Thanks Volkmar,
for the comments. Off-list, I had a look at the images and found that it
was a display issue: with the interpolation set to NN, the values were
shown as is and were not interpolated anymore. There was some discussion
about that a while ago (eg, in a message from Tom,
www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind05&L=SPM&P=R159044&I=-3, or
John, www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind04&L=SPM&P=R670790&I=-3
), but I had completely forgotten about it, so this is just to remind
people that what they see when calling up an image may not quite be the
"ground truth" :)
Best,
Marko
Volkmar Glauche schrieb:
> Dear Eric,
>
> your formula looks ok. You should check your threshold - you could do
> this eg. in CheckReg by using "Image->Window->local->manual" and setting
> min/max to [threshold threshold+eps]. This will display your image
> "binarised", with below-threshold voxels black.
>
> Volkmar
>
> On Tue, 3 Jul 2007, Eric Schumacher wrote:
>
>> Hello,
>>
>> I'm trying to use the Image Calculator built into SPM 5 to mask voxels
>> below a certain threshold. As recommended in the SPM 5 manual, I used
>> the ImCalc to create a binary mask of the image (i1>threshold) and
>> multiplied that times the original image ( i1.*(i1>threshold)).
>> Insignificant voxels should get multiplied by 0 in this case, but when
>> I view the resulting, masked image in software like mricro, all the
>> below threshold voxels are still present. Has anyone had a similar
>> problem? Am I using the calculator incorrectly?
>>
>> Thanks in advance for your help?
--
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Marko Wilke (Dr.med./M.D.)
[log in to unmask]
Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
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