Brain tissue volume estimation based on MRI is crucial to several diseases such as multiple sclerosis (MS). The Images from different scanners with dissimilar magnetic fields have disparities in resolution, Signal to Noise Ratio, contrast, among others. In order to convert volume estimations from different scanners, we suggest and evaluated two methods. The dataset to validate the methods was selected from 14 years follow up study of 72 MS patients with 1.5 and 3.0 Tesla acquisitions. The quantitative study of tissue volume progress is possible using these two methods.