Nominal Cardiac Trigger Time Prior To R-Peak Attribute
| Tag | (0020,9154) |
|---|---|
| Type | Optional (3) |
| Keyword | NominalCardiacTriggerTimePriorToRPeak |
| Value Multiplicity | 1 |
| Value Representation | Single (FL) |
The nominal time in ms from the time of the next R-peak to the value of Frame Reference DateTime (0018,9151) expressed as a negative value. See Section C.7.6.16.2.7.1 for further explanation.
Note
Part of the Cardiac Synchronization Functional Group Macro with usage: C
Required if Cardiac Synchronization Technique (0018,9037) equals other than NONE and if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Section C.7.6.16.2.7.1
C.7.6.16.2.7.1 Relationship of Cardiac Timing Attributes
The Nominal Cardiac Trigger Delay Time (0020,9153) is the nominal trigger delay time in ms from the previous R-peak to the value of Frame Reference DateTime (0018,9151). When frames are acquired with prospective gating, that is, the data acquisition actually begins in response to a timed delay from the R-peak, it may be that Actual Cardiac Trigger Delay Time (0020,9252) and the Nominal Cardiac Trigger Delay Time (0020,9153) have the same value.
However, when frames are the result of retrospective gating, that is, the data is continuously acquired and then later compared with a simultaneously acquired ECG waveform and fitted into time slots corresponding to nominal phases of the cardiac cycle, then Nominal Cardiac Trigger Delay Time (0020,9153) and the Actual Cardiac Trigger Delay Time (0020,9252) may have different values. When applicable the same is valid for the Nominal Cardiac Trigger Time Prior to R-peak (0020,9154) and the Actual Cardiac Trigger Time Prior to R-peak (0020,9155) Attributes.
When multiple cardiac cycles are averaged together, then the Low R-R Value (0018,1081), and High R-R Value (0018,1082) are an average of the cardiac cycles that were accepted in the frame.
Note
For cardiac gated acquisitions the choice of the Frame Reference DateTime (0018,9151) is influenced by the Nominal Cardiac Trigger Delay Time (0020,9153). For respiratory gated acquisitions the choice of the Frame Reference DateTime (0018,9151) is influenced by the Nominal Respiratory Trigger Delay Time (0020,9255).
Figure C.7.6.16-5a depicts the usage.
Figure C.7.6.16-5a. Cardiac Timing Tags
Nominal Cardiac Trigger Time Prior to R-peak (0020,9154) and the Actual Cardiac Trigger Time Prior to R-peak (0020,9155) Attributes can be used to store a time of the next R-peak to the value of Frame Reference DateTime (0018,9151) expressed as a negative value. In this case the Actual Cardiac Trigger Delay Time (0020,9252), when present, and the Nominal Cardiac Trigger Delay Time (0020,9153) shall contain a value calculated based on the R-R interval applicable for this frame. See Figure C.7.6.16-5b.
Figure C.7.6.16-5b. Cardiac Timing Relationships
Note
Specifying the time interval prior to the R-peak is relevant for applications such as capturing P- and Q-wave related morphology.