[Freesurfer] Bad white surfaces

Hi Freesurfers:

I have processed images acquired from GE Sag 3D Bravo sequence, however, the white surfaces are always messy and extend into gray matter (please see the attached example). The CNR is not bad:

white = 96.0+-10.2, gray = 66.4+-18.0, csf = 38.1+-19.3 gray/white CNR = 2.053, gray/csf CNR = 1.149 lh CNR = 1.601 white = 95.8+-10.6, gray = 65.9+-18.4, csf = 36.4+-19.0 gray/white CNR = 1.985, gray/csf CNR = 1.246 rh CNR = 1.616 total CNR = 1.608

Bad white surface seems a sever problem for us, as it happens for every subject. Is it a reason of low GM/WM contrast? Does anyone have an idea about how to fix this kind of error?

Thanks so much. Regards, Yue