Magnetic resonance imaging (MRI) can create detailed images of almost all the tissues of the body, allowing doctors to monitor blood flow in the brain, map the borders of tumors, and find slipped spinal discs. But conventional MRI, which images water in the body, produces poor pictures of the lungs, which are full of air, and gives an incomplete picture of lung functions. Now researchers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, have built a cheap MRI machine that uses a weak magnetic field to image critical aspects of lung physiology that are invisible to conventional imaging techniques.
Led by Matthew Rosen, a visiting scientist at the Harvard-Smithsonian center, and Ronald Walsworth, a senior lecturer in physics at Harvard, the researchers built an MRI scanner that images how gas flows through the lungs and how much oxygen is being absorbed throughout lung tissue. They’ve used the system to study how lung function differs when lying down and sitting or standing up, and are planning a study of asthma in conjunction with the Martinos Center for Biomedical Imaging in Boston. The system has not yet been used to compare healthy and diseased patients. If it proves its worth in clinical trials, the Harvard researchers believe it would be inexpensive and simple enough to be used in pulmonologists’ offices.
Lung function is dependent on the orientation of the body, but it hasn’t been possible to study this before because conventional MRI would require patients to lie on their backs. (PET can be used to look at some aspects of the physiology of the lungs but it gives limited information.) Asthma symptoms can be exacerbated when patients lie down, for example. The Harvard system “allows imaging with the patient in any orientation, something no one has ever been able to do,” says Bastiaan Driehuys, an assistant professor at the Center for In Vivo Microscopy at Duke University.
The open MRI system may also make it possible to monitor the lung function of newborns in intensive care without taking them out of their incubators. The researchers have filed a provisional patent for this application.
Unlike conventional MRI, which images the protons in water molecules, the Harvard MRI system monitors magnetically polarized helium gas inhaled by subjects. Conventional MRI requires a magnet about 150 times stronger than that in the Harvard system to magnetically align protons inside the body. But the helium used in the Harvard system is magnetically aligned before the patient inhales it, making it possible to use a very weak magnet inside the scanner.