There are usually 2 dummy scans (2TR) in the product EPI sequence
in Siemens machine, and that is why you will see the scan time shown in
the protocol UI is 2TR longer than what you expect. But I don't think
you need to worry about the dummies when program your e-prime stimuli.
The sequence send out trigger after these 2 dummies. But this is my
experience, you have to use a stopwatch to check the exact time for
receiving trigger in your scanner, and run the stimuli to the end to see
whether the scan and stimuli end at the same time.
On 8/10/2011 6:49 PM, Xu, Ben (NIH/NINDS) [E] wrote:
> I apologize that this is not an spm question, but a question for those who are familiar with Siemens scanners or, more specifically, EPI volume acquisition on a Siemens' Verio 3T. I hope someone can respond to my question.
> I'm new with Siemens scanner for EPI acquisition. I have a setup that uses the scanner trigger to start my scan run with the E-Prime software. I noticed that the scanner trigger did not trigger the E-Prime till after several TRs, but it gave me the same number of scan volumes (measurements) as I specified. I'm not sure whether the beginning recorded volume is actually the one right after the E-Prime was triggered, or it's part of the pre-trigger scan volume(s). Can anybody tell me? (Is there a way to check on the Siemens scanner?)
> This became a question because our E-Prime run always ended several seconds/TRs later than the scans even though the number of volumes/TRs specified for the EPI run is actually 2 seconds (1 TR) longer than the programmed E-Prime run. We have timed the E-Prime run multiple times. The timing is accurate as programmed.
> I'd appreciate it if anyone can respond to my question.
> Thanks a lot.
Ze Wang, Ph. D
Research Assistant Professor of Biomedical Engineering,
Department of Psychiatry,
Perelman School of Medicine,
Department of Bioengineering
School of Engineering and Applied Science
University of Pennsylvania,
3900 Chestnut Street,
Philadelphia, PA 19104, USA
Tel: 215-222-3200 ext 123