An experimental cancer imaging tool that makes tumors glow brightly during surgery has shown promise in a Penn Medicine clinical study of patients with brain cancer.

The fluorescent dye technique, originally developed by surgeons at the Penn Center for Precision Surgery to treat lung cancer, illuminated brain tumors in real time during surgery, helping physicians distinguish between healthy and cancerous tissue.

One challenge with brain surgery is ensuring the entire tumor is removed. It is difficult to identify the margins of the tumor with current approaches. Cancer tissue not visible to the naked eye or felt by fingers is often missed during tumor removal, leading to recurrence in up to 20-50% of patients.

One challenge with brain surgery is ensuring the entire tumor is removed. One challenge with brain surgery is ensuring the entire tumor is removed. “Fluorescent contrast agents take visualization to a whole new level,” says Dr. John Lee, associate professor of neurosurgery at the University of Pennsylvania. “It has the potential for real-time imaging, identification of disease and, most importantly, precise detection of the tumor’s margins. With this, we know better where to cut.”

The technique uses near-infrared (NIR) imaging and the contrasting agent indocyanine green (ICG), which fluoresces a bright green under NIR light. ICG was developed during World War II as a dye for photography. In 1958, it was approved by the U.S. Food and Drug Administration (FDA) for use in medicine, primarily in liver diagnostics and later in cardiology.

For this study, researchers used a modified version of ICG at a higher concentration delivered intravenously about 24 hours before surgery to ensure margins were included. This is believed to be the first time that this delayed imaging of ICG has been used to visualize brain tumors.

Twelve of the 15 tumors that the technique was used on demonstrated strong intraoperative fluorescence. The lack of glow in the three other tumors could potentially have been due to their disease grade and the timing of the injection, the researchers suggest.

Eight of the 15 patients demonstrated that a visible glow through the dura—a thick membrane on the meninges of the brain—was opened,. This demonstrated the technology’s ability to see deeply within the brain before the tumor is exposed. Once opened, all tumors were picked up by NIR imaging.

Over the past three-plus years, Lee and colleagues have performed more than 300 surgeries with the imaging tool in patients with various types of cancer, including lung, brain, bladder, and breast.

To contact the author of this article, email