Материал: part17

Figure TTT.2.6-3. Attributes of the pre-intervention 3D reconstruction​

Figure TTT.2.6-4. Attributes of the post-intervention 3D reconstruction​

TTT.2.7 Case #7: Spatial Registration of 3D X-Ray Angiography With Enhanced XA​

This application case is related to the spatial registration of the X-Ray 3D volume with a static projection acquisition on the same​ anatomical region during the procedure.​

TTT.2.7.1 User Scenario​

The image acquisition system performs two different 2D acquisitions at two different times of the interventional procedure: one rota-​ tional acquisition with a 3D reconstruction, and one static acquisition.​

Between the two acquisitions, the table position has changed with respect to the Isocenter. As the acquisitions are performed with​ the X-Ray Detector centered on the Isocenter, in the second static acquisition the anatomical region of the 3D volume is not centered​ anymore at the Isocenter due to the table movement. It's assumed that there is still part of the anatomy of the 3D volume that is pro-​ jected in the static acquisition.​

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During the intervention the 3D volume is segmented to extract some anatomy that is less or not visible in the static acquisition (e.g.,​ injected vessels, heart chambers). The user will want to display such 3D anatomy over the 2D static image to visually assess the​ placement of interventional devices like guide wires, needles etc. The patient position on the table does not change during the pro-​ cedure.​

Volume

+X +Z

X-Ray Table

+Y

X-Ray 3D Reconstructed Volume

Figure TTT.2.7-1. Rotational acquisition and the corresponding 3D reconstruction​

Figure TTT.2.7-2. Static Enhanced XA acquisition at different table position​

TTT.2.7.2 Encoding Outline​

The two 2D acquisitions are encoded as two Enhanced XA Images, and both contain the Attributes of the X-Ray Isocenter Reference​ System Macro (see Section C.8.19.6.13 “X-Ray Isocenter Reference System Macro” in PS3.3). The two XA instances (let's call them​ "C1" and "C2") are encoded in two different Series ("B1" and "B2") of the same Study ("A"). They share the same Frame of Reference​ UID.​

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The volume data is encoded as an X-Ray 3D Angiographic instance ("Z1").​

The reconstructed volume contains one acquisition context consisting of all the frames of the corresponding source 2D XA Image.​ To display the volume over the projection image, both volume and projection image share the same Frame of Reference UID.​

Study “A”

1... ...M1

Reconstruction #1

- From Acquisition Context #1

Figure TTT.2.7-3. Encoding of a 3D reconstruction and a registered 2D projection​

TTT.2.7.3 Encoding Details​

TTT.2.7.3.1 Enhanced X-Ray Angiographic Image IOD​

This scenario is based on the encoding of the 2D acquisition as an Enhanced XA Image, containing the Attributes of the X-Ray Iso-​ center Reference System Macro (see Section C.8.19.6.13 “X-Ray Isocenter Reference System Macro” in PS3.3).​

TTT.2.7.3.2 X-Ray 3D Angiographic Image IOD​

TTT.2.7.3.2.1 Frame of Reference Module Recommendations​

This module encodes the identifier for the spatial relationship, which will be the same for the volume and the projection image. The​ reconstruction application will assign the Frame of Reference UID to the reconstruction equal to the Frame of Reference UID of the​ Enhanced XA projection image.​

TTT.2.7.3.2.2 Patient Orientation Module​

This module encodes the patient position and orientation with respect to the table. It is supposed to contain the same values in the​ 3D volume and in the 2D static image.​

TTT.2.7.3.2.3 Image - Equipment Coordinate Relationship Module​

This module encodes the coordinate transformation matrix to allow the spatial registration of the volume with the Isocenter reference​ system of the angiographic equipment.​

The reconstruction application defines the patient origin as an arbitrary point on the equipment. The 3D slices of the volume are all​ related to the patient coordinate system by the Attributes Image Position (Patient) (0020,0032) and Image Orientation (Patient)​ (0020,0037).​

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Figure TTT.2.7-4. Image Position of the slice related to an application-defined patient coordinates​

The patient is related to the Isocenter by the Attribute Image to Equipment Mapping Matrix (0028,9520) which indicates the spatial​ transformation from the patient coordinates to the Isocenter coordinates. A point in the Patient Coordinate System (Bx, By, Bz) can​ be expressed in the Isocenter Coordinate System (Ax, Ay, Az) by applying the Image to Equipment Mapping Matrix as follows.​

Figure TTT.2.7-5. Transformation from patient coordinates to Isocenter coordinates​

The terms (Tx,Ty,Tz) of this matrix indicate the position of the patient origin (i.e., a fixed point on the table) in the Isocenter coordinate​ system.​

Figure TTT.2.7-6. Transformation of the patient coordinates relative to the Isocenter coordinates​

Table TTT.2.7-1. Image-Equipment Coordinate Relationship Module Recommendations​

TTT.2.7.3.2.4 X-Ray 3D Angiographic Acquisition Module Recommendations​

This module encodes the table position and angles used during the rotational acquisition to allow the spatial transformation of the​ volumepointsfromtheIsocentercoordinatestothetablecoordinates.SeeSectionC.8.19.6.13.1“IsocenterReferenceSystemAttribute​ Description”inPS3.3forfurtherexplanationaboutthespatialtransformationfromtheIsocenterreferencesystemtothetablereference​ system.​

As soon as the volume points are related to the table coordinate system, and assuming that the patient does not move on the table​ between the 2D acquisitions, the volume points can be projected on the image plane of any further projection acquisition even if the​

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table has moved between the acquisitions. See Section C.8.19.6.13.1 “Isocenter Reference System Attribute Description” in PS3.3​ for further explanation about the projection on the image plane of a point defined in the table coordinate system.​

TTT.2.7.4 Example​

In this example, one rotational image is acquired before the intervention. It is encoded with the Instance UID "C1". Then a second​ projection static image is acquired during the intervention. It is encoded with the Instance UID "C2". Both acquisitions are encoded​ as Enhanced XA SOP Class.​

In both acquisitions, the patient position with respect to the table is head-first prone, and the table is not rotated nor tilted with respect​ to the Isocenter. Therefore, the axis of the patient coordinate system and the Isocenter coordinate system are aligned, and the 3x3​ matrix Mij of the Image to Equipment Mapping Matrix (0028,9520) is the identity.​

In this example, the patient origin is defined by the application as a fixed point on the table; when the table position is zero, the patient​ origin is the point (0,0,200) in the Isocenter coordinates system (in mm).​

During the rotational acquisition, the table position with respect to the Isocenter in the lateral direction [x] is +20mm, in the vertical​ direction [y] is +40mm, and in the longitudinal direction [z] is +60mm. Therefore, the terms (Tx,Ty,Tz) of the Image to Equipment​ Mapping Matrix (0028,9520) are (20,40,260).​

During the second acquisition, the table position with respect to the Isocenter in the lateral direction [x] is +40mm, in the vertical dir-​ ection [y] is +30mm, and in the longitudinal direction [z] is +20mm.​

Consequently, the second acquisition is performed with a relative table translation of (30,-10,-50) mm vs. the first acquisition in the​ Isocentercoordinatesystem.Thepositionerprimaryangleis-30deg.(RAO)andthesecondaryangleis20deg.(CRA).Thedistances​ from the source to the Isocenter and from the source to the detector are 780 mm and 1200 mm respectively.​

The reconstruction is encoded in an X-Ray 3D Angiographic instance of Instance UID "Z1".​

Figure TTT.2.7-7. Attributes of the pre-intervention 3D reconstruction​

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