| Posted: Tue Jul 8th, 2008 04:34 pm |
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1st Post |
hdhollen
Member
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To what degree do the cardiac acquisition modes on the GE VCT Scanner such as Snapshot segment and Snapshot burst and burst plus have on the severity of misregistration artifact that you would see on study as well as the different pitches within those modes?
For example:In regards to patients that are pre pulmonary vein ablation- if the patients HR is in the range in which you would use Snapshot burst when they get on the table, then they drop to the Snapshot segment range will there be an increased likelyhood of misregistration artifact outside of the fact that the HR varies.
In regards to patients for CCTA in which we would rarely use anything other then snapshot segment, if we select a pitch of .18 becuase the patients HR went low into the 40`s during part of the exam and then varies between 50 and 60 during the CCTA acquisition which a pitch of .20 or .22 is called for ,will there be an increased incidence of misregistration artifact even though the HR is at a nice slow pace?
And "vice versa" for both of these scenario`s .
Also if misregistration artifact is present on a scan, will it always be in increments of 40mm because that is the size of the detector in the "Z" Axis?
Thanks
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| Posted: Wed Jul 9th, 2008 06:55 pm |
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2nd Post |
ctisus
Administrator
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The severity in misregistration comes more from fluctuations of the
heart rate more than the use of Burst or Burst Plus. The higher heart
rates are handled very well with the sector mode of scanning especially
when that rate is very steady. If the heart rate is making frequent and
wide variations then the likelihood of misregistration increases. As to
the effect of pitch on misregistration, the lower the pitch the more
overlap in the 40 mm acquisition is possible, reducing the artifact
potential.
In response to a patient scheduled for a pulmonary vein ablation study,
for a patient in active atrial fibrillation the recommendation would be
to ignore the wildly fluctuating heart rate and set the system to scan
in the segment mode with your lowest pitch capability (0.16 on a
VCT--type in 35 for the heart rate to set this low) in order to have as
much overlap in the data as possible. Second option would be to do the
study as an ungated study and simply capture the heart in a helical
acquisition using your fastest rotation speed for routine scanning ( 0.4
sec ) in order to reduce as much of the cardiac motion as possible. The
cardiac structure itself would be seen very well and 3D post processing
to use navigator views of the Ostia of the pulmonary vessels and atrial
appendage, as well as vessel analysis to lay out the pulmonary vessels
can still be achieved.
In regards to regular CCTA exams, once again, a slower, or lower,
pitch will provide more overlap reducing the potential for
misregistration. The thing to remember is a lower pitch means more time
in the scan field which translates to increased dose possibilities.
Please be careful when selecting your technical parameters and practice
ALARA ( As Low As Reasonably Achievable) on ALL your ct exams.
Jack Risner
Advanced Cardiac Research Specialist
GE Healthcare
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