We have recently developed a robust 2D post-beamforming filter for contrast restoration in ultrasound imaging systems using coarsely-sampled array apertures, e.g. high frequency ultrasound (HFUS). The filter can be derived from a discretized 2D impulse response model in the region of interest (ROI). The key to the robustness of the regularized 2D pseudoinverse filter is transforming the operator to k-space, where the regularized inversion is implemented using 2D DFT instead of computationally intractable matrix operations. Using computer simulations, the 2D PIO was shown to produce complete restoration of contrast loss due to grating lobes resulting from coarse, 2 sampling of HFUS arrays in the 25 - 35 MHz range. In this paper, we present the first in vivo demonstration of the 2D PIO in imaging the carotid artery using a commercially available probe. The results show that the 2D PIO increases the tissue/blood contrast by 4 dB (when imaging a cross section of the vessel). These results are in agreement with experimental results obtained using the same probe in imaging quality assurance phantoms. The 2D PIO's ability to remove the clutter from grating lobe is expected to improve the performance of speckle tracking algorithms for the estimation of tissue and blood displacements in vivo.