Knowledge about dielectric properties of biological tissues is critical for the development and validation of microwave systems, such as Microwave Imaging (MWI) prototypes. However, measurement of dielectric properties of heterogeneous tissues with conventional techniques present some challenges, as most adopted techniques are designed for homogenous tissues, and limited number of samples may be available. In this study, we validate a methodology to estimate dielectric properties from Magnetic Resonance Imaging (MRI) exams. This is based on the interpolation between voxel intensities in MRI and known dielectric properties of homogeneous surrounding tissues. We test a 3D-printed phantom filled with tissue mimicking liquids in an MRI scanner and further test the proposed methodology. The results suggest estimated properties may present high percentage errors but the contrast between mixtures is underestimated, which is a valid indicator to infer the feasibility of MWI systems.