How to save my medical images in various formats into .zraw?

I mean how to compress my image volume data which is in .mhd into .zraw ? I tried using Convert3D GUI. but .zraw is not possible with it.

If you use ITK’s image writer and choose .mhd as file extension and enable compression then you’ll get pixel data compressed in a .zraw file.

If you prefer GUI then you can use 3D Slicer (or other similar medical image computing applications): load images by drag-and-dropping to the application window, use menu: File / Save, choose .mhd as file format and enable compression.