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Allowed values are the same as for
Acquisition Window Part 2
. Allowed values for the mA % are
10%–100%.
3.5.1.5 HR Variation Allowance
The phases acquired within the Acquisition Window are only accurate to the extent that the real-
time predicted heart rate is close to the actual heart rate. The HR Variation Allowance ensures
that the prescribed phases will be acquired as long as the heart rate, in beats per minute, does
not jump by more than the HR Variation Allowance value.
For example, if the HR Variation Allowance is 3 BPM, and the real-time predicted heart rate is
60 BPM, then the system will ensure that the prescribed phases will be acquired so long as the
actual heart rate during the beat when data is being acquired is between 57 (= 60 – 3) and 63 (=
60 + 3) BPM.
A typical value will be the heart rate variation measured during the previous breath hold.
For very low heart rates, such as below 50–55 BPM, it may be possible to reduce this value
when doing mid-diastolic (for example, 75%) imaging, as the quiescent duration is long enough
that acquisition of the exact prescribed phase may not be required.
Allowed values are 0 to 10 BPM.
3.5.1.6 Arrhythmia Retrigger
Turning “On” Arrhythmia Retrigger causes the system to apply the scan prescription on two
nearly consecutive beats. While doubling the dose, having two acquisitions increases the
chances that at least one of the scans will be diagnostic, using the same contrast injection.
A typical value is “Off” for patients in normal sinus rhythm (a relatively steady heart rate with no
or very few pre-ventricular contractions or other irregular beats). A value of “On” may be used
for patients with irregular beats during the prior breath hold, or with multiple irregular beats over
the previous several minutes, indicated by irregular beat counts in the ECG trace.
Turning “On” Arrhythmia Retrigger turns on Single Table Position Acquisition and sets the Scan
Interval to “0” and the Total Scans to 2.
When Auto Gating is “On”, Arrhythmia Retrigger will be turned “Off” for the
One or more
table
position selection.
3.5.1.7 Adaptive Gating
Adaptive Gating tells the system to avoid scanning during beats that are immediately after an
early beat. The system will delay the exposure due to early beats at most two times during a
scan group.
Adaptive Gating is typically turned on when functional information is desired, as the beat after
an early beat will not typically be representative of the patient’s cardiac function, or when it is
important to avoid or reduce incorrect registrations between neighboring images acquired with
multiple table positions.
Set Adaptive Gating to “Off” to allow scanning during compensatory, or unusually long beats
which may occur immediately after early beats.
3.5.1.8 Cardiac Phase Background
Use this information to learn about cardiac phases.
Revolution CT User Manual
Direction 5480385-1EN, Revision 1
Chapter 13 Cardiac 351