The DCM file extension is used for DICOM which stands for Digital Imaging and Communications in Medicine. This is the common file format used to store medical imaging data when a patient undergoes a CT, MRI, PET, UltraSound, and many other types of medical scans.
If you are looking for a free DCM file viewer to open your medical scan, we recommend you try Pro Surgical 3D. This is a free and easy to use software tool designed to load patient scans.
For more sophisticated 3D shape analsys, we recommend you try Checkpoint. This software tool enables you to place 3D anatomic landmark points to make various measurements of complex 3D structures in patient scans.