The ability to image inside the body first became a reality in 1973 with the introduction of computed tomography, an X-ray technique that builds a three-dimensional picture from a series of "slices" through the body. Other techniques, such as positron-emission tomography, single-photon emission computed tomography and magnetic resonance imaging (MRI), have been developed since then, establishing medical imaging as a vital tool for diagnosing a range of medical conditions.
MRI is a powerful clinical tool that has the advantage of being non-invasive and, unlike X-ray imaging, it does not expose the patient to harmful radiation. However, it still cannot be used to image the lung. The problem is that conventional MRI generates digital images from the magnetic resonance signals produced by the hydrogen nuclei (protons) present in water and fat. Areas containing a high proportion of water produce strong signals, but tissues with a low water content produce much weaker signals. The proton density of the lung is about a tenth of that of other tissues, making it practically impossible to generate a clear image.
A new technique is now being developed to overcome this problem. By introducing "hyperpolarized" noble gases into the lungs, the magnetic resonance signal is made strong enough to produce images for monitoring the function of the lungs. This latest advance has once again relied on fundamental progress in atomic and nuclear physics.
In the November issue of Physics World, G Allan Johnson, Laurence Hedlund and James MacFall from the Center for In Vivo Microscopy, Duke University, North Carolina write about the latest research in NMI.