How can I find Pixel spacing of dicom images when it is not included on their metadata

I got dicom images out of "other" modality, that do not have metadata and I am trying to embed them. How can I find out their pixel spacing and add it as tag to their metadata?

[Rik]

Either you are able to infer it from context, or you can't. In the latter case, with this information it is impossible for someone to give you an answer.

Is this still about those US timeseries images you're trying to read?

[Guillaume]

Stelios Fanourakis comment mistakenly posted as an answer moved here:

Yes. No DICOM Viewer can recognize them as series and create its 3d model

[Rik]

Did you try loading the slices individually and concatenating them to a 3D volume yourself?

[Stelios Fanourakis]

Yes and it looks like this. It is not correct. This is just a 3d presentation of the slices stacked together. I want for the real tissue to be visualized