The signals for conventional magnetic resonance imaging (MRI) come from the nuclei of ordinary hydrogen (¹H) atoms in the human body. It is difficult to image body parts such as the lungs which contain relatively few hydrogen atoms. However, excellent magnetic resonance images of the lungs can be obtained if the patient first takes a deep breath of the gases helium-3 (³He) or xenon-129 (¹²⁹Xe) which have had their nuclear spin polarizations increased to tens of percent by laser optical pumping. The magnetic resonance images from the hyperpolarized nuclei of these gases are as good as, and often better than, conventional images from hydrogen in tissue. Because of its high solubility in human tissue, hyperpolarized xenon-129 is useful for imaging other body parts as well as the lungs.