In contrast

scientists have ‘programmed’ cells to make their own contrast agents.

The results, appearing in the April issue of Nature Medicine, hold considerable promise for conducting preclinical studies in the emerging field of molecular therapeutics and for monitoring the delivery of therapeutic genes in patients.

To trigger living cells into producing their own contrast agent, Eric Ahrens, assistant professor of biological sciences in the Mellon College of Science at Carnegie Mellon, gave them a gene that produces a form of ferritin, a protein that normally stores iron in a non-toxic form. This metalloprotein acts like a nano-magnet and a potent MRI ‘reporter.’

A typical MRI scan detects and analyzes signals given off by hydrogen protons in water molecules after they are exposed to a magnetic field and radiofrequency pulses. These signals are then converted into an image. Ahrens' new MRI reporter alters the magnetic field in its proximity, causing nearby protons to give off a distinctly different signal. The resulting image reveals dark areas that indicate the presence of the MRI reporter.