Magnetic-resonance imaging has dramatically improved doctors' views of the body. But obtaining clear pictures of the lungs has been a struggle. Now researchers at Harvard Medical School have found a way to make these MRIs crystal clear.

In an experimental procedure for performing lung MRIs, a patient takes a breath of polarized helium, which naturally spreads through the lungs' branching airways to the oxygen-filtering sacs at their ends. The gas becomes magnetized and highlights the airways in the scan-but the sacs light up, too, which largely blocks the view. The Harvard researchers have improved upon this method: hyperpolarized helium is administered as the patient inhales for several seconds, while the MRI scanner records a series of images of the gas spreading through the airways. Radio-frequency pulses from the scanner also depolarize the helium that reaches the air sacs-producing clear images of just the airways. The technique could aid diagnoses of asthma and cystic fibrosis. Durham, NC-based startup Polarean is commercializing polarization systems that will enable these types of MRIs; the company plans to pursue FDA approval starting in 2005.