# Are there any magnetic particles that are safe to inhale?

In medicine, there is an (old?) experiment where a subject is asked to inhale radioactive Xenon gas, and radiation counters are placed at different positions near the lungs. Using this experiment, it has been demonstrated that the (alveolar?) volume of the lungs is highest in the bottom parts, and smallest in the top parts.

I don't know if this experiment is still used today, since inhaling radioactive gas has the obvious radiation related risks.

I was wondering if there are some magnetic particles that would be safe to inhale? I know that for example helium does not diffuse into blood, and it does not permanently bind into anything. However, I think it does not have any suitable magnetic properties. Let's assume the detector is very very sensitive to any magnetic fields (so, a super-conducting quantum interference device).

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• By "magnetic" I assume you mean ferromagnetic. Ferromagnetism is generally viewed as a property of bulk matter. It has long been debated whether a gas could display "magnetic" properties. A few years ago there was a claim that a magnetic gas had been produced. I think the debate is still going on. – ron Feb 18 '15 at 17:52
• Current state of art in safe imaging of biological objects is NMR-tomography. It relies on magnetism of nucleus, specifically on interaction of radiowave, nuclear spin and magnetic field. It allows very detailed imaging, for example a detailed structure of inteconnections in a living brain. – permeakra Feb 18 '15 at 17:54
• Ferromagnetic nanoparticles do exist, and are more or less safe to inhale in small amounts (though they ARE a health risk, just like any mineral dust). On the contrary, carefully controlled inhalation of selected radioactive gas in low concentration is realtively (relatively!!!) safe. Humans do have radioactivity tolerance above zero and can tolerate minor expositions without negative effects. Nobody cares about plane flights, though they does expose passengers to above-average radioactive background. – permeakra Feb 18 '15 at 18:00

$\ce{O_2}$ is paramagnetic.