Bad 3D model :( How can I fix it?

Operating system: Windows 10
Slicer version: 4.10.1
Expected behavior: I quickly need to create an accurate 3D model (in order to be 3D printed) from the MRI dicom files of my patient
Actual behavior: I can’t get a clean and proper 3d model of the spine

Hi guys:) I’m going crazy with some Slicer issues I can’t solve and I hope you’ll be able to hep me (this would be a really important work to me). I’m supposed to create an accurate 3D model of a spine from MRI dicom files. I’ve been able to load them as a new patient (i just needed to import them as a non-anonymus file), but I still haven’t found a way to make a proper 3D model of my patient. I send you some screenshots of this case, if it may help you. If enable the visibility of each volume (one by one) this is the scene I get, the better view I have is this one ("best view " file), but I can’t obtain a clear and good 3d model from it (I’m using the threshold effect). the stl 3d model that I get really sucks. Could you help me with this? What am I doing wrong? Thank you so much for your support!!

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