Hi,
I don’t think there is a direct command for importing .voi file in MATLAB. You can see the list of supported file formats for Import and Export operations in the link provided below:
But I found implementation of some ways to perform this operation on file exchange. These implementations will help in extracting a sub volume of interest from a given volume of interest. Please refer to following links for some information: https://www.mathworks.com/matlabcentral/fileexchange/47295-voi-extraction-from-a-3d-dataset
Hope this helps!
