The formula should probably be '(i2 - i1) ./ i2'. Note that the formula needs element-wise division (there is a dot before the slash).
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From: SPM (Statistical Parametric Mapping) [[log in to unmask]] on behalf of Devin Sodums [[log in to unmask]]
Sent: Monday, January 21, 2013 8:38 PM
To: [log in to unmask]
Subject: [SPM] imcalc to calculate percent change between scans
Dear SPM experts,
I have used ImCalc as previously suggested to take contrast images from patients who have done our test before and after epileptic surgery, which was successful, but I would now like to do the same but with percent change between scans. My thought was to do the following:
Percent change between Scan 2 and 1:
(Scan 2 contrast- Scan 1 contrast)/Scan 2 contrast
I believe this is logical, but would like to confirm it.
Mainly, as when I have tried running this in ImCalc, I kept running into errors saying that the formula could not be computed.
This is the equation I have utilized:
Two images:
Scan 2 contrast
Scan 1 contrast
Formula: '(i2-i1)/i2'
I don't have access to the error message I had before right now, but can post it in the morning once back at access to the files.
But since I am new to using ImCalc, I was worried that perhaps my expression was wrong and thought to post this in the mean time.
Any help would be greatly appreciated.
Thank you,
Devin
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