Detector Active Origin Attribute
| Tag | (0018,7028) |
|---|---|
| Type | Optional (3) |
| Keyword | DetectorActiveOrigin |
| Value Multiplicity | 2 |
| Value Representation | Decimal String (DS) |
Offset of the TLHC of a rectangle circumscribing the active detector area from the TLHC of a rectangle circumscribing the physical detector area, measured in physical detector pixels as a row offset followed by a column offset.
See Section C.8.11.4.1.1 for further explanation.
Section C.8.11.4.1.1
C.8.11.4.1.1 Physical, Active, Field of View, Exposed and Displayed Areas
The relationship between the Physical Detector Area, the Active Detector Area, the Field of View (what is stored in Pixel Data (7FE0,0010)), the Exposed Area (after X-Ray Collimation) and the Displayed Area is illustrated in the following diagrams.
Note
Some of these Attributes relate the image data to manufacturer specific characteristics of the detector that may be used for quality control purposes, e.g., correlation of image artifacts with a detector defect map, analysis of noise performance, etc.
The Displayed Area is defined in pixel coordinates relative to the stored image pixel values by the Attributes of the Display Shutter Module (see Section C.7.6.11). If this Module is not present or supported, then the Displayed Area is equal to the Field of View.
The Exposed Area is defined in pixel coordinates relative to the stored image pixel values by the Attributes of the X-Ray Collimator Module (see Section C.8.7.3).
For the Digital X-Ray IODs, the Field of View is usually rectangular in shape and usually has the same size as the stored Pixel Data (7FE0,0010). The shape and size of the Field of View and the spacing of the pixels are defined by the following Attributes:
-
Field of View Shape (0018,1147),
-
Field of View Dimensions (0018,1149),
-
Imager Pixel Spacing (0018,1164),
-
Rows (0028,0010),
-
Columns (0028,0011).
In the case where the Field of View has the same size as the stored Pixel Data (7FE0,0010) the following relationships are verified:
If the Field of View Shape (0018,1147) Attribute equals RECTANGLE:
-
Field of View Dimensionsrow dimension = Imager Pixel Spacingrow spacing * Rows
-
Field of View Dimensionscolumn dimension = Imager Pixel Spacingcolumn spacing * Columns
If the Field of View Shape (0018,1147) Attribute equals ROUND or HEXAGONAL:
-
Field of View Dimensionsdiameter = Imager Pixel Spacingrow spacing * Rows
-
Field of View Dimensionsdiameter = Imager Pixel Spacingcolumn spacing * Columns
The following Attributes define the relationship of the Field of View to the Physical Detector Area:
-
Field of View Origin (0018,7030),
-
Field of View Rotation (0018,7032),
-
Field of View Horizontal Flip (0018,7034).
For the Digital X-Ray IODs, the Active Area, i.e., that part of the detector matrix that was activated for this exposure, is usually rectangular in shape. The shape and size of the Active Area and the size and spacing of the detectors are defined by the following Attributes:
-
Detector Active Shape (0018,7024),
-
Detector Active Dimensions (0018,7026),
-
Detector Element Physical Size (0018,7020),
-
Detector Element Spacing (0018,7022).
Note
-
The Detector Element Physical Size (0018,7020) and Detector Element Spacing (0018,7022) may be different if there are insensitive regions between each detector.
-
This model of description is not able to accurately describe multiple matrices of detectors that are "tiled" to produce a single image.
The following optional Attribute defines the relationship of the Active Area to the Physical Detector Area:
-
Detector Active Origin (0018,7028).
In the case where the Field of View has the same size as the stored Pixel Data (7FE0,0010), the relationship between detectors and stored image pixels is defined by Detector Binning (0018,701A), which specifies how many detectors, in each of the row and column directions, contribute to (are pooled or averaged to form) a single stored image pixel.
Note
-
Detector Binning (0018,701A) may have values less than one if sub-sampling is used to derive an image with higher spatial resolution than the detector matrix.
-
The detector binning results in the size of a stored image pixel being different from the contributing physical detector pixels. In this case it is important to notice that the Field Of View Origin (0018,7030) is defined with respect to the center of the detector element located at the TLHC of the Field of View.
-
For images where the Field of View describes an area not equal to the size (rows and columns) of the stored Pixel Data (7FE0,0010), Detector Binning (0018,701A) does not fully specify the relationship between the contributing physical detector pixels and the stored image pixels.
Figure C.8-14. Explanation of Digital Detector Attributes
Figure C.8-15. Explanation of Digital Detector Attributes