An apparatus for determining the arterial structure of the hand of a subject, the apparatus comprising a wrist pulse measurement device configured to measure wrist pulse signals at the wrist of the subject, a digit pulse measurement device configured to measure digit pulse signals at the digits of the hand, the apparatus being configured to compare the arrival time of one or more waveform features in a wrist pulse signal and the arrival time of the corresponding feature in two or more digit pulse signals in order to determine a pulse transit time for each of the one or more waveform features, thereby estimating the arterial structure of the hand.
