MRI of Hyperpolarized Media

What are the problems with observing lungs with MRI? Where can endogenous spin polarization be found in the human body? Senior Lecturer of Physics at Harvard University, Ronald Walsworth, talks on using noble gases as imageable markers for MRI.

If you place a large magnetic field other strong fields will tend to align with the magnetic field and the right orientation is energetically favorable. But even in a field as large as 10 or 50 thousand times the Earth’s magnetic field the magnetic moments are still small, which come from the nuclei inside your body and are only partially aligned. There’s only a net alignment of one out of a hundred thousand. So out of every hundred thousand nuclei, there’s only one axis pointing up along the field.

You can take species of atoms and have most of their spins or magnetic moments all properly aligned. You can do this in weakly interacting gases, and it’s particularly effective in gases like helium-3. So, an isotope of the noble gas, helium, which is a non-radioactive isotope. Also, xenon-129, another noble gas isotope which is non-radioactive. Both are very safe for humans. They’re noble gases or inert gases, because like the nobles of old they were standoffish and don’t want to interact with the commoners.

Unlike helium-3, a little bit of the xenon is taken up into the blood and then flows through the body and can be used as a tracer of blood flow. Even though it’s dissolved in the blood, it loses spin polarization,or magnetization, very slowly. So, it’s a bright unique MRI imageable marker they can be used to study blood flow through the brain and other parts of the body. It’s very safe to breath, eventually it comes back to lungs and you breath it back out.