in the in the isocenter reference system (deg).
See C.8.31.6.1.4 for further explanation.
Note
Part of the Breast X-Ray Isocenter Reference System Functional Group Macro with usage: M
C.8.31.6.1.4
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):
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Stationary Detector
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Rotating Detector
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Translating Detector
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Complex Detector
An infinite variation of detector motions is possible through time- and angle- dependent 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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Detector Reference Point Od, is an arbitrary point, defined by the equipment manufacturer, that lies on the axis of rotation of the detector, if any.
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Xd axis lies in the plane parallel to the detector surface, through the point Od, and perpendicular to the axis of rotation. The +Xd direction is in the same direction as the +X direction when the detector surface is normal to gravity.
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Yd axis is the axis of rotation of the detector and is parallel to Y. The +Yd direction is in the same direction as the +Y direction when the detector surface is normal to gravity.
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Zd axis is normal to the detector surface and through the point Od. The +Zd direction is upward, defined by the right-hand rule from +Xd and +Yd.
Figure C.8.31.6-9. Detector Coordinate System
The Detector coordinate system (Od, Xd, Yd, Zd) is characterized with respect to the Isocenter coordinate system (O, X, Y, Z), by two angles describing the tilt of the detector. These angles are relative to the Isocenter reference system, and independent from the patient position on the equipment.
Detector Isocenter Primary Angle (0018,9550) (so-called Ad1) is defined as the angle between the YZ plane and the YZd plane. The angle is positive when the +Xd axis is lower than the -Xd axis with respect to Z, and is 0°when the detector surface is normal to the +Z axis.
Detector Isocenter Secondary Angle (0018,9551) (so-called Ad2) is defined as the angle between the plane XZ and the plane XZd. The angle is positive when the +Yd axis is lower than the -Yd axis with respect to Z. In most cases this angle is 0°, inferring that the XZ plane is parallel to the Xd plane.
Figure C.8.31.6-10. Detector Isocenter Angles
Detector X Position to Isocenter (0018,9552) (so-called DX) is defined as the translation of the Detector Reference Point Od with respect to the Isocenter coordinate system in the X direction. A translation of DX toward Breast Support Right from Detector Od is positive.
Detector Y Position to Isocenter (0018,9553) (so-called DY) is defined as the translation of the Detector Reference Point Od with respect to the Isocenter coordinate system in the Y direction. A translation of DY toward Breast Support Anterior from Detector Od is positive.
Detector Z Position to Isocenter (0018,9554) (so-called DZ) is defined as the translation of the Detector Reference Point Od with respect to the Isocenter coordinate system in the Z direction. A translation of DZ toward Breast Support Head from Detector Od is positive.
Figure C.8.31.6-11. Translation of the Detector Coordinate System
Although not shown in Figure C.8.31.6-11, translation of the detector moves the Detector Origin Od relative to the Isocenter. Thus during translation of the detector, at least one of DX, DY and DZ will change.
Note
A translation of (DX, DY, DZ) = (0, 0, 0) means that the Detector Reference Point Od is at the System Isocenter.
The case where the detector is stationary during image acquisition is a degenerate case, but still defined in the same manner.
Note
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An angulation of (Ad1, Ad2) = (0, 0) means that the Detector is not rotated relative to the System Isocenter coordinate system.
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A translation of (DX, DY, DZ) = (0, 0, 0) means that the Detector Reference Point Od is at the System Isocenter.