Editing Magnetic resonance imaging (section)

=== Multinuclear imaging ===
{{See also|Helium-3#Medical imaging}}

Hydrogen has the most frequently imaged [[atomic nucleus|nucleus]] in MRI because it is present in biological tissues in great abundance, and because its high [[gyromagnetic ratio]] gives a strong signal. However, any nucleus with a net [[Spin (physics)|nuclear spin]] could potentially be imaged with MRI. Such nuclei include [[deuterium]], [[helium-3]], [[lithium-7]], [[carbon-13]], [[fluorine]]-19, [[oxygen-17]], [[sodium]]-23, [[phosphorus]]-31 and [[Xenon#Isotopes|xenon-129]]. <sup>2</sup>H, <sup>23</sup>Na and <sup>31</sup>P are naturally abundant in the body, so they can be imaged directly. Naturally abundant deuterium at the concentration of around 15mM can be imaged, but suffers from low gamma sensitivity and quadripolar [[Relaxation (NMR)]]. Deuterium imaging however has a sparse chemical shift spectra making it possible to develop tailored multiband selective RF pulses for metabolite selective imaging. Thus, metabolic imaging, similar to what's done with Carbon-13 is possible with Deuterium metabolic imaging (DMI) for insights into vivo metabolic processes. As well, the short T2 of deuterium allows it to be signal averaged rapidly, making up for some of its physical shortcomings. Gaseous isotopes such as <sup>3</sup>He or <sup>129</sup>Xe must be [[hyperpolarization (physics)|hyperpolarized]] and then inhaled as their nuclear density is too low to yield a useful signal under normal conditions. [[oxygen-17|<sup>17</sup>O]] and <sup>19</sup>F can be administered in sufficient quantities in liquid form (e.g. [[oxygen-17|<sup>17</sup>O]]-water) that hyperpolarization is not a necessity.<ref>{{cite journal | vauthors = Gore JC, Yankeelov TE, Peterson TE, Avison MJ | title = Molecular imaging without radiopharmaceuticals? | journal = Journal of Nuclear Medicine | volume = 50 | issue = 6 | pages = 999–1007 | date = June 2009 | pmid = 19443583 | pmc = 2719757 | doi = 10.2967/jnumed.108.059576 | publisher = Society of Nuclear Medicine }}</ref> Using helium or xenon has the advantage of reduced background noise, and therefore increased contrast for the image itself, because these elements are not normally present in biological tissues.<ref>{{cite web |url= http://www.spl.harvard.edu/archive/HypX/currentresult0.html |title= Hyperpolarized Noble Gas MRI Laboratory: Hyperpolarized Xenon MR Imaging of the Brain |publisher= Harvard Medical School |access-date= 2017-07-26 |archive-date= 2018-09-20 |archive-url= https://web.archive.org/web/20180920032925/http://www.spl.harvard.edu/archive/HypX/currentresult0.html |url-status= dead }}</ref>

Moreover, the nucleus of any atom that has a net nuclear spin and that is bonded to a hydrogen atom could potentially be imaged via heteronuclear magnetization transfer MRI that would image the high-gyromagnetic-ratio hydrogen nucleus instead of the low-gyromagnetic-ratio nucleus that is bonded to the hydrogen atom.<ref>{{cite journal |doi=10.1016/0022-2364(91)90395-a |title=Gradient-enhanced proton-detected heteronuclear multiple-quantum coherence spectroscopy |journal=Journal of Magnetic Resonance |volume=91 |issue=3 |pages=648–53 |year=1991 | vauthors = Hurd RE, John BK |bibcode=1991JMagR..91..648H }}</ref> In principle, heteronuclear magnetization transfer MRI could be used to detect the presence or absence of specific chemical bonds.<ref>{{cite journal |doi=10.1006/jmra.1995.1064 |title=A Test for Scaler Coupling between Heteronuclei Using Gradient-Enhanced Proton-Detected HMQC Spectroscopy |journal=Journal of Magnetic Resonance, Series A |volume=113 |issue=1 |pages=117–19 |year=1995 | vauthors=Brown RA, Venters RA, Tang PP, Spicer LD |bibcode=1995JMagR.113..117B }}</ref><ref>{{cite journal | vauthors = Miller AF, Egan LA, Townsend CA | title = Measurement of the degree of coupled isotopic enrichment of different positions in an antibiotic peptide by NMR | journal = Journal of Magnetic Resonance | volume = 125 | issue = 1 | pages = 120–31 | date = March 1997 | pmid = 9245367 | doi = 10.1006/jmre.1997.1107 | s2cid = 14022996 | bibcode = 1997JMagR.125..120M | doi-access = free }}</ref>

Multinuclear imaging is primarily a research technique at present. However, potential applications include functional imaging and imaging of organs poorly seen on <sup>1</sup>H MRI (e.g., lungs and bones) or as alternative contrast agents. Inhaled hyperpolarized <sup>3</sup>He can be used to image the distribution of air spaces within the lungs. Injectable solutions containing <sup>13</sup>C or stabilized bubbles of hyperpolarized <sup>129</sup>Xe have been studied as contrast agents for angiography and perfusion imaging. <sup>31</sup>P can potentially provide information on bone density and structure, as well as functional imaging of the brain. Multinuclear imaging holds the potential to chart the distribution of lithium in the human brain, this element finding use as an important drug for those with conditions such as bipolar disorder.<ref name="NecusSinha2019">{{cite journal | vauthors = Necus J, Sinha N, Smith FE, Thelwall PE, Flowers CJ, Taylor PN, Blamire AM, Cousins DA, Wang Y | display-authors = 6 | title = White matter microstructural properties in bipolar disorder in relationship to the spatial distribution of lithium in the brain | journal = Journal of Affective Disorders | volume = 253 | pages = 224–231 | date = June 2019 | pmid = 31054448 | pmc = 6609924 | doi = 10.1016/j.jad.2019.04.075 | doi-access = free }}</ref>