In this example, the acquisition modality creates two instances of the Enhanced XA object: the instance “A” with mask frames and the instance “B” with contrast frames. A temporal filtering has been applied by the modality before the creation of the instances.
The workstation 1 performs a digital subtraction of the frames of the instance “B” by using the frames of the instance “A” as mask, then the resulting subtracted frames are stored in a new instance “C”.
Finally the workstation 2 processes the instance “C” by applying a zoom and edge enhancement, and the resulting processed frames are stored in a new instance “D”.
Figure FFF.2.4-2Example of various successive derivations
The following figure shows the values of the attributes of the instance “D” in the corresponding modules and macros related to derivation information. The Source Image Sequence (0008,2112) of the Derivation Image Sequence (0008,9124) does not contain the attribute Referenced Frame Number (0008,1160) because all the frames of the source images are used to generate the derived images.
|Image Type||(0008,0008)||=||DERIVED\ …|
|SOP Instance UID||(0020,000E)||=||UID "D"|
|Shared Functional Groups Sequence||(5200,9229)|
|>Derivation Image Sequence||(0008,9124)|
Figure FFF.2.4-3 Attributes of the example of various successive derivations
In this example, the acquisition modality creates the instance “A” of the Enhanced XA object with 14 bits stored where the relationship between the pixel intensity and the X-Ray intensity is linear.
A workstation reads the instance “A”, transforms the pixel values of the stored pixel data by applying a square root function and stores the resulting frames on the instance “B” with 8 bits stored.
Figure FFF.2.4-4Example of derivation by square root transformation
The following figure shows the values of the attributes of the instance “B” in the corresponding modules and macros related to derivation information.
Note that the Derivation Code Sequence (0008,9215) is present when the Derivation Image Sequence (0008,9124) includes one or more items, even if the derivation code is not defined in the Context ID 7203.
The Pixel Intensity Relationship LUT Sequence (0028,9422) contains a LUT with the function “TO_LINEAR” to allow the calculation of the gray level intensity to be linear to the X-Ray intensity. Since the instance “B” has 8 bits stored, this LUT contains 256 entries (starting the mapping at pixel value 0) and is encoded in 16 bits.
The value of the Pixel Intensity Relationship (0028,1040) in the Frame Pixel Data Properties Sequence (0028,9443) could be “OTHER” as it is described in the defined terms. However, a more explicit term like “SQRT” is also allowed and will have the same effect in the reading application.
In the case of a modification of the pixel intensity relationship of an image, the value of the attribute Image Processing Applied (0028,9446) in the Frame Pixel Data Properties Sequence (0028,9443) can be “NONE” in order to indicate to the reading applications that there was no image processing applied to the original image that could modify the spatial or temporal characteristics of the pixels.
|SOP Instance UID||(0020,000E)||=||UID "B"|
|>>Derivation Code Sequence||(0008,9215)|
|>>LUT Data||(0028,3006)||=||LUT data|
|>XA/XRF Frame Characteristics Sequence||(0018,9412)|
|>>Derivation Code Sequence||(0008,9215)|
|>>Pixel Intensity Relationship||(0028,1040)||=||SQRT|
|>>Pixel Intensity Relationship Sign||(0028,1041)||=||1|
|>>Image Processing Applied||(0028,9446)||=||NONE|
|Image||Image Pixel||C.7.6.3||Specifies the dimension of the pixel array of the frames.|
|XA/XRF Acquisition||C.8.19.3||Describes some characteristics of the acquisition system that enables this scenario.|
|X-Ray Detector||C.8.19.5||Specifies the type and characteristics of the image detector.|
Table FFF.2. 5-2 ENHANCED XA IMAGE FUNCTIONAL GROUP MACROS
|Functional Group Macro||PS 3.3 Reference||Usage|
|X-Ray Field of View||C.126.96.36.199||Specifies the dimension of the Field of View as well as the flip and rotation transformations.|
|X-Ray Isocenter Reference System||C.188.8.131.52||Specifies the acquisition geometry in a fixed reference system.|
|X-Ray Geometry||C.184.108.40.206||Specifies the distances of the conic projection.|
|XA/XRF Frame Pixel Data Properties||C.220.127.116.11||Specifies the dimensions of the pixels at the image reception plane.|
The usage of this module is recommended to specify the number of rows and columns of the Pixel Data, as well as the aspect ratio.
The usage of this module is recommended to give the necessary conditions to enable the calculations of this scenario.
Table FFF.2.5-3 XA/XRF ACQUISITION MODULE Recommendations
|X-Ray Receptor Type||(0018,9420)||DIGITAL_DETECTOR is used in this scenario.|
|Positioner Type||(0018,1508)||CARM is used in this scenario.|
|C-arm Positioner Tabletop Relationship||(0018,9474)||YES is necessary in this scenario.|
In case of X-Ray Receptor Type (0018,9420) equals “IMG_INTENSIFIER”, there are some limitations that prevent the calculations described on this scenario:
The position of the projection of the isocenter on the intensifier active area is undefined;
The Field of View Origin (0018,7030) cannot be related to the physical area of the receptor because the Intensifier TLHC is undefined.
As a consequence, in case of image intensifier it is impossible to relate the position of the pixels of the stored area to the isocenter reference system.
In case of X-Ray Receptor Type (0018,9420) equals “DIGITAL_DETECTOR” the usage of this module is recommended to specify the type and characteristics of the image detector.
The usage of this macro is recommended to specify the characteristics of the field of view.
The field of view characteristics may change per-frame across the multi-frame image.
The usage of this macro is recommended to specify the fixed reference system of the acquisition geometry.
The usage of this macro is recommended to specify the distances between the X-Ray source, isocenter and X-Ray detector.
The usage of this macro is recommended to specify the dimensions of the pixels at the image reception plane.