It provides a spectacular and painless view of the knee. Ligaments and cartilage can be separated from bone, and the all-important cushion of the knee, the meniscus, can be identified.

The picture looks just like an X-ray image, but it isn't the product of radiation. It is called magnetic resonance imaging (MRI) and is one of the newest and most advanced technologies designed to provide improved interior views of the body. It is beginning to make an impact on sports medicine.

In the case of Redskins receiver Art Monk, injured Sunday in St. Louis, team doctors felt the injury was not bad enough to warrant surgery. In the past, a minor surgical procedure called arthroscopy was the only way to know for sure. But arthroscopy also slows recovery, so it often is not performed.

"They {Redskins team physicians} have clinical evidence that the injury is stable enough not to do surgery," said Dr. Deborah Blair, a radiologist at the Northern Virginia Center for Magnetic Resonance Imaging, where Monk was tested, and an expert in interpreting MRI images of the muscles. "They used MRI as a confirmatory test to make sure surgery is not necessary.

"MRI also can be used as a screening technique to avoid the need for an invasive procedure like arthroscopy," Blair said.

In some ways, MRI is even better than arthroscopy -- in which a fiberoptic device is inserted through a slit in the skin to examine the knee's internal anatomy. MRI can spot knee damage in ligaments that cannot be seen with the arthroscope. With MRI, all the ligaments can be seen. Said Blair: "In one test, within 40 minutes, you have evaluated all the ligaments."

To perform an MRI exam, the body is placed in a powerful magnetic field. The magnet aligns water molecules within the body, which spin like toy tops along the lines of the field. Radio waves then knock the spinning tops out of alignment. When the radio waves are turned off, the tops realign with the magnetic field, giving off radio signals that can be captured and converted into an image by a computer.

The outgoing signals depend on the density of water in the tissue, so the computer can separate tissue filled with water from tissues containing less water. Muscles contain a great deal of water, ligaments less, bone virtually none. Between X-rays, which can see the bone, and MRI, which can see the soft tissue, physicians can evaluate injuries to the entire musculoskeletal system in ways previously unthinkable.