Resolving DICOM image resolution

Hello everyone,
I need help with understanding why and how to improve resolution. I’m carrying out some basic segmentation on bone models for my research. When I threshold and generate the model, there are a lot of gaps and cavities in the structure that will compromise the anatomy of the bone model. What can I do to remedy this? I am also very new to the software. Here is a picture of what I’m talking about.

You have a few options, they are described in detail here.