Blank spaces after segmentation

Hello everyone,
I was trying to make segmentation of lungs and human soft tissue but after the segmentation I faced some blank spaces between the the lungs and human soft tissue.
I would like to make a FEM analysis by using this CT created image and because of the this blank spaces between the organs there are missing connection between the organs, cannot touch each other.
Could you please help me? How can I fill the blank spaces between the segmented organs?

Could you post a screenshot to make it clear what blank spaces you are referring to? Thank you.

Thank you for your interest. You can reach the image of the segmentation, in the attachment.

I suspect you are tracing two segments manually and separately, causing a misalignment in the border and leaving gaps. If you do the full chest first segment, then do the lungs, and then subtract, you shouldn’t have these double borders.

Yes, you are absolutely right. Thank you for your valuable suggestion!!
Now, I have solved the connection problem; however, I have recognized that if I try to simplify the geometry the connection is detorieted.
I have to simplify the geometry at least I have to remove the spike geometries by preserving the connections. Do you have anyrecommended tool or way to do it ?

You can use Smoothing effect for this. Joint smoothing method is applies to all segments at once and preserves a watertight segmentation.