Image fusion, or combination of two images obtained by different techniques, has been widely used in medical imaging. Vibro-acoustography (VA) is a new imaging modality that has been applied to both medical and industrial imaging. Combining unique diagnostic information of VA with other medical imaging is one of our research interests. In this work, we studied the VA and x-ray image pairs and adopted two methods for fusing the registered VA and x-ray image. In the first method, the fused image is defined as a linear combination of the VA and x-ray images. Moreover, a color-based fusion technique was employed to combine the images for better visualization of structural information. By combining the information from x-ray mammogram and VA modalities into a single image, the accuracy of mammography interpretation which is important for women's health can be increased.