Dear Gao,
There may be scanner specific limits, but I don't know Philips scanners and leave others to advise on that.
In terms of experimental design, you can scan for very long durations provided that the effects of interest (whether based on events or blocks) have high enough frequency (a rule of thumb being twice the hpf frequency), and you model the drift.
On subject tolerance, this is highly variable. For a 'typical' study of young healthy adults, I have found that people get restless and start to move after 20-30 minutes, reducing data quality, but this period can be shorter for some groups of patients (and perhaps children). On the other hand, with experienced subjects, we have also run to 80 (eighty) minutes of continuous EPI-fMRI without an increase in movement or problems with sleepiness - it all depends on the task and the subjects, and taking the time to get people comfortable and well positioned in the scanner.
Best wishes,
James
> Dear SPM experts,
>
> We are considering an fMRI experiment on emotion. We'd like to adopt a same experiment paradigm from an ERP study. However, the ERP experiment last about 18 minutes. I am a bit worried that this 18 min long time could be problematic for fMRI study. The MR signal drift could confound the results, and it is a block design (mixed design actually). Although the technician from Philips says that they have some special manipulation to control the MR signal drift. I am not sure about that. Also too long time may induce fatigue of subjects, as they somehow tend to be sleepy lying in the MRI scanner.
> Did anyone here perform such long-time fMRI session before?
> Any suggestions/hints could be much appreciated. Thank you very much!
>
> Best regards,
> Gao
|