Citation
If you publish research that uses elastix you have to cite it as follows:
S. Klein, M. Staring, K. Murphy, M.A. Viergever, J.P.W. Pluim, "elastix: a toolbox for intensity based medical image registration," IEEE Transactions on Medical Imaging, vol. 29, no. 1, pp. 196 - 205, January 2010, DOI: https://doi.org/10.1109/tmi.2009.2035616.