  Lattices have been conceived as a powerful tool for data hiding. While
conventional studies and applications focus on achieving the optimal robustness
versus distortion tradeoff, in some applications such as data hiding in
medical/physiological signals, the primary concern is to achieve a minimum
amount of distortion to the cover signal. In this paper, we revisit the
celebrated quantization index modulation (QIM) scheme and propose a
minimum-distortion version of it, referred to as MD-QIM. The crux of MD-QIM is
to move the data point to only the boundary of the Voronoi region of the
lattice point indexed by a message, which suffices for subsequent correct
decoding. At any fixed code rate, the scheme achieves the minimum amount of
distortion by sacrificing the robustness to the additive white Gaussian noise
(AWGN) attacks. Simulation results confirm that our scheme significantly
outperforms QIM in terms of mean square error (MSE), peak signal to noise ratio
(PSNR) and percentage residual difference (PRD).
