Editing Magnetic resonance imaging (section)

== Specialized configurations ==

=== Magnetic resonance spectroscopy ===

{{Main|In vivo magnetic resonance spectroscopy|Nuclear magnetic resonance spectroscopy}}

[[In vivo magnetic resonance spectroscopy|Magnetic resonance spectroscopy]] (MRS) is used to measure the levels of different [[metabolites]] in body tissues, which can be achieved through a variety of single voxel or imaging-based techniques.<ref>{{cite journal | vauthors = Landheer K, Schulte RF, Treacy MS, Swanberg KM, Juchem C | title = Theoretical description of modern <sup>1</sup> H in Vivo magnetic resonance spectroscopic pulse sequences | journal = Journal of Magnetic Resonance Imaging | volume = 51 | issue = 4 | pages = 1008–1029 | date = April 2020 | pmid = 31273880 | doi = 10.1002/jmri.26846 | s2cid = 195806833 }}</ref> The MR signal produces a spectrum of resonances that corresponds to different molecular arrangements of the isotope being "excited". This signature is used to diagnose certain metabolic disorders, especially those affecting the brain,<ref>{{cite journal | vauthors = Rosen Y, Lenkinski RE | title = Recent advances in magnetic resonance neurospectroscopy | journal = Neurotherapeutics | volume = 4 | issue = 3 | pages = 330–45 | date = July 2007 | pmid = 17599700 | pmc = 7479727 | doi = 10.1016/j.nurt.2007.04.009 | doi-access = free }}</ref> and to provide information on tumor [[metabolism]].<ref>{{cite journal | vauthors = Golder W | title = Magnetic resonance spectroscopy in clinical oncology | journal = Onkologie | volume = 27 | issue = 3 | pages = 304–9 | date = June 2004 | pmid = 15249722 | doi = 10.1159/000077983 | s2cid = 20644834 }}</ref>

Magnetic resonance spectroscopic imaging (MRSI) combines both spectroscopic and imaging methods to produce spatially localized spectra from within the sample or patient. The spatial resolution is much lower (limited by the available [[Signal-to-noise ratio|SNR]]), but the spectra in each voxel contains information about many metabolites. Because the available signal is used to encode spatial and spectral information, MRSI requires high SNR achievable only at higher field strengths (3 T and above).<ref name="DW Al. 2018">{{cite journal | vauthors = Chakeres DW, Abduljalil AM, Novak P, Novak V | title = Comparison of 1.5 and 8 tesla high-resolution magnetic resonance imaging of lacunar infarcts | journal = Journal of Computer Assisted Tomography | volume = 26 | issue = 4 | pages = 628–32 | year = 2002 | pmid = 12218832 | doi = 10.1097/00004728-200207000-00027 | s2cid = 32536398 }}</ref> The high procurement and maintenance costs of MRI with extremely high field strengths<ref>{{cite web |url=https://www.medischcontact.nl/nieuws/laatste-nieuws/artikel/mri-scanner-van-7-miljoen-in-gebruik.htm |title=MRI-scanner van 7 miljoen in gebruik |trans-title=MRI scanner of €7 million in use |language=nl |publisher=Medisch Contact |date=December 5, 2007 }}</ref> inhibit their popularity. However, recent [[compressed sensing]]-based software algorithms (''e.g.'', [[SAMV (algorithm)|SAMV]]<ref name=AbeidaZhang>{{cite journal |doi=10.1109/tsp.2012.2231676 |title=Iterative Sparse Asymptotic Minimum Variance Based Approaches for Array Processing |journal=IEEE Transactions on Signal Processing |volume=61 |issue=4 |pages=933–44 |year=2013 | vauthors = Abeida H, Zhang Q, Li J, Merabtine N |arxiv=1802.03070 |bibcode=2013ITSP...61..933A |s2cid=16276001 }}</ref>) have been proposed to achieve [[Super-resolution imaging|super-resolution]] without requiring such high field strengths.

=== Real-time ===
[[File:Real-time MRI - Thorax.ogv|thumb|right|Real-time MRI of a [[human heart]] at a resolution of 50&nbsp;ms]]{{Excerpt|Real-time MRI}}

=== Interventional MRI ===
{{Main|Interventional magnetic resonance imaging}}

The lack of harmful effects on the patient and the operator make MRI well-suited for [[interventional radiology]], where the images produced by an MRI scanner guide minimally invasive procedures. Such procedures use no [[ferromagnetic]] instruments.<ref>{{cite journal | vauthors = Lewin JS | title = Interventional MR imaging: concepts, systems, and applications in neuroradiology | journal = AJNR. American Journal of Neuroradiology | volume = 20 | issue = 5 | pages = 735–48 | date = May 1999 | pmid = 10369339 | pmc = 7056143 | url = http://www.ajnr.org/content/20/5/735 }}</ref>

A specialized growing subset of [[Interventional magnetic resonance imaging|interventional MRI]] is [[intraoperative MRI]], in which an MRI is used in surgery. Some specialized MRI systems allow imaging concurrent with the surgical procedure. More typically, the surgical procedure is temporarily interrupted so that MRI can assess the success of the procedure or guide subsequent surgical work.<ref>{{Cite book |url=https://archive.org/details/galeencyclopedia0001unse_r6b8 |title=The Gale Encyclopedia of Nursing and Allied Health |vauthors=Sisk JE |publisher=Gale |year=2013 |isbn=9781414498881 |edition=3rd |location=Farmington, MI |url-access=registration |via=Credo Reference}}</ref>

=== Magnetic resonance guided focused ultrasound ===
In guided therapy, [[high-intensity focused ultrasound]] (HIFU) beams are focused on a tissue, that are controlled using MR thermal imaging. Due to the high energy at the focus, the temperature rises to above 65 [[°C]] (150&nbsp;°F) which completely destroys the tissue. This technology can achieve precise [[ablation]] of diseased tissue. MR imaging provides a three-dimensional view of the target tissue, allowing for the precise focusing of ultrasound energy. The MR imaging provides quantitative, real-time, thermal images of the treated area. This allows the physician to ensure that the temperature generated during each cycle of ultrasound energy is sufficient to cause thermal ablation within the desired tissue and if not, to adapt the parameters to ensure effective treatment.<ref>{{cite journal | vauthors = Cline HE, Schenck JF, Hynynen K, Watkins RD, Souza SP, Jolesz FA | title = MR-guided focused ultrasound surgery | journal = Journal of Computer Assisted Tomography | volume = 16 | issue = 6 | pages = 956–65 | date = 1992 | pmid = 1430448 | doi = 10.1097/00004728-199211000-00024 | s2cid = 11944489 }}</ref>

=== 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>

=== Molecular imaging by MRI ===
{{Main|Molecular imaging}}

MRI has the advantages of having very high spatial resolution and is very adept at morphological imaging and functional imaging. MRI does have several disadvantages though. First, MRI has a sensitivity of around 10<sup>−3</sup> [[concentration#Molarity|mol/L]] <!--is this what M was supposed to be, molarity? if not, explain and link as appropriate--> to 10<sup>−5</sup> mol/L, which, compared to other types of imaging, can be very limiting. This problem stems from the fact that the population difference between the nuclear spin states is very small at room temperature. For example, at 1.5 [[tesla (unit)|teslas]], a typical field strength for clinical MRI, the difference between high and low energy states is approximately 9 molecules per 2&nbsp;million. Improvements to increase MR sensitivity include increasing magnetic field strength and [[Hyperpolarization (physics)|hyperpolarization]] via optical pumping or dynamic nuclear polarization. There are also a variety of signal amplification schemes based on chemical exchange that increase sensitivity.<ref name="Gallagher2010">{{cite journal | vauthors = Gallagher FA | title = An introduction to functional and molecular imaging with MRI | journal = Clinical Radiology | volume = 65 | issue = 7 | pages = 557–66 | date = July 2010 | pmid = 20541655 | doi = 10.1016/j.crad.2010.04.006 }}</ref>

To achieve molecular imaging of disease biomarkers using MRI, targeted MRI [[contrast agent]]s with high specificity and high relaxivity (sensitivity) are required. To date, many studies have been devoted to developing targeted-MRI contrast agents to achieve molecular imaging by MRI. Commonly, peptides, antibodies, or small ligands, and small protein domains, such as HER-2 affibodies, have been applied to achieve targeting. To enhance the sensitivity of the contrast agents, these targeting moieties are usually linked to high payload MRI contrast agents or MRI contrast agents with high relaxivities.<ref>{{cite journal | vauthors = Xue S, Qiao J, Pu F, Cameron M, Yang JJ | title = Design of a novel class of protein-based magnetic resonance imaging contrast agents for the molecular imaging of cancer biomarkers | journal = Wiley Interdisciplinary Reviews. Nanomedicine and Nanobiotechnology | volume = 5 | issue = 2 | pages = 163–79 | year = 2013 | pmid = 23335551 | pmc = 4011496 | doi = 10.1002/wnan.1205 }}</ref> A new class of gene targeting MR contrast agents has been introduced to show gene action of unique mRNA and gene transcription factor proteins.<ref name="pmid17234603">{{cite journal | vauthors = Liu CH, Kim YR, Ren JQ, Eichler F, Rosen BR, Liu PK | title = Imaging cerebral gene transcripts in live animals | journal = The Journal of Neuroscience | volume = 27 | issue = 3 | pages = 713–22 | date = January 2007 | pmid = 17234603 | pmc = 2647966 | doi = 10.1523/JNEUROSCI.4660-06.2007 }}</ref><ref name="pmid24115049">{{cite journal | vauthors = Liu CH, Ren J, Liu CM, Liu PK | title = Intracellular gene transcription factor protein-guided MRI by DNA aptamers in vivo | journal = FASEB Journal | volume = 28 | issue = 1 | pages = 464–73 | date = January 2014 | pmid = 24115049 | pmc = 3868842 | doi = 10.1096/fj.13-234229 | doi-access = free }}</ref> These new contrast agents can trace cells with unique mRNA, microRNA and virus; tissue response to inflammation in living brains.<ref name="pmid19295156">{{cite journal | vauthors = Liu CH, You Z, Liu CM, Kim YR, Whalen MJ, Rosen BR, Liu PK | title = Diffusion-weighted magnetic resonance imaging reversal by gene knockdown of matrix metalloproteinase-9 activities in live animal brains | journal = The Journal of Neuroscience | volume = 29 | issue = 11 | pages = 3508–17 | date = March 2009 | pmid = 19295156 | pmc = 2726707 | doi = 10.1523/JNEUROSCI.5332-08.2009 }}</ref> The MR reports change in gene expression with positive correlation to TaqMan analysis, optical and electron microscopy.<ref name="pmid23150521">{{cite journal | vauthors = Liu CH, Yang J, Ren JQ, Liu CM, You Z, Liu PK | title = MRI reveals differential effects of amphetamine exposure on neuroglia in vivo | journal = FASEB Journal | volume = 27 | issue = 2 | pages = 712–24 | date = February 2013 | pmid = 23150521 | pmc = 3545538 | doi = 10.1096/fj.12-220061 | doi-access = free }}</ref>

=== Parallel MRI ===
It takes time to gather MRI data using sequential applications of magnetic field gradients. Even for the most streamlined of [[MRI sequences|MRI sequence]]s, there are physical and physiologic limits to the rate of gradient switching. Parallel MRI circumvents these limits by gathering some portion of the data simultaneously, rather than in a traditional sequential fashion. This is accomplished using arrays of radiofrequency (RF) detector coils, each with a different 'view' of the body. A reduced set of gradient steps is applied, and the remaining spatial information is filled in by combining signals from various coils, based on their known spatial sensitivity patterns. The resulting acceleration is limited by the number of coils and by the signal to noise ratio (which decreases with increasing acceleration), but two- to four-fold accelerations may commonly be achieved with suitable coil array configurations, and substantially higher accelerations have been demonstrated with specialized coil arrays. Parallel MRI may be used with most [[MRI sequences|MRI sequence]]s.

After a number of early suggestions for using arrays of detectors to accelerate imaging went largely unremarked in the MRI field, parallel imaging saw widespread development and application following the introduction of the SiMultaneous Acquisition of Spatial Harmonics (SMASH) technique in 1996–7.<ref name="SMASH">{{cite journal | vauthors = Sodickson DK, Manning WJ| title =  Simultaneous acquisition of spatial harmonics (SMASH): fast imaging with radiofrequency coil arrays | journal = Magnetic Resonance in Medicine | volume = 38 | issue = 4 | pages = 591–603 | date = October 1997 | pmid = 9324327 | doi = 10.1002/mrm.1910380414 | url=  https://doi.org/10.1002/mrm.1910380414 | hdl-access = | s2cid =  17505246| hdl =  }}</ref> The SENSitivity Encoding (SENSE)<ref name="SENSE">{{cite journal | vauthors = Pruessmann KP, Weiger M, Scheidegger MB, Boesiger P| title =  SENSE: sensitivity encoding for fast MRI | journal = Magnetic Resonance in Medicine | volume = 42 | issue = 5 | pages = 952–62 | date = November 1999 | pmid = 10542355 | doi =  10.1002/(SICI)1522-2594(199911)42:5<952::AID-MRM16>3.0.CO;2-S| hdl-access = | s2cid =  16046989 |s2cid-access=free | hdl =  | doi-access = free }}</ref> and Generalized Autocalibrating Partially Parallel Acquisitions (GRAPPA)<ref name="GRAPPA">{{cite journal | vauthors = Griswold MA, Jakob PM, Heidemann RM, Nittka M, Jellus V, Wang J, Kiefer B, Haase A| title =  Generalized autocalibrating partially parallel acquisitions (GRAPPA) | journal = Magnetic Resonance in Medicine | volume = 47 | issue = 6 | pages = 1202–10 | date = June 2002 | pmid = 12111967 | doi = 10.1002/mrm.10171 | hdl-access = | s2cid =  14724155 |s2cid-access=free | hdl =  | doi-access = free }}</ref> techniques are the parallel imaging methods in most common use today. The advent of parallel MRI resulted in extensive research and development in image reconstruction and RF coil design, as well as in a rapid expansion of the number of receiver channels available on commercial MR systems. Parallel MRI is now used routinely for MRI examinations in a wide range of body areas and clinical or research applications.

=== Quantitative MRI ===
Most MRI focuses on qualitative interpretation of MR data by acquiring spatial maps of relative variations in signal strength which are "weighted" by certain parameters.<ref name="Gulani-Sieberlich-QMRI-2020">{{cite book|last1=Gulani|first1=Vikas|last2=Nicole|first2=Sieberlich|date=2020|title=Quantitative Magnetic Resonance Imaging|chapter=Quantitative MRI: Rationale and Challenges|publisher=Academic Press|page=xxxvii-li|doi=10.1016/B978-0-12-817057-1.00001-9 |doi-access=free |isbn=9780128170571|s2cid=234995365 |s2cid-access=free |name-list-style=amp }}</ref> Quantitative methods instead attempt to determine spatial maps of accurate tissue relaxometry parameter values or magnetic field, or to measure the size of certain spatial features.

Examples of quantitative MRI methods are:

* T1-mapping (notably used in [[cardiac magnetic resonance imaging]]<ref name="pmid27354273">{{cite journal| last1=Captur |first1=G |last2=Manisty |first2=C |last3=Moon |first3=JC| title=Cardiac MRI evaluation of myocardial disease. | journal=Heart | year= 2016 | volume= 102 | issue= 18 | pages= 1429–35 | pmid=27354273 | doi=10.1136/heartjnl-2015-309077 | pmc= | s2cid=23647168 | url=https://pubmed.ncbi.nlm.nih.gov/27354273  }}</ref>)
* T2-mapping<ref name="pmid34008045">{{cite journal| last1=Cobianchi Bellisari |first1=F |last2=De Marino |first2=L |last3=Arrigoni |first3=F |last4=Mariani |first4=S |last5=Bruno |first5=F |last6=Palumbo |first6=P | display-authors=etal| title=T2-mapping MRI evaluation of patellofemoral cartilage in patients submitted to intra-articular platelet-rich plasma (PRP) injections. | journal=Radiol Med | year= 2021 | volume= 126 | issue= 8 | pages= 1085–1094 | pmid=34008045 | doi=10.1007/s11547-021-01372-6 |doi-access=free | pmc=8292236 }}</ref>
* [[Quantitative susceptibility mapping]] (QSM)
* Quantitative fluid flow MRI (i.e. some [[cerebrospinal fluid flow MRI]]<ref name="Radiopedia-CSFflow">{{Cite journal|last1=Gaillard|first1=Frank |first2=Henry |last2=Knipe |doi=10.53347/rID-37401 |doi-access=free |title=CSF flow studies {{!}} Radiology Reference Article |date=13 Oct 2021 |url=https://radiopaedia.org/articles/csf-flow-studies?lang=us|access-date=2021-11-24|website=Radiopaedia|language=en-US}}</ref>)
* [[Magnetic resonance elastography]] (MRE)<ref>{{cite book |url=https://www.onlinelibrary.wiley.com/doi/book/10.1002/9783527696017 |title=Magnetic Resonance Elastography &#124; Wiley Online Books |year=2016 |doi=10.1002/9783527696017 |last1=Hirsch |first1=Sebastian |last2=Braun |first2=Jürgen |last3=Sack |first3=Ingolf |isbn=9783527696017 |access-date=2022-03-06 |archive-date=2022-03-05 |archive-url=https://web.archive.org/web/20220305222408/https://onlinelibrary.wiley.com/doi/book/10.1002/9783527696017 |url-status=dead }}</ref>

Quantitative MRI aims to increase the [[reproducibility]] of MR images and interpretations, but has historically require longer scan times.<ref name="Gulani-Sieberlich-QMRI-2020"/>

Quantitative MRI (or qMRI) sometimes more specifically refers to multi-parametric quantitative MRI, the mapping of multiple tissue relaxometry parameters in a single imaging session.<ref name="pmid33763021">{{cite journal| vauthors=Seiler A, Nöth U, Hok P, Reiländer A, Maiworm M, Baudrexel S | display-authors=etal| title=Multiparametric Quantitative MRI in Neurological Diseases. | journal=Front Neurol | year= 2021 | volume= 12 | issue=  | pages= 640239 | pmid=33763021 | doi=10.3389/fneur.2021.640239 | pmc=7982527 | doi-access=free}}</ref>
Efforts to make multi-parametric quantitative MRI faster have produced sequences which map multiple parameters simultaneously, either by building separate encoding methods for each parameter into the sequence,<ref name="pmid18666127">{{cite journal| vauthors=Warntjes JB, Leinhard OD, West J, Lundberg P| title=Rapid magnetic resonance quantification on the brain: Optimization for clinical usage. | journal=Magn Reson Med | year= 2008 | volume= 60 | issue= 2 | pages= 320–9 | pmid=18666127 | doi=10.1002/mrm.21635 | pmc= | s2cid=11617224 | doi-access=free }}</ref>
or by fitting MR signal evolution to a multi-parameter model.<ref name="pmid22378141">{{cite journal| vauthors=Ehses P, Seiberlich N, Ma D, Breuer FA, Jakob PM, Griswold MA | display-authors=etal| title=IR TrueFISP with a golden-ratio-based radial readout: fast quantification of T1, T2, and proton density. | journal=Magn Reson Med | year= 2013 | volume= 69 | issue= 1 | pages= 71–81 | pmid=22378141 | doi=10.1002/mrm.24225 | pmc= | s2cid=24244167| doi-access=free }}</ref><ref name="pmid23486058">{{cite journal| vauthors=Ma D, Gulani V, Seiberlich N, Liu K, Sunshine JL, Duerk JL | display-authors=etal| title=Magnetic resonance fingerprinting. | journal=Nature | year= 2013 | volume= 495 | issue= 7440 | pages= 187–92 | pmid=23486058 | doi=10.1038/nature11971 | pmc=3602925 | bibcode=2013Natur.495..187M}}</ref>

=== Hyperpolarized gas MRI ===
{{Main|Hyperpolarized gas MRI}}

Traditional MRI generates poor images of lung tissue because there are fewer water molecules with protons that can be excited by the magnetic field. Using hyperpolarized gas an MRI scan can identify ventilation defects in the lungs. Before the scan, a patient is asked to inhale hyperpolarized [[xenon]] mixed with a buffer gas of helium or nitrogen. The resulting lung images are much higher quality than with traditional MRI.