Using a biopsy needle, doctors may be able to deliver a device that monitors cancer—whether it's the growth of a tumor or the progress of chemotherapy. Developed by researchers at the Massachusetts Institute of Technology, the monitor, which is about the size of a grain of rice, has been tested in mice. Once deployed in the body, the coated particles inside the device bind with specific molecules and can be visualized under MRI scans, for example. Instead of relying on biopsies for additional information about tumors and their response to treatment, the monitors provide doctors with constant data. The device uses magnetic nanoparticles developed by a Harvard professor who is also a cofounder of the company that is commercializing the technology. The nanoparticles can detect biomarkers that could potential help doctors decide which cancer treatments are best for patients in the long run. The researchers also suggest that a second device could be used for releasing drugs.