MRI is a medical application of nuclear magnetic resonance which can be used for imaging in other NMR applications, such as NMR spectroscopy.
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MRI is widely used in hospitals and clinics for medical diagnosis, staging and follow-up of disease.
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MRI was originally called NMRI, but "nuclear" was dropped to avoid negative associations.
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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 region to be scanned and the RF system, which excites the sample and detects the resulting NMR signal.
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MRI requires a magnetic field that is both strong and uniform to a few parts per million across the scan volume.
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Recently, MRI has been demonstrated at ultra-low fields, i e, in the microtesla-to-millitesla range, where sufficient signal quality is made possible by prepolarization and by measuring the Larmor precession fields at about 100 microtesla with highly sensitive superconducting quantum interference devices .
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Standard display of MRI images is to represent fluid characteristics in black and white images, where different tissues turn out as follows:.
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MRI affects diagnosis and treatment in many specialties although the effect on improved health outcomes is disputed in certain cases.
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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, as well as for determining areas of tissue for sampling in biobanking.
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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.
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MRI 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.
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Cardiac MRI is complementary to other imaging techniques, such as echocardiography, cardiac CT, and nuclear medicine.
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An MRI sequence is a particular setting of radiofrequency pulses and gradients, resulting in a particular image appearance.
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Real-time MRI refers to the continuous imaging of moving objects in real time.
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Some specialized MRI systems allow imaging concurrent with the surgical procedure.
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In principle, heteronuclear magnetization transfer MRI could be used to detect the presence or absence of specific chemical bonds.
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MRI has the advantages of having very high spatial resolution and is very adept at morphological imaging and functional imaging.
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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.
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Parallel MRI is used routinely for MRI examinations in a wide range of body areas and clinical or research applications.
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Quantitative MRI aims to increase the reproducibility of MR images and interpretations, but has historically require longer scan times.
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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, or by fitting MR signal evolution to a multi-parameter model.
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Contraindications to MRI include most cochlear implants and cardiac pacemakers, shrapnel, and metallic foreign bodies in the eyes.
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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.
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An MRI artifact is a visual artifact, that is, an anomaly during visual representation.
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MRI is used industrially mainly for routine analysis of chemicals.
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CT scanning provides quick whole-body imaging of skeletal and parenchymal alterations, whereas MRI imaging gives better representation of soft tissue pathology.
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MRI 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.
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Advances in semiconductor technology were crucial to the development of practical MRI, which requires a large amount of computational power.
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