Call for expertise: across session fMRI analyses

Dear Users, Concatenation or higher level stats? We would value the input of any users who have experience of 'combining' fMRI data across multiple runs for more robust averaging. The issue arises when trials of an experient are acquired in different data blocks due to technical limitations of scan scquisition protocols or often to reduce the strain on participants in a single session. I have searched many available resources. There are well documented routines for (1) analysinng the sessions individually and then compring them with a higher level analysis or (2) demeaning the two timeseries and combining them into a single one .. then following the standard analysis individual subject routine. Comments would be appreciated (especially from anyone has first hand experience of doing this). Thanks Andre'