Unpaired, dependent data comparison, or comparison of paired means

#1
Hi

I'm trying to find a statistical test that can help me compare the means of two dependent groups.

My data:
1: parameter values from white matter region in an in vivo rat brain
2: parameter values from white matter region in the same rat brain, bur after the tissue has been fixated.

I cannot align/register the two brains to each other, so the region I have outlined in vivo is not exactly the same as the region I have outlined in the fixated tissue.


My wish: I would like to compare the means of the two white matter regions.
My suggestion: A paired t-test, but as I know that each pixel value in data set 1 does not exactly correspond to the pixel value in data set 2, the paired t-test is not exactly right to do.

Is there a test of dependent but NOT paired data?

Thank you for your help!

Nanna