For doctors as well as patients, detecting metastases can be a notoriously burdensome affair. Often, the only way to see whether a patient’s lymph nodes are invaded by cancer cells is to surgically remove and inspect them. In some cases, such as gastric cancer, this can mean several hours of sorting through the nodes in the abdominal cavity before even tackling the primary tumor. Even then surgeons are not sure they are looking in the right place. Now a new imagining technique — which employs a fleet of tiny magnetic particles — reveals lymph node metastases that are invisible to other approaches. “You have to understand that the importance of this is tremendous. It is going to change the way we do clinical practice,” said Ralph Weissleder, Harvard Medical School (HMS) professor of radiology at Massachusetts General Hospital. “I cross surgeons in the corridor and they say if we could have something like this right now, it would save them a tremendous amount of effort,” said Mukesh Harisinghani, HMS instructor in radiology at MGH. Weissleder, Harisinghani and colleagues reported on the new method in the June 19, 2003 New England Journal of Medicine.