Answer:
MRI uses strong magnetic field and electromagnetic waves to create an image, while the x-ray imaging (regular x-ray like chest x-ray, or CT scan xray) reconstruct the image by finding how much x-ray was able to penetrate the body. For example, the x-ray can easy penetrate soft tissue like fat and muscle (looks dark on the film), while bone absorb large amount of the x-ray (looks white on the film).