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magnetic resonance imaging
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| MedlinePlus = 003335| MeshID = D008279}}Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body. MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from CT or CAT scans and PET scans. Magnetic resonance imaging is a medical application of nuclear magnetic resonance (NMR). NMR can also be used for imaging in other NMR applications such as NMR spectroscopy.While the hazards of X-rays are now well controlled in most medical contexts, an MRI scan may still be seen as a better choice than a CT scan. MRI is widely used in hospitals and clinics for medical diagnosis, staging of disease and follow-up without exposing the body to radiation. An MRI may yield different information compared with CT. Risks and discomfort may be associated with MRI scans. Compared with CT scans, MRI scans typically take longer and are louder, and they usually need the subject to enter a narrow, confining tube. In addition, people with some medical implants or other non-removable metal inside the body may be unable to undergo an MRI examination safely.MRI was originally called NMRI (nuclear magnetic resonance imaging), but "nuclear" was dropped to avoid negative associations.BOOK, Donald W., McRobbie, Elizabeth A., Moore, Martin J., Graves, Martin R., Prince, vanc, MRI from Picture to Proton, Cambridge University Press, 2007, 978-1-139-45719-4, 1, Certain atomic nuclei are able to absorb and emit radio frequency energy when placed in an external magnetic field. In clinical and research MRI, hydrogen atoms are most often used to generate a detectable radio-frequency signal that is received by antennas close to the anatomy being examined. Hydrogen atoms are naturally abundant in people and other biological organisms, particularly in water and fat. For this reason, most MRI scans essentially map the location of water and fat in the body. Pulses of radio waves excite the nuclear spin energy transition, and magnetic field gradients localize the signal in space. By varying the parameters of the pulse sequence, different contrasts may be generated between tissues based on the 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 diagnostic medicine and biomedical research, it also may be used to form images of non-living objects. MRI scans are capable of producing a variety of chemical and physical data, in addition to detailed spatial images. The sustained increase in demand for MRI within health systems has led to concerns about cost effectiveness and overdiagnosis.JOURNAL, Smith-Bindman R, 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, 6, Use of diagnostic imaging studies and associated radiation exposure for patients enrolled in large integrated health care systems, 1996–2010, JAMA, 307, 22, 2400–09, June 2012, 22692172, 3859870, 10.1001/jama.2012.5960, BOOK, 2009, Health at a glance 2009 OECD indicators, 10.1787/health_glance-2009-en, Health at a Glance, 978-92-64-07555-9,

Mechanism

Construction and physics

(File:Mri scanner schematic labelled.svg|thumb|upright=1.5 |Schematic of construction of a cylindrical superconducting MR scanner.)To perform a study, the person is positioned within an MRI scanner that forms a strong magnetic field around the area to be imaged. 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. First, energy from an oscillating magnetic field is temporarily applied to the patient at the appropriate resonance frequency. The excited hydrogen atoms emit a radio frequency signal, which is measured by a receiving coil. The radio signal may be made to encode position information by varying the main magnetic field using gradient coils. As these coils are rapidly switched on and off they create the characteristic repetitive noise of an MRI scan. The contrast between different tissues is determined by the rate at which excited atoms return to the equilibrium state. Exogenous contrast agents may be given to the person to make the image clearer.BOOK, McRobbie, Donald W., vanc, MRI from picture to proton, 2007, Cambridge University Press, Cambridge, UK; New York, 978-0-521-68384-5, The major components of an MRI scanner are the main magnet, which polarizes the sample, the shim coils for correcting shifts in the homogeneity of the main magnetic field, the gradient system which is used to localize the MR signal and the RF system, which excites the sample and detects the resulting NMR signal. The whole system is controlled by one or more computers.MRI requires a magnetic field that is both strong and uniform. The field strength of the magnet is measured in teslas – and while the majority of systems operate at 1.5 T, commercial systems are available between 0.2 and 7 T. Most clinical magnets are superconducting magnets, which require liquid helium. Lower field strengths can be achieved with permanent magnets, which are often used in "open" MRI scanners for claustrophobic patients.JOURNAL, Sasaki M, Ehara S, Nakasato T, Tamakawa Y, Kuboya Y, Sugisawa M, Sato T, MR of the shoulder with a 0.2-T permanent-magnet unit, AJR. American Journal of Roentgenology, 154, 4, 777–78, April 1990, 2107675, 10.2214/ajr.154.4.2107675, 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 (SQUIDs).JOURNAL, McDermott R, Lee S, ten Haken B, Trabesinger AH, Pines A, Clarke J, Microtesla MRI with a superconducting quantum interference device, Proceedings of the National Academy of Sciences of the United States of America, 101, 21, 7857–61, May 2004, 15141077, 419521, 10.1073/pnas.0402382101, 2004PNAS..101.7857M, JOURNAL, 10.1088/0953-2048/20/11/S13, SQUID-based instrumentation for ultralow-field MRI, Superconductor Science and Technology, 20, 11, S367–73, 2007, Zotev, Vadim S, Matlashov, Andrei N, Volegov, Petr L, Urbaitis, Algis V, Espy, Michelle A, Kraus Jr, Robert H, vanc, 0705.0661, 2007SuScT..20S.367Z, JOURNAL, 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, Hybrid ultra-low-field MRI and magnetoencephalography system based on a commercial whole-head neuromagnetometer, Magnetic Resonance in Medicine, 69, 6, 1795–804, June 2013, 22807201, 10.1002/mrm.24413,

T1 and T2

{{see|Relaxation (NMR)}}(File:TR TE.jpg|thumb|Effects of TR and TE on MR signal)File:T1t2PD.jpg|thumb|Examples of T1 weighted, T2 weighted and PD weighted MRI scans]]Each tissue returns to its equilibrium state after excitation by the independent relaxation processes of T1 (spin-lattice; that is, magnetization in the same direction as the static magnetic field) and T2 (spin-spin; transverse to the static magnetic field).{{anchor|T1-weighted_MRI}}To create a T1-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 post-contrast imaging.{{anchor|T2-weighted_MRI}}To create a T2-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 white matter lesions, and assessing zonal anatomy in the prostate and uterus.The standard display of MRI images is to represent fluid characteristics in black and white images, where different tissues turn out as follows:{|class="wikitable"! Signal !! T1-weighted !! T2-weighted High| Inter- mediateGray matter darker than white matterHTTP://WWW.SLIDESHARE.NET/DRTUSHARPATIL/MRI-SEQUENCESAUTHOR=TUSHAR PATILDATE=2013-01-18, | White matter darker than grey matter Low|

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 more than 25,000 scanners are estimated to be in use worldwide.WEB, Magnetic Resonance, a critical peer-reviewed introduction, European Magnetic Resonance Forum, 17 November 2014,weblink MRI affects diagnosis and treatment in many specialties although the effect on improved health outcomes is uncertain.JOURNAL, Hollingworth W, Todd CJ, Bell MI, Arafat Q, Girling S, Karia KR, Dixon AK, The diagnostic and therapeutic impact of MRI: an observational multi-centre study, Clinical Radiology, 55, 11, 825–31, November 2000, 11069736, 10.1053/crad.2000.0546, {{Obsolete source|reason=This source is almost 20 years old|date=December 2018}}MRI is the investigation of choice in the preoperative staging of rectal and prostate cancer and, has a role in the diagnosis, staging, and follow-up of other tumors.BOOK, Husband J, Recommendations for Cross-Sectional Imaging in Cancer Management: Computed Tomography – CT Magnetic Resonance Imaging – MRI Positron Emission Tomography – PET-CT, 2008,weblink Royal College of Radiologists, 978-1-905034-13-0,

Neuroimaging

{{See also|Neuroimaging}}File:White Matter Connections Obtained with MRI Tractography.png|thumb|MRI image of white matterwhite matterMRI 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 and white matter makes MRI the best choice for many conditions of the central nervous system, including demyelinating diseases, dementia, cerebrovascular disease, infectious diseases, Alzheimer's disease and epilepsy.WEB,weblink ACR-ASNR Practice Guideline for the Performance and Interpretation of Magnetic Resonance Imaging (MRI) of the Brain, American Society of Neuroradiology, 2013, JOURNAL, Rowayda, A. Sadek, vanc, An improved MRI segmentation for atrophy assessment, International Journal of Computer Science Issues (IJCSI), May 2012, 9, 3, JOURNAL, Rowayda, A. Sadek, vanc, Regional atrophy analysis of MRI for early detection of alzheimer's disease, International Journal of Signal Processing, Image Processing and Pattern Recognition, February 2013, 6, 1, 49–53, 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.BOOK, Nolen-Hoeksema, Susan, vanc, Abnormal Psychology, 2014, McGraw-Hill Education, New York, 67, Sixth, MRI also is used in 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.JOURNAL, Brown RA, Nelson JA, The Invention and Early History of the N-Localizer for Stereotactic Neurosurgery, Cureus, 8, 6, e642, June 2016, 27462476, 4959822, 10.7759/cureus.642, JOURNAL, Leksell L, Leksell D, Schwebel J, Stereotaxis and nuclear magnetic resonance, Journal of Neurology, Neurosurgery, and Psychiatry, 48, 1, 14–18, January 1985, 3882889, 1028176, 10.1136/jnnp.48.1.14, JOURNAL, Heilbrun MP, Sunderland PM, McDonald PR, Wells TH, Cosman E, Ganz E, Brown-Roberts-Wells stereotactic frame modifications to accomplish magnetic resonance imaging guidance in three planes, Applied Neurophysiology, 50, 1–6, 143–52, 1987, 3329837, 10.1159/000100700,

Cardiovascular

(File:PAPVR.gif|thumb|MR angiogram in congenital heart disease)Cardiac MRI is complementary to other imaging techniques, such as echocardiography, cardiac CT, and nuclear medicine. Its applications include assessment of myocardial ischemia and viability, cardiomyopathies, myocarditis, iron overload, vascular diseases, and congenital heart disease.JOURNAL, 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 of the American College of Radiology, 3, 10, 751–71, October 2006, 17412166, 10.1016/j.jacr.2006.08.008, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, American Society of Nuclear Cardiology, North American Society for Cardiac Imaging, Society for Cardiovascular Angiography Interventions, Society of Interventional Radiology,

Musculoskeletal

Applications in the musculoskeletal system include spinal imaging, assessment of joint disease, and soft tissue tumors.BOOK, Helms C, Musculoskeletal MRI, 2008, Saunders, 978-1-4160-5534-1,

Liver and gastrointestinal

Hepatobiliary MR is used to detect and characterize lesions of the liver, pancreas, and bile ducts. Focal or diffuse disorders of the liver may be evaluated using diffusion-weighted, opposed-phase imaging, and 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 (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.JOURNAL, Frydrychowicz A, Lubner MG, Brown JJ, Merkle EM, Nagle SK, Rofsky NM, Reeder SB, Hepatobiliary MR imaging with gadolinium-based contrast agents, Journal of Magnetic Resonance Imaging, 35, 3, 492–511, March 2012, 22334493, 3281562, 10.1002/jmri.22833, JOURNAL, Sandrasegaran K, Lin C, Akisik FM, Tann M, State-of-the-art pancreatic MRI, AJR. American Journal of Roentgenology, 195, 1, 42–53, July 2010, 20566796, 10.2214/ajr.195.3_supplement.0s42, JOURNAL, Masselli G, Gualdi G, MR imaging of the small bowel, Radiology, 264, 2, 333–48, August 2012, 22821694, 10.1148/radiol.12111658, JOURNAL, Zijta FM, Bipat S, Stoker J, Magnetic resonance (MR) colonography in the detection of colorectal lesions: a systematic review of prospective studies, European Radiology, 20, 5, 1031–46, May 2010, 19936754, 2850516, 10.1007/s00330-009-1663-4,

Angiography

(File:mra1.jpg|thumb|Magnetic resonance angiography)Magnetic resonance angiography (MRA) generates pictures of the arteries to evaluate them for stenosis (abnormal narrowing) or aneurysms (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).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.BOOK, Haacke, E Mark, Brown, Robert F, Thompson, Michael, Venkatesan, Ramesh, Magnetic resonance imaging: Physical principles and sequence design, J. Wiley & Sons, New York, 1999, 978-0-471-35128-3, {{page needed|date=July 2013}}

Contrast agents

MRI for imaging anatomical structures or blood flow do not require contrast agents as the varying properties of the tissues or blood provide natural contrasts. However, for more specific types of imaging, exogenous contrast agents may be given intravenously, orally, or intra-articularly. The most commonly used intravenous contrast agents are based on chelates of gadolinium.BOOK, Rinck PA, Magnetic Resonance in Medicine, Chapter 13: Contrast Agents,weblink 2014, In general, these agents have proved safer than the iodinated contrast agents used in X-ray radiography or CT. Anaphylactoid reactions are rare, occurring in approx. 0.03–0.1%.JOURNAL, Murphy KJ, Brunberg JA, Cohan RH, Adverse reactions to gadolinium contrast media: a review of 36 cases, AJR. American Journal of Roentgenology, 167, 4, 847–49, October 1996, 8819369, 10.2214/ajr.167.4.8819369, 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 contrast-enhanced CT.WEB,weblink ACR guideline, guideline.gov, 2005, 2006-11-22,weblink" title="web.archive.org/web/20060929182051weblink">weblink 2006-09-29, dead, 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.WEB,weblink fda-drug-safety-communication-fda-warns-gadolinium-based-contrast-agents-gbcas-are-retained-body; requires new class warnings, 2018-05-16, USA FDA, Although gadolinium agents have proved useful for patients with renal impairment, in patients with severe renal 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.JOURNAL, Thomsen HS, Morcos SK, Dawson P, Is there a causal relation between the administration of gadolinium based contrast media and the development of nephrogenic systemic fibrosis (NSF)?, Clinical Radiology, 61, 11, 905–06, November 2006, 17018301, 10.1016/j.crad.2006.09.003, 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 dialysis should be performed as soon as possible after the scan to remove the agent from the body promptly.WEB, FDA Drug Safety Communication: New warnings for using gadolinium-based contrast agents in patients with kidney dysfunction,weblink Information on Gadolinium-Based Contrast Agents, U.S. Food and Drug Administration, 12 March 2011, 23 December 2010, WEB,weblink FDA Public Health Advisory: Gadolinium-containing Contrast Agents for Magnetic Resonance Imaging, fda.gov, dead,weblink" title="web.archive.org/web/20060928204027weblink">weblink 2006-09-28, In Europe, where more gadolinium-containing agents are available, a classification of agents according to potential risks has been released.JOURNAL, Gadolinium-containing contrast agents: new advice to minimise the risk of nephrogenic systemic fibrosis, Drug Safety Update, January 2010, 3, 6, 3,weblink WEB,weblink MRI Questions and Answers, 2010-08-02, International Society for Magnetic Resonance in Medicine, Concord, CA, Recently,{{update inline|date=July 2019}} a new contrast agent named gadoxetate, brand name Eovist (US) or Primovist (EU), was approved for diagnostic use: this has the theoretical benefit of a dual excretion path.WEB,weblinkweblink" title="archive.is/20120719004253weblink">weblink dead, 2012-07-19, Response to the FDA's May 23, 2007, Nephrogenic Systemic Fibrosis Update1 — Radiology, Radiological Society of North America, 2007-09-12, 2010-08-02,

Sequences

An MRI sequence is a particular setting of radiofrequency pulses and gradients, resulting in a particular image appearance.WEB,weblink MRI sequences (overview), Jones J, Gaillard F, Radiopaedia, 2017-10-15, The T1 and T2 weighting can also be described as MRI sequences.{{Table of MRI sequences|header= ====Overview table====}}

Other specialized configurations

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.JOURNAL, Landheer, Karl, Schulte, Rolf F., Treacy, Michael S., Swanberg, Kelley M., Juchem, Christoph, Theoretical description of modern 1H in Vivo magnetic resonance spectroscopic pulse sequences, Journal of Magnetic Resonance Imaging, 0, 10.1002/jmri.26846, 31273880, 1522-2586, 2019, 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,JOURNAL, Rosen Y, Lenkinski RE, Recent advances in magnetic resonance neurospectroscopy, Neurotherapeutics, 4, 3, 330–45, July 2007, 17599700, 10.1016/j.nurt.2007.04.009, and to provide information on tumor metabolism.JOURNAL, Golder W, Magnetic resonance spectroscopy in clinical oncology, Onkologie, 27, 3, 304–09, June 2004, 15249722, 10.1159/000077983, 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 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).JOURNAL, Chakeres DW, Abduljalil AM, Novak P, Novak V, Comparison of 1.5 and 8 tesla high-resolution magnetic resonance imaging of lacunar infarcts, Journal of Computer Assisted Tomography, 26, 4, 628–32, 2002, 12218832, 10.1097/00004728-200207000-00027, The high procurement and maintenance costs of MRI with extremely high field strengthsWEB,weblink MRI-scanner van 7 miljoen in gebruik, MRI scanner of €7 million in use, nl, Medisch Contact, December 5, 2007, inhibit their popularity. However, recent compressed sensing-based software algorithms (e.g., SAMVJOURNAL, 10.1109/tsp.2012.2231676, Iterative Sparse Asymptotic Minimum Variance Based Approaches for Array Processing, IEEE Transactions on Signal Processing, 61, 4, 933–44, 2013, Abeida, Habti, Zhang, Qilin, Li, Jian, Merabtine, Nadjim, vanc, 1802.03070, 2013ITSP...61..933A, ) have been proposed to achieve super-resolution without requiring such high field strengths.

Real-time MRI

File:Real-time MRI - Thorax.ogv|thumb|right|Real-time MRI of a human hearthuman heartReal-time MRI refers to the continuous imaging of moving objects (such as the heart) in real time. One of the many different strategies developed since the early 2000s is based on radial FLASH MRI, and iterative reconstruction. This gives a temporal resolution of 20–30 ms for images with an in-plane resolution of 1.5–2.0 mm.JOURNAL, Uecker M, Zhang S, Voit D, Karaus A, Merboldt KD, Frahm J, Real-time MRI at a resolution of 20 ms, NMR in Biomedicine, 23, 8, 986–94, October 2010, 20799371, 10.1002/nbm.1585, Balanced steady-state free precession (bSSFP) imaging has a better image contrast between the blood pool and myocardium than the FLASH MRI, yet it will produce severe banding artifact when the B0 inhomogeneity is strong. Real-time MRI is likely to add important information on diseases of the heart and the joints, and in many cases may make MRI examinations easier and more comfortable for patients, especially for the patients who cannot hold their breathings or who have arrhythmia.BOOK, Uyanik, Ilyas, Functional Imaging and Modeling of the Heart, Lindner, Peggy, Tsiamyrtzis, Panagiotis, Shah, Dipan, Tsekos, Nikolaos V., Pavlidis, Ioannis T., vanc, 7945, 2013, 466–473, 0302-9743, 10.1007/978-3-642-38899-6_55, Lecture Notes in Computer Science, 978-3-642-38898-9,

Interventional MRI

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.{{citation needed|date=November 2017}}A specialized growing subset of 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.BOOK, The Gale Encyclopedia of Nursing and Allied Health, Sisk, J. E., Gale, 2013, 9781414498881, 3rd, Farmington, MI, Credo Reference,

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 Â°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.JOURNAL, Cline HE, Schenck JF, Hynynen K, Watkins RD, Souza SP, Jolesz FA, MR-guided focused ultrasound surgery, Journal of Computer Assisted Tomography, 16, 6, 956–65, 1992, 1430448, 10.1097/00004728-199211000-00024,

Multinuclear imaging

Hydrogen has the most frequently imaged 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 nuclear spin could potentially be imaged with MRI. Such nuclei include helium-3, lithium-7, carbon-13, fluorine-19, oxygen-17, sodium-23, phosphorus-31 and xenon-129. 23Na and 31P are naturally abundant in the body, so can be imaged directly. Gaseous isotopes such as 3He or 129Xe must be hyperpolarized and then inhaled as their nuclear density is too low to yield a useful signal under normal conditions. 17O and 19F can be administered in sufficient quantities in liquid form (e.g. 17O-water) that hyperpolarization is not a necessity.{{Citation needed|date=December 2010}} 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.WEB,weblink Hyperpolarized Noble Gas MRI Laboratory: Hyperpolarized Xenon MR Imaging of the Brain, Harvard Medical School, 2017-07-26, 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.JOURNAL, 10.1016/0022-2364(91)90395-a, Gradient-enhanced proton-detected heteronuclear multiple-quantum coherence spectroscopy, Journal of Magnetic Resonance, 91, 3, 648–53, 1991, Hurd, Ralph E, John, Boban K, vanc, 1991JMagR..91..648H, In principle, hetereonuclear magnetization transfer MRI could be used to detect the presence or absence of specific chemical bonds.JOURNAL, 10.1006/jmra.1995.1064, A Test for Scaler Coupling between Heteronuclei Using Gradient-Enhanced Proton-Detected HMQC Spectroscopy, Journal of Magnetic Resonance, Series A, 113, 1, 117–19, 1995, Brown RA, Venters RA, Tang PP, Spicer LD, 1995JMagR.113..117B, JOURNAL, Miller AF, Egan LA, Townsend CA, Measurement of the degree of coupled isotopic enrichment of different positions in an antibiotic peptide by NMR, Journal of Magnetic Resonance, 125, 1, 120–31, March 1997, 9245367, 10.1006/jmre.1997.1107, 1997JMagR.125..120M, Multinuclear imaging is primarily a research technique at present. However, potential applications include functional imaging and imaging of organs poorly seen on 1H MRI (e.g., lungs and bones) or as alternative contrast agents. Inhaled hyperpolarized 3He can be used to image the distribution of air spaces within the lungs. Injectable solutions containing 13C or stabilized bubbles of hyperpolarized 129Xe have been studied as contrast agents for angiography and perfusion imaging. 31P 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.{{Citation needed|date=December 2010}}

Molecular imaging by MRI

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 10−3 mol/L to 10−5 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 teslas, a typical field strength for clinical MRI, the difference between high and low energy states is approximately 9 molecules per 2 million. Improvements to increase MR sensitivity include increasing magnetic field strength, and hyperpolarization via optical pumping or dynamic nuclear polarization. There are also a variety of signal amplification schemes based on chemical exchange that increase sensitivity.{{citation needed|date=July 2013}}To achieve molecular imaging of disease biomarkers using MRI, targeted MRI contrast agents 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.JOURNAL, Xue S, Qiao J, Pu F, Cameron M, Yang JJ, Design of a novel class of protein-based magnetic resonance imaging contrast agents for the molecular imaging of cancer biomarkers, Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology, 5, 2, 163–79, 2013, 23335551, 4011496, 10.1002/wnan.1205, A new class of gene targeting MR contrast agents (CA) has been introduced to show gene action of unique mRNA and gene transcription factor proteins.JOURNAL, Liu CH, Kim YR, Ren JQ, Eichler F, Rosen BR, Liu PK, Imaging cerebral gene transcripts in live animals, The Journal of Neuroscience, 27, 3, 713–22, January 2007, 17234603, 2647966, 10.1523/JNEUROSCI.4660-06.2007, JOURNAL, Liu CH, Ren J, Liu CM, Liu PK, Intracellular gene transcription factor protein-guided MRI by DNA aptamers in vivo, FASEB Journal, 28, 1, 464–73, January 2014, 24115049, 3868842, 10.1096/fj.13-234229, This new CA can trace cells with unique mRNA, microRNA and virus; tissue response to inflammation in living brains.JOURNAL, Liu CH, You Z, Liu CM, Kim YR, Whalen MJ, Rosen BR, Liu PK, Diffusion-weighted magnetic resonance imaging reversal by gene knockdown of matrix metalloproteinase-9 activities in live animal brains, The Journal of Neuroscience, 29, 11, 3508–17, March 2009, 19295156, 2726707, 10.1523/JNEUROSCI.5332-08.2009, The MR reports change in gene expression with positive correlation to TaqMan analysis, optical and electron microscopy.JOURNAL, Liu CH, Yang J, Ren JQ, Liu CM, You Z, Liu PK, MRI reveals differential effects of amphetamine exposure on neuroglia in vivo, FASEB Journal, 27, 2, 712–24, February 2013, 23150521, 3545538, 10.1096/fj.12-220061,

Economics

{{update-section|date=July 2019}}In the UK, the price of a clinical 1.5-tesla MRI scanner is around £920,000/{{USD|1.4 million}}, with the lifetime maintenance cost broadly similar to the purchase cost.WEB,weblink Managing high value capital equipment in the NHS in England, National Audit Office (United Kingdom), 30 November 2013, dead,weblink" title="web.archive.org/web/20131203002732weblink">weblink 3 December 2013, In the Netherlands, the average MRI scanner costs around €1 million,WEB,weblink MRI-scanner big financial success for Philips (Dutch), Eindhovens Dagblad (ED), 18 February 2009, with a 7-T MRI having been taken in use by the UMC Utrecht in December 2007, costing €7 million.WEB,weblink MRI scanner of €7 million in use(Dutch), Medisch Contact, 5 December 2007, dead,weblink" title="web.archive.org/web/20150904002346weblink">weblink 4 September 2015, Construction of MRI suites could cost up to {{USD|500,000}}/€370.000 or more, depending on project scope. Pre-polarizing MRI (PMRI) systems using resistive electromagnets have shown promise as a low-cost alternative and have specific advantages for joint imaging near metal implants; however, they are likely unsuitable for routine whole-body or neuroimaging applications.JOURNAL, Morgan P, Conolly S, Scott G, Macovski A, A readout magnet for prepolarized MRI, Magnetic Resonance in Medicine, 36, 4, 527–36, October 1996, 8892203, 10.1002/mrm.1910360405, JOURNAL, Blamire AM, The technology of MRI – the next 10 years?, The British Journal of Radiology, 81, 968, 601–17, August 2008, 18628329, 10.1259/bjr/96872829, File:Modern 3T MRI.JPG|thumb|A 3 tesla clinical MRI scanner.]]MRI scanners have become significant sources of revenue for healthcare providers in the US. This is because of favorable reimbursement rates from insurers and federal government programs. Insurance reimbursement is provided in two components, an equipment charge for the actual performance and operation of the MRI scan and a professional charge for the radiologist's review of the images and/or data. In the US Northeast, an equipment charge might be $3,500/€2,600 and a professional charge might be $350/€260,Stamford Hospital price quotation October 2008, Stamford CT US although the actual fees received by the equipment owner and interpreting physician are often significantly less and depend on the rates negotiated with insurance companies or determined by the Medicare fee schedule. For example, an orthopedic surgery group in Illinois billed a charge of $1,116/€825 for a knee MRI in 2007, but the Medicare reimbursement in 2007 was only $470.91/€350.CONFERENCE, Wayne M., Goldstein, Alexander C., Gordon, Jill Jasperson, Branson, Christopher, Simmons, Kimberly, Berland, Daniel S., Willsey, Amanda L., Andrews, vanc, March 5–9, 2008, Over-Utilization of MRI in the Osteoarthritis Patient,weblink Annual Meeting AAOS, San Francisco, 2013-07-27,weblink" title="web.archive.org/web/20150904002346weblink">weblink 2015-09-04, dead, Many insurance companies require advance approval of an MRI procedure as a condition for coverage.In the United States, an MRI of the brain with and without contrast billed to Medicare Part B entails, on average, a technical payment of {{USD|403}}/€300 and a separate payment to the radiologist of {{USD|93}}/€70.Current Procedural Terminology code #70553 "2010 Medicare Part B National Summary Data File" {{Webarchive|url=https://web.archive.org/web/20120214030717weblink |date=2012-02-14 }}. Data.gov, An Official Website of the United States Government. In France, the cost of an MRI exam is approximately €150/{{USD|205}}. This covers three basic scans including one with an intravenous contrast agent as well as a consultation with the technician and a written report to the patient's physician.WEB, How long does an MRI take?,weblink WebMD.com, WebMD, In Japan, the cost of an MRI examination (excluding the cost of contrast material and films) ranges from {{USD|155}}/€115 to {{USD|180}}/€133, with an additional radiologist professional fee of {{USD|17}}/€12.50.JOURNAL, Ehara S, Nakajima Y, Matsui O, Radiology in Japan in 2008, AJR. American Journal of Roentgenology, 191, 2, 328–29, August 2008, 18647897, 10.2214/AJR.07.3940,

Clinical MRI installation in a general hospital

File:Wx camera 1507509040946.jpg|Control consoleFile:Wx camera 1507509050808.jpg|Bore cameraFile:Wx camera 1507512102648.jpg|Operator performing a scanFile:Wx camera 1507514479961.jpg|Technical area

Safety

MRI is in general a safe technique, although injuries may occur as a result of failed safety procedures or human error.JOURNAL, 10.1007/s40134-015-0122-z, Lessons Learned from MRI Safety Events, Current Radiology Reports, 3, 10, 2015, Watson, Robert E, vanc, Contraindications to MRI include most cochlear implants and cardiac pacemakers, shrapnel, and metallic foreign bodies in the eyes. Magnetic resonance imaging in pregnancy appears to be safe at least during the second and third trimesters if done without contrast agents.JOURNAL, Mervak, Benjamin M., Altun, Ersan, McGinty, Katrina A., Hyslop, W. Brian, Semelka, Richard C., Burke, Lauren M., MRI in pregnancy: Indications and practical considerations, Journal of Magnetic Resonance Imaging, 49, 3, 2019, 621–31, 1053-1807, 10.1002/jmri.26317, 30701610, Since MRI does not use any ionizing radiation, its use is generally favored in preference to CT when either modality could yield the same information.WEB, iRefer,weblink Royal College of Radiologists, 10 November 2013, In certain cases, MRI is not preferred as it may be more expensive, time-consuming, and claustrophobia-exacerbating.MRI uses powerful magnets and can therefore cause magnetic materials to move at great speeds posing risk. Deaths have occurred.Man dies after being sucked into MRI scanner at Indian hospital The Guardian, 2018 However, as millions of MRIs are performed globally each year,Magnetic Resonance Imaging (MRI) Exams per 1,000 Population, 2014 OECD, 2016 fatalities are extremely rare.

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 this procedure as unlikely to result in a positive outcome for the patient.JOURNAL, Consumer Reports, American College of Physicians, Consumer Reports, American College of Physicians, presented by ABIM Foundation, Five Things Physicians and Patients Should Question, Choosing Wisely,weblink August 14, 2012, dead,weblink" title="web.archive.org/web/20120624075449weblink">weblink June 24, 2012, JOURNAL, Consumer Reports, American College of Physicians, Consumer Reports, American College of Physicians, April 2012, Imaging tests for lower-back pain: Why you probably don't need them, High Value Care,weblinkweblink" title="web.archive.org/web/20130115221844weblink">weblink 15 January 2013, dead, August 14, 2012,

Artifacts

(File:MRI with motion artifacts.jpg|thumb|Motion artifact (T1 coronal study of cervical vertebrae).)An MRI artifact is a visual artifact, that is, an anomaly during visual representation. Many different artifacts can occurduring 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.JOURNAL, 10.4102/sajr.v8i2.127, A short overview of MRI artefacts, South African Journal of Radiology, 8, 2, 13, 2004, Erasmus LJ, Hurter D, Naude M, Kritzinger HG, Acho S,

Non-medical use

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.BOOK, Rinck PA,weblink Chapter Nineteen Non-Medical Applications of NMR and MRI, Magnetic Resonance, 11th, 2017, 2017-12-18,

History

In 1971, 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, 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 later replaced by (N)MR imaging.JOURNAL, Rinck PA, Spectroscopy Europe, 20, 1, 7, 2008, A short history of magnetic resonance imaging,weblink In the late 1970s, physicists Peter Mansfield and Paul Lauterbur, developed MRI-related techniques, like the echo-planar imaging (EPI) technique.JOURNAL, 10.1103/physrevb.12.3618, "Diffraction" and microscopy in solids and liquids by NMR, Physical Review B, 12, 9, 3618–34, 1975, Mansfield P, Grannell PK, 1975PhRvB..12.3618M, Mansfield and Lauterbur were awarded the 2003 Nobel Prize in Physiology or Medicine for their "discoveries concerning magnetic resonance imaging".

See also

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References

{{Reflist}}

Further reading

  • WEB, TRTF/EMRF, The history of MRI, Rinck PA,weblink
  • JOURNAL, Eustace SJ, Nelson E, Whole body magnetic resonance imaging, BMJ, 328, 7453, 1387–88, June 2004, 15191954, 421763, 10.1136/bmj.328.7453.1387,
  • JOURNAL, Pykett IL, NMR imaging in medicine, Scientific American, 246, 5, 78–88, May 1982, 7079720, 10.1038/scientificamerican0582-78, 1982SciAm.246e..78P,
  • BOOK, Simon, Merrill, Mattson, James S, vanc, The pioneers of NMR and magnetic resonance in medicine: The story of MRI, Bar-Ilan University Press, Ramat Gan, Israel, 1996, 978-0-9619243-1-7,weblink
  • BOOK, Haacke, E Mark, Brown, Robert F, Thompson, Michael, Venkatesan, Ramesh, vanc, Magnetic resonance imaging: Physical principles and sequence design, J. Wiley & Sons, New York, 1999, 978-0-471-35128-3,
  • JOURNAL, Lee SC, Kim K, Kim J, Lee S, Han Yi J, Kim SW, Ha KS, Cheong C, One micrometer resolution NMR microscopy, Journal of Magnetic Resonance, 150, 2, 207–13, June 2001, 11384182, 10.1006/jmre.2001.2319, 2001JMagR.150..207L,
  • BOOK, Perry, Sprawls, vanc, 2000, Magnetic Resonance Imaging Principles, Methods, and Techniques,weblink Medical Physics Publishing, 978-0-944838-97-6,
  • BOOK, Mansfield P, NMR Imaging in Biomedicine: Supplement 2 Advances in Magnetic Resonance, Elsevier, 1982, 978-0-323-15406-2,
  • BOOK, Eiichi, Fukushima, vanc, NMR in Biomedicine: The Physical Basis, Springer Science & Business Media, 1989, 978-0-88318-609-1,
  • BOOK, Bernhard, Blümich, Winfried, Kuhn, vanc, Magnetic Resonance Microscopy: Methods and Applications in Materials Science, Agriculture and Biomedicine, Wiley, 1992, 978-3-527-28403-0,
  • BOOK, Peter, Blümer, Peter, Blümler, Bernhard, Blümich, Robert E., Botto, Eiichi, Fukushima, vanc, Spatially Resolved Magnetic Resonance: Methods, Materials, Medicine, Biology, Rheology, Geology, Ecology, Hardware, Wiley-VCH, 1998, 978-3-527-29637-8,
  • BOOK, Zhi-Pei, Liang, Paul C., Lauterbur, vanc, Principles of Magnetic Resonance Imaging: A Signal Processing Perspective, Wiley, 1999, 978-0-7803-4723-6,weblink
  • BOOK, Franz, Schmitt, Michael K., Stehling, Robert, Turner, vanc, Echo-Planar Imaging: Theory, Technique and Application, Springer Berlin Heidelberg, 1998, 978-3-540-63194-1,
  • BOOK, Vadim, Kuperman, vanc, Magnetic Resonance Imaging: Physical Principles and Applications, Academic Press, 2000, 978-0-08-053570-8,
  • BOOK, Bernhard, Blümich, vanc, NMR Imaging of Materials, Clarendon Press, 2000, 978-0-19-850683-6,
  • BOOK, Jianming, Jin, vanc, Electromagnetic Analysis and Design in Magnetic Resonance Imaging, CRC Press, 1998, 978-0-8493-9693-9,
  • BOOK, Imad Akil, Farhat, P.S., Belton, Graham Alan, Webb, vanc, Magnetic Resonance in Food Science: From Molecules to Man, Royal Society of Chemistry, 2007, 978-0-85404-340-8,

External links

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