Материал: part17

FFF.2.1.7.2 Encoding Outline​

TheXASOPClassencodestheAttributeskVp,mAandpulsedurationasauniquevalueforthewholeMulti-frameImage.Forsystems​ that can provide only average values of these Attributes, this SOP Class is more appropriate.​

TheEnhancedXASOPClassencodesper-framekVp,mAandpulseduration,thustheestimateddoseperframecanbenowcorrelated​ to the positioner angles and table position of each frame.​

In order to accurately estimate the dose per body area, other Attributes are needed such as positioner angles, table position, SID,​ ISO distances, Field of View, etc.​

FFF.2.1.7.3 Encoding Details​

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

Table FFF.2.1-49. Enhanced X-Ray Angiographic Image IOD Modules​

Table FFF.2.1-50. Enhanced XA Image Functional Group Macros​

FFF.2.1.7.3.1 XA/XRF Acquisition Module Recommendations​

The usage of this module is recommended to specify the average values of time, voltage and current applied during the acquisition​ of the Multi-frame Image.​

It gives general information of the X-Ray radiation during the acquisition of the image. In case of dynamic acquisitions, this module​ is not sufficient to estimate the radiation per body area and additional per-frame information is needed.​

Table FFF.2.1-51. XA/XRF Acquisition Module Recommendations​

Note that the three Attributes X-Ray Tube Current in mA (0018,9330), Exposure Time in ms (0018,9328) and Exposure in mAs​ (0018,9332) are mutually conditional to each other but all three may be present. In this scenario it is recommended to include the​ three Attributes.​

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FFF.2.1.7.3.2 Frame Content Macro Recommendations​

The usage of this macro is recommended to specify the duration of each frame of the Multi-frame Image.​

Note that this macro is allowed to be used only in a per-frame context, even if the pulse duration is constant for all the frames.​

FFF.2.1.7.3.3 X-Ray Frame Acquisition Macro Recommendations​

The usage of this macro is recommended to specify the values of voltage (kVp) and current (mA) applied for the acquisition of each​ frame of the Multi-frame Image.​

If the system can provide only average values of kVp and mA, the usage of the X-Ray Frame Acquisition macro is not recommended,​ only the XA/XRF Acquisition Module is recommended.​

IfthesystempredefinesthevaluesofthekVpandmAtobeconstantduringtheacquisition,theusageoftheX-RayFrameAcquisition​ macro in a shared context is recommended in order to indicate that the value of kVp and mA is identical for each frame.​

If the system is able to change dynamically the kVp and mA during the acquisition, the usage of the X-Ray Frame Acquisition macro​ in a per-frame context is recommended.​

Table FFF.2.1-52. X-Ray Frame Acquisition Macro Recommendations​

FFF.2.1.7.4 Example​

For more details, refer to the Section FFF.1.4​

FFF.2.2 Review​

FFF.2.2.1 Variable Frame-rate Acquisition With Skip Frames​

This application case provides information on how X-Ray acquisitions with variable time between frames can be organized by groups​ of frames to be reviewed with individual group settings.​

FFF.2.2.1.1 User Scenario​

The image acquisition system performs complex acquisition protocols with groups of frames to be displayed at different frame rates​ and others to be skipped.​

Allow frame-rates in viewing applications to be different than acquired rates.​

FFF.2.2.1.2 Encoding Outline​

The XA IOD provides only one group of frames between start and stop trim.​

The Enhanced XA/XRF IOD allows encoding of multiple groups of frames (frame collections) with dedicated display parameters.​

The Enhanced XA IOD provides an exact acquisition time for each frame.​

FFF.2.2.1.3 Encoding Details​

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

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Table FFF.2.2-1. Enhanced X-Ray Angiographic Image IOD Modules​

FFF.2.2.1.3.1 XA/XRF Multi-frame Presentation Module Recommendations​

Theusageofthismoduleisrecommendedtoencodethegroupingofframes(oneormoregroups)fordisplaypurposesandtherelated​ parameters for each group.​

Table FFF.2.2-2. XA/XRF Multi-frame Presentation Module Recommendations​

FFF.2.2.1.4 Example​

An example of a 4 position peripheral stepping acquisition with different frame-rates is provided. One group is only 2 Frames (e.g.,​ due to fast contrast bolus) and will be skipped for display purposes.​

The whole image is reviewed in looping mode:​

•​The first group, from frames 1 to 17, is to be reviewed at 4 frames per second;​

•​The second group, from frames 18 to 25, is to be reviewed at 2 frames per second;​

•​The third group, of frames 26 and 27, is not to be displayed;​

•​The fourth group, from frames 28 to 36, is to be reviewed at 1.5 frames per second.​

The encoded values of the key Attributes of this example are shown in Figure FFF.2.2-1.​

Figure FFF.2.2-1. Attributes of the Example of the Variable Frame-rate Acquisition with Skip Frames​

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FFF.2.3 Display​

FFF.2.3.1 Standard Pipeline With Enhanced XA​

This section provides information on the encoding of the density and geometry characteristics of the stored pixel data and the ways​ to display it.​

FFF.2.3.1.1 User Scenario​

The image acquisition may be performed with a variety of settings on the detector image pre-processing component that modifies​ the way the gray levels are stored in the pixel data.​

In particular, it may impact the relationship between the X-Ray intensity and the gray level stored (e.g., non-linear function), as well​ as the geometry of the X-Ray beam (e.g., pincushion distortion).​

Based on the characteristics of the stored pixel data, the acquisition system determines automatically an optimal way to display the​ pixel data on a frame-by-frame basis, which is expected to be applied by the viewing applications.​

FFF.2.3.1.2 Encoding Outline​

The XA SOP Class encodes the VOI settings to be common to all the frames of the image. It also restricts the Photometric Interpret-​ ation (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 character-​ istics and settings can be defined, such as:​

•​Relationship between X-Ray intensity and the pixel value stored;​

•​Edge Enhancement filter strength;​

•​Geometrical properties.​

FFF.2.3.1.3 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​

Table FFF.2.3-2. Enhanced XA Image Functional Group Macros​

FFF.2.3.1.3.1 Enhanced XA/XRF Image Module Recommendations​

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.​

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Table FFF.2.3-3. Enhanced XA/XRF Image Module Recommendations​

FFF.2.3.1.3.2 XA/XRF Multi-frame Presentation Module Recommendations​

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.​

FFF.2.3.1.3.3 Frame VOI LUT Macro Recommendations​

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.​

FFF.2.3.1.3.4 Pixel Intensity Relationship LUT Macro Recommendations​

Theusageofthismacroisrecommendedtoenabletheapplicationstogetthevaluesofthestoredpixeldatabacktoalinearrelationship​ 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.​

FFF.2.3.1.3.5 XA/XRF Frame Pixel Data Properties Macro Recommendations​

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).​

FFF.2.3.1.4 Example​

Inthisexample,twodifferentsystemsperformanX-RayAcquisitionofthecoronaryarteriesinjectedwithradio-opaquecontrastagent.​

The system A is equipped with a digital detector, and stores the pixel data with the lower level corresponding to the lower X-Ray in-​ tensity. Then the user creates two instances: one to display the injected vessels as black, and other to display the injected vessels​ as white.​

The system B is equipped with an image intensifier configured to store the pixel data with the lower level corresponding to the higher​ X-Ray intensity. Then the user creates two instances: one to display the injected vessels as black, and other to display the injected​ vessels as white.​

The figure below illustrates, for the two systems, the gray levels of the injected vessels on both the stored pixel data and the displayed​ pixels,whichdependonthevalueoftheAttributesPixelIntensityRelationshipSign(0028,1041),PhotometricInterpretation(0028,0004),​ and Presentation LUT Shape (2050,0020).​

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