Материал: part17

Page 516​ DICOM PS3.17 2020a - Explanatory Information​

Table FFF.2.1-30. XA/XRF Acquisition Module Example​

FFF.2.1.3.1.3.3 X-Ray Isocenter Reference System Macro Recommendations​

If the value of the C-arm Positioner Tabletop Relationship (0018,9474) is NO, the following macro may not be provided by the acquis-​ ition modality. This macro is used in the per-frame context in this scenario.​

Table FFF.2.1-32. X-Ray Isocenter Reference System Macro Example​

FFF.2.1.3.1.4 Example​

In this example, the patient is on the table, in position "Head First Prone". The table horizontal, tilt and rotation angles are equal to​ zero.​

The positioner performs a rotation of 180 deg from the left to the right side of the patient, with the image detector going above the​ back of the patient, around an axis parallel to the head-feet axis of the patient.​

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Frame 1

+Y

Figure FFF.2.1-14. Detector Trajectory during Rotational Acquisition​

The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-15.​

Figure FFF.2.1-15. Attributes of X-Ray Positioning Per-frame on Rotational Acquisition​

FFF.2.1.3.2 Peripheral/stepping Acquisition​

ThissectionprovidesinformationontheencodingofthemovementoftheX-RayTableduringtheacquisitionofasteppingangiography.​

The related image presentation parameters of the stepping acquisition that are defined in the Enhanced XA SOP Class, such as the​ mask information of subtracted display, are described in further sections of this annex.​

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FFF.2.1.3.2.1 User Scenario​

The Multi-frame Image acquisition is performed during a movement of the X-Ray Table, starting from the initial position and acquiring​ frames in a given direction along the Z axis of the table at variable steps and variable time intervals.​

There may be one or more "stepping movements" of the X-Ray Table during the same image acquisition, leading to one or more in-​ stances of the Enhanced XA SOP Class. The stepping may be performed by different patterns, such as:​

•​One stepping for non-subtracted angiography;​

•​Two stepping acquisitions, one for each leg, for non-subtracted angiography, stored in two different Multi-frame Images;​

•​Two or more stepping acquisitions for subtracted angiography, in the same or in opposite directions.​

FFF.2.1.3.2.2 Encoding Outline​

The XA SOP Class encodes table position as increments relative to the position of the first frame, while the position of the first frame​ is not encoded.​

The Enhanced XA SOP Class encodes per-frame absolute table vertical, longitudinal and lateral position, as well as table horizontal​ rotation angle, table head tilt angle and table cradle tilt angle.​

This allows registration between separate Multi-frame Images in the same table frame of reference, as well as accounting for magni-​ ficationratioandotheraspectsofgeometryduringregistration.Issuesofpatientmotionduringacquisitionoftheimagesisnotaddressed​ in this scenario.​

FFF.2.1.3.2.3 Encoding Details​

This section provides detailed recommendations of the key Attributes to address this particular scenario.​

Table FFF.2.1-33. Enhanced X-Ray Angiographic Image IOD Modules​

Table FFF.2.1-34. Enhanced XA Image Functional Group Macros​

FFF.2.1.3.2.3.1 XA/XRF Acquisition Module Recommendations​

The usage of this module is recommended to specify the relationship between the table and the positioner.​

Table FFF.2.1-35. XA/XRF Acquisition Module Example​

Relationship​

Note​

On mobile systems where this Attribute equals NO, it is possible to​ do table stepping. In such case, the system is not able to determine​ the absolute table position relative to the Isocenter, which is​ necessary for 2D-2D registration.​

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FFF.2.1.3.2.3.2 X-Ray Table Position Macro Recommendations​

This macro is used in the per-frame context in this scenario.​

Table FFF.2.1-36. X-Ray Table Position Macro Example​

FFF.2.1.3.2.3.3 X-Ray Isocenter Reference System Macro Recommendations​

If the value of the C-arm Positioner Tabletop Relationship (0018,9474) is NO, the following macro may not be provided by the acquis-​ ition modality. This macro is used in the per-frame context in this scenario.​

Table FFF.2.1-37. X-Ray Isocenter Reference System Macro Example​

FFF.2.1.3.2.4 Example​

Inthisexample,thepatientisonthetableinposition"HeadFirstSupine".Thetableistiltedof-10degrees,withtheheadofthepatient​ below the feet, and the image detector is parallel to the tabletop plane. The table cradle and rotation angles are equal to zero.​

The image acquisition is performed during a movement of the X-Ray Table in the tabletop plane, at constant speed and of one meter​ of distance, acquiring frames from the abdomen to the feet of the patient in one stepping movement for non-subtracted angiography.​

The table is related to the C-arm positioner so that the coordinates of the table position are known in the isocenter reference system.​ This allows determining the projection magnification of the table top plane with respect to the detector plane.​

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Figure FFF.2.1-16. Table Trajectory during Table Stepping​

Figure FFF.2.1-17. Example of table positions per-frame during table stepping​

The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-18.​

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