DICOM PS3.17 2019b - Explanatory Information

FFF.2 Application Cases

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.

FFF.2.1 Acquisition

FFF.2.1.1 ECG Recording at Acquisition Modality

This application case is related to the results of an X-Ray acquisition and parallel ECG data recording on the same equipment.

FFF.2.1.1.1 User Scenario

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.

Scenario of ECG Recording at Acquisition Modality

Figure FFF.2.1-1. Scenario of ECG Recording at Acquisition Modality


FFF.2.1.1.2 Encoding Outline

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.

FFF.2.1.1.3 Encoding Details

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

FFF.2.1.1.3.1 Enhanced XA Image

Table FFF.2.1-1. Enhanced X-Ray Angiographic Image IOD Modules

IE

Module

PS3.3 Reference

Usage

Series

General Series

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.

Frame of Reference

Synchronization

C.7.4.2

Specifies that the image acquisition is synchronized. Will have the same content as the General ECG SOP Instance.

Equipment

General Equipment

C.7.5.1

Same as in the General ECG SOP Instance.

Image

Cardiac Synchronization

C.7.6.18.1

Contains information of the type of relationship between the ECG waveform and the image.

Enhanced XA/XRF 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

Functional Group Macro

PS3.3 Reference

Usage

Frame Content

C.7.6.16.2.2

Provides timing information to correlate each frame to the recorded ECG samples.

Cardiac Synchronization

C.7.6.16.2.7

Provides time relationships between the angiographic frames and the cardiac cycle.


FFF.2.1.1.3.1.1 Synchronization Module Recommendations

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

Attribute Name

Tag

Comment

Synchronization Frame of Reference UID

(0020,0200)

Same UID as in the related General ECG SOP Instance.

Synchronization Trigger

(0018,106A)

In this scenario with no external trigger signal, the value "NO TRIGGER" is used.

Acquisition Time Synchronized

(0018,1800)

The value "Y" is used in this scenario.


FFF.2.1.1.3.1.2 General Equipment 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.

FFF.2.1.1.3.1.3 Cardiac Synchronization Module Recommendations

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.

Table FFF.2.1-4. Cardiac Synchronization Module Recommendations

Attribute Name

Tag

Comment

Cardiac Synchronization Technique

(0018,9037)

The value "REAL TIME" is used in this scenario.

Cardiac Signal Source

(0018,9085)

In this scenario, the value "ECG" is used to indicate that the cardiac waveform is an electrocardiogram.


FFF.2.1.1.3.1.4 Enhanced XA/XRF Image Module Recommendations

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

Attribute Name

Tag

Comment

Referenced Instance Sequence

(0008,114A)

Reference to "General ECG SOP Instance" acquired in conjunction with this image. Contains a single item.

>Referenced SOP Class UID

(0008,1150)

"1.2.840.10008.5.1.4.1.1.9.1.2" i.e., reference to an General ECG SOP Instance

>Referenced SOP Instance UID

(0008,1155)

Instance UID of referenced waveform

>Purpose of Reference Code Sequence

(0040,A170)

CID 7004 “Waveform Purposes of Reference” is used; identify clear reason for the Reference.


FFF.2.1.1.3.1.5 Cardiac Synchronization Macro Recommendations

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.

FFF.2.1.1.3.1.6 Frame Content Macro Recommendations

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.

Table FFF.2.1-6. Frame Content Macro Recommendations

Attribute Name

Tag

Comment

Frame Content Sequence

(0020,9111)

>Frame Reference DateTime

(0018,9151)

Exact Time taken from the internal clock.

>Frame Acquisition DateTime

(0018,9074)

Exact Time taken from the internal clock.

>Cardiac Cycle Position

(0018,9236)

Optional, if ECG analysis is available.


FFF.2.1.1.3.2 General ECG Object

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

IE

Module

PS3.3 Reference

Usage

Series

General Series

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.

Frame of Reference

Synchronization

C.7.4.2

Specifies that the waveform acquisition is synchronized. Will have the same content as the image.

Equipment

General Equipment

C.7.5.1

Same as in the image.

Waveform

Waveform Identification

C.10.8

Contains references to the related image object.

Waveform

C.10.9

Contains one multiplex group with the same sampling rate.


FFF.2.1.1.3.2.1 General Series Module Recommendations

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.

Table FFF.2.1-8. General Series Module Recommendations

Attribute Name

Tag

Comment

Modality

(0008,0060)

"ECG"

Series Instance UID

(0020,000E)

Different from the one of the image object.

Series Date

(0008,0021)

Identical to the contents of related image object

Series Time

(0008,0031)

Identical to the contents of related image object.

Other Attributes of General Series Module

Match contents of related image object, if set there.


FFF.2.1.1.3.2.2 Synchronization Module Recommendations

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

Attribute Name

Tag

Comment

Synchronization Frame of Reference UID

(0020,0200)

Same UID as in the related image object.

Synchronization Trigger

(0018,106A)

The value "NO TRIGGER" is used in this scenario with no external trigger signal.

Acquisition Time Synchronized

(0018,1800)

The value "Y" is used to allow synchronized navigation.


FFF.2.1.1.3.2.3 General Equipment 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.

FFF.2.1.1.3.2.4 Waveform Identification Recommendations

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

Attribute Name

Tag

Comment

Acquisition DateTime

(0008,002A)

Exact start of the waveform acquisition taken from common (or synchronized) clock.

Note

In case the ECG acquisition started before the image acquisition itself, the given DateTime value is not the same as for the image.

Referenced Instance Sequence

(0008,114A)

Only one item used in this application case.

>Referenced SOP Class UID

(0008,1150)

"1.2.840.10008.5.1.4.1.1.12.1.1" i.e., Enhanced XA

>Referenced SOP Instance UID

(0008,1155)

Instance UID of Enhanced XA Image Object to which this parallel ECG recording is related.

>Purpose of Reference Code Sequence

(0040,A170)

The referenced image is related to this ECG.


FFF.2.1.1.3.2.5 Waveform 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

Attribute Name

Tag

Comment

Waveform Sequence

(5400,0100)

Only one item is used in this application case, as all the ECG signals have the same sampling rate.

> Multiplex Group Time Offset

(0018,1068)

If needed, specify the Group Offset from the Acquisition DateTime.

> Waveform Originality

(003A,0004)

The value "ORIGINAL" is used in this scenario.


FFF.2.1.1.4 Examples

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.

Example of ECG Recording at Acquisition Modality

Figure FFF.2.1-2. Example of ECG Recording at Acquisition Modality


FFF.2.1.1.4.1 Enhanced XA Image Without Cardiac Synchronization

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.

Enhanced XA SOP Instance

Attributes of ECG Recording at Acquisition Modality
Attributes of ECG Recording at Acquisition Modality

Figure FFF.2.1-3. Attributes of ECG Recording at Acquisition Modality


FFF.2.1.1.4.2 Enhanced XA Image With Cardiac Synchronization

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.

Example of ECG information in the Enhanced XA image

Figure FFF.2.1-4. Example of ECG information in the Enhanced XA image


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.

Enhanced XA SOP Instance

Attributes of Cardiac Synchronization in ECG Recording at Acquisition Modality

Figure FFF.2.1-5. Attributes of Cardiac Synchronization in ECG Recording at Acquisition Modality


FFF.2.1.2 Multi-modality Waveform Synchronization

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).

FFF.2.1.2.1 Both Modalities Synchronized Via NTP
FFF.2.1.2.1.1 User Scenario

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.

Scenario of Multi-modality Waveform Synchronization

Figure FFF.2.1-6. Scenario of Multi-modality Waveform Synchronization


FFF.2.1.2.1.2 Encoding Outline

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.

FFF.2.1.2.1.3 Encoding Details

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

FFF.2.1.2.1.3.1 Enhanced XA Image

Table FFF.2.1-12. Enhanced X-Ray Angiographic Image IOD Modules

IE

Module

PS3.3 Reference

Usage

Frame of Reference

Synchronization

C.7.4.2

Specifies that the image acquisition is time synchronized with the ECG acquisition. Will have the same content as the General ECG SOP Instance.

Image

Enhanced XA/XRF Image

C.8.19.2

Specifies the date and time of the image acquisition.


Table FFF.2.1-13. Enhanced XA Image Functional Group Macros

Functional Group Macro

PS3.3 Reference

Usage

Frame Content

C.7.6.16.2.2

Provides timing information to correlate each frame to any externally recorded waveform.


FFF.2.1.2.1.3.1.1 Synchronization Module Recommendations

This Module is used to document the synchronization of the two modalities.

Table FFF.2.1-14. Synchronization Module Recommendations

Attribute Name

Tag

Comment

Synchronization Frame of Reference UID

(0020,0200)

The UTC Synchronization UID "1.2.840.10008.15.1.1" is used in this case.

Synchronization Trigger

(0018,106A)

The value "NO TRIGGER" is used for the case of time synchronization via NTP.

Acquisition Time Synchronized

(0018,1800)

The value "Y" is used in this scenario.

Time Source

(0018,1801)

The same value as in the related General ECG SOP Instance is used in this scenario.

Time Distribution Protocol

(0018,1802)

The value "NTP" is used in this scenario.

NTP Source Address

(0018,1803)

The same value as in the related General ECG SOP Instance is used in this scenario.


FFF.2.1.2.1.3.1.2 Enhanced XA/XRF Image 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.

FFF.2.1.2.1.3.1.3 Frame Content Macro Recommendations

In this scenario the timing information is important to correlate each frame to any externally recorded waveform.

Table FFF.2.1-15. Frame Content Macro Recommendations

Attribute Name

Tag

Comment

Frame Content Sequence

(0020,9111)

>Frame Reference DateTime

(0018,9151)

Exact date and time taken from the synchronized clock.

>Frame Acquisition DateTime

(0018,9074)

Exact date and time taken from the synchronized clock.


FFF.2.1.2.1.3.2 Waveform Object

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

IE

Module

PS3.3 Reference

Usage

Frame of Reference

Synchronization

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.

Waveform

Waveform Identification

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).

Table FFF.2.1-18. Waveform Identification Module Recommendations

Attribute Name

Tag

Comment

Acquisition DateTime

(0008,002A)

Exact start of the waveform acquisition: taken from synchronized clock.


FFF.2.1.2.1.4 Example

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.

Example of Multi-modality Waveform Synchronization

Figure FFF.2.1-7. Example of Multi-modality Waveform Synchronization


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.

Attributes of Multi-modality Waveform NTP Synchronization
Attributes of Multi-modality Waveform NTP Synchronization

Figure FFF.2.1-8. Attributes of Multi-modality Waveform NTP Synchronization


FFF.2.1.2.2 One Modality Sends Trigger to The Other Modality
FFF.2.1.2.2.1 User Scenario

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.

Scenario of Multi-modality Waveform Synchronization

Figure FFF.2.1-9. Scenario of Multi-modality Waveform Synchronization


FFF.2.1.2.2.2 Encoding Outline

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.

FFF.2.1.2.2.3 Encoding Details

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

FFF.2.1.2.2.3.1 Enhanced XA Image

Table FFF.2.1-19. Enhanced X-Ray Angiographic Image IOD Modules

IE

Module

PS3.3 Reference

Usage

Frame of Reference

Synchronization

C.7.4.2

Specifies that the image acquisition triggers (or is triggered by) the ECG acquisition, and that they are time synchronized.

Image

Enhanced XA/XRF Image

C.8.19.2

Specifies the date and time of the image acquisition.

.


Table FFF.2.1-20. Enhanced XA Image Functional Group Macros

Functional Group Macro

PS3.3 Reference

Usage

Frame Content

C.7.6.16.2.2

Provides timing information of each frame.


FFF.2.1.2.2.3.1.1 Synchronization Module Recommendations

The usage of this Module is recommended to document the triggering role of the image modality.

Table FFF.2.1-21. Synchronization Module Recommendations

Attribute Name

Tag

Comment

Synchronization Frame of Reference UID

(0020,0200)

The UTC Synchronization UID "1.2.840.10008.15.1.1" is used in this case.

Synchronization Trigger

(0018,106A)

The value "SOURCE" is used when the image modality sends a trigger signal to the waveform modality.

The value "EXTERNAL" is used when the image modality receives a trigger signal from the waveform modality.

Trigger Source or Type

(0018,1061)

If Synchronization Trigger (0018,106A) equals SOURCE, then ID of image equipment.

If Synchronization Trigger (0018,106A) equals EXTERNAL, then ID of waveform equipment if it is known.

Acquisition Time Synchronized

(0018,1800)

The value "Y" is used in this scenario.

Time Source

(0018,1801)

The same value as in the related General ECG SOP Instance is used in this scenario.

Time Distribution Protocol

(0018,1802)

The value "NTP" is used in this scenario.

NTP Source Address

(0018,1803)

The same value as in the related General ECG SOP Instance is used in this scenario.


FFF.2.1.2.2.3.1.2 Enhanced XA/XRF Image Module Recommendations

This module includes the acquisition date and time of the image.

Table FFF.2.1-22. Enhanced XA/XRF Image Module Recommendations

Attribute

Tag

Comment

Acquisition DateTime

(0008,002A)

Exact date and time taken from the synchronized clock.


FFF.2.1.2.2.3.1.3 Frame Content Macro Recommendations

In this scenario the timing information does not allow relating each frame to any externally recorded waveform.

Table FFF.2.1-23. Frame Content Macro Recommendations

Attribute Name

Tag

Comment

Frame Content Sequence

(0020,9111)

>Frame Reference DateTime

(0018,9151)

Exact date and time taken from the synchronized clock.

>Frame Acquisition DateTime

(0018,9074)

Exact date and time taken from the synchronized clock.


FFF.2.1.2.2.3.2 Waveform Object

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

IE

Module

PS3.3 Reference

Usage

Frame of Reference

Synchronization

C.7.4.2

Specifies that the ECG acquisition triggers (or is triggered by) the image acquisition, and that they are time synchronized.

Waveform

Waveform Identification

C.10.8

Specifies the date and time of the ECG acquisition.

Waveform

C.10.9

Specifies the time relationship between the trigger signal and the ECG samples.


FFF.2.1.2.2.3.2.2 Synchronization Module Recommendations

The usage of this Module is recommended to document the triggering role of the waveform modality.

Table FFF.2.1-25. Synchronization Module Recommendations

Attribute Name

Tag

Comment

Synchronization Frame of Reference UID

(0020,0200)

The UTC Synchronization UID "1.2.840.10008.15.1.1" is used in this case.

Synchronization Trigger

(0018,106A)

The value "EXTERNAL" is used when the waveform modality receives a trigger signal from the image modality.

The value "SOURCE" is used when the waveform modality sends a trigger signal to the image modality.

Trigger Source or Type

(0018,1061)

If Synchronization Trigger (0018,106A) equals SOURCE, then ID of Waveform equipment.

If Synchronization Trigger (0018,106A) equals EXTERNAL, then ID of image equipment if it is known.

Synchronization Channel

(0018,106C)

Number or ID of Synchronization channel recorded in this waveform.

Acquisition Time Synchronized

(0018,1800)

The value "Y" is used in this scenario.

Time Source

(0018,1801)

The same value as in the related image SOP Instance is used in this scenario.

Time Distribution Protocol

(0018,1802)

The value "NTP" is used in this scenario.

NTP Source Address

(0018,1803)

The same value as in the related image SOP Instance is used in this scenario.


FFF.2.1.2.2.3.2.3 Waveform Identification 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.

Table FFF.2.1-26. Waveform Identification Module Recommendations

Attribute Name

Tag

Comment

Acquisition DateTime

(0008,002A)

Exact date and time taken from the internal clock of the Waveform modality.

It may be different from the Acquisition DateTime of the Enhanced XA SOP instance.


FFF.2.1.2.2.3.2.4 Waveform Module Recommendations

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

Attribute Name

Tag

Comment

Waveform Sequence

(5400,0100)

Only one item is used in this application case, as all the ECG signals have the same sampling rate.

>Multiplex Group Time Offset

(0018,1068)

If needed, specify the Group Offset from the Acquisition DateTime.

>Waveform Originality

(003A,0004)

The value "ORIGINAL" is used in this scenario.

>Trigger Time Offset

(0018,1069)

In case the waveform recording started with a synchronization trigger from the image modality, this value allows specifying the time relationship between the trigger and the ECG samples.

>Trigger Sample Position

(0018,106E)

In case the waveform recording started with a synchronization trigger from the image modality, this value allows specifying the waveform sample corresponding to the trigger sent from the image modality.


FFF.2.1.2.2.4 Examples
FFF.2.1.2.2.4.1 Image modality sends trigger to the waveform modality

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.

Example of Image Modality as Source of Trigger

Figure FFF.2.1-10. Example of Image Modality as Source of Trigger


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.

Attributes when Image Modality is the Source of Trigger
Attributes when Image Modality is the Source of Trigger

Figure FFF.2.1-11. Attributes when Image Modality is the Source of Trigger


FFF.2.1.2.2.4.2 Waveform modality sends trigger to the image modality

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.

Example of Waveform Modality as Source of Trigger

Figure FFF.2.1-12. Example of Waveform Modality as Source of Trigger


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.

Attributes when Waveform Modality is the Source of Trigger
Attributes when Waveform Modality is the Source of Trigger

Figure FFF.2.1-13. Attributes when Waveform Modality is the Source of Trigger


FFF.2.1.3 Mechanical Movement

FFF.2.1.3.1 Rotational Acquisition

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.

FFF.2.1.3.1.1 User Scenario

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:

  • One rotation for non-subtracted angiography;

  • Two rotations in the same or in opposite angular directions, for subtracted angiography;

  • Several rotations at different time intervals for cardiac triggered acquisitions.

FFF.2.1.3.1.2 Encoding Outline

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.

FFF.2.1.3.1.3 Encoding Details

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

Table FFF.2.1-28. Enhanced X-Ray Angiographic Image IOD Modules

IE

Module

PS3.3 Reference

Usage

Image

XA/XRF Acquisition

C.8.19.3

Specifies the type of positioner.


Table FFF.2.1-29. Enhanced XA Image Functional Group Macros

Functional Group Macro

PS3.3 Reference

Usage

X-Ray Positioner

C.8.19.6.10

Specifies the anatomical angles per-frame.

X-Ray Isocenter Reference System

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…).


FFF.2.1.3.1.3.1 XA/XRF Acquisition Module Recommendations

The usage of this module is recommended to define the type of positioner.

Table FFF.2.1-30. XA/XRF Acquisition Module Example

Attribute Name

Tag

Comment

Positioner Type

(0018,1508)

The value CARM is used in this scenario.

C-arm Positioner Tabletop Relationship

(0018,9474)

Both values YES and NO are applicable to this scenario.

Note

On mobile systems where this Attribute equals NO, it is possible to do rotation and 3D reconstruction. In such case, the table is assumed to be static during the acquisition.


FFF.2.1.3.1.3.2 X-Ray Positioner Macro Recommendations

This macro is used in the per-frame context in this scenario.

Table FFF.2.1-31. X-Ray Positioner Macro Example

Attribute Name

Tag

Comment

Positioner Position Sequence

(0018,9405)

>Positioner Primary Angle

(0018,1510)

Angle with respect to the patient coordinate system.

>Positioner Secondary Angle

(0018,1511)

Angle with respect to the patient coordinate system.


FFF.2.1.3.1.3.3 X-Ray Isocenter Reference System Macro Recommendations

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

Attribute Name

Tag

Comment

Isocenter Reference System Sequence

(0018,9462)

>Positioner Isocenter Primary Angle

(0018,9463)

Angle with respect to the Isocenter coordinate system, independent of table angulations and how the patient is positioned on the table.

>Positioner Isocenter Secondary Angle

(0018,9464)

Angle with respect to the Isocenter coordinate system, independent of table angulations and how the patient is positioned on the table.

>Positioner Isocenter Detector Rotation Angle

(0018,9465)

Angle with respect to the Isocenter coordinate system, independent of table angulations and how the patient is positioned on the table.


FFF.2.1.3.1.4 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.

Detector Trajectory during Rotational Acquisition

Figure FFF.2.1-14. Detector Trajectory during Rotational Acquisition


The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-15.

Attributes of X-Ray Positioning Per-frame on Rotational Acquisition

Figure FFF.2.1-15. Attributes of X-Ray Positioning Per-frame on Rotational Acquisition


FFF.2.1.3.2 Peripheral/stepping Acquisition

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.

FFF.2.1.3.2.1 User Scenario

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:

  • One stepping for non-subtracted angiography;

  • Two stepping acquisitions, one for each leg, for non-subtracted angiography, stored in two different Multi-frame Images;

  • Two or more stepping acquisitions for subtracted angiography, in the same or in opposite directions.

FFF.2.1.3.2.2 Encoding Outline

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.

FFF.2.1.3.2.3 Encoding Details

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

IE

Module

PS3.3 Reference

Usage

Image

XA/XRF Acquisition

C.8.19.3

Specifies the relationship between the table and the positioner.


Table FFF.2.1-34. Enhanced XA Image Functional Group Macros

Functional Group Macro

PS3.3 Reference

Usage

X-Ray Table Position

C.8.19.6.11

Specifies the table position per-frame in three dimensions.

X-Ray Isocenter Reference System

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…).


FFF.2.1.3.2.3.1 XA/XRF Acquisition Module Recommendations

The usage of this module is recommended to specify the relationship between the table and the positioner.

Table FFF.2.1-35. XA/XRF Acquisition Module Example

Attribute Name

Tag

Comment

C-arm Positioner Tabletop Relationship

(0018,9474)

Both values YES and NO are applicable to this scenario.

Note

On mobile systems where this Attribute equals NO, it is possible to do table stepping. In such case, the system is not able to determine the absolute table position relative to the Isocenter, which is necessary for 2D-2D registration.


FFF.2.1.3.2.3.2 X-Ray Table Position Macro Recommendations

This macro is used in the per-frame context in this scenario.

Table FFF.2.1-36. X-Ray Table Position Macro Example

Attribute Name

Tag

Comment

Table Position Sequence

(0018,9406)

>Table Top Vertical Position

(300A,0128)

The same value for all frames.

>Table Top Longitudinal Position

(300A,0129)

The same value for all frames.

>Table Top Lateral Position

(300A,012A)

Different values per frame, corresponding to the "stepping" intervals in the table plane.

>Table Horizontal Rotation Angle

(0018,9469)

The same value for all frames.

>Table Head Tilt Angle

(0018,9470)

The same value for all frames.

>Table Cradle Tilt Angle

(0018,9471)

The same value for all frames.


FFF.2.1.3.2.3.3 X-Ray Isocenter Reference System Macro Recommendations

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

Attribute Name

Tag

Comment

Isocenter Reference System Sequence

(0018,9462)

>Table X Position to Isocenter

(0018,9466)

X-position of a fixed point in the table top, it changes per-frame if table horizontal rotation is not zero

>Table Y Position to Isocenter

(0018,9467)

Vertical position of a fixed point in the table top, it changes per-frame if table head tilt is not zero

>Table Z Position to Isocenter

(0018,9468)

Z-position of a fixed point in the table top, it changes per-frame

>Table Horizontal Rotation Angle

(0018,9469)

The same value for all frames.

>Table Head Tilt Angle

(0018,9470)

The same value for all frames.

>Table Cradle Tilt Angle

(0018,9471)

The same value for all frames.


FFF.2.1.3.2.4 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.

Table Trajectory during Table Stepping

Figure FFF.2.1-16. Table Trajectory during Table Stepping


Example of table positions per-frame during table stepping

Figure FFF.2.1-17. Example of table positions per-frame during table stepping


The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-18.

Attributes of the X-Ray Table Per Frame on Table Stepping

Figure FFF.2.1-18. Attributes of the X-Ray Table Per Frame on Table Stepping


FFF.2.1.4 Changes in X-Ray Controls

FFF.2.1.4.1 Exposure Regulation Control

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.

FFF.2.1.4.1.1 User Scenario

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.

FFF.2.1.4.1.2 Encoding Outline

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.

FFF.2.1.4.1.3 Encoding Details

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

Functional Group Macro

PS3.3 Reference

Usage

X-Ray Exposure Control Sensing Regions

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.


FFF.2.1.4.1.3.1 X-Ray Exposure Control Sensing Regions Macro Recommendations

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.

Table FFF.2.1-39. X-Ray Exposure Control Sensing Regions Macro Recommendations

Attribute Name

Tag

Comment

Exposure Control Sensing Regions Sequence

(0018,9434)

As many items as number of regions.


FFF.2.1.4.1.4 Example

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).

Example of X-Ray Exposure Control Sensing Regions inside the Pixel Data matrix

Figure FFF.2.1-19. Example of X-Ray Exposure Control Sensing Regions inside the Pixel Data matrix


The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-20.

Attributes of the First Example of the X-Ray Exposure Control Sensing Regions

Figure FFF.2.1-20. Attributes of the First Example of the X-Ray Exposure Control Sensing Regions


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.

Example of X-Ray Exposure Control Sensing Regions partially outside the Pixel Data 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.

Attributes of the Second Example of the X-Ray Exposure Control Sensing Regions

Figure FFF.2.1-22. Attributes of the Second Example of the X-Ray Exposure Control Sensing Regions


FFF.2.1.5 Image Detector and Field of View

This section provides information on the encoding of the image detector parameters and field of view applied during the X-Ray acquisition.

FFF.2.1.5.1 User Scenario

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.

FFF.2.1.5.2 Encoding Outline

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.

FFF.2.1.5.3 Encoding Details

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

Table FFF.2.1-40. Enhanced X-Ray Angiographic Image IOD Modules

IE

Module

PS3.3 Reference

Usage

Image

XA/XRF Acquisition

C.8.19.3

Specifies the type of detector.

X-Ray Image Intensifier

C.8.19.4

Conditional to type of detector. Applicable in case of IMG_INTENSIFIER.

X-Ray Detector

C.8.19.5

Conditional to type of detector. Applicable in case of DIGITAL_DETECTOR.


Table FFF.2.1-41. Enhanced XA Image Functional Group Macros

Functional Group Macro

PS3.3 Reference

Usage

X-Ray Field of View

C.8.19.6.2

Specifies the field of view.

XA/XRF Frame Pixel Data Properties

C.8.19.6.4

Specifies the Imager Pixel Spacing.


FFF.2.1.5.3.1 XA/XRF Acquisition Module Recommendations

The usage of this module is recommended to specify the type and details of the receptor.

Table FFF.2.1-42. XA/XRF Acquisition Module Recommendations

Attribute Name

Tag

Comment

X-Ray Receptor Type

(0018,9420)

Two values are applicable to this scenario:

IMG_INTENSIFIER

or

DIGITAL_DETECTOR

Distance Receptor Plane to Detector Housing

(0018,9426)

Applicable to this scenario, regardless the type of 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.

FFF.2.1.5.3.2 X-Ray Image Intensifier Module Recommendations

When the X-Ray Receptor Type (0018,9420) equals "IMG_INTENSIFIER" this module specifies the type and characteristics of the image intensifier.

Schema of the Image Intensifier

Figure FFF.2.1-23. Schema 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.

FFF.2.1.5.3.3 X-Ray Detector Module Recommendations

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:

Generation of the Stored Image from the Detector Matrix

Figure FFF.2.1-24. Generation of the Stored Image from the Detector Matrix


Table FFF.2.1-43. X-Ray Detector Module Recommendations

Attribute Name

Tag

Comment

Detector Binning

(0018,701A)

The ratio between the pixel spacing of the detector matrix and the pixel spacing of the digital image. It does not describe any further post-processing to resize the pixels to generate the stored image.

Detector Element Spacing

(0018,7022)

Pixel spacing of the detector matrix.

Position of Isocenter Projection

(0018,9430)

Relates the position of the detector elements to the isocenter reference system. It is independent from the detector binning and from the field of view origin.

This Attribute is defined if the Isocenter Reference System Sequence (0018,9462) is present.


FFF.2.1.5.3.4 X-Ray Field of View Macro 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

Attribute Name

Tag

Comment

Field of View Sequence

(0018,9432)

>Field of View Shape

(0018,1147)

Applicable in this scenario.

>Field of View Dimension(s) in Float

(0018,9461)

Applicable in this scenario.

>Field of View Origin

(0018,7030)

Applicable only in the case of digital detector.

>Field of View Rotation

(0018,7032)

Applicable regardless the type of receptor.

>Field of View Horizontal Flip

(0018,7034)

Applicable regardless the type of receptor.

>Field of View Description

(0018,9433)

Free text defining the type of field of view as displayed by the manufacturer on the acquisition system. For display purposes.


FFF.2.1.5.3.5 XA/XRF Frame Pixel Data Properties 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.

Table FFF.2.1-45. XA/XRF Frame Pixel Data Properties Macro Recommendations

Attribute Name

Tag

Comment

Frame Pixel Data Properties Sequence

(0028,9443)

>Imager Pixel Spacing

(0018,1164)

Applicable regardless the type of receptor.


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).

FFF.2.1.5.4 Examples
FFF.2.1.5.4.1 Field of View On Image Intensifier

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.

Attributes of the Example of Field of View on Image Intensifier

Figure FFF.2.1-25. Attributes of the Example of Field of View on Image Intensifier


FFF.2.1.5.4.2 Field of View On Digital Detector

The following examples show three different ways to create the stored image from the same detector matrix.

In the figures below:

  • 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 all the examples,

  • The physical detector area is a matrix of 10x10 square detector elements, the TLHC element being the element (1,1);

  • The detector elements irradiated during this acquisition (defining the field of view) are in a matrix of 8x8 whose TLHC element is the element (3,3) of the physical detector area.

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.

Attributes of the First Example of Field of View on Digital Detector
Attributes of the First Example of Field of View on Digital Detector

Figure FFF.2.1-26. Attributes of the First Example of Field of View on Digital Detector


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.

Attributes of the Second Example of Field of View on Digital Detector
Attributes of the Second Example of Field of View on Digital Detector

Figure FFF.2.1-27. Attributes of the Second Example of Field of View on Digital Detector


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.

Attributes of the Third Example of Field of View on Digital Detector
Attributes of the Third Example of Field of View on Digital Detector

Figure FFF.2.1-28. Attributes of the Third Example of Field of View on Digital Detector


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.

FFF.2.1.6 Acquisitions With Contrast

This section provides information on the encoding of the presence and type of contrast bolus administered during the X-Ray acquisition.

FFF.2.1.6.1 User Scenario

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.

FFF.2.1.6.2 Encoding Outline

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.

FFF.2.1.6.3 Encoding Details

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

Table FFF.2.1-46. Enhanced X-Ray Angiographic Image IOD Modules

IE

Module

PS3.3 Reference

Usage

Image

Enhanced Contrast/Bolus

C.7.6.4b

Specifies the characteristics of the contrast agent(s) administered.


Table FFF.2.1-47. Enhanced XA Image Functional Group Macros

Functional Group Macro

PS3.3 Reference

Usage

Contrast/Bolus Usage

C.7.6.16.2.12

Specifies the presence of contrast in the frame(s).


FFF.2.1.6.3.1 Enhanced Contrast/bolus Module Recommendations

The usage of this module is recommended to specify the type and characteristics of the contrast agent administered.

FFF.2.1.6.3.2 Contrast/bolus Usage Macro Recommendations

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

Attribute Name

Tag

Comment

Contrast/Bolus Usage Sequence

(0018,9341)

One item per contrast agent used in this frame.

>Contrast/Bolus Agent Number

(0018,9337)

Contains the internal number of the agent administered as specified in the Enhanced Contrast/Bolus Module.

>Contrast/Bolus Agent Administered

(0018,9342)

The value "YES" indicates that the contrast may be visible on the frame, but not necessarily if the frame is acquired before the contrast reaches the imaged region.

>Contrast/Bolus Agent Detected

(0018,9343)

The value "YES" is used if the contrast is visible on that particular frame.

Note that it is not expected to be YES if Contrast/Bolus Agent Administered (0018,9342) equals NO.


FFF.2.1.6.4 Example

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.

  • 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.

Example of contrast agent injection

Figure FFF.2.1-29. Example of contrast agent injection


The encoded values of the key Attributes of this example are shown in Figure FFF.2.1-30.

Attributes of Contrast Agent Injection

Figure FFF.2.1-30. Attributes of Contrast Agent Injection


FFF.2.1.7 Acquisition Parameters For X-Ray Generation (kVp, mA, …)

This section provides information on the encoding of the parameters related to the X-Ray generation.

FFF.2.1.7.1 User Scenario

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.

FFF.2.1.7.2 Encoding Outline

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.

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

IE

Module

PS3.3 Reference

Usage

Image

XA/XRF Acquisition

C.8.19.3

Specifies average values for the X-Ray generation techniques.


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

Functional Group Macro

PS3.3 Reference

Usage

Frame Content

C.7.6.16.2.2

Specifies the frame duration.

X-Ray Frame Acquisition

C.8.19.6.8

Specifies the kVp and mA per frame.


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

Attribute Name

Tag

Comment

KVP

(0018,0060)

Recommended in this scenario.

Radiation Setting

(0018,1155)

The values "SC" and "GR" give a rough indication of the level of the dose such as "low" or "high", nevertheless they are used more for quality assurance and/or display purposes, not for estimation of radiation values.

X-Ray Tube Current in mA

(0018,9330)

Recommended in this scenario.

Exposure Time in ms

(0018,9328)

Recommended in this scenario.

Exposure in mAs

(0018,9332)

Recommended in this scenario.

Average Pulse Width

(0018,1154)

Recommended in this scenario.

Radiation Mode

(0018,115A)

The value of this Attribute is used more for quality assurance and/or display purposes, not for estimation of radiation values.


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.

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.

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.

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

Attribute Name

Tag

Comment

Frame Acquisition Sequence

(0018,9417)

Recommended in this scenario if both values kVp and mA are known for each frame.


FFF.2.1.7.4 Example

For more details, refer to the Section FFF.1.4

DICOM PS3.17 2019b - Explanatory Information