Mathis says that one of the advantages of the combined imaging system is simply logistical. For patients who have Alzheimer's disease, depression, or bipolar disorder, "getting [them] in is half the battle," he says. Elderly and sick volunteers and their caretakers often have to go to the clinic on two different days for a PET and an MRI; each scan takes about an hour and can cause discomfort in feeble patients, who must lie still. Subjecting patients to one simultaneous scan, instead of two, would cut in half the time spent in the radiology department.

For studying the effects of pharmaceuticals on the brain, the element of time is critical, says Mathis, and performing PET and MRI scans separately means that researchers are making a lot of assumptions. Mathis suspects that, using the combined system, it will take "fewer experiments to nail down the source of pharmaceutical effects."

Darrow says that Siemens has sent a few PET/MRI machines to researchers and is about 18 months from releasing the first commercial device. The company is also working on developing a whole-body simultaneous PET/MRI imaging system. The primary application for the whole-body system will be to search for cancerous tumors that have spread beyond their initial site.