handling of 4D-data: update

jan-mathijs schoffelen j.schoffelen at PSY.GLA.AC.UK
Mon Mar 30 16:15:38 CEST 2009

Dear 4D-neuroimagers,

I just committed an updated version of read_4d_hdr to fieldtrip's
release which I would like to draw your attention to.
The reason for this is twofold: it handles some fields in the header
in a different way, which might lead to backward
compatitibility problems, and it has some functional improvements.
Moreover, even though this new version works alright
on the data acquired in Glasgow, I am not sure whether this holds
true for all 4D-systems.
Specifically, what changed is the following: user_block_data which
are stored in the run-specific config file are now stored
differently in fieldtrip's hdr-structure. Originally, it was stored
as a structure-array in hdr.orig.user_block_data. I changed this
into a cell-array. Moreover, I made some efforts to make sense of the
content of these user_blocks, so some of these now
actually contain some data (such as digitized positions of the coils-
on-head, estimated coil-on-head positions in dewar space etc).
Most consequentially, read_4d_hdr now attempts to read in the weight
table used during acquisition of the data. The digital weights
from this table are subsequently incorporated into the balancing
matrix of the gradiometer-array (this is now done in bti2grad). This is
necessary for correct computation of the leadfields.
I'd like to ask you to keep your eyes open and to check whether it
also works for data acquired at your system. Please let me know of
any problems arising from these changes. Moreover, if you would like
to contribute to perfecting read_4d_hdr, just let me know.



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