Thank you for the reply.
I tried to do that but following error poped up because I loaded it through the code that I have taken from the YouTube video (above mentioned). When I run torch.cat as you suggested, the following error comes up:
TypeError                                 Traceback (most recent call last)
<ipython-input-155-0d3078352cfb> in <module>
----> 1 data = torch.cat((orig_dataset,verti_dataset,horiz_dataset),0)

TypeError: expected Tensor as element 0 in argument 0, but got MRI_Dataset

the datasaet is of __main__.MRI_Dataset type