Dear SPM developers and experts,
I am using the realignment tool in the spatial preprocessing toolbox of SPM9.
I noticed some strange effects when the resulting realigned images
are viewed e.g. with Medx.
This led me to take a closer look at the .hdr file of the realigned
image and I noticed some peculiarities.
Now I wonder if this is deliberate and these special settings are
needed for proper performance of SPM
-or the opposite-
the fields in question are disregarded by SPM, and hence no effort to
preserve information or to put proper values was made.
here is a list of fields of the .hdr file that puzzled me:
data_type: this is a 10 char field, SPM puts 'dsr ' (6
blanks, 9 char altogether), what does it mean ?
db_name: this is an 18 char field which usually contains the
original filename, but spm puts the first 17 characters of the path,
effectively loosing the filename
extents: as I understand it should always be 16384, but SPM
sets it to 0 (what is the meaning of extents anyway ?)
hkey_un0: SPM overwrites it with '0', what does hkey_un0 mean anyway ?
funused2 and 3: SPM overwrites the values of these fields with 0,
effectively erasing the stored info, (funused1 is the scale factor,
ok)
cal_max: SPM puts 0, the same applies for cal_min, what is the
difference between cal_max and gl_max (see below) ?
gl_max: SPM puts 1 regardless of the real maximum value in
the image, this causes Medx to come up with a wrong Display Range
gl_min: SPM puts 0 regardless of the real minimum value in the image
originator: SPM puts '@', what does it mean ?
patient_id:
exp_date:
exp_time:
hist_un0: SPM overwrites all these fields with an empty string,
effectively erasing the information
Any comments will be greatly appreciated, thanks in advance,
Roman
-----------------------------------------------------
Roman Koetitz, Ph.D.
Division on Substance Abuse, Department of Psychiatry
Columbia University/NYSPI Unit 66
1051 Riverside Drive
New York City, NY 10032
Voice: 212-543-5209 Fax: 212-543-5854
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