Dear all,
I have an artifact problem in my fMRI data that I don´t know so far what exactly is and how to solve it.
This artifact is depicted by either a big decay or a big rise on the signal intensity of images subtraction in the very bottom of the occipital area (close to the boundaries of the image).
I discovered it when I was subtracting one specific volume (already preprocessed), whose global mean signal intensity dropped off or rose more than 3*sigma from the mean
of a specific session, by a volume whose global signal intensity is aprox. that mean. However, when I applied the same procedure for the several steps of the preprocessing
I realized that this artifact appeared when I performed the Realignment&Unwarp. I tried to use Realignment&Reslice and the artifact disappeared.
This option apparently solves my problem. Nevertheless, I want to avoid it because I don´t want to include a regressor for movements on my design matrix,
since they are highly related with the nature of my study. That´s why I decided to use the Unwarp instead.
My fMRI preproc analysis consists on this sequence: Slice Timing Correction, Realignment&Unwarp, Normalization (meanEPI), Smooth(8mm).
I used a 3T fMRI scanner with an interleaved slice acquisition. I don´t use any mask in the Unwarp Reslicing options.
Can anyone help me to figure out what actually this is and how to overcome it?
Thank you very much in advance.
Best,
Ana Luísa
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