Editing Magnetic resonance imaging

{{short description|Medical imaging technique}}
{{About|magnetic resonance imaging|X-ray tomographic imaging|CT scan}}
{{Redirect|MRI}}
{{Good article}}
{{Infobox diagnostic
| name=Magnetic resonance imaging
| image=[[File:Structural MRI animation.ogv|frameless]]
| caption=[[Sagittal plane#Variations in terminology|Para-sagittal]] MRI of the head, with [[aliasing]] [[Visual artifact|artifacts]] (nose and forehead appear at the back of the head)
| pronounce =
| synonyms=Nuclear magnetic resonance imaging (NMRI), magnetic resonance tomography (MRT)
| ICD9={{ICD9proc|88.91}}
| MedlinePlus=003335
| MeshID=D008279
}}

'''Magnetic resonance imaging''' ('''MRI''') is a [[medical imaging]] technique used in [[radiology]] to generate  pictures of the [[anatomy]] and the [[physiological]] processes inside the body. [[Physics of magnetic resonance imaging#MRI scanner|MRI scanners]] use strong [[magnetic field]]s, magnetic field gradients, and [[radio wave]]s to form images of the organs in the body. MRI does not involve [[X-rays]] or the use of [[ionizing radiation]], which distinguishes it from [[CT scan|computed tomography]] (CT) and [[positron emission tomography]] (PET) scans. MRI is a [[nuclear magnetic resonance#Medicine|medical application]] of [[nuclear magnetic resonance]] (NMR) which can also be used for imaging in other [[nuclear magnetic resonance#Applications|NMR applications]], such as [[nuclear magnetic resonance spectroscopy|NMR spectroscopy]].<ref name="Rinck">
{{cite book
 |last1= Rinck |first1=Peter A.
 |year=2024
 |title=Magnetic Resonance in Medicine: A Critical Introduction 
 |edition=14th (ebook)
 |publisher=TRTF – The Round Table Foundation: TwinTree Media
 |isbn=
}}
{{cite web
 |title=Magnetic Resonance in Medicine
 |website=www.magnetic-resonance.org
 |url=http://magnetic-resonance.org/
}}
</ref>

MRI is widely used in hospitals and clinics for [[medical diagnosis]], [[cancer staging|staging]] and follow-up of disease. Compared to CT, MRI provides better [[Contrast (vision)|contrast]] in images of soft tissues, e.g. in the [[magnetic resonance imaging of the brain|brain]] or abdomen. However, it may be perceived as less comfortable by patients, due to the usually longer and louder measurements with the subject in a long, confining tube, although "open" MRI designs mostly relieve this. Additionally, [[Implant (medicine)|implants]] and other non-removable metal in the body can pose a risk and may exclude some patients from undergoing an MRI examination safely.

MRI was originally called NMRI (nuclear magnetic resonance imaging), but "nuclear" was dropped to avoid [[Radiophobia|negative associations]].<ref>{{cite book |vauthors=McRobbie DW, Moore EA, Graves MJ, Prince MR |date=2007 |title=MRI from Picture to Proton |publisher=Cambridge University Press |page=1 |isbn=978-1-139-45719-4}}</ref> Certain [[Atomic nucleus|atomic nuclei]] are able to absorb [[radio frequency]] (RF) energy when placed in an external [[magnetic field]]; the resultant evolving [[spin polarization]] can induce an RF signal in a radio frequency coil and thereby be detected.<ref name="hoult">{{Cite journal |vauthors=Hoult DI, Bahkar B |title=NMR Signal Reception: Virtual Photons and Coherent Spontaneous Emission |journal=Concepts in Magnetic Resonance |year=1998 |volume=9 |issue=5 |pages=277–297 |doi=10.1002/(SICI)1099-0534(1997)9:5<277::AID-CMR1>3.0.CO;2-W}}</ref> In other words, the nuclear magnetic spin of protons in the hydrogen nuclei resonates with the RF incident waves and emit coherent radiation with compact direction, energy (frequency) and phase. This coherent amplified radiation is easily detected by RF antennas close to the subject being examined. It is a process similar to [[masers]]. In clinical and research MRI, [[hydrogen|hydrogen atoms]] are most often used to generate a macroscopic polarized radiation that is detected by the antennas.<ref name="hoult" /> Hydrogen atoms are [[Composition of the human body|naturally abundant in humans]] and other biological organisms, particularly in [[properties of water|water]] and [[Lipid|fat]]. For this reason, most MRI scans essentially map the location of water and fat in the body. Pulses of radio waves excite the [[Spin (physics)|nuclear spin]] energy transition, and magnetic field gradients localize the polarization in space. By varying the parameters of the [[pulse sequence]], different contrasts may be generated between tissues based on the [[relaxation (NMR)|relaxation]] properties of the hydrogen atoms therein.

Since its development in the 1970s and 1980s, MRI has proven to be a versatile imaging technique. While MRI is most prominently used in [[medical diagnosis|diagnostic medicine]] and biomedical research, it also may be used to form images of non-living objects, such as [[Mummy|mummies]]. [[Diffusion MRI]] and [[functional magnetic resonance imaging|functional MRI]] extend the utility of MRI to capture neuronal tracts and blood flow respectively in the nervous system, in addition to detailed spatial images. The sustained increase in demand for MRI within [[health system]]s has led to concerns about [[cost-effectiveness analysis|cost effectiveness]] and [[overdiagnosis]].<ref name="Smith-Bindman2012">{{irrelevant citation|date=November 2021|reason=source does not explicitly address these points.}}{{cite journal | vauthors = Smith-Bindman R, [[Diana Miglioretti|Miglioretti DL]], Johnson E, Lee C, Feigelson HS, Flynn M, Greenlee RT, Kruger RL, Hornbrook MC, Roblin D, Solberg LI, Vanneman N, Weinmann S, Williams AE | display-authors = 6 | title = Use of diagnostic imaging studies and associated radiation exposure for patients enrolled in large integrated health care systems, 1996-2010 | journal = JAMA | volume = 307 | issue = 22 | pages = 2400–9 | date = June 2012 | pmid = 22692172 | pmc = 3859870 | doi = 10.1001/jama.2012.5960 }}</ref><ref>{{cite book |date=2009 |title=Health at a glance 2009 OECD indicators |doi=10.1787/health_glance-2009-en |isbn=978-92-64-07555-9}}</ref>{{Dubious|date=November 2021}}

==Mechanism==

===Construction and physics===
{{Main |Physics of magnetic resonance imaging}}
[[File:Mri scanner schematic labelled.svg|class=skin-invert-image|thumb|upright=1.5 |Schematic of a cylindrical superconducting MR scanner. Top: cross section of the cylinder with primary coil, gradient coils and RF transmit coils. Bottom: longitudinal section of the cylinder and table, showing the same coils and the RF receive coil.]]

In most medical applications, [[hydrogen]] nuclei, which consist solely of a [[proton]], that are in tissues create a signal that is processed to form an image of the body in terms of the density of those nuclei in a specific region. Given that the protons are affected by fields from other atoms to which they are bonded, it is possible to separate responses from hydrogen in specific compounds. To perform a study, the person is positioned within an [[Physics of magnetic resonance imaging#MRI scanner|MRI scanner]] that forms a strong [[magnetic field]] around the area to be imaged. First, energy from an [[oscillation|oscillating]] magnetic field is temporarily applied to the patient at the appropriate [[resonance]] frequency. Scanning with X and Y gradient coils causes a selected region of the patient to experience the exact magnetic field required for the energy to be absorbed. The atoms are [[Excited state|excited]] by a [[Radio frequency|RF]] pulse and the resultant signal is measured by a [[Radiofrequency coil|receiving coil]]. The RF signal may be processed to deduce position information by looking at the changes in RF level and phase caused by varying the local magnetic field using [[Physics of magnetic resonance imaging#Gradients|gradient coils]]. As these coils are rapidly switched during the excitation and response to perform a moving line scan, they create the characteristic repetitive noise of an MRI scan as the windings move slightly due to [[magnetostriction]]. The contrast between different tissues is determined by the rate at which excited atoms return to the [[Thermodynamic equilibrium|equilibrium state]]. [[Exogeny|Exogenous]] [[contrast agent]]s may be given to the person to make the image clearer.<ref name ="McRobbie">{{cite book | vauthors = McRobbie DW | title=MRI from picture to proton | date=2007 | publisher=Cambridge University Press | location=Cambridge, UK; New York | isbn=978-0-521-68384-5}}</ref>

The major components of an MRI scanner are the main [[magnet]], which polarizes the sample, the [[Shim (magnetism)|shim coils]] for correcting shifts in the [[homogeneity (physics)|homogeneity]] of the main magnetic field, the gradient system which is used to localize the region to be scanned and the RF system, which excites the sample and detects the resulting NMR signal. The whole system is controlled by one or more computers.

[[File:Glebefields Health Centre - 2020-03-22 - Andy Mabbett - 03.jpg|thumb|left|A mobile MRI unit]]
{{Listen| filename = MRI - 2020-03-22 - Andy Mabbett.ogg |title = Audio recording |type = speech |description = A short extract of a 20-minute scanning session, recorded outside the above unit }}

MRI requires a magnetic field that is both strong and [[Homogeneity (physics)|uniform]] to a few parts per million across the scan volume. The field strength of the magnet is measured in [[tesla (unit)|teslas]] – and while the majority of systems operate at 1.5 T, commercial systems are available between 0.2 and 7 T. '''3T MRI''' systems, also called 3 Tesla MRIs, have stronger magnets than 1.5 systems and are considered better for images of organs and soft tissue.<ref>{{Cite web |title=National Cancer Institute |url=https://www.cancer.gov/publications/dictionaries/cancer-terms/def/3t-mri |access-date=2024-09-16 |website=Cancer.gov|language=en}}</ref> Whole-body MRI systems for research applications operate in e.g. 9.4T,<ref>{{Cite web |title=Tesla Engineering Ltd - Magnet Division - MRI Supercon |url=http://www.tesla.co.uk/magnet/phone/tesla-engineering-magnet-division-superconducting-magnets-mobile/tesla-engineering-magnet-division-mri-magnets-mobile.html |access-date=2022-08-16 |website=www.tesla.co.uk |language=en}}</ref><ref>{{Cite web |last=Qiuliang |first=Wang |date=January 2022 |title=Successful Development of a 9.4T/800mm Whole-body MRI Superconducting Magnet at IEE CAS |url=https://snf.ieeecsc.org/sites/ieeecsc.org/files/documents/snf/abstracts/HP149-9.4T%20whole-body%20MRI%20superconducting%20magnet.pdf |url-status=live |website=snf.ieeecsc.org |archive-url=https://web.archive.org/web/20230322153825/https://snf.ieeecsc.org/sites/ieeecsc.org/files/documents/snf/abstracts/HP149-9.4T%20whole-body%20MRI%20superconducting%20magnet.pdf |archive-date=Mar 22, 2023}}</ref> 10.5T,<ref>{{Cite journal |last=Nowogrodzki |first=Anna |date=2018-10-31 |title=The world's strongest MRI machines are pushing human imaging to new limits |url=https://www.nature.com/articles/d41586-018-07182-7 |journal=Nature |language=en |volume=563 |issue=7729 |pages=24–26 |doi=10.1038/d41586-018-07182-7|pmid=30382222 |bibcode=2018Natur.563...24N |s2cid=53153608 }}</ref> 11.7T.<ref>{{Cite web |last=CEA |date=2021-10-07 |title=The most powerful MRI scanner in the world delivers its first images! |url=https://www.cea.fr/english/Pages/News/premieres-images-irm-iseult-2021.aspx |access-date=2022-08-16 |website=CEA/English Portal |language=en}}</ref> Even higher field whole-body MRI systems e.g. 14 T and beyond are in conceptual proposal<ref>{{Cite journal |last1=Budinger |first1=Thomas F. |last2=Bird |first2=Mark D. |date=2018-03-01 |title=MRI and MRS of the human brain at magnetic fields of 14T to 20T: Technical feasibility, safety, and neuroscience horizons |journal=NeuroImage |series=Neuroimaging with Ultra-high Field MRI: Present and Future |language=en |volume=168 |pages=509–531 |doi=10.1016/j.neuroimage.2017.01.067 |pmid=28179167 |s2cid=4054160 |issn=1053-8119|doi-access=free }}</ref> or in engineering design.<ref>{{Cite journal |last1=Li |first1=Yi |last2=Roell |first2=Stefan |date=2021-12-01 |title=Key designs of a short-bore and cryogen-free high temperature superconducting magnet system for 14 T whole-body MRI |url=https://iopscience.iop.org/article/10.1088/1361-6668/ac2ec8 |journal=Superconductor Science and Technology |volume=34 |issue=12 |pages=125005 |doi=10.1088/1361-6668/ac2ec8 |bibcode=2021SuScT..34l5005L |s2cid=242194782 |issn=0953-2048}}</ref> Most clinical magnets are [[superconductivity|superconducting]] magnets, which require [[liquid helium]] to keep them at low temperatures. Lower field strengths can be achieved with permanent magnets, which are often used in "open" MRI scanners for [[Claustrophobia|claustrophobic]] patients.<ref>{{cite journal | vauthors = Sasaki M, Ehara S, Nakasato T, Tamakawa Y, Kuboya Y, Sugisawa M, Sato T | title = MR of the shoulder with a 0.2-T permanent-magnet unit | journal = AJR. American Journal of Roentgenology | volume = 154 | issue = 4 | pages = 777–8 | date = April 1990 | pmid = 2107675 | doi = 10.2214/ajr.154.4.2107675 }}</ref> Lower field strengths are also used in a [[Portable magnetic resonance imaging|portable MRI]] scanner approved by the FDA in 2020.<ref>{{cite news |title=Guildford company gets FDA approval for bedside MRI |url=https://www.ctinsider.com/business/nhregister/article/Guilford-company-gets-FDA-approval-for-bedside-MRI-15050860.php |access-date=15 April 2020 |work=[[New Haven Register]] |date=12 February 2020 |archive-date=3 April 2020 |archive-url=https://web.archive.org/web/20200403211038/https://www.ctinsider.com/business/nhregister/article/Guilford-company-gets-FDA-approval-for-bedside-MRI-15050860.php |url-status=dead }}</ref> Recently, MRI has been demonstrated also at ultra-low fields, i.e., in the microtesla-to-millitesla range, where sufficient signal quality is made possible by prepolarization (on the order of 10–100 mT) and by measuring the [[Larmor precession]] fields at about 100 microtesla with highly sensitive superconducting quantum interference devices ([[SQUID]]s).<ref>{{cite journal | vauthors = McDermott R, Lee S, ten Haken B, Trabesinger AH, Pines A, Clarke J | title = Microtesla MRI with a superconducting quantum interference device | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 101 | issue = 21 | pages = 7857–61 | date = May 2004 | pmid = 15141077 | pmc = 419521 | doi = 10.1073/pnas.0402382101 | bibcode = 2004PNAS..101.7857M | doi-access = free }}</ref><ref>{{cite journal | vauthors = Zotev VS, Matlashov AN, Volegov PL, Urbaitis AV, Espy MA, Kraus RH |doi=10.1088/0953-2048/20/11/S13 |title=SQUID-based instrumentation for ultralow-field MRI |journal=Superconductor Science and Technology |volume=20 |issue=11 |pages=S367–73 |year=2007  |s2cid=119160258 |arxiv=0705.0661 |bibcode=2007SuScT..20S.367Z }}</ref><ref>{{cite journal | vauthors = Vesanen PT, Nieminen JO, Zevenhoven KC, Dabek J, Parkkonen LT, Zhdanov AV, Luomahaara J, Hassel J, Penttilä J, Simola J, Ahonen AI, Mäkelä JP, Ilmoniemi RJ | display-authors = 6 | title = Hybrid ultra-low-field MRI and magnetoencephalography system based on a commercial whole-head neuromagnetometer | journal = Magnetic Resonance in Medicine | volume = 69 | issue = 6 | pages = 1795–804 | date = June 2013 | pmid = 22807201 | doi = 10.1002/mrm.24413 | s2cid = 40026232 | doi-access = free }}</ref>

===T1 and T2===
{{Further|Relaxation (NMR)}}
[[File:TR TE.jpg|class=skin-invert-image|thumb|upright=1.2|Effects of TR and TE on MR signal]]
[[File:T1t2PD.jpg|thumb|upright=1.2|Examples of T1-weighted, T2-weighted and [[MRI sequence#Proton density|PD-weighted]] MRI scans]]
[[File:Spin Orientations During Relaxation.jpg|class=skin-invert-image|thumb|upright=1.2|Diagram of changing magnetization and spin orientations throughout spin-lattice relaxation experiment]]

Each tissue returns to its equilibrium state after excitation by the independent relaxation processes of T<sub>1</sub> ([[Spin–lattice relaxation|spin-lattice]]; that is, magnetization in the same direction as the static magnetic field) and T<sub>2</sub> ([[Spin-spin relaxation time|spin-spin]]; transverse to the static magnetic field).
To create a T<sub>1</sub>-weighted image, magnetization is allowed to recover before measuring the MR signal by changing the [[repetition time]] (TR). This image weighting is useful for assessing the cerebral cortex, identifying fatty tissue, characterizing focal liver lesions, and in general, obtaining morphological information, as well as for [[MRI contrast agent|post-contrast]] imaging.
{{anchor|T2-weighted_MRI}}
To create a T<sub>2</sub>-weighted image, magnetization is allowed to decay before measuring the MR signal by changing the [[echo time]] (TE). This image weighting is useful for detecting [[edema]] and inflammation, revealing [[Hyperintensity|white matter lesions]], and assessing zonal anatomy in the [[prostate]] and [[uterus]].

The information from MRI scans comes in the form of [[Contrast resolution|image contrasts]] based on differences in the rate of relaxation of [[spin quantum number|nuclear spins]] following their perturbation by an oscillating magnetic field (in the form of radiofrequency pulses through the sample).<ref>{{cite journal |last1=De Leon-Rodriguez |first1=L.M. |title=Basic MR Relaxation Mechanisms and Contrast Agent Design |journal=Journal of Magnetic Resonance Imaging |date=2015 |volume=42 |issue=3|pages=545–565 |doi=10.1002/jmri.24787 |pmid=25975847 |pmc=4537356 }}</ref> The relaxation rates are a measure of the time it takes for a signal to decay back to an equilibrium state from either the longitudinal or transverse plane.

[[Magnetization]] builds up along the z-axis in the presence of a magnetic field, B<sub>0</sub>, such that the [[magnetic dipole]]s in the sample will, on average, align with the z-axis summing to a total magnetization M<sub>z</sub>. This magnetization along z is defined as the equilibrium magnetization; magnetization is defined as the sum of all magnetic dipoles in a sample. Following the equilibrium magnetization, a 90° radiofrequency (RF) pulse flips the direction of the magnetization vector in the xy-plane, and is then switched off. The initial magnetic field B<sub>0</sub>, however, is still applied. Thus, the spin magnetization vector will slowly return from the xy-plane back to the equilibrium state. The time it takes for the magnetization vector to return to its equilibrium value, M<sub>z</sub>, is referred to as the longitudinal relaxation time, T<sub>1</sub>.<ref>{{Cite web|url=http://imserc.northwestern.edu/downloads/nmr-t1.pdf|title=T1 relaxation experiment}}</ref> Subsequently, the rate at which this happens is simply the reciprocal of the relaxation time: <math>\frac {1}{T_1} = R_1</math>. Similarly, the time in which it takes for M<sub>xy</sub> to return to zero is T<sub>2</sub>, with the rate <math>\frac {1}{T_2} = R_2</math>.<ref>{{cite book |last1=McHale |first1=J. |title=Molecular Spectroscopy |date=2017 |publisher=CRC Press/Taylor and Francis Group |pages=73–80}}</ref> Magnetization as a function of time is defined by the [[Bloch equations]].

T<sub>1</sub> and T<sub>2</sub> values are dependent on the chemical environment of the sample; hence their utility in MRI. Soft tissue and muscle tissue relax at different rates, yielding the image contrast in a typical scan.

The standard display of MR images is to represent fluid characteristics in [[black-and-white]] images, where different tissues turn out as follows:

{|class="wikitable"
|+ Signals from different materials
! scope="col" | Signal 
! scope="col" | T1-weighted 
! scope="col" | T2-weighted
|-
! scope="row" style="background: #c8ccd1;" | High
|style="vertical-align:top;"|
* [[Fat]]<ref name=wisconsin/><ref name=johnson2>{{cite web |url=http://www.med.harvard.edu/aanlib/basicsMR.html | vauthors = Johnson KA |title=Basic proton MR imaging. Tissue Signal Characteristics }}{{MEDRS|date=September 2018}}</ref>
* Subacute hemorrhage<ref name=johnson2/>
* [[Melanin]]<ref name=johnson2/>
* Protein-rich fluid<ref name=johnson2/>
* Slowly flowing blood<ref name=johnson2/>
* [[Paramagnetism|Paramagnetic]] or [[diamagnetism|diamagnetic]] substances, such as [[gadolinium]], [[manganese]], [[copper]]<ref name=johnson2/>
* [[Cortical pseudolaminar necrosis]]<ref name=johnson2/>
* Anatomy
|style="vertical-align:top;"|
* Fat
* More water content,<ref name=wisconsin/> as in [[edema]], [[tumor]], [[infarction]], [[inflammation]] and [[infection]]<ref name=johnson2/>
* [[Extracellular]]ly located [[methemoglobin]] in subacute hemorrhage<ref name=johnson2/>
* Pathology
|-
! scope="row" style="background: #a2a9b1;" | Intermediate
|style="vertical-align:top;"|
* [[Gray matter]] darker than [[white matter]]<ref name=patil>{{cite web|url=http://www.slideshare.net/DrTusharPatil/mri-sequences|title=MRI sequences| vauthors = Patil T |access-date=2016-03-14|date=2013-01-18}}</ref>
|style="vertical-align:top;"|
* [[White matter]] darker than [[grey matter]]<ref name=patil/>
|-
! scope="row" style="background: #101418; color: #fff;" | Low
|style="vertical-align:top;"|
* Bone<ref name=wisconsin>{{cite web|url=https://www.radiology.wisc.edu/education/med_students/neuroradiology/NeuroRad/Intro/MRIintro.htm|title=Magnetic Resonance Imaging|publisher=[[University of Wisconsin]]|access-date=2016-03-14|archive-url=https://web.archive.org/web/20170510065614/https://www.radiology.wisc.edu/education/med_students/neuroradiology/NeuroRad/Intro/MRIintro.htm|archive-date=2017-05-10|url-status=dead}}</ref>
* Air<ref name=wisconsin/>
* Low [[proton]] density as in [[calcification]]<ref name=johnson2/>
* Urine
* [[Cerebrospinal fluid|CSF]]
* More water content,<ref name=wisconsin/> as in [[edema]], [[tumor]], [[infarction]], [[inflammation]], [[infection]], hyperacute or chronic [[hemorrhage]]<ref name=johnson2/>
|style="vertical-align:top;"|
* [[Bone]]<ref name=wisconsin/>
* [[Air]]<ref name=wisconsin/>
* Low proton density, as in [[calcification]] and [[fibrosis]]<ref name=johnson2/>
* [[Paramagnetism|Paramagnetic]] material, such as [[deoxyhemoglobin]], intracellular [[methemoglobin]], [[iron]], [[ferritin]], [[hemosiderin]], [[melanin]]<ref name=johnson2/>
* Protein-rich fluid<ref name=johnson2/>
|}

== Diagnostics ==

=== Usage by organ or system ===
[[File:Siemens Magnetom Aera MRI scanner.jpg|thumb|Patient being positioned for MR study of the head and abdomen]]

MRI has a wide range of applications in [[medical diagnosis]] and around 50,000 scanners are estimated to be in use worldwide.<ref>{{cite web |title=Magnetic Resonance, a critical peer-reviewed introduction |publisher=European Magnetic Resonance Forum |access-date=17 November 2014 |url=http://www.magnetic-resonance.org/ch/21-01.html}}</ref> MRI affects diagnosis and treatment in many specialties although the effect on improved health outcomes is disputed in certain cases.<ref name="ACPfive" /><ref name="backimage" />
[[File:Radiologist interpreting MRI.jpg|thumb|[[Radiology|Radiologist]] interpreting MRI images of head and neck]]
MRI is the investigation of choice in the preoperative [[cancer staging|staging]] of [[Colorectal cancer|rectal]] and [[prostate cancer]] and has a role in the diagnosis, staging, and follow-up of other tumors,<ref>{{cite book | vauthors=Husband J | title=Recommendations for Cross-Sectional Imaging in Cancer Management: Computed Tomography – CT Magnetic Resonance Imaging – MRI Positron Emission Tomography – PET-CT | date=2008 | url=http://www.rcr.ac.uk/docs/oncology/pdf/Cross_Sectional_Imaging_12.pdf | publisher=Royal College of Radiologists | isbn=978-1-905034-13-0 | access-date=2014-05-29 | archive-date=2012-09-07 | archive-url=https://web.archive.org/web/20120907100310/http://www.rcr.ac.uk/docs/oncology/pdf/Cross_Sectional_Imaging_12.pdf | url-status=dead }}</ref> as well as for determining areas of tissue for sampling in biobanking.<ref>{{cite journal | vauthors = Heavey S, Costa H, Pye H, Burt EC, Jenkinson S, Lewis GR, Bosshard-Carter L, Watson F, Jameson C, Ratynska M, Ben-Salha I, Haider A, Johnston EW, Feber A, Shaw G, Sridhar A, Nathan S, Rajan P, Briggs TP, Sooriakumaran P, Kelly JD, Freeman A, Whitaker HC | display-authors = 6 | title = PEOPLE: PatiEnt prOstate samPLes for rEsearch, a tissue collection pathway utilizing magnetic resonance imaging data to target tumor and benign tissue in fresh radical prostatectomy specimens | journal = The Prostate | volume = 79 | issue = 7 | pages = 768–777 | date = May 2019 | pmid = 30807665 | pmc = 6618051 | doi = 10.1002/pros.23782 }}</ref><ref>{{cite journal | vauthors = Heavey S, Haider A, Sridhar A, Pye H, Shaw G, Freeman A, Whitaker H | title = Use of Magnetic Resonance Imaging and Biopsy Data to Guide Sampling Procedures for Prostate Cancer Biobanking | journal = Journal of Visualized Experiments | issue = 152 | date = October 2019 | pmid = 31657791 | doi = 10.3791/60216 | doi-access = free }}</ref>

==== Neuroimaging ====
{{Main|Magnetic resonance imaging of the brain}}
{{See also|Neuroimaging}}
[[File:White Matter Connections Obtained with MRI Tractography.png|thumb|MRI diffusion tensor imaging of [[white matter]] tracts]]

MRI is the investigative tool of choice for neurological cancers over CT, as it offers better visualization of the [[posterior cranial fossa]], containing the [[brainstem]] and the [[cerebellum]]. The contrast provided between [[Grey matter|grey]] and [[white matter]] makes MRI the best choice for many conditions of the [[central nervous system]], including [[demyelinating disease]]s, [[dementia]], [[cerebrovascular disease]], [[List of infections of the central nervous system|infectious diseases]], [[Alzheimer's disease]] and [[epilepsy]].<ref>{{cite web |url=http://www.acr.org/~/media/ACR/Documents/PGTS/guidelines/MRI_Brain.pdf |title=ACR-ASNR Practice Guideline for the Performance and Interpretation of Magnetic Resonance Imaging (MRI) of the Brain |author=American Society of Neuroradiology |date=2013 |access-date=2013-11-10 |archive-url=https://web.archive.org/web/20170712013017/https://www.acr.org/~/media/ACR/Documents/PGTS/guidelines/MRI_Brain.pdf |archive-date=2017-07-12 |url-status=dead }}</ref><ref>{{cite journal| vauthors = Rowayda AS |title=An improved MRI segmentation for atrophy assessment|journal= International Journal of Computer Science Issues  |date=May 2012|volume=9|issue=3 }}</ref><ref>{{cite journal| vauthors = Rowayda AS |title=Regional atrophy analysis of MRI for early detection of alzheimer's disease|journal= International Journal of Signal Processing, Image Processing and Pattern Recognition |date=February 2013|volume=6|issue=1|pages=49–53}}</ref> Since many images are taken milliseconds apart, it shows how the brain responds to different stimuli, enabling researchers to study both the functional and structural brain abnormalities in psychological disorders.<ref name="Abnormal Psychology">{{cite book | vauthors = Nolen-Hoeksema S |title=Abnormal Psychology |date=2014 |publisher=McGraw-Hill Education |location=New York |page=67 |edition=Sixth}}</ref> MRI also is used in [[image guided surgery|guided]] [[stereotactic surgery]] and [[radiosurgery]] for treatment of intracranial tumors, arteriovenous malformations, and other surgically treatable conditions using a device known as the [[N-localizer]].<ref>{{cite journal | vauthors = Brown RA, Nelson JA | title = The Invention and Early History of the N-Localizer for Stereotactic Neurosurgery | journal = Cureus | volume = 8 | issue = 6 | pages = e642 | date = June 2016 | pmid = 27462476 | pmc = 4959822 | doi = 10.7759/cureus.642 | doi-access = free }}</ref><ref>
{{cite journal | vauthors = Leksell L, Leksell D, Schwebel J | title = Stereotaxis and nuclear magnetic resonance | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 48 | issue = 1 | pages = 14–8 | date = January 1985 | pmid = 3882889 | pmc = 1028176 | doi = 10.1136/jnnp.48.1.14 }}</ref><ref>{{cite journal | vauthors = Heilbrun MP, Sunderland PM, McDonald PR, Wells TH, Cosman E, Ganz E | title = Brown-Roberts-Wells stereotactic frame modifications to accomplish magnetic resonance imaging guidance in three planes | journal = Applied Neurophysiology | volume = 50 | issue = 1–6 | pages = 143–52 | year = 1987 | pmid = 3329837 | doi = 10.1159/000100700 }}</ref> New tools that implement [[artificial intelligence in healthcare]] have demonstrated higher image quality and morphometric analysis in [[neuroimaging]] with the application of a denoising system.<ref name="JON-December-2021">{{cite journal|title=The effect of a post-scan processing denoising system on image quality and morphometric analysis|first1=Noriko|last1=Kanemaru|first2=Hidemasa|last2=Takao|first3=Shiori|last3=Amemiya|first4=Osamu|last4=Abe|journal=Journal of Neuroradiology|date=2 December 2021|volume=49 |issue=2 |pages=205–212 |doi=10.1016/j.neurad.2021.11.007|pmid=34863809|s2cid=244907903|doi-access=free}}</ref>

The record for the highest spatial resolution of a whole intact brain (postmortem) is 100 microns, from Massachusetts General Hospital. The data was published in NATURE on 30 October 2019.<ref>{{Cite web|url=https://www.sciencealert.com/100-hour-mri-marathon-gives-the-world-its-closest-ever-3d-view-of-the-human-brain|title = 100-Hour-Long MRI of Human Brain Produces Most Detailed 3D Images Yet| date=10 July 2019 }}</ref><ref>{{Cite web|url=https://medicalxpress.com/news/2019-10-team-publishes-highest-resolution-brain.html|title = Team publishes on highest resolution brain MRI scan}}</ref>

Though MRI is used widely in research on mental disabilities, based on a 2024 systematic literature review and meta analysis commissioned by the Patient-Centered Outcomes Research Institute (PCORI), available research using MRI scans to diagnose ADHD showed great variability.<ref name=":0">{{Cite journal |title=ADHD Diagnosis and Treatment in Children and Adolescents |url=https://effectivehealthcare.ahrq.gov/products/attention-deficit-hyperactivity-disorder/research |access-date=2024-06-19 |website=effectivehealthcare.ahrq.gov |date=2024 |language=en |doi=10.23970/ahrqepccer267 |last1=Peterson |first1=Bradley S. |last2=Trampush |first2=Joey |last3=Maglione |first3=Margaret |last4=Bolshakova |first4=Maria |last5=Brown |first5=Morah |last6=Rozelle |first6=Mary |last7=Motala |first7=Aneesa |last8=Yagyu |first8=Sachi |last9=Miles |first9=Jeremy |last10=Pakdaman |first10=Sheila |last11=Gastelum |first11=Mario |last12=Nguyen |first12=Bich Thuy (Becky) |last13=Tokutomi |first13=Erin |last14=Lee |first14=Esther |last15=Belay |first15=Jerusalem Z. |last16=Schaefer |first16=Coleman |last17=Coughlin |first17=Benjamin |last18=Celosse |first18=Karin |last19=Molakalapalli |first19=Sreya |last20=Shaw |first20=Brittany |last21=Sazmin |first21=Tanzina |last22=Onyekwuluje |first22=Anne N. |last23=Tolentino |first23=Danica |last24=Hempel |first24=Susanne |pmid=38657097 }}</ref> The authors conclude that MRI cannot be reliably used to assist in making a clinical diagnosis of ADHD.<ref name=":0" />

==== Cardiovascular ====
{{Main|Cardiac magnetic resonance imaging}}
[[File:PAPVR.gif|thumb|MR angiogram in congenital heart disease]]

Cardiac MRI is complementary to other imaging techniques, such as [[echocardiography]], [[Computed tomography of the heart|cardiac CT]], and [[nuclear medicine]]. It can be used to assess the structure and the function of the heart.<ref>{{cite journal | vauthors = Petersen SE, Aung N, Sanghvi MM, Zemrak F, Fung K, Paiva JM, Francis JM, Khanji MY, Lukaschuk E, Lee AM, Carapella V, Kim YJ, Leeson P, Piechnik SK, Neubauer S | display-authors = 6 | title = Reference ranges for cardiac structure and function using cardiovascular magnetic resonance (CMR) in Caucasians from the UK Biobank population cohort | journal = Journal of Cardiovascular Magnetic Resonance | volume = 19 | issue = 1 | pages = 18 | date = February 2017 | pmid = 28178995 | pmc = 5304550 | doi = 10.1186/s12968-017-0327-9 | publisher = Springer Science and Business Media LLC | doi-access = free }}</ref> Its applications include assessment of [[Coronary artery disease|myocardial ischemia and viability]], [[Cardiomyopathy|cardiomyopathies]], [[myocarditis]], [[iron overload]], vascular diseases, and [[congenital heart defect|congenital heart disease]].<ref>{{cite journal | title = ACCF/ACR/SCCT/SCMR/ASNC/NASCI/SCAI/SIR 2006 appropriateness criteria for cardiac computed tomography and cardiac magnetic resonance imaging. A report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group | journal = Journal of the American College of Radiology | volume = 3 | issue = 10 | pages = 751–71 | date = October 2006 | pmid = 17412166 | doi = 10.1016/j.jacr.2006.08.008 | author1 = American College of Radiology | author2 = Society of Cardiovascular Computed Tomography | author3 = Society for Cardiovascular Magnetic Resonance | author4 = American Society of Nuclear Cardiology | author5 = North American Society for Cardiac Imaging | author6 = Society for Cardiovascular Angiography Interventions | author7 = Society of Interventional Radiology }}</ref>

==== Musculoskeletal ====
{{Main|Spinal fMRI}}
Applications in the musculoskeletal system include [[Spinal cord|spinal imaging]], assessment of [[joint]] disease, and [[Soft tissue pathology|soft tissue tumors]].<ref>{{cite book | vauthors=Helms C | title=Musculoskeletal MRI | date=2008 | publisher=Saunders | isbn=978-1-4160-5534-1 }}</ref> MRI techniques can also be used for diagnostic imaging of
[[Myopathy#Systemic diseases|systemic muscle diseases]] including genetic muscle diseases.<ref>{{cite journal |last1=Aivazoglou |first1=LU |last2=Guimarães |first2=JB |last3=Link |first3=TM |last4=Costa |first4=MAF |last5=Cardoso |first5=FN |last6=de Mattos Lombardi Badia |first6=B |last7=Farias |first7=IB |last8=de Rezende Pinto |first8=WBV |last9=de Souza |first9=PVS |last10=Oliveira |first10=ASB |last11=de Siqueira Carvalho |first11=AA |last12=Aihara |first12=AY |last13=da Rocha Corrêa Fernandes |first13=A |title=MR imaging of inherited myopathies: a review and proposal of imaging algorithms. |journal=European Radiology |date=21 April 2021 |volume=31 |issue=11 |pages=8498–8512 |doi=10.1007/s00330-021-07931-9 |pmid=33881569|s2cid=233314102 }}</ref><ref>{{cite journal | vauthors = Schmidt GP, Reiser MF, Baur-Melnyk A | title = Whole-body imaging of the musculoskeletal system: the value of MR imaging | journal = Skeletal Radiology | volume = 36 | issue = 12 | pages = 1109–19 | date = December 2007 | pmid = 17554538 | pmc = 2042033 | doi = 10.1007/s00256-007-0323-5 | publisher = Springer Nature | doi-access = free }}</ref>

Swallowing movements of the throat and esophagus can cause motion artifacts over the imaged spine. Therefore, a saturation pulse{{clarify|date=March 2022}} applied over this region the throat and esophagus can help to avoid these artifacts. Motion artifacts arising due to pumping of the heart can be reduced by timing the MRI pulse according to heart cycles.<ref name="pmid28611728">{{cite journal | vauthors = Havsteen I, Ohlhues A, Madsen KH, Nybing JD, Christensen H, Christensen A | title = Are Movement Artifacts in Magnetic Resonance Imaging a Real Problem?-A Narrative Review | journal = Frontiers in Neurology | volume = 8 | issue = | pages = 232 | date = 2017 | pmid = 28611728 | pmc = 5447676 | doi = 10.3389/fneur.2017.00232 | url = | doi-access = free }}</ref> Blood vessel flow artifacts can be reduced by applying saturation pulses above and below the region of interest.<ref>{{Cite journal |last1=Taber |first1=K H |last2=Herrick |first2=R C |last3=Weathers |first3=S W |last4=Kumar |first4=A J |last5=Schomer |first5=D F |last6=Hayman |first6=L A |date=November 1998 |title=Pitfalls and artifacts encountered in clinical MR imaging of the spine. |url=http://pubs.rsna.org/doi/10.1148/radiographics.18.6.9821197 |journal=RadioGraphics |language=en |volume=18 |issue=6 |pages=1499–1521 |doi=10.1148/radiographics.18.6.9821197 |pmid=9821197 |issn=0271-5333}}</ref>

==== Liver and gastrointestinal ====
[[Hepatobiliary system|Hepatobiliary]] MR is used to detect and characterize lesions of the [[liver]], [[pancreas]], and [[bile duct]]s. Focal or diffuse disorders of the liver may be evaluated using [[Diffusion MRI|diffusion-weighted]], opposed-phase imaging and [[Dynamic Contrast Enhanced MRI|dynamic contrast enhancement]] sequences. Extracellular contrast agents are used widely in liver MRI, and newer hepatobiliary contrast agents also provide the opportunity to perform functional biliary imaging. Anatomical imaging of the bile ducts is achieved by using a heavily T2-weighted sequence in [[Magnetic resonance cholangiopancreatography|magnetic resonance cholangiopancreatography (MRCP)]]. Functional imaging of the pancreas is performed following administration of [[secretin]]. MR enterography provides non-invasive assessment of inflammatory bowel disease and small bowel tumors. MR-colonography may play a role in the detection of large polyps in patients at increased risk of colorectal cancer.<ref name="FrydrychowiczLubner2012">{{cite journal | vauthors = Frydrychowicz A, Lubner MG, Brown JJ, Merkle EM, Nagle SK, Rofsky NM, Reeder SB | title = Hepatobiliary MR imaging with gadolinium-based contrast agents | journal = Journal of Magnetic Resonance Imaging | volume = 35 | issue = 3 | pages = 492–511 | date = March 2012 | pmid = 22334493 | pmc = 3281562 | doi = 10.1002/jmri.22833 }}</ref><ref name="SandrasegaranLin2010">{{cite journal | vauthors = Sandrasegaran K, Lin C, Akisik FM, Tann M | title = State-of-the-art pancreatic MRI | journal = AJR. American Journal of Roentgenology | volume = 195 | issue = 1 | pages = 42–53 | date = July 2010 | pmid = 20566796 | doi = 10.2214/ajr.195.3_supplement.0s42 }}</ref><ref name="MasselliGualdi2012">{{cite journal | vauthors = Masselli G, Gualdi G | title = MR imaging of the small bowel | journal = Radiology | volume = 264 | issue = 2 | pages = 333–48 | date = August 2012 | pmid = 22821694 | doi = 10.1148/radiol.12111658 }}</ref><ref name="ZijtaBipat2009">{{cite journal | vauthors = Zijta FM, Bipat S, Stoker J | title = Magnetic resonance (MR) colonography in the detection of colorectal lesions: a systematic review of prospective studies | journal = European Radiology | volume = 20 | issue = 5 | pages = 1031–46 | date = May 2010 | pmid = 19936754 | pmc = 2850516 | doi = 10.1007/s00330-009-1663-4 }}</ref>

==== Angiography ====
[[File:mra1.jpg|thumb|Magnetic resonance angiography]]
{{Main|Magnetic resonance angiography}}

Magnetic resonance [[angiography]] (MRA) generates pictures of the arteries to evaluate them for [[stenosis]] (abnormal narrowing) or [[aneurysm]]s (vessel wall dilatations, at risk of rupture). MRA is often used to evaluate the arteries of the neck and brain, the thoracic and abdominal aorta, the renal arteries, and the legs (called a "run-off"). A variety of techniques can be used to generate the pictures, such as administration of a [[paramagnetic]] contrast agent ([[gadolinium]]) or using a technique known as "flow-related enhancement" (e.g., 2D and 3D time-of-flight sequences), where most of the signal on an image is due to blood that recently moved into that plane (see also [[FLASH MRI]]).<ref name="Wheaton Miyazaki pp. 286–304">{{cite journal | vauthors = Wheaton AJ, Miyazaki M | title = Non-contrast enhanced MR angiography: physical principles | journal = Journal of Magnetic Resonance Imaging | volume = 36 | issue = 2 | pages = 286–304 | date = August 2012 | pmid = 22807222 | doi = 10.1002/jmri.23641 | publisher = Wiley | s2cid = 24048799 | doi-access = free }}</ref>

Techniques involving phase accumulation (known as phase contrast angiography) can also be used to generate flow velocity maps easily and accurately. Magnetic resonance venography (MRV) is a similar procedure that is used to image veins. In this method, the tissue is now excited inferiorly, while the signal is gathered in the plane immediately superior to the excitation plane—thus imaging the venous blood that recently moved from the excited plane.<ref name="haacke">{{cite book | vauthors = Haacke EM, Brown RF, Thompson M, Venkatesan R |title=Magnetic resonance imaging: Physical principles and sequence design |publisher=J. Wiley & Sons |location=New York |date=1999 |isbn=978-0-471-35128-3 }}{{page needed|date=July 2013}}</ref>

{{anchor|Contrast agents}}

== Contrast agents ==
{{Main|MRI contrast agent}}
MRI for imaging anatomical structures or blood flow do not require contrast agents since the varying properties of the tissues or blood provide natural contrasts. However, for more specific types of imaging, [[Exogeny|exogenous]] contrast agents may be given [[Intravenous therapy|intravenously]], [[Oral administration|orally]], or [[Joint injection|intra-articularly]].<ref name ="McRobbie"/> Most contrast agents are either paramagnetic (e.g.: gadolinium, manganese, europium), and are used to shorten T1 in the tissue they accumulate in, or super-paramagnetic (SPIONs), and are used to shorten T2 and T2* in healthy tissue reducing its signal intensity (negative contrast agents). The most commonly used intravenous contrast agents are based on [[chelate]]s of [[gadolinium]], which is highly paramagnetic.<ref>{{cite book | vauthors=Rinck PA | title=Magnetic Resonance in Medicine | chapter=Chapter 13: Contrast Agents | chapter-url=http://www.magnetic-resonance.org/ch/13-01.html |date=2014 }}</ref> In general, these agents have proved safer than the iodinated contrast agents used in X-ray radiography or CT. [[Anaphylaxis|Anaphylactoid reactions]] are rare, occurring in approx. 0.03–0.1%.<ref>{{cite journal | vauthors = Murphy KJ, Brunberg JA, Cohan RH | title = Adverse reactions to gadolinium contrast media: a review of 36 cases | journal = AJR. American Journal of Roentgenology | volume = 167 | issue = 4 | pages = 847–9 | date = October 1996 | pmid = 8819369 | doi = 10.2214/ajr.167.4.8819369 | doi-access = free }}</ref> Of particular interest is the lower incidence of nephrotoxicity, compared with iodinated agents, when given at usual doses—this has made contrast-enhanced MRI scanning an option for patients with renal impairment, who would otherwise not be able to undergo [[Radiocontrast|contrast-enhanced CT]].<ref>{{cite web|url=http://www.guideline.gov/summary/summary.aspx?doc_id=8283|title=ACR guideline|website=guideline.gov|date=2005|access-date=2006-11-22|archive-url=https://web.archive.org/web/20060929182051/http://www.guideline.gov/summary/summary.aspx?doc_id=8283|archive-date=2006-09-29|url-status=dead}}</ref>

Gadolinium-based contrast reagents are typically [[polydentate|octadentate]] complexes of [[gadolinium|gadolinium(III)]]. The complex is [[Stability constants of complexes|very stable]] (log K > 20) so that, in use, the concentration of the un-complexed Gd<sup>3+</sup> ions should be below the toxicity limit. The 9th place in the metal ion's [[coordination sphere]] is occupied by a water molecule which exchanges rapidly with water molecules in the reagent molecule's immediate environment, affecting the magnetic resonance [[relaxation time]].<ref>{{cite book|first1=Sergey |last1=Shugaev |first2=Peter |last2=Caravan|chapter=Metal Ions in Bio-imaging Techniques: A Short Overview |pages= 1–37 |title=Metal Ions in Bio-Imaging Techniques|year=2021 |editor-first1= Astrid |editor-last1=Sigel|editor-first2=Eva |editor-last2=Freisinger |editor-first3=Roland K.O. |editor-last3=Sigel|publisher= Walter de Gruyter|location= Berlin|chapter-url=https://www.deGruyter.com/document/doi/10.1515/9783110685701-007|doi= 10.1515/9783110685701-007|isbn=978-3-11-068570-1 }}</ref>

In December 2017, the [[Food and Drug Administration]] (FDA) in the [[United States]] announced in a drug safety communication that new warnings were to be included on all gadolinium-based contrast agents (GBCAs). The FDA also called for increased patient education and requiring gadolinium contrast vendors to conduct additional animal and clinical studies to assess the safety of these agents.<ref>{{cite web|url=https://www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-fda-warns-gadolinium-based-contrast-agents-gbcas-are-retained-body|title= FDA Drug Safety Communication: FDA warns that gadolinium-based contrast agents (GBCAs) are retained in the body; requires new class warnings|date=2018-05-16|website=USA [[FDA]]}}</ref>
Although gadolinium agents have proved useful for patients with kidney impairment, in patients with severe [[kidney failure]] requiring dialysis there is a risk of a rare but serious illness, [[nephrogenic systemic fibrosis]], which may be linked to the use of certain gadolinium-containing agents. The most frequently linked is [[gadodiamide]], but other agents have been linked too.<ref>{{cite journal | vauthors = Thomsen HS, Morcos SK, Dawson P | title = Is there a causal relation between the administration of gadolinium based contrast media and the development of nephrogenic systemic fibrosis (NSF)? | journal = Clinical Radiology | volume = 61 | issue = 11 | pages = 905–6 | date = November 2006 | pmid = 17018301 | doi = 10.1016/j.crad.2006.09.003 }}</ref> Although a causal link has not been definitively established, current guidelines in the [[United States]] are that dialysis patients should only receive gadolinium agents where essential and that [[Kidney dialysis|dialysis]] should be performed as soon as possible after the scan to remove the agent from the body promptly.<ref>{{cite web|title=FDA Drug Safety Communication: New warnings for using gadolinium-based contrast agents in patients with kidney dysfunction|url=https://www.fda.gov/Drugs/DrugSafety/ucm223966.htm|website=Information on Gadolinium-Based Contrast Agents|publisher=U.S. Food and Drug Administration|access-date=12 March 2011|date=23 December 2010}}</ref><ref>{{cite web|url=https://www.fda.gov/cder/drug/advisory/gadolinium_agents.htm |title=FDA Public Health Advisory: Gadolinium-containing Contrast Agents for Magnetic Resonance Imaging |website=fda.gov |url-status=dead |archive-url=https://web.archive.org/web/20060928204027/https://www.fda.gov/cder/drug/advisory/gadolinium_agents.htm |archive-date=2006-09-28 }}</ref>

In Europe, where more gadolinium-containing agents are available, a classification of agents according to potential risks has been released.<ref>{{cite journal | title=Gadolinium-containing contrast agents: new advice to minimise the risk of nephrogenic systemic fibrosis | journal=Drug Safety Update | date=January 2010 | volume=3 | issue=6 | page=3 | url=https://www.gov.uk/drug-safety-update/gadolinium-containing-contrast-agents-new-advice-to-minimise-the-risk-of-nephrogenic-systemic-fibrosis }}</ref><ref>{{cite web|url=http://www.ismrm.org/special/EMEA2.pdf |title=MRI Questions and Answers |access-date=2010-08-02 | publisher=International Society for Magnetic Resonance in Medicine | location=Concord, CA }}</ref> In 2008, a new contrast agent named [[Gadoxetic acid|gadoxetate]], brand name Eovist (US) or Primovist (EU), was approved for diagnostic use: This has the theoretical benefit of a dual excretion path.<ref>{{cite web |url=http://radiology.rsna.org/content/246/1/11.full?searchid=1&HITS=10&hits=10&sortspec=relevance&resourcetype=HWCIT&maxtoshow=&RESULTFORMAT=&author1=kanal&FIRSTINDEX=0 |archive-url=https://archive.today/20120719004253/http://radiology.rsna.org/content/246/1/11.full?searchid=1&HITS=10&hits=10&sortspec=relevance&resourcetype=HWCIT&maxtoshow=&RESULTFORMAT=&author1=kanal&FIRSTINDEX=0 |url-status=dead |archive-date=2012-07-19 |title=Response to the FDA's May 23, 2007, Nephrogenic Systemic Fibrosis Update1 — Radiology |publisher=Radiological Society of North America |date=2007-09-12 |access-date=2010-08-02 }}</ref>

== Sequences ==
{{Main|MRI sequences}}

An [[MRI sequences|MRI sequence]] is a particular setting of radiofrequency pulses and gradients, resulting in a particular image appearance.<ref>{{cite web|url=https://radiopaedia.org/articles/mri-sequences-overview|title=MRI sequences (overview)| vauthors=Jones J, Gaillard F|website=[[Radiopaedia]]|access-date=2017-10-15}}</ref> The [[#T1 and T2|T1 and T2]] weighting can also be described as MRI sequences.

{{Table of MRI sequences|header= ====Overview table====}}

== 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.

==Safety==
{{Main |Safety of magnetic resonance imaging}}

MRI is, in general, a safe technique, although injuries may occur as a result of failed safety procedures or human error.<ref>{{cite journal |doi=10.1007/s40134-015-0122-z |title=Lessons Learned from MRI Safety Events |journal=Current Radiology Reports |volume=3 |issue=10 |year=2015 | vauthors = Watson RE |s2cid=57880401 }}</ref> [[Contraindications]] to MRI include most [[cochlear implant]]s and [[Artificial cardiac pacemaker|cardiac pacemakers]], [[Fragmentation (weaponry)|shrapnel]], and metallic [[foreign body|foreign bodies]] in the [[Orbit (anatomy)|eyes]]. [[Magnetic resonance imaging in pregnancy]] appears to be safe, at least during the second and third [[Pregnancy|trimesters]] if done without contrast agents.<ref name="MervakAltun2019">{{cite journal | vauthors = Mervak BM, Altun E, McGinty KA, Hyslop WB, Semelka RC, Burke LM | title = MRI in pregnancy: Indications and practical considerations | journal = Journal of Magnetic Resonance Imaging | volume = 49 | issue = 3 | pages = 621–631 | date = March 2019 | pmid = 30701610 | doi = 10.1002/jmri.26317 | s2cid = 73412175 }}</ref> Since MRI does not use any ionizing radiation, its use is generally favored in preference to [[X-ray computed tomography|CT]] when either modality could yield the same information.<ref name="iRefer">{{cite web |title=iRefer |url=http://www.rcr.ac.uk/content.aspx?PageID=995 |publisher=Royal College of Radiologists |access-date=10 November 2013 |archive-date=3 February 2014 |archive-url=https://web.archive.org/web/20140203182954/http://www.rcr.ac.uk/content.aspx?PageID=995 |url-status=dead }}</ref> Some patients experience claustrophobia and may require sedation or shorter MRI protocols.<ref>{{cite journal | vauthors = Murphy KJ, Brunberg JA | title = Adult claustrophobia, anxiety and sedation in MRI | journal = Magnetic Resonance Imaging | volume = 15 | issue = 1 | pages = 51–4 | year = 1997 | pmid = 9084025 | doi = 10.1016/s0730-725x(96)00351-7 | publisher = Elsevier BV }}</ref><ref>{{Cite journal|last1=Shahrouki|first1=Puja|last2=Nguyen|first2=Kim-Lien|last3=Moriarty|first3=John M.|last4=Plotnik|first4=Adam N.|last5=Yoshida|first5=Takegawa|last6=Finn|first6=J. Paul|date=2021-09-01|title=Minimizing table time in patients with claustrophobia using focused ferumoxytol-enhanced MR angiography ( f -FEMRA): a feasibility study|journal=The British Journal of Radiology|language=en|volume=94|issue=1125|pages=20210430|doi=10.1259/bjr.20210430|pmid=34415199|pmc=9327752 |issn=0007-1285}}</ref> Amplitude and rapid switching of gradient coils during image acquisition may cause peripheral nerve stimulation.<ref>{{cite journal | vauthors = Klein V, Davids M, Schad LR, Wald LL, Guérin B | title = Investigating cardiac stimulation limits of MRI gradient coils using electromagnetic and electrophysiological simulations in human and canine body models | journal = Magnetic Resonance in Medicine | volume = 85 | issue = 2 | pages = 1047–1061 | date = February 2021 | pmid = 32812280 | pmc = 7722025 | doi = 10.1002/mrm.28472 }}</ref>

{{external media
| float  = right
| width  = 300px
| video1 = [https://www.youtube.com/watch?v=IF6CMrjGNN4 Magnetic objects thrown at an MRI magnet]
}}
MRI uses powerful magnets and can therefore cause [[Ferromagnetism|magnetic materials]] to move at great speeds, posing a projectile risk, and may cause fatal accidents.<ref>{{cite news |author=[[Agence France-Presse]] |url=https://www.theguardian.com/world/2018/jan/30/mri-scanner-india-death |title=Man dies after being sucked into MRI scanner at Indian hospital |work=The Guardian |date=30 January 2018}}</ref> However, as millions of MRIs are performed globally each year,<ref>{{cite web |url=https://international.commonwealthfund.org/stats/mri_exams/ |title=Magnetic Resonance Imaging (MRI) Exams per 1,000 Population, 2014 |publisher=[[OECD]] |date=2016}}</ref> fatalities are extremely rare.<ref>{{cite journal | vauthors = Mansouri M, Aran S, Harvey HB, Shaqdan KW, Abujudeh HH | title = Rates of safety incident reporting in MRI in a large academic medical center | journal = Journal of Magnetic Resonance Imaging | volume = 43 | issue = 4 | pages = 998–1007 | date = April 2016 | pmid = 26483127 | doi = 10.1002/jmri.25055 | publisher = [[John Wiley and Sons]] | s2cid = 25245904 | doi-access = free }}</ref>

MRI machines can produce loud noise, up to 120 [[A-weighted|dB(A)]].<ref>{{Cite journal |last1=Price |first1=D. L. |last2=De Wilde |first2=J. P. |last3=Papadaki |first3=A. M. |last4=Curran |first4=J. S. |last5=Kitney |first5=R. I. |date=February 2001 |title=Investigation of acoustic noise on 15 MRI scanners from 0.2 T to 3 T |journal=Journal of Magnetic Resonance Imaging  |volume=13 |issue=2 |pages=288–293 |doi=10.1002/1522-2586(200102)13:2<288::aid-jmri1041>3.0.co;2-p |issn=1053-1807 |pmid=11169836|s2cid=20684100 |doi-access=free }}</ref> This can cause [[hearing loss]], [[tinnitus]] and [[hyperacusis]], so appropriate [[Hearing protection device|hearing protection]] is essential for anyone inside the MRI scanner room during the examination.

===Overuse===
{{See also |Overdiagnosis}}

Medical societies issue guidelines for when physicians should use MRI on patients and recommend against overuse. MRI can detect health problems or confirm a diagnosis, but medical societies often recommend that MRI not be the first procedure for creating a plan to diagnose or manage a patient's complaint. A common case is to use MRI to seek a cause of [[low back pain]]; the [[American College of Physicians]], for example, recommends against imaging (including MRI) as unlikely to result in a positive outcome for the patient.<ref name="ACPfive">{{cite journal |author1=Consumer Reports |author2=American College of Physicians |author1-link=Consumer Reports |author2-link=American College of Physicians |others=presented by [[ABIM Foundation]] |title=Five Things Physicians and Patients Should Question |journal=Choosing Wisely |url=http://choosingwisely.org/wp-content/uploads/2012/04/5things_12_factsheet_Amer_College_Phys.pdf |access-date=August 14, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120624075449/http://choosingwisely.org/wp-content/uploads/2012/04/5things_12_factsheet_Amer_College_Phys.pdf |archive-date=June 24, 2012 }}</ref><ref name="backimage">{{cite journal |author1=Consumer Reports |author2=American College of Physicians |author1-link=Consumer Reports |author2-link=American College of Physicians |date=April 2012 |title=Imaging tests for lower-back pain: Why you probably don't need them |journal=High Value Care |url=http://consumerhealthchoices.org/wp-content/uploads/2012/04/High-Value-Care-Back-Pain-ACP.pdf | archive-url=https://web.archive.org/web/20130115221844/http://consumerhealthchoices.org/wp-content/uploads/2012/04/High-Value-Care-Back-Pain-ACP.pdf | archive-date=15 January 2013 | url-status=dead |access-date=August 14, 2012}}</ref>

==Artifacts==
{{Main|MRI artifact}}
[[File:MRI with motion artifacts.jpg|thumb|upright=1.2|Motion artifact (T1 coronal study of cervical vertebrae)<ref name="ErasmusHurter2004"/>]]

An [[MRI artifact]] is a [[visual artifact]], that is, an anomaly during visual representation. Many different artifacts can occur during magnetic resonance imaging (MRI), some affecting the diagnostic quality, while others may be confused with pathology. Artifacts can be classified as patient-related, signal processing-dependent and hardware (machine)-related.<ref name="ErasmusHurter2004">{{cite journal |doi=10.4102/sajr.v8i2.127 |title=A short overview of MRI artefacts |journal=South African Journal of Radiology |volume=8 |issue=2 |page=13 |year=2004 | vauthors=Erasmus LJ, Hurter D, Naude M, Kritzinger HG, Acho S |doi-access=free }}</ref>

==Non-medical use==
{{Main|Nuclear magnetic resonance#Applications}}

MRI is used industrially mainly for routine analysis of chemicals. The [[nuclear magnetic resonance]] technique is also used, for example, to measure the ratio between water and fat in foods, monitoring of flow of corrosive fluids in pipes, or to study molecular structures such as catalysts.<ref name="Rinck"/>

Being non-invasive and non-damaging, MRI can be used to study the anatomy of plants, their water transportation processes and water balance.<ref>{{cite journal | vauthors = Van As H | title = Intact plant MRI for the study of cell water relations, membrane permeability, cell-to-cell and long distance water transport | journal = Journal of Experimental Botany | volume = 58 | issue = 4 | pages = 743–56 | date = 2006-11-30 | pmid = 17175554 | doi = 10.1093/jxb/erl157 | publisher = Oxford University Press (OUP) | doi-access = free }}</ref> It is also applied to veterinary radiology for diagnostic purposes. Outside this, its use in zoology is limited due to the high cost; but it can be used on many species.<ref>{{cite journal | vauthors = Ziegler A, Kunth M, Mueller S, Bock C, Pohmann R, Schröder L, Faber C, Giribet G | s2cid=43555012 | title=Application of magnetic resonance imaging in zoology | journal=Zoomorphology | publisher=Springer Science and Business Media LLC | volume=130 | issue=4 | date=2011-10-13 | issn=0720-213X | doi=10.1007/s00435-011-0138-8 | pages=227–254| hdl=11858/00-001M-0000-0013-B8B0-B | hdl-access=free }}</ref>

In palaeontology it is used to examine the structure of fossils.<ref>{{cite journal | vauthors = Giovannetti G, Guerrini A, Salvadori PA | title = Magnetic resonance spectroscopy and imaging for the study of fossils | journal = Magnetic Resonance Imaging | volume = 34 | issue = 6 | pages = 730–742 | date = July 2016 | pmid = 26979538 | doi = 10.1016/j.mri.2016.03.010 | publisher = Elsevier BV }}</ref>

[[Forensic science|Forensic]] imaging provides graphic documentation of an [[autopsy]], which manual autopsy does not. CT scanning provides quick whole-body imaging of skeletal and [[parenchyma]]l alterations, whereas MR imaging gives better representation of soft tissue [[pathology]].<ref name="pmid30686369">{{cite journal | vauthors = Filograna L, Pugliese L, Muto M, Tatulli D, Guglielmi G, Thali MJ, Floris R | title = A Practical Guide to Virtual Autopsy: Why, When and How | journal = Seminars in Ultrasound, CT, and MR | volume = 40 | issue = 1 | pages = 56–66 | date = February 2019 | pmid = 30686369 | doi = 10.1053/j.sult.2018.10.011 | s2cid = 59304740 }}</ref> All that being said, MRI is more expensive, and more time-consuming to utilize.<ref name="pmid30686369" /> Moreover, the quality of MR imaging deteriorates below 10&nbsp;°C.<ref name="pmid24191122">{{cite journal | vauthors = Ruder TD, Thali MJ, Hatch GM | title = Essentials of forensic post-mortem MR imaging in adults | journal = The British Journal of Radiology | volume = 87 | issue = 1036 | pages = 20130567 | date = April 2014 | pmid = 24191122 | pmc = 4067017 | doi = 10.1259/bjr.20130567 }}</ref>

==History==
{{Main|History of magnetic resonance imaging}}

In 1971 at [[Stony Brook University]], [[Paul Lauterbur]] applied magnetic field gradients in all three dimensions and a back-projection technique to create NMR images. He published the first images of two tubes of water in 1973 in the journal ''Nature'',<ref name="LAUTERBUR 1973 pp. 190–191">{{cite journal | last=LAUTERBUR | first=P. C. | title=Image Formation by Induced Local Interactions: Examples Employing Nuclear Magnetic Resonance | journal=Nature | publisher=Springer Science and Business Media LLC | volume=242 | issue=5394 | year=1973 | issn=0028-0836 | doi=10.1038/242190a0 | pages=190–191| bibcode=1973Natur.242..190L | s2cid=4176060 }}</ref> followed by the picture of a living animal, a clam, and in 1974 by the image of the thoracic cavity of a mouse. Lauterbur called his imaging method zeugmatography, a term which was replaced by (N)MR imaging.<ref name="Rinck"/> In the late 1970s, physicists [[Peter Mansfield]] and [[Paul Lauterbur]] developed MRI-related techniques, like the [[echo-planar imaging]] (EPI) technique.<ref name="Mansfield-EPI">{{cite journal |doi=10.1103/physrevb.12.3618 |title="Diffraction" and microscopy in solids and liquids by NMR |journal=Physical Review B |volume=12 |issue=9 |pages=3618–34 |year=1975 | vauthors=Mansfield P, Grannell PK |bibcode=1975PhRvB..12.3618M }}</ref>

[[Raymond Damadian]]'s work into [[nuclear magnetic resonance]] (NMR) has been incorporated into MRI, having built one of the first scanners.<ref>{{Cite news|url=https://www.nytimes.com/2022/08/17/science/raymond-damadian-dead.html|title=Raymond Damadian, Creator of the First M.R.I. Scanner, Dies at 86|first=Richard|last=Sandomir|work=The New York Times |date=August 17, 2022|via=NYTimes.com}}</ref>

Advances in [[semiconductor]] technology were crucial to the development of practical MRI, which requires a large amount of [[computational power]]. This was made possible by the rapidly increasing number of [[transistors]] on a single [[integrated circuit]] chip.<ref>{{cite book | vauthors = Rosenblum B, Kuttner F |title=Quantum Enigma: Physics Encounters Consciousness |date=2011 |publisher=[[Oxford University Press]] |isbn=9780199792955 |page=127 |url={{google books|plainurl=yes|id=I9kGFX1_oGAC|page=127}}}}</ref> Mansfield and Lauterbur were awarded the 2003 [[Nobel Prize in Physiology or Medicine]] for their "discoveries concerning magnetic resonance imaging".<ref>{{cite web|title=The Nobel Prize in Physiology or Medicine 2003|url=http://www.nobelprize.org/nobel_prizes/medicine/laureates/2003/index.html|publisher=Nobel Foundation|access-date=28 July 2007|archive-url=https://web.archive.org/web/20070718172340/http://nobelprize.org/nobel_prizes/medicine/laureates/2003/index.html|archive-date=18 July 2007|url-status=live}}</ref>

== See also ==
{{Portal|Medicine}}
{{colbegin|colwidth=22em}}
* [[Amplified magnetic resonance imaging]]
* [[Cerebrospinal fluid flow MRI]]
* [[Electron paramagnetic resonance]]
* [[High-definition fiber tracking]]
* [[High-resolution computed tomography]]
* [[History of neuroimaging]]
* [[International Society for Magnetic Resonance in Medicine]]
* [[Jemris]]
* [[List of neuroimaging software]]
* [[Magnetic immunoassay]]
* [[Magnetic particle imaging]]
* [[Magnetic resonance elastography]]
* [[Magnetic Resonance Imaging (journal)|''Magnetic Resonance Imaging'' (journal)]]
* [[Magnetic resonance microscopy]]
* [[Nobel Prize controversies#Physiology or medicine|Nobel Prize controversies – Physiology or medicine]]
* [[Rabi cycle]]
* [[Robinson oscillator]]
* [[Sodium MRI]]
* [[Virtopsy]]
{{colend}}

== References ==
{{Reflist}}

== Further reading ==
{{refbegin}}
* {{cite book |last1=Blümer |first1=Peter |editor-first1=Peter |editor-last1=Blümler |editor-first2=Bernhard |editor-last2=Blümich |editor-first3=Robert E. |editor-last3=Botto |editor-first4=Eiichi |editor-last4=Fukushima |name-list-style=vanc |title=Spatially Resolved Magnetic Resonance: Methods, Materials, Medicine, Biology, Rheology, Geology, Ecology, Hardware |publisher=Wiley-VCH |date=1998 |isbn=978-3-527-29637-8}}
* {{cite book |last1=Blümich |first1=Bernhard |first2=Winfried |last2=Kuhn |name-list-style=vanc |title=Magnetic Resonance Microscopy: Methods and Applications in Materials Science, Agriculture and Biomedicine |publisher=Wiley |date=1992 |isbn=978-3-527-28403-0}}
* {{cite book  |last=Blümich |first=Bernhard |name-list-style=vanc |title=NMR Imaging of Materials |publisher=Clarendon Press |date=2000 |isbn=978-0-19-850683-6}}
* {{cite journal |vauthors = Eustace SJ, Nelson E |title = Whole body magnetic resonance imaging |journal = BMJ |volume = 328 |issue = 7453 |pages = 1387–8 |date = June 2004 |pmid = 15191954 |pmc = 421763 |doi = 10.1136/bmj.328.7453.1387 }}
* {{cite book |last1=Farhat |first1=Imad Akil |first2=P.S. |last2=Belton |first3=Graham Alan |last3=Webb |name-list-style=vanc |title=Magnetic Resonance in Food Science: From Molecules to Man |publisher=Royal Society of Chemistry |date=2007 |isbn=978-0-85404-340-8}}
* {{cite book |last=Fukushima |first= Eiichi |name-list-style=vanc |title=NMR in Biomedicine: The Physical Basis |publisher=Springer Science & Business Media |date=1989 |isbn=978-0-88318-609-1}}
* {{cite book |last1=Haacke |first1=E Mark |last2=Brown |first2=Robert F |last3=Thompson |first3=Michael |last4=Venkatesan |first4=Ramesh |name-list-style=vanc |title=Magnetic resonance imaging: Physical principles and sequence design |publisher=J. Wiley & Sons |location=New York |date=1999 |isbn=978-0-471-35128-3 }}
* {{cite book |last=Jin |name-list-style=vanc |title=Electromagnetic Analysis and Design in Magnetic Resonance Imaging |publisher=CRC Press |date=1998 |isbn=978-0-8493-9693-9}}
* {{cite book |last=Kuperman |first=Vadim |name-list-style=vanc |title=Magnetic Resonance Imaging: Physical Principles and Applications |publisher=Academic Press |date=2000 |isbn=978-0-08-053570-8}}
* {{cite journal |vauthors = Lee SC, Kim K, Kim J, Lee S, Han Yi J, Kim SW, Ha KS, Cheong C |display-authors = 6 |title = One micrometer resolution NMR microscopy |journal = Journal of Magnetic Resonance |volume = 150 |issue = 2 |pages = 207–13 |date = June 2001 |pmid = 11384182 |doi = 10.1006/jmre.2001.2319 |bibcode = 2001JMagR.150..207L }}
* {{cite book |last1=Liang |first1=Zhi-Pei |first2=Paul C. |last2=Lauterbur |name-list-style=vanc |title=Principles of Magnetic Resonance Imaging: A Signal Processing Perspective |publisher=Wiley |date=1999 |isbn=978-0-7803-4723-6 |url=https://archive.org/details/principlesofmagn00zhip }}
* {{cite book |vauthors=Mansfield P |title=NMR Imaging in Biomedicine: Supplement 2 Advances in Magnetic Resonance |publisher=Elsevier |date=1982 |isbn=978-0-323-15406-2 }}
* {{cite journal |vauthors = Pykett IL |title = NMR imaging in medicine |journal = Scientific American |volume = 246 |issue = 5 |pages = 78–88 |date = May 1982 |pmid = 7079720 |doi = 10.1038/scientificamerican0582-78 |bibcode = 1982SciAm.246e..78P }}
* {{cite web |veditors=Rinck PA |work=TRTF/EMRF |title=The history of MRI |url=http://www.magnetic-resonance.org/ch/20-01.html }}
* {{cite journal |last1=Sakr |first1=HM |last2=Fahmy |first2=N |last3=Elsayed |first3=NS |last4=Abdulhady |first4=H |last5=El-Sobky |first5=TA |last6=Saadawy |first6=AM |last7=Beroud |first7=C |last8=Udd |first8=B |title=Whole-body muscle MRI characteristics of LAMA2-related congenital muscular dystrophy children: An emerging pattern. |journal=Neuromuscular Disorders |date=1 July 2021 |volume=31 |issue=9 |pages=814–823 |doi=10.1016/j.nmd.2021.06.012 |pmid=34481707|s2cid=235691786 }}
* {{cite book |last1=Schmitt |first1=Franz |first2=Michael K. |last2=Stehling |first3=Robert |last3=Turner |name-list-style=vanc |title=Echo-Planar Imaging: Theory, Technique and Application |url=https://archive.org/details/springer_10.1007-978-3-642-80443-4 |publisher=Springer Berlin Heidelberg |date=1998 |isbn=978-3-540-63194-1}}
* {{cite book |last1=Simon |first1=Merrill |last2=Mattson |first2=James S |name-list-style=vanc |title=The pioneers of NMR and magnetic resonance in medicine: The story of MRI |publisher=Bar-Ilan University Press |location=Ramat Gan, Israel |date=1996 |isbn=978-0-9619243-1-7 |url=https://archive.org/details/pioneersofnmrmag0000matt }}
* {{cite book |last=Sprawls |first=Perry |name-list-style=vanc |date=2000 |title=Magnetic Resonance Imaging: Principles, Methods, and Techniques |url=http://www.sprawls.org/mripmt/index.html |publisher=Medical Physics Publishing |isbn=978-0-944838-97-6 }}
{{refend}}

== External links ==
{{commons category|Magnetic resonance imaging}}
* {{cite web | url=http://www.magnetic-resonance.org | title=MRI: A Peer-Reviewed, Critical Introduction | work=European Magnetic Resonance Forum (EMRF)/The Round Table Foundation (TRTF) | veditors=Rinck PA }}
* [https://nationalmaglab.org/education/magnet-academy/learn-the-basics/stories/mri-a-guided-tour A Guided Tour of MRI: An introduction for laypeople] National High Magnetic Field Laboratory
* [http://www.cis.rit.edu/htbooks/mri/ The Basics of MRI]. ''Underlying physics and technical aspects''.
* [http://www.imrser.org/PatientVideo.html Video: What to Expect During Your MRI Exam] from the Institute for Magnetic Resonance Safety, Education, and Research (IMRSER)
* [http://www.vega.org.uk/video/programme/73 Royal Institution Lecture – MRI: A Window on the Human Body]
* [https://web.archive.org/web/20070413032705/http://www.emrf.org/FAQs%20MRI%20History.html A Short History of Magnetic Resonance Imaging from a European Point of View]
* [https://www.howequipmentworks.com/mri_basics/ How MRI works explained simply using diagrams]
* [http://www.biomednmr.mpg.de/index.php?option=com_content&task=view&id=132&Itemid=39 Real-time MRI videos: Biomedizinische NMR Forschungs GmbH].
* Paul C. Lauterbur, [https://digital.sciencehistory.org/works/0c483j46q Genesis of the MRI (Magnetic Resonance Imaging) notebook, September 1971] (all pages freely available for download in variety of formats from [[Science History Institute]] Digital Collections at [https://web.archive.org/web/20190202042542/https://digital.sciencehistory.org/ digital.sciencehistory.org])

{{Medical imaging}}
{{Superconductivity}}
{{Authority control}}

{{DEFAULTSORT:Magnetic Resonance Imaging}}
[[Category:Magnetic resonance imaging| ]]
[[Category:1973 introductions]]
[[Category:20th-century inventions]]
[[Category:American inventions]]
[[Category:Articles containing video clips]]
[[Category:Biomagnetics]]
[[Category:Cryogenics]]
[[Category:Discovery and invention controversies]]
[[Category:Radiology]]