A surgeon removes a breast tumor, but how do you know no cancer cells are left at the edge? Right now, the tissue goes to a lab, and the answer comes back days later. If the margin is not clean, a second surgery is needed. The new method promises to give the answer right in the operating room, while the patient is still on the table.

The device works like a microwave 'lamp': it illuminates the removed tissue with invisible radiation, and a single pixel captures the reflected signal. Under the tissue lies a silicon wafer that changes its transparency to microwaves when exposed to light. This allows scanning a 10 by 10 centimeter area with a step of just one millimeter, like running your finger over a surface and feeling every bump.

The authors tested the method on gelatin models of tumors with varying water content. The device found and measured even a thin layer of diseased tissue 2 millimeters thick — exactly the threshold surgeons consider dangerous. Numerical simulations showed the method is not thrown off by individual differences in patients' tissues.

Such a scanner fits into an operating room and requires no lengthy setup. If trials on real tissues confirm the results, repeat surgeries due to unclean margins could become rare.