Unexplained weight loss is defined as the unintentional loss of at least 10 pounds or 5 percent of body weight over a period of 6 to 12 months. This would be equivalent to a 200-pound man losing 10 pounds or a 130-pound woman losing six to seven pounds.
What It Is. Magnetic resonance imaging (MRI) of the brain is a safe and painless test that uses a magnetic field and radio waves to produce detailed images of the brain and the brain stem. An MRI differs from a CAT scan (also called a CT scan or a computed axial tomography scan) because it does not use radiation.
Your body contains millions of hydrogen atoms. When you are in an MRI scanner: 1  A strong magnetic field aligns particles called protons which are within the hydrogen atoms. 2  All the protons line up in parallel to the magnetic field, like tiny magnets. ( 3 Normally the millions of protons all lie in random directions.).