In this paper, we report on a novel quantitative elastography technique that combines optical coherence tomography (OCT) with acoustic radiation force (ARF) excitation to estimate the complex modulus. Sinusoidally modulated ARF excitations between 200 - 4000 Hz generate a surface wave at the tissue surface that can be related to bulk viscoelastic (VE) properties in a manner that is both precise and quantitative. This method is very well suited to studying media at high spatial resolution and over a very broad range of force frequencies. Mechanical characterization was calibrated using hydropolymers before studying liver samples. Fresh porcine liver samples were measured over time with and without formalin fixation. These data were used to evaluate the utility of the Kelvin-Voigt rheological model commonly used to fit dispersion data when estimating modulus values. We also investigated use of square-wave force excitation to measure the step response of tissues.