This chapter describes different scenarios and application cases organized by domains of application. Each application case is basically structured in four sections:
1) User Scenario : Describes the user needs in a specific clinical context, and/or a particular system configuration and equipment type.
2) Encoding Outline : Describes the specificities of the XA SOP Class and the Enhanced XA SOP Class related to this scenario, and highlights the key aspects of the Enhanced XA SOP Class to address it.
3) Encoding Details : Provides detailed recommendations of the key Attributes of the object(s) to address this particular scenario.
4) Example : Presents a typical example of the scenario, with realistic sample values, and gives details of the encoding of the key Attributes of the object(s) to address this particular scenario. In the values of the Attributes, the text in bold face indicates specific Attribute values; the text in italic face gives an indication of the expected value content.
This application case is related to the results of an X-Ray acquisition and parallel ECG data recording on the same equipment.
The image acquisition system records ECG signals simultaneously with the acquisition of the Enhanced XA Multi-frame Image. All the ECG signals are acquired at the same sampling rate.
The acquisition of both image and ECG data are not triggered by an external signal.
The information can be exchanged via Offline Media or Network.
Synchronization between the ECG Curve and the image frames allows synchronized navigation.
The General ECG IOD is used to store the waveform data recorded in parallel to the image acquisition encoded as Enhanced XA IOD.
The Synchronization Module is used to specify a common time-base.
The option of encoding trigger information is not recommended by this case.
The solution assumes implementation on a single imaging modality and therefore the mutual UID references between the General ECG and Enhanced XA objects is recommended. This will allow faster access to the related object.
This section provides detailed recommendations of the key Attributes to address this particular scenario.
Table FFF.2.1-1. Enhanced X-Ray Angiographic Image IOD Modules
| C.7.3.1 |
The General Series Module Modality (0008,0060) Attribute description in PS3.3 enforces the storage of waveform and pixel data in different Series IE. |
||
| C.7.4.2 |
Specifies that the image acquisition is synchronized. Will have the same content as the General ECG SOP Instance. |
||
| C.7.5.1 | |||
| C.7.6.18.1 |
Contains information of the type of relationship between the ECG waveform and the image. |
||
| C.8.19.2 |
Contains UID references to the related General ECG SOP Instance. |
Table FFF.2.1-2. Enhanced XA Image Functional Group Macros
| C.7.6.16.2.2 |
Provides timing information to correlate each frame to the recorded ECG samples. |
|
| C.7.6.16.2.7 |
Provides time relationships between the angiographic frames and the cardiac cycle. |
The usage of this Module is recommended to encode a "synchronized time" condition.
The specialty of Synchronization Triggers is not part of this scenario.
Table FFF.2.1-3. Synchronization Module Recommendations
The usage of this Module is recommended to assure that the image contains identical equipment identification information as the referenced General ECG SOP Instance.
The usage of this module is recommended to indicate that the ECG is not used to trig the X-Ray acquisition, rather to time relate the frames to the ECG signal.
The usage of this module is recommended to reference from the image object to the related General ECG SOP Instance that contains the ECG data recorded simultaneously.
Table FFF.2.1-5. Enhanced XA/XRF Image Module Recommendations
|
Reference to "General ECG SOP Instance" acquired in conjunction with this image. Contains a single item. |
||
|
"1.2.840.10008.5.1.4.1.1.9.1.2" i.e., reference to an General ECG SOP Instance |
||
|
CID 7004 “Waveform Purpose of Reference” is used; identify clear reason for the Reference. |
If there is a specific ECG analysis that determines the time between the R-peaks and the angiographic frames, the usage of this macro is recommended.
As the frames are acquired at a frame rate independent of cardiac phases, this macro is used in a "per frame functional group" to encode the position of each frame relative to its prior R-peak.
In this scenario the timing information is important to correlate each frame to the recorded ECG.
If there is a specific ECG analysis, this macro allows the encoding of the position in the cardiac cycle that is most representative of each frame.
The following table gives recommendations for usage in this scenario.
This IOD will encode the recorded ECG waveform data, which is done by the image acquisition system. Since this is not a dedicated waveform modality device, appropriate defaults for most of the data have to be recommended to fulfill the requirements according to PS3.3.
Table FFF.2.1-7. General ECG IOD Modules
A new Series is created to set the modality "ECG" for the waveform.
Most of the Attributes are aligned with the contents of the related series level Attributes in the image object.
The Related Series Sequence (0008,1250) is not recommended because instance level relationship can be applied to reference the image instances.
The usage of this Module is recommended to encode a "synchronized time" condition, which was previously implicit when using the curve module.
Table FFF.2.1-9. Synchronization Module Recommendations
The usage of this Module is recommended to assure that the General ECG SOP Instance contains identical equipment identification information as the referenced image objects.
The usage of this module is recommended to relate the acquisition time of the waveform data to the image acquired simultaneously.
The module additionally includes an instance level reference to the related image.
Table FFF.2.1-10. Waveform Identification Module Recommendations
The usage of this module is a basic requirement of the General ECG IOD.
Any application displaying the ECG is recommended to scale the ECG contents to its output capabilities (esp. the amplitude resolution).
If more than one ECG signal needs to be recorded, the grouping of the channels in multiplex groups depends on the ECG sampling rate. All the channels encoded in the same multiplex group have identical sampling rate.
Table FFF.2.1-11. Waveform Module Recommendations
In the two following examples, the Image Modality acquires a Multi-frame Image of the coronary arteries lasting 4 seconds, at 30 frames per second.
Simultaneously, the same modality acquires two channels of ECG from a 2-Lead ECG (the first channel on Lead I and the second on Lead II) starting one second before the image acquisition starts, and lasting 5 seconds, with a sampling frequency of 300 Hz on 16 bits signed encoding, making up a number of 1500 samples per channel. The first ECG sample is 10 ms after the nominal start time of the ECG acquisition. Both ECG channels are sampled simultaneously. The time skew of both channels is 0 ms.
In this example, the Enhanced XA image does not contain information of the cardiac cycle phases.
The Attributes that define the two different SOP Instances (Enhanced XA and General ECG) of this example are described in Figure FFF.2.1-3.
In this example, the heart rate is 75 beats per minute. As the image is acquired during a period of four seconds, it contains five heartbeats.
The ECG signal is analyzed to determine the R-peaks and to relate them to the angiographic frames. Thus the Enhanced XA image contains information of this relationship between the ECG signal and the frames.
The Attributes that define the two different SOP Instances (Enhanced XA and General ECG) of this example are described in the figures of the previous example, in addition to the Attributes described in Figure FFF.2.1-5.
These application cases are related to the results of an X-Ray acquisition and simultaneous ECG data recording on different equipment. The concepts of synchronized time and triggers are involved.
The two modalities may share references on the various entity levels below the Study, i.e., Series and Image UID references using non-standard mechanisms. Nothing in the workflow requires such references. For more details about UID referencing, refer to the previous application case "ECG Recording at Acquisition Modality" (see Section FFF.2.1.1).
If both modalities share a common data store, a dedicated post-processing station can be used for combined display of waveform and image information, and/or combined functional analysis of signals and pixel data to time relate the cardiac cycle phases to the angiographic frames. The storage of the waveform data and images to PACS or media will preserve the combined functional capabilities.
In these application cases, this post-processing activity is outside the scope of the acquisition modalities. For more details about the relationship between cardiac cycle and angiographic frames, refer to the previous application case "ECG Recording at Acquisition Modality" (see Section FFF.2.1.1).
Image runs are taken by the image acquisition modality. Waveforms are recorded by the waveform acquisition modality. Both modalities are time synchronized via NTP. The time server may be one of the modalities or an external server. The resulting objects will include the time synchronization concept.
Dedicated Waveform IODs exist to store captured waveforms. In this case, General ECG IOD is used to store the waveform data.
Depending on the degree of coupling of the modalities involved, the usage of references on the various entity levels can vary. While there is a standard DICOM service to share Study Instance UID between modalities (i.e., Worklist), there are no standard DICOM services for sharing references below the Study level, so any UID reference to the Series and Image levels is shared in a proprietary manner.
With the Synchronization Module information, the method to implement the common time-base can be documented.
The Enhanced XA IOD provides a detailed "per frame" timing to encode timing information related to each frame.
This section provides detailed recommendations of the key Attributes to address this particular scenario.
Table FFF.2.1-12. Enhanced X-Ray Angiographic Image IOD Modules
Table FFF.2.1-13. Enhanced XA Image Functional Group Macros
| C.7.6.16.2.2 |
Provides timing information to correlate each frame to any externally recorded waveform. |
This Module is used to document the synchronization of the two modalities.
Table FFF.2.1-14. Synchronization Module Recommendations
This module includes the acquisition date and time of the image, which is in the same time basis as the acquisition date and time of the ECG in this scenario.
The ECG recording system will take care of filling in the waveform-specific contents in the General ECG SOP Instance. This section will address only the specifics for Attributes related to synchronization.
Table FFF.2.1-16. Waveform IOD Modules
| C.7.4.2 |
Specifies that the ECG acquisition is time synchronized with the image acquisition. Will have the same content as the Enhanced XA SOP Instance. See Section FFF.2.1.2.1.3.1.1. |
||
| C.10.8 |
Provides timing information to correlate the waveform data to any externally recorded image. |
FFF.2.1.2.1.3.2.1 Waveform Identification Recommendations
The usage of this module is recommended to relate the acquisition time of the waveform data to the related image(s).
In this example, there are two modalities that are synchronized with an external clock via NTP. The Image Modality acquires three Multi-frame Images within the same Study and same Series. Simultaneously, the Waveform Modality acquires the ECG non-stop during the same period, leading to one single Waveform SOP Instance on a different Study.
In this example, there is no UID referencing capability between the two modalities.
The Attributes that define the relevant content in the two different SOP Instances (Enhanced XA and General ECG) are described in Figure FFF.2.1-8.
Image runs are taken by the image acquisition modality. Waveforms are recorded by waveform recording modality. Both modalities are time synchronized via NTP. The acquisition in one modality is triggered by the other modality. The resulting objects will include the time synchronization and trigger synchronization concepts.
There are two cases depending on the triggering modality:
1- At X-Ray start, the image modality sends a trigger signal to the waveform modality.
2- The waveform modality sends trigger signals to the image modality to start the acquisition of each frame.
Dedicated Waveform IODs exist to store captured waveforms. In this case, General ECG IOD is used to store the waveform data.
With the Synchronization Module information, the method to implement the triggers can be documented.
The Enhanced XA IOD provides per-frame encoding of the timing information related to each frame.
This section provides detailed recommendations of the key Attributes to address this particular scenario.
The usage of this Module is recommended to document the triggering role of the image modality.
Table FFF.2.1-21. Synchronization Module Recommendations
This module includes the acquisition date and time of the image.
The recording system will take care of filling in the waveform-specific contents, based on the IOD relevant for the type of system (e.g., EP, Hemodynamic, etc.). This section will address only the specifics for Attributes related to synchronization.
Table FFF.2.1-24. Waveform IOD Modules
The usage of this Module is recommended to document the triggering role of the waveform modality.
Table FFF.2.1-25. Synchronization Module Recommendations
This module includes the acquisition date and time of the waveform, which may be different than the acquisition date and time of the image in this scenario.
The usage of this module is recommended to encode the time relationship between the trigger signal and the ECG samples.
Table FFF.2.1-27. Waveform Module Recommendations
In this example, there are two modalities that are synchronized with an external clock via NTP. The Image Modality acquires three Multi-frame Images within the same Study and same Series. Simultaneously, the Waveform Modality acquires the ECG non-stop during the same period, leading to one single Waveform SOP Instance on a different Study. The ECG sampling frequency is 300 Hz on 16 bits signed encoding, making up a number of 1500 samples per channel. The first ECG sample is acquired at nominal start time of the ECG acquisition.
The image modality sends a trigger to the waveform modality at the start time of each of the three images. This signal is stored in one channel of the waveform modality, together with the ECG signal.
In this example, there is no UID referencing capability between the two modalities.
The Attributes that define the relevant content in the two different SOP Instances (Enhanced XA and General ECG) are described in Figure FFF.2.1-11.
In this example, there are two modalities that are synchronized with an external clock via NTP.
The Image Modality starts the X-Ray image acquisition and simultaneously the Waveform Modality acquires the ECG and analyzes the signal to determine the phases of the cardiac cycles. At each cycle, the waveform modality sends a trigger to the image modality to start the acquisition of a frame. This trigger is stored in one channel of the waveform modality, together with the ECG signal.
The ECG sampling frequency is 300 Hz on 16 bits signed encoding, making up a number of 1500 samples per channel. The first ECG sample is acquired 10 ms after the nominal start time of the ECG acquisition.
In this example, there is no UID referencing capability between the two modalities.
The Attributes that define the relevant content in the two different SOP Instances (Enhanced XA and General ECG) are described in Figure FFF.2.1-13.
This section provides information on the encoding of the movement of the X-Ray Positioner during the acquisition of a rotational angiography.
The related image presentation parameters of the rotational acquisition that are defined in the Enhanced XA SOP Class, such as the mask information of subtracted display, are described in further sections of this annex.
The Multi-frame Image acquisition is performed during a continuous rotation of the X-Ray Positioner, starting from the initial incidence and acquiring frames in a given angular direction at variable angular steps and variable time intervals.
Typically such rotational acquisition is performed with the purpose of further 3D reconstruction. The rotation axis is not necessarily the patient head-feet direction, which may lead to images where the patient is not heads-up oriented.
There may be one or more rotations of the X-Ray Positioner during the same image acquisition, performed by following different patterns, such as:
The XA SOP Class encodes the absolute positioner angles as the sum of the angle of the first frame and the increments relative to the first frame. The Enhanced XA SOP Class encodes per-frame absolute angles.
In the XA SOP Class, the encoding of the angles is always with respect to the patient, so-called anatomical angles, and the image is assumed to be patient-oriented (i.e., heads-up display). In case of positioner rotation around an axis oblique to the patient, not aligned with the head-feet axis, it is not possible to encode the rotation of the image necessary for 3D reconstruction.
The Enhanced XA SOP Class encodes the positioner angles with respect to the patient as well as with respect to a fixed coordinate system of the equipment.
This section provides detailed recommendations of the key Attributes to address this particular scenario.
Table FFF.2.1-29. Enhanced XA Image Functional Group Macros
| C.8.19.6.10 | ||
| C.8.19.6.13 |
Specifies the angles of the positioner per-frame in equipment coordinates for further applications based on the acquisition geometry (e.g., 3D reconstruction, registration…). |
The usage of this module is recommended to define the type of positioner.
This macro is used in the per-frame context in this scenario.
If the value of the C-arm Positioner Tabletop Relationship (0018,9474) is NO, the following macro may not be provided by the acquisition modality. This macro is used in the per-frame context in this scenario.
Table FFF.2.1-32. X-Ray Isocenter Reference System Macro Example
In this example, the patient is on the table, in position "Head First Prone". The table horizontal, tilt and rotation angles are equal to zero.
The positioner performs a rotation of 180 deg from the left to the right side of the patient, with the image detector going above the back of the patient, around an axis parallel to the head-feet axis of the patient.
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-15.
This section provides information on the encoding of the movement of the X-Ray Table during the acquisition of a stepping angiography.
The related image presentation parameters of the stepping acquisition that are defined in the Enhanced XA SOP Class, such as the mask information of subtracted display, are described in further sections of this annex.
The Multi-frame Image acquisition is performed during a movement of the X-Ray Table, starting from the initial position and acquiring frames in a given direction along the Z axis of the table at variable steps and variable time intervals.
There may be one or more "stepping movements" of the X-Ray Table during the same image acquisition, leading to one or more instances of the Enhanced XA SOP Class. The stepping may be performed by different patterns, such as:
The XA SOP Class encodes table position as increments relative to the position of the first frame, while the position of the first frame is not encoded.
The Enhanced XA SOP Class encodes per-frame absolute table vertical, longitudinal and lateral position, as well as table horizontal rotation angle, table head tilt angle and table cradle tilt angle.
This allows registration between separate Multi-frame Images in the same table frame of reference, as well as accounting for magnification ratio and other aspects of geometry during registration. Issues of patient motion during acquisition of the images is not addressed in this scenario.
This section provides detailed recommendations of the key Attributes to address this particular scenario.
Table FFF.2.1-33. Enhanced X-Ray Angiographic Image IOD Modules
| C.8.19.3 |
Specifies the relationship between the table and the positioner. |
Table FFF.2.1-34. Enhanced XA Image Functional Group Macros
| C.8.19.6.11 | ||
| C.8.19.6.13 |
Specifies the position and the angles of the table per-frame in equipment coordinates, for further applications based on the acquisition geometry (e.g., registration…). |
The usage of this module is recommended to specify the relationship between the table and the positioner.
This macro is used in the per-frame context in this scenario.
Table FFF.2.1-36. X-Ray Table Position Macro Example
If the value of the C-arm Positioner Tabletop Relationship (0018,9474) is NO, the following macro may not be provided by the acquisition modality. This macro is used in the per-frame context in this scenario.
Table FFF.2.1-37. X-Ray Isocenter Reference System Macro Example
In this example, the patient is on the table in position "Head First Supine". The table is tilted of -10 degrees, with the head of the patient below the feet, and the image detector is parallel to the tabletop plane. The table cradle and rotation angles are equal to zero.
The image acquisition is performed during a movement of the X-Ray Table in the tabletop plane, at constant speed and of one meter of distance, acquiring frames from the abdomen to the feet of the patient in one stepping movement for non-subtracted angiography.
The table is related to the C-arm positioner so that the coordinates of the table position are known in the isocenter reference system. This allows determining the projection magnification of the table top plane with respect to the detector plane.
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-18.
This section provides information on the encoding of the "sensitive areas" used for regulation control of the X-Ray generation of an image that resulted from applying these X-Rays.
The user a) takes previous selected regulation settings or b) manually enters regulation settings or c) automatically gets computer-calculated regulation settings from requested procedures.
Acquired images are networked or stored in offline media.
Later problems of image quality are determined and user wants to check for reasons by assessing the positions of the sensing regions.
The Enhanced XA IOD includes a module to supply information about active regulation control sensing fields, their shape and position relative to the pixel matrix.
This section provides detailed recommendations of the key Attributes to address this particular scenario.
Table FFF.2.1-38. Enhanced XA Image Functional Group Macros
| C.8.19.6.3 |
Specifies the shape and size of the sensing regions in pixels, as well as their position relative to the top left pixel of the image. |
This macro is recommended to encode details about sensing regions.
If the position of the sensing regions is fixed during the multi-frame acquisition, the usage of this macro is shared.
If the position of the sensing regions was changed during the multi-frame acquisition, this macro is encoded per-frame to reflect the individual positions.
The same number of regions is typically used for all the frames of the image. However it is technically possible to activate or deactivate some of the regions during a given range of frames, in which case this macro is encoded per-frame.
In this section, two examples are given.
The first example shows how three sensing regions are encoded: 1) central (circular), 2) left (rectangular) and 3) right (rectangular).
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-20.
The second example shows the same regions, but the field of view region encoded in the Pixel Data matrix has been shifted of 240 pixels right and 310 pixels down, thus the left rectangular sensing region is outside the Pixel Data matrix as well as both rectangular regions overlap the top row of the image matrix.
Figure FFF.2.1-21. Example of X-Ray Exposure Control Sensing Regions partially outside the Pixel Data matrix
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-22.
This section provides information on the encoding of the image detector parameters and field of view applied during the X-Ray acquisition.
The user selects a given size of the field of view before starting the acquisition. This size can be smaller than the size of the Image Detector.
The position of the field of view in the detector area changes during the acquisition in order to focus on an object of interest.
Acquired image is networked or stored in offline media, then the image is:
-
Displayed and reviewed in cine mode, and the field of view area needs to be displayed on the viewing screen;
-
Used for quality assurance, to relate the pixels of the stored image to the detector elements, for instance to understand the image artifacts due to detector defects;
-
Used to measure the dimension of organs or other objects of interest;
-
Used to determine the position in the 3D space of the projection of the objects of interest.
The XA SOP Class does not encode some information to fully characterize the geometry of the conic projection acquisition, such as the position of the Positioner Isocenter on the FOV area. Indeed, the XA SOP Class assumes that the isocenter is projected in the middle of the FOV.
The Enhanced XA SOP Class encodes the position of the Isocenter on the detector, as well as specific FOV Attributes (origin, rotation, flip) per-frame or shared. It encodes some existing Attributes from DX to specify information of the Digital Detector and FOV. It also allows differentiating the image intensifier vs. the digital detector and then defines conditions on Attributes depending on image intensifier or digital detector.
This section provides detailed recommendations of the key Attributes to address this particular scenario.
The usage of this module is recommended to specify the type and details of the receptor.
Distance Receptor Plane to Detector Housing (0018,9426) is a positive value except in the case of an image intensifier where the receptor plane is a virtual plane located outside the detector housing, which depends on the magnification factor of the intensifier.
The Distance Receptor Plane to Detector Housing (0018,9426) may be used to calculate the pixel size of the plane in the patient when markers are placed on the detector housing.
When the X-Ray Receptor Type (0018,9420) equals "IMG_INTENSIFIER" this module specifies the type and characteristics of the image intensifier.
The Intensifier Size (0018,1162) is defined as the physical diameter of the maximum active area of the image intensifier. The active area is the region of the input phosphor screen that is projected on the output phosphor screen. The image intensifier device may be configured for several predefined active areas to allow different levels of magnification.
The active area is described by the Intensifier Active Shape (0018,9427) and the Intensifier Active Dimension(s) (0018,9428).
The field of view area is a region equal to or smaller than the active area, and is defined as the region that is effectively irradiated by the X-Ray beam when there is no collimation. The stored image is the image resulting from digitizing the field of view area.
There is no Attribute that relates the FOV origin to the intensifier. It is commonly assumed that the FOV area is centered in the intensifier.
The position of the projection of the isocenter on the active area is undefined. It is commonly understood that the X-Ray positioner is calibrated so that the isocenter is projected in the approximate center of the active area, and the field of view area is centered in the active area.
When the X-Ray Receptor Type (0018,9420) equals "DIGITAL_DETECTOR" this module specifies the type and characteristics of the image detector.
The size and pixel spacing of the digital image generated at the output of the digital detector are not necessarily equal to the size and element spacing of the detector matrix. The detector binning is defined as the ratio between the pixel spacing of the detector matrix and the pixel spacing of the digital image.
If the detector binning is higher than 1.0 several elements of the detector matrix contribute to the generation of one single digital pixel.
The digital image may be processed, cropped and resized in order to generate the stored image. The schema below shows these two steps of the modification of the pixel spacing between the detector physical elements and the stored image:
Table FFF.2.1-43. X-Ray Detector Module Recommendations
The usage of this macro is recommended to specify the characteristics of the field of view.
When the field of view characteristics change across the Multi-frame Image, this macro is encoded on a per-frame basis.
The field of view region is defined by a shape, origin and dimension. The region of irradiated pixels corresponds to the interior of the field of view region.
When the X-Ray Receptor Type (0018,9420) equals "IMG_INTENSIFIER", the intensifier TLHC is undefined. Therefore the field of view origin cannot be related to the physical area of the receptor. It is commonly understood that the field of view area corresponds to the intensifier active area, but there is no definition in the DICOM Standard that forces a manufacturer to do so. As a consequence, it is impossible to relate the position of the pixels of the stored area to the isocenter reference system.
Table FFF.2.1-44. X-Ray Field of View Macro Recommendations
The usage of this macro is recommended to specify the Imager Pixel Spacing.
When the field of view characteristics change across the Multi-frame Image, this macro is encoded on a per-frame basis.
In case of image intensifier, the Imager Pixel Spacing (0018,1164) may be non-uniform due to the pincushion distortion, and this Attribute corresponds to a manufacturer-defined value (e.g., average, or value at the center of the image).
This example illustrates the encoding of the dimensions of the intensifier device, the intensifier active area and the field of view in case of image intensifier.
In this example, the diameter of the maximum active area is 410 mm. The image acquisition is performed with an electron lens that focuses the photoelectron beam inside the intensifier so that an active area of 310 mm of diameter is projected on the output phosphor screen.
The X-Ray beam is projected on an area of the input phosphor screen of 300 mm of diameter, and the corresponding area on the output phosphor screen is digitized on a matrix of 1024 x1024 pixels. This results on a pixel spacing of the digitized matrix of 0.3413 mm.
The distance from the Receptor Plane to the Detector Housing in the direction from the intensifier to the X-Ray tube is 40 mm.
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-25.
The following examples show three different ways to create the stored image from the same detector matrix.
-
The blue dotted-line squares
represent the physical detector pixels; -
The blue square
represents the TLHC pixel of the physical detector area; -
The purple square
represents the physical detector pixel in whose center the Isocenter is projected; -
The dark green square
represents the TLHC pixel of the region of the physical detector that is exposed to X-Ray when there is no collimation inside the field of view; -
The light green square
represents the TLHC pixel of the stored image; -
The thick black straight line square
represents the stored image, which is assumed to be the field of view area. The small thin black straight line squares represent the pixels of the stored image; -
The blue dotted-line arrow
represents Field Of View Origin (0018,7030); -
The purple arrow
represents the position of the Isocenter Projection (0018,9430).
Note that the detector active dimension is not necessarily the FOV dimension.
In the first example, there is neither binning nor resizing between the detector matrix and the stored image.
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-26.
In the second example, there is a binning factor of 2 between the detector matrix and the digital image. There is no resizing between the digital image (binned) and the stored image.
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-27.
In the third example, in addition to the binning factor of 2 between the detector matrix and the digital image, there is a resizing of 0.5 (downsizing) between the digital image (binned) and the stored image.
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-28.
Note that the description of the field of view Attributes (dimension, origin) is the same in these three examples. The field of view definition is independent from the binning and resizing processes.
This section provides information on the encoding of the presence and type of contrast bolus administered during the X-Ray acquisition.
The user performs image acquisition with injection of contrast agent during the X-Ray acquisition. Some frames are acquired without contrast, some others with contrast.
The type of contrast agent can be radio-opaque (e.g., iodine) or radio-transparent (e.g., CO2).
The information of the type of contrast and its presence or absence in the frames can be used by post-processing applications to set up e.g., vessel detection or image quality algorithms automatically.
The Enhanced XA SOP Class encodes the characteristics of the contrast agent(s) used during the acquisition of the image, including the type of absorption (radio-opaque or radio-transparent).
The Enhanced XA SOP Class also allows encoding the presence of contrast in a particular frame or set of frames, by encoding the Contrast/Bolus Usage per-frame.
This section provides detailed recommendations of the key Attributes to address this particular scenario.
The usage of this module is recommended to specify the type and characteristics of the contrast agent administered.
The usage of this macro is recommended to specify the characteristics of the contrast per-frame.
Table FFF.2.1-48. Contrast/Bolus Usage Macro Recommendations
In this example, the user starts the X-Ray acquisition at 4 frames per second at 3:35pm. After one second the user starts the injection of 45 milliliters of contrast media Iodipamide (350 mg/ml Cholographin (Bracco) ) at a flow rate of 15 ml/sec during three seconds, in intra-arterial route. When the injection of contrast agent is finished, the user continues the X-Ray acquisition for two seconds until wash out of the contrast agent.
There could be two ways to determine the presence of contrast agent on the frames:
-
The injector is connected to the X-Ray acquisition system, the presence of contrast agent is determined based on the injector start/stop signals and a preconfigured delay to allow the contrast to reach the artery of interest, or.
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The X-Ray system processes the images in real time and detects the presence or absence of contrast agent on the images.
In this example, the image acquired contains 25 frames: From frames 5 to 17, the contrast is being injected. From frames 8 to 23, the contrast is visible on the pixel data.
The figure below shows the Attributes of this example in a graphical representation of the multi-frame acquisition.
The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-30.
This section provides information on the encoding of the parameters related to the X-Ray generation.
The user performs X-Ray acquisitions during the examination. Some of them are dynamic acquisitions where the positioner and/or the table have moved between frames of the Multi-frame Image, the acquisition parameters such as kVp, mA and pulse width may change per-frame to be adapted to the different anatomy characteristics.
Later quality assurance wants to assess the X-Ray generation techniques in order to understand possible degradation of image quality, or to estimate the level of irradiation at different skin areas and body parts examined.
The XA SOP Class encodes the Attributes kVp, mA and pulse duration as a unique value for the whole Multi-frame Image. For systems that can provide only average values of these Attributes, this SOP Class is more appropriate.
The Enhanced XA SOP Class encodes per-frame kVp, mA and pulse duration, thus the estimated dose per frame can be now correlated 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.
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
| C.8.19.3 |
Specifies average values for the X-Ray generation techniques. |
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.
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.
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.
If the system predefines the values of the kVp and mA to be constant during the acquisition, the usage of the X-Ray Frame Acquisition 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.
For more details, refer to the Section FFF.1.4