Unlike a CT scan, MRI does<span> not </span>use<span> X-rays. Instead, it </span>uses<span> a strong </span>magnetic<span> field and </span>radio waves to produce<span> very clear and detailed computerized </span>images of the inside<span> of the </span>body<span>. </span>MRI<span> is commonly </span>used<span> to examine the </span>brain<span>, spine, joints, abdomen, and pelvis.</span>
by comparing the gravitational mass of galaxies to the luminous mass of galaxies
