1Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong, China, People's Republic of, 2Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China, People's Republic of, 3School of Biomedical Sciences, The University of Hong Kong, Hong Kong, China, People's Republic of, 4School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China, People's Republic of