The XA SOP Class encodes the VOI settings to be common to all the frames of the image. It also restricts the Photometric Interpretation (0028,0004) to MONOCHROME2.
The Enhanced XA SOP Class encodes per-frame VOI settings. Additionally it allows the Photometric Interpretation (0028,0004) to be MONOCHROME1 in order to display low pixel values in white while using window width and window center VOI. Other characteristics and settings can be defined, such as:
Relationship between X-Ray intensity and the pixel value stored;
Edge Enhancement filter strength;
FFF.126.96.36.199 Encoding details
This section provides detailed recommendations of the key attributes to address this particular scenario.
Table FFF.2. 3-1 ENHANCED X-RAY ANGIOGRAPHIC IMAGE IOD MODULES
|IE||Module||PS 3.3 Reference||Usage|
|Image||Enhanced XA/XRF Image||C.8.19.2||Specifies the sign of the slope of the VOI transformation to be applied during display.|
|XA/XRF Multi-frame Presentation||C.8.19.7||Specifies the subtractive mode and the edge enhancement filter characteristics to be applied during display.|
Table FFF.2. 3-2 ENHANCED XA IMAGE FUNCTIONAL GROUP MACROS
|Functional Group Macro||PS 3.3 Reference||Usage|
|Frame VOI LUT||C.188.8.131.52.10||Specifies the VOI transformation to be applied during display.|
|Pixel Intensity Relationship LUT||C.184.108.40.206.13||Specifies the different LUTs to transform the stored pixel values to a given function of the X-Ray intensity.|
|XA/XRF Frame Pixel Data Properties||C.220.127.116.11||Specifies geometrical characteristics of the pixel data.|
The usage of this module is recommended to specify the sign of the slope of the VOI transformation to be applied during display of the multi-frame image.
Table FFF.2.3-3 ENHANCED XA/XRF IMAGE MODULE Recommendations
|Photometric Interpretation||(0028,0004)||The value MONOCHROME1 indicates negative slope (i.e. minimum pixel value is intended to be displayed as white), and the value MONOCHROME2 indicates positive slope (i.e. minimum pixel value is intended to be displayed as black).|
|Presentation LUT Shape||(2050,0020)||The values IDENTITY and INVERSE are applicable.|
The usage of this module is recommended to specify some presentation settings:
Whether the viewing mode is subtracted or not by using the Recommended Viewing Mode (0028,1090), and
The recommended edge enhancement filter as a percentage of subjective sensitivity by using the Display Filter Percentage (0028,9411).
The recommended filter percentage does not guaranty a full consistency of the image presentation across applications, rather gives an indication of the user sensitivity to such filtering to be applied consistently. To optimize the consistency of the filtering perception, the applications sharing the same images should be customized to calibrate the highest filtering (i.e. 100%) to similar perception by the users. Setting the application to the lowest filtering (i.e. 0%) means that no filter is applied at all.
The usage of this macro is recommended to specify the windowing to be applied to the pixel data in native mode, i.e. non-subtracted.
The usage of this macro is recommended to enable the applications to get the values of the stored pixel data back to a linear relationship with the X-Ray intensity.
When the value of Pixel Intensity Relationship (0028,1040) equals LOG, a LUT to get back to linear relationship (TO_LINEAR) is present to allow applications to handle linear pixel data.
Other LUTs can be added, for instance to transform to logarithmic relationship for subtraction (TO_LOG) in case the relationship of the stored pixel data is linear. Other LUTs with manufacturer-defined relationships are also allowed.
The LUTs of this macro are not used for the standard display pipeline.
The usage of this macro is recommended to specify some properties of the values of the stored pixel data with respect to the X-Ray intensity (i.e. gray level properties) and with respect to the geometry of the detector (i.e. pixel geometrical properties).