U-Net Implementation for 4D vectors

I am using U-Net with Conv3D and ConvTranspose3D over vectors of size (3,100,100,100). My input size is (32,3,100,100,100) and target size is the same as well. I am having trouble comparing predictions and the output. I can’t understand how to reshape them properly to compare. The code I am using is as follows:

Format : [N , C, D , W , H ]
Input_shape : [32, 3, 100, 100, 100]
Label_shape : [32, 3, 100, 100, 100]
Output_shape : [32, 3, 100, 100, 100]
Optimizer : Adam

Loss and Train:

def dice_loss(pred, target, smooth = 1.):
    pred            = pred.contiguous()
    target          = target.contiguous()    
    intersection = (pred * target).sum(dim=2).sum(dim=2)
    loss             = (1 - ((2. * intersection + smooth) / (pred.sum(dim=2).sum(dim=2) + 
    target.sum(dim=2).sum(dim=2) + smooth)))
    return loss.mean()


def train():
    unet.train(True)
    torch.set_grad_enabled(True)
    running_loss        = 0.0
    running_corrects = 0
    num_samples      = 0

    for data in train_dataloader:
        inputs, labels  = data
        inputs             = inputs.cuda(cuda3)
        labels             = labels.cuda(cuda3)
        optimizer.zero_grad()
        outputs = unet (inputs)
        _,preds = torch.max(outputs, 1)
        loss       = dice_loss(outputs, labels)
        loss.backward()
        optimizer.step()
        num_samples      += inputs.size(0)
        running_loss        += loss.item() * inputs.size(0)
        running_corrects  += torch.sum(preds == labels.long().data)
    epoch_loss  = running_loss / num_samples
    epochs_acc = running_corrects / num_samples
    return epoch_loss, epochs_acc