Материал: part17

In the reconstruction from rotational projections the figure C.7.6.16-2 of Section C.7.6.16.2.2.1 “Timing Parameter Relationships” in​ PS3.3 should be interpreted carefully. All the frames forming one X-Ray 3D Angiographic volume have been reconstructed simultan-​ eously, therefore all of them have a same time reference and the same acquisition duration.​

The projections have been acquired over a period of time, all of them contributing to each 3D frame. Therefore, it's recommended to​ encode the 3D frame acquisition duration as the elapsed time from the first to the last projection frame time that contributed to that​ volume.​

Table TTT.2.1-9. Frame Content Macro Recommendations​

TTT.2.1.3.1.13 Derivation Image Macro Recommendations​

The volume is directly reconstructed from the original set of projections and therefore not "derived" in this sense. Thus this macro is​ not applicable in this scenario as the contents of the Contributing Sources Sequence (0018,9506) and the X-Ray 3D Acquisition Se-​ quence (0018,9507) are sufficient to describe the relationship to the originating image.​

TTT.2.1.3.1.14 Frame Anatomy Macro Recommendations​

This macro encodes the anatomical context. It can be important to parameterize the presentation of the volumes. For a single volume​ this macro is encoded "shared". Typically the anatomy of the volume is only available if the information is already provided within the​ originating projection image, either by detection algorithm or by user input.​

TTT.2.1.3.1.15 X-Ray 3D Frame Type Macro Recommendations​

This macro encodes the general characteristics of the volume slices like color information for presentation, volumetric properties for​ geometrical manipulations etc. In case of a single volume, this macro is encoded "shared" as each slice of the volume has identical​ characteristics. If multiple volumes are encoded in a single instance, this macro may be encoded "per frame".​

TTT.2.1.4 Example​

TTT.2.1.4.1 Reconstruction Using All Frames of An Enhanced XA Image​

This basic example is the reconstruction of a volume by a back-projection from all frames of a rotational acquisition which have been​ encoded as an Enhanced XA Instance. The rotational acquisition takes 5 seconds to acquire all the projections.​

Note​

The example would be very similar if the rotational acquisition was encoded as an XA Image.​

The dimension organization is based on the spatial position of the 3D frames. The frames are to be displayed in the same order as​ stored.​

- Standard -​

The UIDs of this example correspond to the diagram shown in Figure TTT.2.1-1​

Figure TTT.2.1-2a. Attributes of 3D Reconstruction using all frames​

- Standard -​

Figure TTT.2.1-2b. Attributes of 3D Reconstruction using all frames (continued)​

TTT.2.2 Case #2: Reconstruction From A Sub-set of Projection Frames​

This application case is related to a reconstruction from a sub-set of projection frames.​

TTT.2.2.1 User Scenario​

The image acquisition system performs one rotational acquisition. Not all of the acquired frames, but every Nth frame is used to recon-​ struct the volume, e.g., to speed-up the reconstruction.​

TTT.2.2.2 Encoding Outline​

Only selected frames of the original XA instance or Enhanced XA instance are used to reconstruct the volume.​

The X-Ray 3D instance references the original XA instance or Enhanced XA instance and uses Attributes to define the context on​ how and which of the original image frames are used to create the volume.​

- Standard -​

XA 2D Projection SOP Instance “C”

Contrast Frames

Acquisition Context #1

Reconstruction #1

X-Ray 3D SOP Instance “Z”

Contrast Volume

Reconstruction #1

- From Acquisition Context #1

Figure TTT.2.2-1. Encoding of one 3D reconstruction from a sub-set of projection frames​

TTT.2.2.3 Encoding Details​

TTT.2.2.3.1 X-Ray 3D Angiographic Image IOD​

TTT.2.2.3.1.1 X-Ray 3D Angiographic Acquisition Module Recommendations​

This module encodes the important technical and physical parameters of the source SOP instances and the frames used to create​ the X-Ray 3D Angiographic instance.​

Table TTT.2.2-1. X-Ray 3D Angiographic Acquisition Module Recommendations​

The contents of the Per Projection Acquisition Sequence (0018,9538) need​ tobecarefullyalignedwiththelistofframenumbersintheReferencedFrame​ Numbers (0008,1160) Attribute in the Source Image Sequence (0008,2112).​

TTT.2.2.3.1.2 Frame Content Macro Recommendations​

This module encodes the timing information of the frames, as well as dimension and stack index values.​

- Standard -​

Page 690​ DICOM PS3.17 2020a - Explanatory Information​

Table TTT.2.2-2. Frame Content Macro Recommendations​

TTT.2.2.4 Example​

Thisspecificexampleisthereconstructionofavolumebyaback-projectionfromevery5th frameofarotationalacquisitionandencoded​

as an Enhanced XA Image.​

Note​

The example would be very similar if the rotational acquisition was encoded as an XA Image.​

Figure TTT.2.2-2. Attributes of 3D Reconstruction using every 5th frame​

TTT.2.3 Case #3: Reconstruction From A Sub-region of All Image Frames​

This application case is related to a regular reconstruction of the full field of view of a rotational acquisition followed by a specific re-​ construction of a sub-region that contains an object of interest (e.g., interventional device implanted, stent, coils etc.).​

TTT.2.3.1 User Scenario​

The image acquisition system performs one rotational acquisition after the intervention, on the region of the patient where an implant​ has been placed.​

Two3Dvolumesarereconstructed;oneofthefullfieldofviewoftheprojectionimages,anotherofasub-regionofeachoftheacquired​ frames, e.g., to extract the object of interest into a smaller volume. The second volume is likely performed at higher resolution and​ likely applies different 3D reconstruction techniques, for instance to highlight the material of the implant. The purpose is to overlap​ the two volumes and enhance the visibility of the object of interest over the full field volume.​

TTT.2.3.2 Encoding Outline​

The rotational acquisition can either be encoded as XA Image or as Enhanced XA Image.​

Each reconstruction is encoded in a different X-Ray 3D Angiographic instance.​

Not all parts of each frame of the original XA instance or Enhanced XA instance are used to reconstruct the second volume.​

The X-Ray 3D instance references the original XA instance or Enhanced XA instance and uses Attributes to define the context on​ how and which part of the original image frames are used to create the Volume.​

- Standard -​