Fat suppression artifact
Example fat suppression artifact
Rationale: if the fat suppression frequency is wrongly set, the CSF signal is shifted in some images but not in some other images, which creates an unwanted variability in the ASL images that changes rapidly in time (temporal high frequency), but is smooth on the image (spatial low frequency), this effect is visible around the ventricles but can spread quite a bit.
This is not always easily to see on the mean CBF image (/dartel/ASL_CHECK/qCBF_Subject_Session.jpg), note here the too high signal in the posterior cingulate/precuneus/paracentral lobule
But can be easily detected on the temporal SD image (/dartel/SD_SNR_images /SD_map_Subject_Session.jpg)
So the ventricles shows a smooth region with high variability, which should not be there. Instead, it should look like:
In this image, we see similar variability/noise everywhere, except for vascular regions.
In the case of this artifacts, we repeat the ASL module, but set symbols.BILAT_FILTER = 2; in the DATA_PAR.m. For this, make sure to remove any present lock files from a previous run: e.g. 003_reslice_ASL.status 005_quantification.status 006_visualize.status 999_ready.status