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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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  • $\begingroup$ Welcome to chemistry.SE! If you had any questions about the policies of our community, you can ‎visit the help center or take a ‎‎tour of the websit‎e. || Not bad, not bad! We're starting to get good questions from everyone, basically. $\endgroup$
    – M.A.R.
    Commented Feb 18, 2015 at 17:37
  • $\begingroup$ 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. $\endgroup$
    – ron
    Commented Feb 18, 2015 at 17:52
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    $\begingroup$ 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. $\endgroup$
    – permeakra
    Commented Feb 18, 2015 at 17:54
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    $\begingroup$ 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. $\endgroup$
    – permeakra
    Commented Feb 18, 2015 at 18:00

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$\ce{O_2}$ is paramagnetic.

enter image description here

source: http://www.chem1.com/acad/webtext/chembond/CB-images/liquidoxygeninmagnet.jpg

The stable Xenon isotope Xe-129 has been used in MRI studies:

Hyperpolarized Xenon MR Imaging of the Brain

A radically new magnetic resonance imaging (MRI) technique, using hyperpolarized 3He and 129Xe, is being developed to produce high-contrast images of important body tissues that have resisted conventional MRI techniques. Hyperpolarization of the noble gas nuclei is achieved by spin exchange with rubidium atoms that have been optically pumped into one electronic spin state with the use of circularly polarized light from a high-power diode laser system. Hyperpolarization can increase the detectability of 3He and 129Xe up to a hundred thousand times. This technology is showing dramatic results for diagnostic imaging of the lungs, brain, and other parts of the body. Most notably, we have achieved high-resolution dynamic images of the lungs and airways using 3He, and measured cerebral perfusion in the brain using 129Xe.

See video of lung being imaged: http://www.spl.harvard.edu/archive/HypX/about.html

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  • $\begingroup$ Does NMR/MRI count here? If so, then any NMR active nucleus should be considered 'magnetic'? $\endgroup$
    – jerepierre
    Commented Feb 18, 2015 at 18:29
  • $\begingroup$ As @DavePhD states, hyperpolarized xenon is used as an MRI [NMR for the non-PC] contrast medium and is not radioactive. For a study on the lungs, see ultra.bu.edu/projects.asp?project=mri. $\endgroup$
    – DrMoishe Pippik
    Commented Feb 18, 2015 at 19:06

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