Материал: part17

If the image is derived from one or more SOP Instances, the XA/XRF Frame Characteristics Sequence always contains the same​ values as the last item of the Derivation Image Sequence.​

If the image is derived but not from other SOP Instances, it means that the derivation was performed on the Acquisition system, and​ the Acquisition Device Processing Description (0018,1400) and the Acquisition Device Processing Code (0018,1401) contain the in-​ formation of that derivation.​

An image derived from a derived image will change the Derivation Description but not the Acquisition Device Processing Description.​

FFF.2.4.2.3.5 XA/XRF Frame Pixel Data Properties Macro Recommendations​

The usage of this macro is recommended to specify the type of processing applied to the stored pixel data of the derived frames.​

Table FFF.2.4-11. XA/XRF Frame Pixel Data Properties Macro Recommendations​

FFF.2.4.2.4 Examples​

FFF.2.4.2.4.1 Various Successive Derivations​

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.2.4-2. Example of various successive derivations​

FigureFFF.2.4-3showsthevaluesoftheAttributesoftheinstance"D"inthecorrespondingmodulesandmacrosrelatedtoderivation​ 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.​

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Figure FFF.2.4-3. Attributes of the Example of Various Successive Derivations​

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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.​

Figure FFF.2.4-4. Example 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 deriv-​ ation 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 CID 7203 “Image Derivation”.​

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.​

ThevalueofthePixelIntensityRelationship(0028,1040)intheFramePixelDataPropertiesSequence(0028,9443)couldbe"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.​

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Figure FFF.2.4-5. Attributes of the Example of Derivation by Square Root Transformation​

FFF.2.5 Registration​

FFF.2.5.1 Tracking An Object of Interest On Multiple 2d Images​

This section provides information on the encoding of the acquisition geometry in a fixed reference system.​

FFF.2.5.1.1 User Scenario​

The operator identifies the position of an object of interest projected on the stored pixel data of an image A, and estimates the magni-​ fication of the conic projection by a calibration process.​

The operator wants to know the position of the projection of such object of interest on a second image B acquired under different​ geometry,assumingthatthepatientdoesnotmovebetweenimageAandimageB(i.e.,theimagessharethesameframeofreference).​

FFF.2.5.1.2 Encoding Outline​

The XA SOP Class encodes the information in a patient-related coordinate system.​

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The Enhanced XA SOP Class additionally encodes the geometry of the acquisition system with respect to a fixed reference system​ defined by the manufacturer, so-called Isocenter reference system. Therefore, it allows encoding the absolute position of an object​ of interest and to track the projection of such object across the different images acquired under different geometry.​

FFF.2.5.1.3 Encoding Details​

This section provides detailed recommendations of the key Attributes to address this particular scenario.​

Table FFF.2.5-1. Enhanced X-Ray Angiographic Image IOD Modules​

Table FFF.2.5-2. Enhanced XA Image Functional Group Macros​

FFF.2.5.1.3.1 Image Pixel Module Recommendations​

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.​

FFF.2.5.1.3.2 XA/XRF Acquisition Module Recommendations​

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​

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;​

•​TheFieldofViewOrigin(0018,7030)cannotberelatedtothephysicalareaofthereceptorbecausetheIntensifierTLHCisundefined.​

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.​

FFF.2.5.1.3.3 X-Ray Detector Module Recommendations​

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.​

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