[MINC-users] mincconcat problem

[Soren Christensen]

Hi,
 I have a problem with mincconcat where I get an unexpected result when
first merging, then splitting across time. I do not get back to the starting
point in terms of values altough it is close.
I originally encountered this as mnc files created by mincconcat (time
concat) in some cases differed by integer values of +/-1 relative to the
original DICOMs or individual mincfiles prior to running mincconcat.

Example:
I have two minc files
v1.mnc
v2.mnc
(mincinfo below for all files)

I use mincconcat to merge them across time:
mincconcat -clobber -concat_dimension time v1.mnc v2.mnc v_concat.mnc

Then splitting:
mincreshape -clobber -dimrange time=1,0 v_concat.mnc v2_split.mnc


Now compare v2_split.mnc to v2.mnc - although valid range is changed, real
value should be identical. (I think)


mincmath -clobber -ne  v2_split.mnc v2.mnc neq_img.mnc

mincstats neq_img.mnc
File:              neq_img.mnc
Mask file:         (null)
Total voxels:      327680
# voxels:          327680
% of total:        100
Volume (mm3):      8064000
Min:               0
Max:               1
Sum:               26235
Sum^2:             26235

Mincstats show 26235 pixels differ by nummerical value 1 (actual difference
not shown here but it was +/-1 in all cases when read into matlab and the
short images subtracted)

This does not happen systematicallly, indeed for some files the above
procedure will not result in any discrepancies at all. Out of a perfusion
time series I had concatenated, discrepancies only appeared in 2 out of 50
time points, but at these time point there were +1000 discrepancies.

Is this expected behavior of mincconcat?
And if so - is there a way to get around this?

Thanks,
Soren












 mi v1.mnc v2.mnc v2_split.mnc
file: v1.mnc
image: signed__ short 0 to 1361
image dimensions: zspace yspace xspace
    dimension name         length         step        start
    --------------         ------         ----        -----
    zspace                     20            7     -32.1618
    yspace                    128       -1.875      127.876
    xspace                    128       -1.875      116.527


file: v2.mnc
image: signed__ short 0 to 1438
image dimensions: zspace yspace xspace
    dimension name         length         step        start
    --------------         ------         ----        -----
    zspace                     20            7     -32.1618
    yspace                    128       -1.875      127.876
    xspace                    128       -1.875      116.527


file: v2_split.mnc
image: signed__ short -32768 to 32767
image dimensions: zspace yspace xspace
    dimension name         length         step        start
    --------------         ------         ----        -----
    zspace                     20            7     -32.1618
    yspace                    128       -1.875      127.876
    xspace                    128       -1.875      116.527