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.

[pic]

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 PS 3.3 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 PS 3.3 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 PS 3.3 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.

[pic]

Figure FFF.2.1-10Example 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 the following figure:

ENHANCED XA SOP INSTANCES

Study Instance UID (0020,000D) = UID “A”
Series Instance UID (0020,000E) = UID “B”
Modality (0008,0060) = XA
Synchronization Frame of Reference UID (0020,0200) = 1.2.840.10008.15.1.1
Synchronization Trigger (0018,106A) = SOURCE
Trigger Source or Type (0018,1061) = Imaging System ID
Acquisition Time Synchronized (0018,1800) = Y
Time Source (0018,1801) = Clock System ID
Time Distribution Protocol (0018,1802) = NTP
NTP Source Address (0018,1803) = aaa.bbb.ccc.ddd
SOP Instance UID (0008,0018) = UID “D1”, “D2” and “D3” resp.

GENERAL ECG SOP INSTANCE

Study Instance UID (0020,000D) = UID “E”
Series Instance UID (0020,000E) = UID “F”
Modality (0008,0060) = ECG
Synchronization Frame of Reference UID (0020,0200) = 1.2.840.10008.15.1.1
Synchronization Trigger (0018,106A) = EXTERNAL
Trigger Source or Type (0018,1061) = Imaging System ID
Synchronization Channel (0018,106C) = 1\2
Acquisition Time Synchronized (0018,1800) = Y
Time Source (0018,1801) = Clock System ID
Time Distribution Protocol (0018,1802) = NTP
NTP Source Address (0018,1803) = aaa.bbb.ccc.ddd
SOP Instance UID (0008,0018) = UID “H”

Waveform Sequence (5400,0100)
Item 1 Only one ECG Multiplex Group
>Multiplex Group Time Offset (0018,1068) = 0
>Waveform Originality (003A,0004) = ORIGINAL
>Number of Waveform Channels (003A,0005) = 2
>Number of Waveform Samples (003A,0010) = 1500
>Sampling Frequency (003A,001A) = 300
>Channel Definition Sequence (003A,0200)
Item 1
>Waveform Sample Interpretation (5400,1006) = SS

Figure FFF.2.1-11Attributes 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.

[pic]

Figure FFF.2.1-12Example 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 the following figure:

ENHANCED XA SOP INSTANCES

Study Instance UID (0020,000D) = UID “A”
Series Instance UID (0020,000E) = UID “B”
Modality (0008,0060) = XA
Synchronization Frame of Reference UID (0020,0200) = 1.2.840.10008.15.1.1
Synchronization Trigger (0018,106A) = EXTERNAL
Trigger Source or Type (0018,1061) = ECG Equipment ID
Acquisition Time Synchronized (0018,1800) = Y
Time Source (0018,1801) = Clock System ID
Time Distribution Protocol (0018,1802) = NTP
NTP Source Address (0018,1803) = aaa.bbb.ccc.ddd
SOP Instance UID (0008,0018) = UID “D”

GENERAL ECG SOP INSTANCE

Study Instance UID (0020,000D) = UID “E”
Series Instance UID (0020,000E) = UID “F”
Modality (0008,0060) = ECG
Synchronization Frame of Reference UID (0020,0200) = 1.2.840.10008.15.1.1
Synchronization Trigger (0018,106A) = SOURCE
Trigger Source or Type (0018,1061) = ECG Equipment ID
Synchronization Channel (0018,106C) = 1\2
Acquisition Time Synchronized (0018,1800) = Y
Time Source (0018,1801) = Clock System ID
Time Distribution Protocol (0018,1802) = NTP
NTP Source Address (0018,1803) = aaa.bbb.ccc.ddd
SOP Instance UID (0008,0018) = UID “H”

Waveform Sequence (5400,0100)
Item 1 Only one ECG Multiplex Group
>Multiplex Group Time Offset (0018,1068) = 10
>Waveform Originality (003A,0004) = ORIGINAL
>Number of Waveform Channels (003A,0005) = 2
>Number of Waveform Samples (003A,0010) = 1500
>Sampling Frequency (003A,001A) = 300
>Channel Definition Sequence (003A,0200)
Item 1
>Waveform Sample Interpretation (5400,1006) = SS

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