DICOM PS3.3 2018b - Information Object Definitions

C.8.15.3.6 CT Geometry Macro
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##### C.8.15.3.6 CT Geometry Macro

Table C.8-122 specifies the Attributes of the CT Geometry Functional Group Macro.

Table C.8-122. CT Geometry Macro Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
CT Geometry Sequence | (0018,9312) | 1 | Contains the Attributes defining the CT geometry. Only a single Item shall be included in this Sequence.
>Distance Source to Detector | (0018,1110) | 1C | Distance in mm from source to detector center. See Section C.8.15.3.6.1. ### Note This value is traditionally referred to as Source Image Receptor Distance (SID). Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Distance Source to Data Collection Center | (0018,9335) | 1C | Distance in mm from source to data collection center. See Section C.8.15.3.6.1. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.

###### C.8.15.3.6.1 Relationships Between CT Geometric Attributes (Informative)

In Figure C.8-19 the relationship of the Geometric Attributes within the CT Geometry and CT Reconstruction Functional Groups is shown. In this example, the Pixel Data is shown encoding the entire reconstructed region with no outside padding or clipping, and the reconstructed region is illustrated as being square, i.e., the value of Reconstruction Diameter would be the same as both values of Reconstruction Field of View, whichever Attribute is present. Figure C.8-19, viewed from the front of the gantry (where the table enters the gantry), is informative only and is not meant to represent a standardization of an equipment-based Frame of Reference.

Figure C.8-19. Geometry of CT Acquisition System

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DICOM PS3.3 2018b - Information Object Definitions