New Hi-Tech Images Guide Surgeons' Hands
So Golby and her colleagues have taught MRI a new way of seeing. The trick is to combine three different types of MRI scan into one image. First, they use a technique known as "functional MRI" to identify brain regions linked to vital abilities; fMRI maps blood flow in the brain as patients perform such tasks as pointing to an object or reading. Areas that show increased blood flow are the ones responsible for those abilities.
Next, Golby marries the fMRI image to another MRI scan, tweaked by powerful computer programs to reveal the nerve fibers. Water molecules move in particular patterns along such fibers; the computer can pick out those patterns in the scan and turn them into an image outlining the fibers. Finally, a detailed MRI showing brain anatomy is fused with the other two. "We can visualize functional areas, along with the nerve tracts and the cancer, see them all in one image," Golby says–and then plan a safe way to remove the tumor before making a single cut.
Once an operation begins, neurosurgeons have to cope with a second big hurdle: "brain shift." The brain moves slightly in the skull during surgery, so landmarks identifying healthy brain tissue in even the most detailed pre-op scan end up a centimeter or so away from where they started. At Brigham, surgeons have responded by moving an MRI scanner into the operating room. Unlike the long tube dreaded by the typical MRI candidate, the OR version features two large, circular magnets, one at the head of the surgical table and the other surrounding its middle; Brigham doctors call it "the double donut." They stand between the magnets to operate. Scans made as the operation progresses capture any changes and project them on a monitor, Golby says. Recent advances have produced a smaller, more portable version of the scanner that's now used in other hospitals.
With MRI capability in the operating room, surgeons also can check to see that they got all of the cancer before closing up the patient, reducing the chances of recurrence and the need for more surgery. "You really don't want to go back in," says radiologist Ferenc Jolesz, director of the National Center for Image Guided Therapy, based at Brigham. In a 2003 study, this kind of MRI found residues of brain cancer in 36 percent of patients while they were still on the table, which surgeons were then able to remove. In another 31 percent, imaging revealed the cancer had been fully removed, avoiding the need for addition probing and cutting of the brain.
The Brigham MRI is being used to guide cancer therapy at the other end of the body, too. For many patients with early-stage, localized prostate tumors, brachytherapy–implanting 50 to 100 or so tiny radioactive seeds in the prostate, using needles–is very effective. Usually, however, the location of these implants is guided by ultrasound images, which can give a muddy view of the prostate. That's a weakness: In addition to targeting and curing the cancer, radiologists want to avoid damaging nerves and other tissues, which can cause impotence and incontinence. By taking a finely detailed image as each needle is inserted, urologists and radiologists can make sure it is going into the right place.
advertisement
