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Magnetic resonance imaging
Magnetic resonance imaging
is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body in both health and disease. MRI scanners use strong magnetic fields, electric field gradients, and radio waves to generate images of the organs in the body. MRI does not involve X-rays and the use of ionizing radiation, which distinguishes it from CT or CAT scans. Magnetic resonance imaging
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
X-rays
are now well-controlled in most medical contexts, MRI may still be seen as a better choice than CT. MRI is widely used in hospitals and clinics for medical diagnosis, staging of disease and follow-up without exposing the body to radiation. However, MRI may often yield different diagnostic information compared with CT. There may be risks and discomfort 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) and is a form of NMR, though the use of 'nuclear' in the acronym was dropped to avoid negative associations with the word.[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 in close proximity to the anatomy being examined. Hydrogen
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 highly 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.[2][3]

Contents

1 Mechanism

1.1 Construction and physics 1.2 T1 and T2

2 Diagnostics

2.1 Usage by organ or system

2.1.1 Neuroimaging 2.1.2 Cardiovascular 2.1.3 Musculoskeletal 2.1.4 Liver
Liver
and gastrointestinal 2.1.5 Angiography

2.2 Contrast agents 2.3 Sequences

2.3.1 Overview table

2.4 Other specialized configurations

2.4.1 Magnetic resonance spectroscopy 2.4.2 Real-time MRI 2.4.3 Interventional MRI 2.4.4 Magnetic resonance guided focused ultrasound 2.4.5 Multinuclear imaging 2.4.6 Molecular imaging
Molecular imaging
by MRI

3 Economics 4 Safety

4.1 Overuse

5 Artifacts 6 Non-medical use 7 History 8 See also 9 References 10 Further reading 11 External links

Mechanism[edit] Construction and physics[edit] Main article: Physics of magnetic resonance imaging

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, protons (hydrogen atoms) in tissues containing water molecules create a signal that is processed to form an image of the body. First, energy from an oscillating magnetic field temporarily is 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.[4] 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.[5] 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).[6][7][8] T1 and T2[edit] Further information: Relaxation (NMR)

Effects of TR and TE on MR signal

Examples of T1 weighted, T2 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). 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 for obtaining morphological information, as well as for post-contrast imaging. 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:

Signal T1-weighted T2-weighted

High

Fat[9][10] Subacute hemorrhage[10] Melanin[10] Protein-rich fluid[10] Slowly flowing blood[10] Paramagnetic
Paramagnetic
substances, such as gadolinium, manganese, copper[10] Cortical pseudolaminar necrosis[10]

More water content,[9] as in edema, tumor, infarction, inflammation and infection[10] Extracellularly located methemoglobin in subacute hemorrhage[10]

Inter- mediate Gray matter
Gray matter
darker than white matter[11] White matter
White matter
darker than grey matter[11]

Low

Bone[9] Urine CSF Air[9] More water content,[9] as in edema, tumor, infarction, inflammation, infection, hyperacute or chronic hemorrhage[10] Low proton density as in calcification[10]

Bone[9] Air[9] Fat[9] Low proton density, as in calcification and fibrosis[10] Paramagnetic
Paramagnetic
material, such as deoxyhemoglobin, intracelullar methemoglobin, iron, ferritin, hemosiderin, melanin[10] Protein-rich fluid[10]

Diagnostics[edit] Usage by organ or system[edit]

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.[12] MRI affects diagnosis and treatment in many specialties although the effect on improved health outcomes is uncertain.[13] 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.[14] Neuroimaging[edit] Main article: MRI of brain and brain stem See also: Neuroimaging

MRI image of white matter tracts

MRI is the investigative tool of choice for neurological cancers, as it has better resolution than CT and offers better visualization of the posterior fossa. 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, and epilepsy.[15] 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.[16] 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.[17][18][19] Cardiovascular[edit] Main article: Cardiac magnetic resonance imaging

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.[20] Musculoskeletal[edit] Applications in the musculoskeletal system include spinal imaging, assessment of joint disease, and soft tissue tumors.[21] Liver
Liver
and gastrointestinal[edit] 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.[22][23][24][25] Angiography[edit]

Magnetic resonance angiography

Main article: Magnetic resonance angiography 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.[26] Contrast agents[edit] Main article: MRI contrast agent 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.[4] The most commonly used intravenous contrast agents are based on chelates of gadolinium.[27] In general, these agents have proved safer than the iodinated contrast agents used in X-ray
X-ray
radiography or CT. Anaphylactoid reactions are rare, occurring in approx. 0.03–0.1%.[28] 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.[29] 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.[30] Although a causal link has not been definitively established, current guidelines in the United States
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.[31][32] In Europe, where more gadolinium-containing agents are available, a classification of agents according to potential risks has been released.[33][34] Recently, 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.[35] Sequences[edit] Main article: MRI sequences An MRI sequence
MRI sequence
is a particular setting of radiofrequency pulses and gradients, resulting in a particular image appearance.[36] The T1 and T2 weighting can also be described as MRI sequences. Overview table edit This table does not include uncommon and experimental sequences.

Group Sequence Abbr. Physics Main clinical distinctions Example

Spin echo T1 weighted T1 Measuring spin–lattice relaxation by using a short repetition time (TR) and echo time (TE)

Lower signal for more water content, [9]as in edema, tumor, infarction, inflammation, infection, hyperacute or chronic hemorrhage [10] High signal for fat[9][10] High signal for paramagnetic substances, such as MRI contrast agents[10]

Standard foundation and comparison for other sequences.

T2 weighted T2 Measuring spin–spin relaxation by using long TR and TE times.

Higher signal for more water content.[9] Low signal for fat.[9] Low signal for paramagnetic substances.[10]

Standard foundation and comparison for other sequences.

Proton
Proton
density weighted PD Long TR (to reduce T1) and short TE (to minimize T2)[37] Joint
Joint
disease and injury.[38]

High signal from meniscus tears[39] (pictured)

Gradient echo Steady-state free precession SSFP Maintenance of a steady, residual transverse magnetisation over successive cycles.[40] Creation of cardiac MRI videos (pictured).[40]

Inversion recovery Short tau inversion recovery STIR Fat
Fat
suppression by setting an inversion time where the signal of fat is zero.[41] High signal in edema, such as in more severe stress fracture.[42] Shin splints pictured:

Fluid attenuated inversion recovery FLAIR Fluid suppression by setting an inversion time that nulls fluids. High signal in lacunar infarction, multiple sclerosis (MS) plaques, subarachnoid haemorrhage and meningitis (pictured).[43]

Double inversion recovery DIR Simultaneous suppression of cerebrospinal fluid and white matter by two inversion times.[44] High signal of multiple sclerosis plaques (pictured).[44]

Diffusion weighted (DWI) Conventional DWI Measure of Brownian motion
Brownian motion
of water molecules.[45] High signal within minutes of cerebral infarction (pictured).[46]

Apparent diffusion coefficient ADC Reduced T2 weighting by taking multiple conventional DWI images with different DWI weighting, and the change corresponds to diffusion.[47] Low signal minutes after cerebral infarction (pictured).[48]

Diffusion tensor DTI Mainly tractography (pictured) by an overall greater Brownian motion of water molecules in the directions of nerve fibers.[49]

Evaluating white matter deformation by tumors[49] Reduced fractional anisotropy may indicate dementia[50]

Perfusion weighted (PWI) Dynamic susceptibility contrast DSC Gadolinium
Gadolinium
contrast is injected, and rapid repeated imaging (generally gradient-echo echo-planar T2 weighted) quantifies susceptibility-induced signal loss.[51] In cerebral infarction, the infarcted core and the penumbra have decreased perfusion (pictured).[52]

Dynamic contrast enhanced DCE Measuring shortening of the spin–lattice relaxation (T1) induced by a gadolinium contrast bolus.[53]

Arterial spin labelling ASL Magnetic labeling of arterial blood below the imaging slab, which subsequently enters the region of interest.[54] It does not need gadolinium contrast.[55]

Functional MRI (fMRI) Blood-oxygen-level dependent
Blood-oxygen-level dependent
imaging BOLD Changes in oxygen saturation-dependent magnetism of hemoglobin reflects tissue activity.[56] Localizing highly active brain areas before surgery.[57]

Magnetic resonance angiography
Magnetic resonance angiography
(MRA) and venography Time-of-flight TOF Blood entering the imaged area is not yet magnetically saturated, giving it a much higher signal when using short echo time and flow compensation. Detection of aneurysm, stenosis or dissection.[58]

Phase-contrast MRA PC-MRA Two gradients with equal magnitude but opposite direction are used to encode a phase shift, which is proportional to the velocity of spins.[59] Detection of aneurysm, stenosis or dissection (pictured).[58]

(VIPR)

Susceptibility weighted SWI Sensitive for blood and calcium, by a fully flow compensated, long echo, gradient recalled echo (GRE) pulse sequence to exploit magnetic susceptibility differences between tissues. Detecting small amounts of hemorrhage (diffuse axonal injury pictured) or calcium.[60]

Other specialized configurations[edit] Magnetic resonance spectroscopy[edit] Main articles: In vivo magnetic resonance spectroscopy
In vivo magnetic resonance spectroscopy
and Nuclear magnetic resonance spectroscopy Magnetic resonance spectroscopy (MRS) is used to measure the levels of different metabolites in body tissues. 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,[61] and to provide information on tumor metabolism.[62] 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).[citation needed] Real-time MRI[edit]

Play media

Real-time MRI of a human heart at a resolution of 50 ms

Main article: Real-time MRI Real-time MRI refers to the continuous monitoring ("filming") of moving objects in real time. While many different strategies have been developed since the early 2000s, a recent development reported a real-time MRI technique based on radial FLASH and iterative reconstruction that yields a temporal resolution of 20 to 30 milliseconds for images with an in-plane resolution of 1.5 to 2.0 mm. The new method promises to add important information about diseases of the joints and the heart. In many cases MRI examinations may become easier and more comfortable for patients.[63] Interventional MRI[edit] Main article: 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 must be done with no ferromagnetic instruments.[citation needed] A specialized growing subset of interventional MRI is intraoperative MRI, in which doctors use an MRI in surgery. Some specialized MRI systems allow imaging concurrent with the surgical procedure. More typical, however, is that the surgical procedure is temporarily interrupted so that MRI can verify the success of the procedure or guide subsequent surgical work.[citation needed] Magnetic resonance guided focused ultrasound[edit] In MRgFUS therapy, ultrasound beams are focused on a tissue—guided and controlled using MR thermal imaging—and due to the significant energy deposition at the focus, temperature within the tissue rises to more than 65 °C
°C
(150 °F), completely destroying it. This technology can achieve precise ablation of diseased tissue. MR imaging provides a three-dimensional view of the target tissue, allowing for 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.[64] Multinuclear imaging[edit] Hydrogen
Hydrogen
is 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] 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.[65] 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.[66] In principle, hetereonuclear magnetization transfer MRI could be used to detect the presence or absence of specific chemical bonds.[67][68] 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] Molecular imaging
Molecular imaging
by MRI[edit] Main article: 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 10−3 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] 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.[69] 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.[70][71] This new CA can trace cells with unique mRNA, microRNA and virus; tissue response to inflammation in living brains.[72] The MR reports change in gene expression with positive correlation to TaqMan analysis, optical and electron microscopy.[73] Economics[edit] In the UK, the price of a clinical 1.5-tesla MRI scanner is around £920,000/US$1.4 million, with the lifetime maintenance cost broadly similar to the purchase cost.[74] In the Netherlands, the average MRI scanner costs around €1 million,[75] with a 7-T MRI having been taken in use by the UMC Utrecht in December 2007, costing €7 million.[76] Construction of MRI suites could cost up to US$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.[77][78]

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,[79] 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.[80] Many insurance companies require advance approval of an MRI procedure as a condition for coverage. In the US, the Deficit Reduction Act of 2005 significantly reduced reimbursement rates paid by federal insurance programs for the equipment component of many scans, shifting the economic landscape. Many private insurers have followed suit.[citation needed] 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 US$403/€300 and a separate payment to the radiologist of US$93/€70.[81] In France, the cost of an MRI exam is approximately €150/US$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.[82] In Japan, the cost of an MRI examination (excluding the cost of contrast material and films) ranges from US$155/€115 to US$180/€133, with an additional radiologist professional fee of US$17/€12.50.[83] In India, the cost of an MRI examination including the fee for the radiologist's opinion comes to around Rs 3000–4000 (€37–49/US$50–60), excluding the cost of contrast material. In the UK the retail price for an MRI scan privately ranges between £350 and £700 (€405–810).[84] Safety[edit] Main article: 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.[85] Contraindications to MRI include most cochlear implants and cardiac pacemakers, shrapnel, and metallic foreign bodies in the eyes. The safety of MRI during the first trimester of pregnancy is uncertain, but it may be preferable to other options.[86] 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.[87] 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.[88] Overuse[edit] 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.[89][90] Artifacts[edit]

Motion artifact (T1 coronal study of cervical vertebrae).[91]

Main article: MRI artifact An MRI artifact
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.[91] Artifacts remain a problematic in magnetic resonance imaging (MRI). Some affect the quality of the examination, while others may be confused with pathology.[91] Non-medical use[edit] Main article: Nuclear magnetic resonance
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.[92] History[edit] Main article: History of magnetic resonance imaging In the late 1970s, physicists Peter Mansfield
Peter Mansfield
and Paul Lauterbur, developed MRI-related techniques, like the echo-planar imaging (EPI) technique.[93] Mansfield and Lauterbur were awarded the 2003 Nobel Prize in Physiology or Medicine for their "discoveries concerning magnetic resonance imaging". See also[edit]

Medicine portal

Earth's field NMR Electron paramagnetic resonance High-definition fiber tracking History of neuroimaging International Society of Magnetic Resonance
Resonance
in Medicine Jemris List of neuroimaging software Magnetic immunoassay Magnetic particle imaging Magnetic resonance elastography Magnetic Resonance
Resonance
Imaging (journal) Magnetic resonance microscopy Nobel Prize controversies Rabi cycle Robinson oscillator Sodium
Sodium
MRI Virtopsy

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Further reading[edit]

TRTF/EMRF: The history of MRI (Peter A. Rinck, ed). url = http://www.magnetic-resonance.org/ch/20-01.html Guadalupe Portal; Aliosvi Rodriguez Whole body magnetic resonance imaging in early diagnosis in Trinidad BMJ (2010) ISSN 1756-1833 url = http://www.bmj.com/rapid-response/2011/12/19/re-whole-body-magnetic-resonance-imaging Ian L. Pykett (May 1, 1982). "NMR Imaging in Medicine" (PDF). Scientific American. 246 (5): 78–88. Bibcode:1982SciAm.246e..78P. doi:10.1038/scientificamerican0582-78. Archived from the original (PDF) on March 10, 2016.  Simon, Merrill; Mattson, James S (1996). The pioneers of NMR and magnetic resonance in medicine: The story of MRI. Ramat Gan, Israel: Bar-Ilan University Press. ISBN 0-9619243-1-4.  Haacke, E Mark; Brown, Robert F; Thompson, Michael; Venkatesan, Ramesh (1999). Magnetic resonance imaging: Physical principles and sequence design. New York: J. Wiley & Sons. ISBN 0-471-35128-8.  Lee SC; Kim K; Kim J; Lee S; Han Yi J; Kim SW; Ha KS; Cheong C (June 2001). "One micrometer resolution NMR microscopy". J. Magn. Reson. 150 (2): 207–13. Bibcode:2001JMagR.150..207L. doi:10.1006/jmre.2001.2319. PMID 11384182.  Perry Sprawls (2000). Magnetic Resonance
Resonance
Imaging Principles, Methods, and Techniques. Medical Physics Publishing. ISBN 9780944838976.  P Mansfield (1982). NMR Imaging in Biomedicine: Supplement 2 Advances in Magnetic Resonance. Elsevier. ISBN 9780323154062.  Eiichi Fukushima (1989). NMR in Biomedicine: The Physical Basis. Springer Science & Business Media. ISBN 9780883186091.  Bernhard Blümich; Winfried Kuhn (1992). Magnetic Resonance Microscopy: Methods and Applications in Materials Science, Agriculture and Biomedicine. Wiley. ISBN 9783527284030.  Peter Blümer (1998). Peter Blümler; Bernhard Blümich; Robert E. Botto; Eiichi Fukushima, eds. Spatially Resolved Magnetic Resonance: Methods, Materials, Medicine, Biology, Rheology, Geology, Ecology, Hardware. Wiley-VCH. ISBN 9783527296378.  Zhi-Pei Liang; Paul C. Lauterbur (1999). Principles of Magnetic Resonance
Resonance
Imaging: A Signal Processing Perspective. Wiley. ISBN 9780780347236.  Franz Schmitt; Michael K. Stehling; Robert Turner (1998). Echo-Planar Imaging: Theory, Technique and Application. Springer Berlin Heidelberg. ISBN 9783540631941.  Vadim Kuperman (2000). Magnetic Resonance
Resonance
Imaging: Physical Principles and Applications. Academic Press. ISBN 9780080535708.  Bernhard Blümich (2000). NMR Imaging of Materials. Clarendon Press. ISBN 9780198506836.  Jianming Jin (1998). Electromagnetic Analysis and Design in Magnetic Resonance
Resonance
Imaging. CRC Press. ISBN 9780849396939.  Imad Akil Farhat; P. S. Belton; Graham Alan Webb; Royal Society of Chemistry (Great Britain) (2007). Magnetic Resonance
Resonance
in Food Science: From Molecules to Man. Royal Society of Chemistry. ISBN 9780854043408. 

External links[edit]

Wikimedia Commons has media related to Magnetic resonance imaging.

Library resources about Magnetic resonance imaging

Resources in your library

MRI: A Peer-Reviewed, Critical Introduction. European Magnetic Resonance
Resonance
Forum (EMRF)/The Round Table Foundation (TRTF); Peter A. Rinck (editor) A Guided Tour of MRI: An introduction for laypeople National High Magnetic Field Laboratory The Basics of MRI. Underlying physics and technical aspects. Video: What to Expect During Your MRI Exam from the Institute for Magnetic Resonance
Resonance
Safety, Education, and Research (IMRSER) Royal Institution Lecture – MRI: A Window on the Human Body A SHORT HISTORY OF MAGNETIC RESONANCE IMAGING FROM A EUROPEAN POINT OF VIEW Animal Imaging Database (AIDB) How MRI works explained simply using diagrams Real-time MRI videos: Biomedizinische NMR Forschungs GmbH.

v t e

Medical imaging
Medical imaging
(ICD-9-CM V3 87–88, ICD-10-PCS B, CPT 70010–79999)

X-ray/ Radiography

2D

Medical:

Pneumoencephalography Dental radiography Sialography Myelography CXR

Bronchography

AXR KUB DXA/DXR Upper gastrointestinal series/Small-bowel follow-through/Lower gastrointestinal series Cholangiography/Cholecystography Mammography Pyelogram Cystography Arthrogram Hysterosalpingography Skeletal survey Angiography

Angiocardiography Aortography

Venography Lymphogram

Industrial:

Radiographic testing

CT scan

Techniques:

General operation of CT Quantitative CT High resolution CT X-ray
X-ray
microtomography Electron beam tomography

Targets

Coronary

Calcium scan CT angiography

Abdominal and pelvic CT

Virtual colonoscopy

CT angiography

Coronary CT Pulmonary CT

Head CT Whole body imaging

Full-body CT scan

Other

Fluoroscopy X-ray
X-ray
motion analysis

MRI

MRI of the brain MR neurography Cardiac MRI/Cardiac MRI perfusion MR angiography MR cholangiopancreatography Breast MRI Functional MRI Sequences

Diffusion MRI Perfusion MRI Tractography

Synthetic MRI

Ultrasound

Echocardiography Doppler ultrasonography

Doppler echocardiography

TTE TEE

Transcranial Doppler

Intravascular Gynecologic Obstetric Echoencephalography Abdominal ultrasonography Transrectal Breast ultrasound Transscrotal ultrasound Carotid ultrasonography Contrast-enhanced 3D ultrasound Endoscopic ultrasound Emergency ultrasound

FAST Pre-hospital ultrasound

Duplex

Radionuclide

2D / scintigraphy

Cholescintigraphy Scintimammography Ventilation/perfusion scan Radionuclide ventriculography Radionuclide angiography Radioisotope renography Sestamibi parathyroid scintigraphy Radioactive iodine uptake test Bone
Bone
scintigraphy Immunoscintigraphy Dacryoscintigraphy DMSA scan Gastric emptying scan

Full body:

Octreotide scan Gallium 67 scan Indium-111 WBC scan

3D / ECT

SPECT

gamma ray: Myocardial perfusion imaging

PET (positron):

Brain PET Cardiac PET PET mammography PET-CT

Optical laser

Optical tomography

Optical coherence tomography

Confocal microscopy Endomicroscopy

Thermography

non-contact thermography contact thermography dynamic angiothermography

Authority control

LCCN: sh85079741 GND: 4120806-7 BNF:

.