ABSTRACT

During the 1980s, the tomographic imaging modalities of magnetic resonance (MR) imaging and x-ray computed tomography (CT) entered widespread clinical use, especially for imaging the brain. These two modalities are based on very different physical principles, and the images they produce have different properties. MR imaging generates images showing the distribution of protons in

mobile molecules (water and fat), with the contrast between structures in the images determined by the visible proton density and the relaxation times of excited spins in the tissues and, in some cases, also by flow, diffusion, and other parameters. X-ray CT provides a map of x-ray attenuation within the body.