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Der Gao In my experience healthy subjects will be able to cope with a 18 minute paradigm, and so will most patients. Concerning the scanner drift it is the duration of the different blocks and not of the paradigm, that matters. On most scanners the default 128s highpass filter words well, but if you want to be sure you could acquirre images from a phantom and analyse the data in the same way as you would with the human data. One thing you may find on Philips scanners is that N/2 ghosting increases over time, because Philips acquirres the data for ghost correction only in the beginning. The same apply for the sensitivety maps used in parallel imaging, so in Tour case I would try a gel filled phantom. Best Torben Torben Ellegaard Lund Associate Professor, PhD Center of Functionally Integrative Neuroscience (CFIN) Aarhus University Aarhus University Hospital Building 10G, 5th floor, room 31 Noerrebrogade 44 8000 Aarhus C Denmark Phone: +4589494380 Fax: +4589494400 http://www.cfin.au.dk [log in to unmask] Den 25/05/2012 kl. 05.01 skrev Gao Junling <[log in to unmask]>: > 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