 |
 |
You can model scanner effects as a covariate of no interest. In SPM, it just means another column of ones and zeros in the design matrix for the case on 2 scanners. For more than scanners, you'd need additional columns. Best regards, -John On 4 November 2013 08:11, Ben Becker <[log in to unmask]> wrote: > Dear SPMers, > > I used VBM8 to compare grey matter volumens in a priori specified ROIs in > a group of patients vs controls. Next I analyzed data from an independent > sample (again: patients & controls, but from a different scanner) to > replicate the initial findings. > For further analyses I extracted ind. grey matter volumes from the ROIs > were I find group differences using marsbar. To increase power I would like > to pool the extracted data from both samples. However, both samples were > acquired on different Scanners (Philips 1.5 vs Siemens 3T Trio) using > different sequences. Are the extracted values study- & scanner-specific or > do they represent absolute scanner-unspecific indices of grey matter > volumes? > > Thanks in advance & best regards > > Ben >