X-rays are a form of radiation, like light or radio waves that can be focused into a beam, much like a flashlight beam. Unlike a beam of light, however, X-rays can pass through most objects, including the human body.
When X-rays strike a piece of photographic film, they can produce a picture. Dense tissues in the body, such as bones, block (absorb) many of the X-rays and appear white on an X-ray picture. Less dense tissues, such as muscles and organs, block fewer of the X-rays (more of the X-rays pass through) and appear in shades of gray. X-rays that pass only through air appear black on an X-ray picture.
Ultrasound is a test that uses reflected sound waves to produce an image of organs and other structures in the body. It does not use X-rays or other types of possibly harmful radiation.
For ultrasound testing, gel or oil is applied to the skin to help transmit the sound waves. A small, handheld instrument called a transducer is passed back and forth over the area of the body being examined. The transducer sends out high-pitched sound waves (above the range of human hearing) that are reflected back to the transducer. A computer analyzes the sound waves and converts them into a picture that is displayed on a TV screen. The picture produced by ultrasound is called a sonogram, echogram, or ultrasound scan. Pictures or videos of the ultrasound images may be made for a permanent record.
CT or CAT scan
A computed tomography (CT) scan uses X-rays to make detailed pictures of structures inside of the body.
During the test, you will lie on a table that is hooked to the CT scanner, which is a large doughnut-shaped machine. The CT scanner sends X-ray pulses through the body. Each pulse lasts less than a second and takes a picture of a thin slice of the organ or area being studied. One part of the scanning machine can tilt to take pictures from different positions. The pictures are saved on a computer.
A CT scan can be used to study any body organ, such as the liver, pancreas, intestines, kidneys, adrenal glands, lungs, and heart. It also can study blood vessels, bones, and the spinal cord.
An iodine dye (contrast material) is often used to make structures and organs easier to see on the CT pictures. The dye may be used to check blood flow, find tumors, and look for other problems. Dye can be put in a vein (IV) in your arm, or you may drink the dye for some tests. CT pictures may be taken before and after the dye is used.
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body. In many cases MRI gives information that cannot be seen on an X-ray, ultrasound, or computed tomography (CT) scan.
For an MRI test, the area of the body being studied is placed inside a special machine that is a strong magnet. Information from an MRI can be saved and stored on a computer for more study. Photographs or films of certain views can also be made. In some cases, a dye (contrast material) may be used during the MRI to show pictures of organs or structures more clearly.
MRI can be used to find problems such as bleeding, tumors, infection, blockage, or injury in the brain, organs and glands, blood vessels, and joints.