Brain tumor survivors live with the constant worry that their cancer might come back. And even if they have a brain scan every few months to check, doctors often can’t tell the difference between new cancer growth and tissue changes related to their treatment with radiation or chemotherapy. That leaves patients with a tricky choice. Do they wait and watch? Let doctors take a brain biopsy? Or, in some cases, endure another brutal round of treatment just in case the tumor has returned? But a new University of Michigan study shows that a relatively new kind of brain scan may give these patients the reassurance -- or early warning -- that they can’t get from the usual scans. U-M radiologists will present the evidence today at the annual meeting of the American Roentgen Ray Society, a major radiology organization.The approach is called 2D CSI MRS, short for two-dimensional chemical shift imaging magnetic resonance spectroscopy. It allows doctors to non-invasively detect the levels of certain chemicals in brain tissue. Using the relative quantities of these chemicals, doctors can tell what’s really going on near a tumor’s original location.