We investigate the possibility to limit refraction effect at interfaces between a sample and a liquid medium to improve resolution in 2D and 3D terahertz imaging. Indeed, an important part of the terahertz beam is reflected, diffracted and refracted at each interfaces because of refractive index mismatch. We propose to adapt the refractive index of medium around the sample replacing surrounding air by medium with an optimized refractive index and low absorption coefficient. This approach will be developed to recover good dimension for metrology and to improve reconstruction by tomography algorithm.