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Brain surgery advances — precision targeting

Lasers, heat maps, fluorescence and real-time imaging help guide surgeons who are developing new ways to enhance precision brain surgery.

Two things have traditionally guided neurosurgeons in the midst removing a brain tumor: sight and touch. Visual inspection and palpation is a good place to start, neurosurgeon Gordon Li, MD, will tell you, but it still leaves room for guesswork.

And in the tumor-resecting business, precision in key.

Now, surgeon-scientists at Stanford are developing new, more detailed ways to peer into the brain as they cut away diseased tissue. In my latest feature for Stanford Medicine magazine, I highlight two new tactics: precision fluorescence and intraoperative magnetic resonance imaging, or iMRI.

The former, led by otolaryngologist Eben Rosenthal, MD, harnesses fluorescent dyes to better show where in a patient's brain a tumor starts and stops. The idea is to improve tumor margins by literally illuminating it -- a glowing mass is hard to miss.

As I describe in the story:

The luminescence agent developed by Rosenthal and colleagues combines two ingredients: an antibody that latches onto tumor cells and the bright green fluorescent label. When injected into a patient intravenously, the tandem molecules flow throughout the bloodstream, binding to cancer cells.

The surgeon can see the location to which the molecules have docked using infrared light, which hits the fluorescent marker and refracts light to a special camera. The refracted light forms an image, revealing where Rosenthal, and other surgeons who use the technology, should cut.

Neurosurgeons Casey Halpern, MD, and Jaimie Henderson, MD, however, have swapped fluorescence in the OR for lasers and MRIs.

Using an MRI machine, which is typically used for diagnosing injury or disease, Halpern and Henderson have devised a tactic that lets them control a laser with high precision to kill or "ablate" specific portions of tissue in the brain. By consistently taking images with the MRI during a surgery, the surgeons can see exactly where the laser is, what it's targeting, and if it's killed the problematic tissue.

Laser surgery with the iMRI happens in a series of small steps: With the patient's body inside the MRI and head poking out, the surgeon zaps parts of the brain tumor with the laser. To check on progress, the surgeon stops and moves the patient into the center of the MRI machine, turns it on, and takes images of the brain tissue and ablated tumor. (In an iMRI image, ablated tissue appears as a different shade than normal tissue.)

The iMRI approach, though seemingly promising, might not be for everyone, said Halpern. But it adds to a growing number of ways to address life-threatening or life-altering diseases, which is critical to providing the best possible patient care.

Illustration by Stuart Bradford

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