Method and apparatus for estimating an arrival time (PAT) value of a subject in an automatic and unsupervised fashion from a sequence of electrical impedance tomography (EIT) images. The method comprises: providing an EIT imaging device adapted to record impedance signal distribution within a measurement region of the subject； measuring a sequence of temporally discrete EIT images during a predetermined measuring time period in the measurement region using the EIT imaging device, each EIT image comprising one or a plurality of EIT pixel subsets, each of said one or a plurality of EIT pixel subset representing an impedance value； generating one or a plurality of time series, each of said one or a plurality of time series representing a variation of the impedance value of the sequence of EIT images； and estimating the PAT value from each of said one or a plurality of time series.
