Dear Matt., Thanks for your reply. I have only one machine with 16GB RAM and the others with 8GB. for a dtseries.nii file, if I calculate pairwise correlation for a 91282 by 1200 matrix. It would cost 60GB RAM in matlab. Although we find a way to calculate a sparse pairwise correlation matrix, we still can not handle a 91282 by 4800 (or more) matrix easily.
Now that using all four files is essential, I plan to first calculate the pairwise correlation matrix for each run, then average the correlation matrix from 4 runs for each subject. Is this ok? Many thanks! Chao > On 23 Jan 2015, at 13:57, Glasser, Matthew <[email protected]> wrote: > > How much RAM do you have? The CIFTI files use far less RAM than the > volume files, but contain all the grey matter information represented in a > way that makes combining across subjects more accurate. If you don¹t use > all the data your estimates of the subject¹s functional connectivity will > be noisier and generally less stable (one 15 min run looks more different > than another than if you compared two sets of 1 hour¹s worth of data). > Also there are some left/right asymmetries in the data induced by the > LR/RL phase encoding directions, which some people perceive as a problem > (though if we had used AP/PA there would still be asymmetries > posterior/anterior). > > Peace, > > Matt. > > On 1/23/15, 6:44 AM, "Chao Liu" <[email protected]> wrote: > >> Dear HCP Experts, >> >> I am inspecting the HCP rfMRI data. For each subject, there are two >> sessions with 2 runs (LR&RL) in each session, yielding 4 files in total. >> Although we can concatenate all the four time series and do the >> correlation, I found the memory needed is more than the memory I have on >> lab computer, leading to a very slow calculation. So I am wondering the >> difference between using only one run and using all the four runs. Will >> it give wrong results if I use only one run? >> >> Many thanks! >> Chao > > > ________________________________ > The materials in this message are private and may contain Protected > Healthcare Information or other information of a sensitive nature. If you are > not the intended recipient, be advised that any unauthorized use, disclosure, > copying or the taking of any action in reliance on the contents of this > information is strictly prohibited. If you have received this email in error, > please immediately notify the sender via telephone or return mail. > > -- > This message has been scanned for viruses and > dangerous content by MailScanner, and is > believed to be clean. >
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