SPIE Proceedings [SPIE Saratov Fall Meeting and Workshop on Laser Physics and Photonics 2012 - Saratov, Russian Federation (Tuesday 25 September 2012)] Saratov Fall Meeting 2012: Optical Technologies in Biophysics and Medicine XIV; and Laser Physics and Photonics XIV - Case study of ECG signal used as a reference signal in optical pulse transit time measurement of blood flow: the effect of different electrode placements on pulse transit time