Fig. 2. The harmonic analysis of the frequency response of the liquid-filled catheter-transducer system (CT) allowed determination of the parameters of the transfer function. The maximal amplitude of the transfer function at resonant frequency (F^r), namely the gain (G), was obtained from the amplitude ratio of the CT signal to the reference signal of the catheter-tipped pressure transducer for F^r. The phase of the transfer function was obtained from the phase lag of the CT pressure signal vs.  the reference pressure signal.