FFF.2.4.2.4.2 Derivation by applying a square root transformation

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.

[pic]

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"
Bits Stored (0028,0101) = 8
item 1
Item 1
>>Derivation Code Sequence (0008,9215)
Item 1
Item 1
Item 1
>>LUT Data (0028,3006) = LUT data
>>LUT Function (0028,9474) = TO_LINEAR
>XA/XRF Frame Characteristics Sequence (0018,9412)
Item 1
>>Derivation Code Sequence (0008,9215)
Item 1
Item 1
>>Pixel Intensity Relationship (0028,1040) = SQRT
>>Pixel Intensity Relationship Sign (0028,1041) = 1
>>Geometrical Properties (0028,9444) = UNIFORM
>>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.8.19.6.2 Specifies the dimension of the Field of View as well as the flip and rotation transformations.
X-Ray Isocenter Reference System C.8.19.6.13 Specifies the acquisition geometry in a fixed reference system.
X-Ray Geometry C.8.19.6.14 Specifies the distances of the conic projection.
XA/XRF Frame Pixel Data Properties C.8.19.6.4 Specifies the dimensions of the pixels at the image reception plane.