def bbox_mean(mask_bbox, data):
    """Mean value of time-series in each non-zero cell in bbox mask
    Parameters
    ----------
    mask_bbox: 'numpy.ndarray', (e1, e2, e3)
    data: 'numpy.ndarray', (N_voxels, N_time_steps)
    Returns
    -------
    bbox_mean: 'numpy.ndarray', (e1, e2, e3)
    """
    import numpy as np
    bbox_mean = np.zeros(np.shape(mask_bbox))
    bbox_mean[mask_bbox == 1] = np.mean(data, axis=0)
    return bbox_mean
