Make MRI Images Crisper with Iron Oxide Nanoparticles
Medical imaging has come a long way in the last hundred years. The next great improvements in imaging may be largely due to nanotechnology, which helps diagnosticians pinpoint problem spots and improve the quality of images.
Physicians often use magnetic resonance imaging (MRI) to obtain images of the organs in a patient and avoid potentially harmful imaging methods such as x-raying.
So how does MRI work? Most of the molecules in your body contain hydrogen. Water molecules have two hydrogen atoms, and the organic molecules that make up the rest of our bodies are called hydrocarbons because they contain hydrogen and carbon. The magnetic fields generated by the MRI machine interact with hydrogen atoms throughout the body, producing an image of all the organs.
Hydrogen has just one proton in its nucleus. It’s this proton in hydrogen that the MRI uses to produce images of the inside of a patient. In the magnetic field generated by the MRI machine, the spin of the protons in the hydrogen atoms are set in one direction.
If you’ve been unfortunate enough to plow through about 200 advanced mathematics classes to study quantum mechanics, you know that protons have spin. The direction of that spin determines the direction of a magnet, which is composed of the spins of all the charged particles (protons and electrons) together.
To take an MRI image, the MRI machine generates a radio frequency pulse that has just the right amount of energy to flip the spin direction of the protons. When the protons flip back to the spin direction aligned with the magnetic field, they send out another radio frequency pulse. This pulse is detected by the machine, which then uses the pulse to generate an image.
The time it takes for the protons to flip back and generate the return radio frequency pulse depends on the protons’ location and the density of the tissue. This relaxation time is different for protons in an organ than for protons in the bloodstream and is different for healthy tissue than it is for cancer tumors. These differences in the relaxation time are used to generate the MRI images.
By now, you’re asking yourself, where do nanoparticles enter the picture? Remember that iron oxide is paramagnetic. You get a better MRI image if paramagnetic nanoparticles are attached to the object you’re imaging.
Paramagnetic nanoparticles reduce the time it takes for the protons to flip back to the spin direction aligned with the magnetic field. Therefore, the difference in the relaxation time of the tissue that has nanoparticles attached versus the relaxation time of the surrounding tissue is greater, which creates more contrast and produces a clearer image.
Because of this effect, researchers are functionalizing iron oxide nanoparticles by coating them with molecules attracted to specific sites, such as cancer tumors, to provide a better MRI image.