CHICAGO -- Brain surgeons will soon use computers in the operating room to guide their way in the delicate business of removing tumors without destroying vital tissue.

Using a wand hooked to a computer, a surgeon points to the patient's head at the expected point of entry for surgery. Watching a computer screen and using computer controls, the surgeon can peer inside the patient's skull and do a simulated operation in three dimensions on the screen before ever making an actual cut in the patient's skin.

This technology, which should become commercially available next spring, is just one of numerous medical imaging advances that promise to alter significantly how physicians work. Abundant, inexpensive computing power is giving doctors a much better understanding of individual patient conditions, and it is helping them make better therapy choices.

Unlike in the 1980s, when new hardware such as magnetic resonance imagers opened new vistas for medical practice, the new high-tech medical revolution is fueled mostly by software advances, with hardware playing second fiddle.

This trend, highlighted this month at the annual meeting of the Radiological Society of North America at Chicago's McCormick Place, is likely not only to reshape health care but also may begin to reduce, rather than boost, medical costs.

Physicians hope that instead of costing more, the new software will make existing equipment more useful, more efficient and more cost-effective.

The $2 million magnetic resonance imagers that hospitals bought a few years ago won't become obsolete any time soon, radiologists say, but they should become more useful in helping physicians diagnose and treat patients thanks to new software programs and, perhaps, some relatively minor hardware upgrades.

Procedures that once took 15 minutes or half an hour can now be done in a few minutes thanks to innovative software that gathers data much more quickly to assemble images on a screen. Not only can these sophisticated machines process more patients than ever, but the information gathered is being presented in user-friendly ways, often in three-dimensional pictures, so that physicians make much better use of it.

Such advances should cut costs, possibly trimming the $1,000 fees now common for magnetic resonance scans. New technology also promises to cut costs by diagnosing a problem more quickly and reducing the need to hospitalize a patient or invade a patient's body.

The surgical viewing wand was just one among dozens of innovations on display at the radiology meeting.

Dr. Bill Gannon, clinical director at ISG Technologies Inc., the Toronto firm that developed the system, said the technology probably will be approved by the federal Food and Drug Administration for general use in the spring.

The viewing-wand technology is based on software that takes anatomical information about a patient obtained from X-ray tomography or magnetic resonance and puts it into a 3-D format on a computer screen, Dr. Gannon said.

"Our goal is to reduce trauma to the patient, reduce recovery time and cut the cost of care," he said. "When a surgeon gets the specific information he needs to plan surgery, he can make a smaller entry cut. The whole procedure is less invasive. The more you can plan prior to actual surgery, the better off the patient will be and the more you save."

Dr. Leonard Cerullo, medical director of the Chicago Neurosurgical Center at Columbus Hospital, predicted that the viewing wand "will be routine technology in a few years."

Dr. Cerullo and his Chicago colleagues have used the wand experimentally on 20 patients since October and found it helpful, especially in the difficult cases where tumors are hard to reach.

"Once you open a skull," said Dr. Cerullo, "everything looks alike. If you're a little off, you can miss a lesion. The viewing wand puts us on target and keeps us there."

The information that makes the wand system work is a digitized image of the patient's brain made using standard technology, such as X-ray computerized tomography or magnetic resonance. Computerized tomography uses X-rays and magnetic resonance uses magnetic fields and radio waves to probe the human body with signals that computers analyze and convert into images of human anatomy.

What is new is the packaging. Instead of static pictures of slices through the patient's brain, surgeons can look at 3-D images they can move around at will, peeling away skin, bone and soft tissue as they please.

Several other companies are developing 3-D computer images in formats similar to the surgical wand system. And in radiology labs around the globe, physicists are experimenting and finding new capabilities in their equipment that few would have thought possible just three years ago.

Dr. William Lees, chief of body imaging at the Middlesex Hospital in London, uses ultrasound, the sophisticated offspring of submarine sonar, to make 3-D pictures of fetuses as they develop in the womb. He predicted that within five years, computer programs containing normal fetal growth patterns will automatically compare them with individual 3-D scans of fetuses as they grow in their mothers' wombs.

Disorders such as Down's syndrome will be spotted without removing any tissue from the mother or the fetus, Dr. Lees predicted.

"A program like that would need the power of a Cray supercomputer, but we'll have that in a desktop machine in five years," Dr. Lees said.

Programs to integrate information from different imaging techniques, such as X-ray scanning, magnetic imaging and ultrasound, will give physicians detailed three-dimensional pictures of their patients' organs, he predicted.

Magnetic resonance imaging is arguably the most versatile technology available to physicians. Placing people in strong magnetic fields aligns the nuclei of atoms within their tissue in specific ways, much like members of a marching band fall into formation before a parade.

Sending certain radio signals to the nuclei causes them to respond with weak signals of their own -- again, like a director instructing certain band musicians to play their instruments.

Physicists are finding that their ability to evoke responses from various atomic nuclei is amazingly flexible. They have found ways, for instance, to run the equipment so that it suppresses signals from fatty tissue while highlighting other materials.

By suppressing fatty tissue, Dr. Steven Harms of Baylor University in Dallas has apparently found a way to identify all cancerous tissue within a breast using magnetic resonance imaging. If his software-based technique stands up to further study, it would give physicians a tool much more reliable than X-ray mammography to diagnose breast cancer.

Guided by hospital-based physicists, magnetic-imaging equipment-makers have designed their products to be flexible, said Mark Haacke, a physicist at Case Western Reserve University in Cleveland. The physicists are experimenting with new software almost like computer hackers play with personal computers, he said.

Dr. Haacke said, "By reducing the time it takes to acquire an image to one-tenth or one-hundredth of a second, you can use magnetic resonance in ways never thought possible. "You can look at the ways a diseased region of an organ takes up blood to determine its viability. You can look at the movement of the knee to diagnose pathology.

"All these new applications require very fast data uptake, and that's just what we're exploring now."