Gray matter atrophy related airtifact

Submitted by Christine on Fri, 08/05/2011 - 14:52

Hi,

I am new to the ALFF analysis and recently applied this to a group of neurodegenerative patients, who have severe atrophy. When I did a two-sample t test on the mALFF maps between patients and normal controls. I found the atrophied regions showed stronger activation in patients than normal control. This difference is very robust and remains even after atrophy correction with BPM. I wonder whether this could be due to the contamination of CSF accumulated at the atrophied region in patients. But it seems weird, since I thought CSF BLOD signal oscillation should be lower than GM? Or maybe their signal is more consistent than GM and turned out to be higher in a 2-sample t test.

Thanks for your input.
Christine

Re

Dear Christine, I am very very sorry for the delay because I was out these days. This is an interesting phenomenon. Actually, previous study (Zou, Q.H., Zhu, C.Z., Yang, Y., Zuo, X.N., Long, X.Y., Cao, Q.J., Wang, Y.F., Zang, Y.F., 2008. An improved approach to detection of amplitude of low-frequency fluctuation (ALFF) for resting-state fMRI: fractional ALFF. J Neurosci Methods 172, 137-141.) has reported that the ALFF was greater (noisily?) in CSF regions. It may caused by the CSF signal has high amplitude in the full frequency band. I guess this might be the reason of what you found. However, in one of our previous study (Wang, Z., Yan, C., Zhao, C., Qi, Z., Zhou, W., Lu, J., He, Y., Li, K., in press. Spatial patterns of intrinsic brain activity in mild cognitive impairment and alzheimer's disease: A resting-state functional MRI study. Hum Brain Mapp.), we found the PCC (which with atrophy) in AD patients has a lower ALFF than normal controls. Just for your reference. Best wishes!

Thanks for the reply. I

Thanks for the reply. I read the article you mentioned. Interestingly, that article also found an increase in parietal lobe (looks like right angular gyrus to me), which usually has severe atrophy in AD. You also showed increased in bilateral Hippocampus regions, which are also atrophy hotspots in AD. I am not saying these are all due to atrophy, but not sure how to interpret it yet. Just out of curiosity. Why you didn't do fALFF analysis in this study? C

Re

Hi! In considering the ALFF decrease in PCC and the increase in Hippocampus region although these regions demonstrated atrophy. I think these effects can not solely explained by atrophy. There should be, at least some, functional changes in these regions. fALFF showed better DMN results in one-sample t-test (zou et al., 2008). However, fALFF is not always a good measure for detecting functional changes in patients (two-sapmle t-test). For our studies, I just feel ALFF demonstrated more sensitivity in disease than fALFF. This may need to be validated in future studies. Best wishes!

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