How to use dataloader for BRATS2015

Hello, I have this dataset, and I make a data loader, it returns image, mask, and label. but when I make use it, it occurs this issue.

Traceback (most recent call last):
  File "test/", line 16, in test_dataset
    for i, j in enumerate(dataload):
  File "/home/ubuntu/fzh/.conda/envs/rando/lib/python3.6/site-packages/torch/utils/data/", line 582, in __next__
    return self._process_next_batch(batch)
  File "/home/ubuntu/fzh/.conda/envs/rando/lib/python3.6/site-packages/torch/utils/data/", line 608, in _process_next_batch
    raise batch.exc_type(batch.exc_msg)
RuntimeError: Traceback (most recent call last):
  File "/home/ubuntu/fzh/.conda/envs/rando/lib/python3.6/site-packages/torch/utils/data/_utils/", line 99, in _worker_loop
    samples = collate_fn([dataset[i] for i in batch_indices])
  File "/home/ubuntu/fzh/.conda/envs/rando/lib/python3.6/site-packages/torch/utils/data/_utils/", line 68, in default_collate
    return [default_collate(samples) for samples in transposed]
  File "/home/ubuntu/fzh/.conda/envs/rando/lib/python3.6/site-packages/torch/utils/data/_utils/", line 68, in <listcomp>
    return [default_collate(samples) for samples in transposed]
  File "/home/ubuntu/fzh/.conda/envs/rando/lib/python3.6/site-packages/torch/utils/data/_utils/", line 52, in default_collate
    return default_collate([torch.from_numpy(b) for b in batch])
  File "/home/ubuntu/fzh/.conda/envs/rando/lib/python3.6/site-packages/torch/utils/data/_utils/", line 43, in default_collate
    return torch.stack(batch, 0, out=out)
RuntimeError: Expected object of scalar type Byte but got scalar type Short for sequence element 1 in sequence argument at position #1 'tensors'

and here is what I have done briefly:

    def __getitem__(self, idx):
        im = []
        for i in range(self.num_input):
            direct, _ = self.root_dir[self.num_input * idx + i].split("\n")
            if i < self.num_input - 1:

                image = nib.load(direct).get_data()
                image = np.expand_dims(image, axis=0)
                if i == 0 :
                    direct = os.path.split(direct)[0] + "/mask"
                    mask = nib.load(direct + "/mask.nii.gz").get_data()
                labels =nib.load(direct).get_data()
                labels = np.asarray(labels)
        iamges = np.concatenate(im, axis=0).astype(float)
        # iamges shape: 4 X H X W X D
        # labels shape : HXWXD
        # mask shape : HxWxD
        images = np.transpose(iamges,(0,3,1,2))
        labels = np.transpose(labels,(2,0,1))
        mask  = np.transpose(mask,(2,0,1))
        return images,labels,mask  

Thank you for your help