Cima says his group can design the nanoparticles to detect almost anything by choosing the right antibody. He and his colleagues are currently testing implants that can detect one molecule, the hormone hCG (which is made by several tumors), in mice. Cima's MIT lab is working with that of Ralph Weissleder, director of Harvard University's Center for Molecular Imaging Research, to develop the nanoparticles. Other collaborators include MIT professor Robert Langer, who is a leader in nanomedicine.

Cima is also developing tumor implants with multiple chambers, each of which holds nanoparticles that can detect a different molecule. (The nanoparticles can't be combined in the same chamber because they can't be distinguished in an MRI scan unless they are in spatially distinct locations.) Such devices could be read again and again over the course of a patient's treatment; each chamber would show up as a different spot on an MRI image. Particles in one chamber might detect the presence of a drug in the tumor. Those in another chamber might detect a product of cancer metabolism like glucose, which would help doctors monitor the effects of a drug on a tumor's activity. Once their tumors have shrunk, patients harboring the implant could be monitored for signs that the cancer has come back.

Looking to the future, Cima says he hopes the process won't involve running patients through an MRI scanner again and again. His group is working to modify a portable MRI machine to function with the detecting implant. About the size of a box of tissues, the scanner could be waved over the part of the body that harbors the device and take a quick image.

Molnar says the monitoring implant could provide peace of mind for patients. "The earlier you detect [cancer recurrence], the easier it is to treat," she says.