Dear FieldTrip user.<div><br></div><div><br></div><div><br></div><div><div>Hi, I'm processing MEG data of Neuromag 306 system after removing some bad channels using fieldtrip-20120620 toolbox.</div><div><br></div><div>
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</div><div><br></div><div>To repair the bad channels with its neighbours, I firstly found the neighbor of all channel based on distance using 'ft_prepare_neighbours'.</div><div><br></div><div>However, the outcome of neighbour was far more than default distance, 4cm, from a target channel.</div>
<div><br></div><div>So, I checked thoroughly the code 'ft_prepare_neighbours', finding it used information of channel label and position from data’s hdr.grad to find neighbour of the target.</div><div><br></div><div>
<br></div><div><br></div><div>The problem is channel label and position in hdr.grad are arranged differently.</div><div><br></div><div>As far as I found, both information come from different source: the channel label was from code 'fiff_read_meas_info', while the channel position was from ‘channelposition’ in 'ft_datatype_sens'. </div>
<div><br></div><div>And the channel label is sorted into the sensor location, e. g. MEG 0113, MEG 0112, MEG 0111, MEG 0122, etc, however, the channel position is arranged along the sensor type (magnetometer and gradiometer) according to its ending number (1, 2, or 3), e.g. MEG 0111, MEG 0121, MEG 0131, ...., MEG 0112, MEG 0122, MEG 0132, ...MEG 0113, MEG 0123, MEG 0133, etc.</div>
<div><br></div><div>Thus, the label and position of channel in hdr.grad were mismatched so that we got somewhat weired neighbour after using 'ft_prepare_neighbours'.</div><div><br></div><div><br></div><div>It should be matched correctly to find the proper neighbour and ensure the result of repair as well.</div>
<div><br></div><div>In fact, the code 'channelposition' in 'ft_datatype_sens' yield the channel label as well as the channel position. It might help to solve this problem. </div><div><br></div><div><br></div>
<div><br></div><div>Is there any other way to solve this problem?</div><div><br></div><div><br></div><div><br></div><div><br></div><div>Best,</div><div><br></div>
<div><br>Jarang Hahm</div><div><br></div><br>
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