Magnetic resonance imaging: Difference between revisions

Latest revision as of 01:11, 20 February 2025

Pronunciation
Other names
Medical specialty
Uses
Complications
Approach
Types
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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.

History[edit]

MRI developed from the principles of Nuclear Magnetic Resonance (NMR), a technique used by scientists to study the properties of atomic nuclei. The development of MRI as a medical tool began in the 1970s and was credited to the work of Dr. Raymond Damadian, who created the first MRI scan in 1977.

Principles[edit]

MRI is based on the principles of NMR, which involves the alignment of magnetized nuclei in a strong magnetic field. When these nuclei are subjected to a second oscillating magnetic field, they produce a rotating magnetic field detectable by the scanner. This signal is used to construct an image of the scanned area of the body.

Procedure[edit]

During an MRI scan, the patient lies in a large magnet bore. A radiofrequency coil is used to send signals to the body and receive them back. The returning signals are converted into images by a computer attached to the MRI scanner. The quality of the MRI image is dependent on signal strength and field homogeneity.

Applications[edit]

MRI is widely used in hospitals and clinics for medical diagnosis, staging of disease, and follow-up without exposure to ionizing radiation. It is particularly useful for the imaging of the brain, spine, and joints, as well as soft tissues of the musculoskeletal system.

Safety[edit]

MRI is generally safe; it does not involve exposure to ionizing radiation, such as X-rays. However, the presence of strong magnetic fields requires that metal objects are not present in the scanner, and patients with certain types of medical implants, such as pacemakers, may not be suitable candidates for an MRI.

Advancements[edit]

Recent advancements in MRI technology include high-field MRI, functional MRI (fMRI), which measures brain activity by detecting changes associated with blood flow, and real-time MRI, which provides images in real time.

Challenges[edit]

Challenges in MRI technology include reducing scan time, improving image quality, and making MRI accessible in terms of cost and availability.

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-[[File:MRI-Philips.JPG|thumb|Magnetic Resonance Imaging (MRI) Scan]]
+{{Infobox medical intervention
+| name          = Magnetic Resonance Imaging (MRI)
+| image         =
+| caption       =
+| ICD10         =
+| ICD9          =
+| ICDO          =
+| MeshID        = D008279
+| other_codes   =
+}}
-==What is MRI?==
+'''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 is a non-invasive imaging technology that produces three dimensional detailed anatomical images. It is often used for disease detection, [[diagnosis]], and treatment monitoring. It is based on sophisticated technology that excites and detects the change in the direction of the rotational axis of protons found in the water that makes up living tissues.
-==How does MRI work?==
+==History==
-MRIs employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. When a radio frequency current is then pulsed through the patient, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field. When the radio frequency field is turned off, the MRI sensors are able to detect the energy released as the protons realign with the magnetic field. The time it takes for the protons to realign with the magnetic field, as well as the amount of energy released, changes depending on the environment and the chemical nature of the molecules. Physicians are able to tell the difference between various types of tissues based on these magnetic properties.
+MRI developed from the principles of [[Nuclear Magnetic Resonance]] (NMR), a technique used by scientists to study the properties of atomic nuclei. The development of MRI as a medical tool began in the 1970s and was credited to the work of Dr. Raymond Damadian, who created the first MRI scan in 1977.
-To obtain an MRI image, a patient is placed inside a large magnet and must remain very still during the imaging process in order not to blur the image. Contrast agents (often containing the element Gadolinium) may be given to a patient intravenously before or during the MRI to increase the speed at which protons realign with the magnetic field. The faster the protons realign, the brighter the image.
+==Principles==
+MRI is based on the principles of NMR, which involves the alignment of magnetized nuclei in a strong magnetic field. When these nuclei are subjected to a second oscillating magnetic field, they produce a rotating magnetic field detectable by the scanner. This signal is used to construct an image of the scanned area of the body.
-==What is MRI used for?==
+==Procedure==
-MRI scanners are particularly well suited to image the non-bony parts or soft tissues of the body. They differ from computed tomography (CT), in that they do not use the damaging ionizing radiation of x-rays. The brain, spinal cord and nerves, as well as muscles, ligaments, and tendons are seen much more clearly with MRI than with regular x-rays and CT; for this reason MRI is often used to image knee and shoulder injuries.
+During an MRI scan, the patient lies in a large magnet bore. A [[radiofrequency]] coil is used to send signals to the body and receive them back. The returning signals are converted into images by a computer attached to the MRI scanner. The quality of the MRI image is dependent on signal strength and field homogeneity.
-In the brain, MRI can differentiate between white matter and grey matter and can also be used to diagnose aneurysms and tumors. Because MRI does not use x-rays or other radiation, it is the imaging modality of choice when frequent imaging is required for diagnosis or therapy, especially in the brain. However, MRI is more expensive than x-ray imaging or CT scanning.
+==Applications==
+MRI is widely used in hospitals and clinics for [[medical diagnosis]], staging of disease, and follow-up without exposure to ionizing radiation. It is particularly useful for the imaging of the brain, [[spine]], and joints, as well as soft tissues of the musculoskeletal system.
-One kind of specialized MRI is functional Magnetic Resonance Imaging (fMRI.) This is used to observe brain structures and determine which areas of the brain “activate” (consume more oxygen) during various cognitive tasks. It is used to advance the understanding of brain organization and offers a potential new standard for assessing neurological status and neurosurgical risk.
+==Safety==
+MRI is generally safe; it does not involve exposure to ionizing radiation, such as X-rays. However, the presence of strong magnetic fields requires that metal objects are not present in the scanner, and patients with certain types of [[medical implant]]s, such as pacemakers, may not be suitable candidates for an MRI.
-==Are there risks?==
+==Advancements==
-Although MRI does not emit the ionizing radiation that is found in x-ray and CT imaging, it does employ a strong magnetic field. The magnetic field extends beyond the machine and exerts very powerful forces on objects of iron, some steels, and other magnetizable objects; it is strong enough to fling a wheelchair across the room. Patients should notify their physicians of any form of medical or implant prior to an MR scan.
+Recent advancements in MRI technology include high-field MRI, functional MRI ([[fMRI]]), which measures brain activity by detecting changes associated with blood flow, and real-time MRI, which provides images in real time.
-When having an MRI scan, the following should be taken into consideration:
+==Challenges==
+Challenges in MRI technology include reducing scan time, improving image quality, and making MRI accessible in terms of cost and availability.
-*People with implants, particularly those containing iron, — pacemakers, vagus nerve stimulators, implantable cardioverter- defibrillators, loop recorders, insulin pumps, cochlear implants, deep brain stimulators, and capsules from capsule endoscopy should not enter an MRI machine.
+==See also==
-*Noise—loud noise commonly referred to as clicking and beeping, as well as sound intensity up to 120 decibels in certain MR scanners, may require special ear protection.
+* [[Computed Tomography (CT)]]
-*Nerve Stimulation—a twitching sensation sometimes results from the rapidly switched fields in the MRI.
+* [[Ultrasound imaging]]
-*Contrast agents—patients with severe renal failure who require dialysis may risk a rare but serious illness called nephrogenic systemic fibrosis that may be linked to the use of certain gadolinium-containing agents, such as gadodiamide and others. Although a causal link has not been established, current guidelines in the United States recommend that dialysis patients should only receive gadolinium agents when essential, and that dialysis should be performed as soon as possible after the scan to remove the agent from the body promptly.
+* [[Positron Emission Tomography (PET)]]
-*Pregnancy—while no effects have been demonstrated on the fetus, it is recommended that MRI scans be avoided as a precaution especially in the first trimester of pregnancy when the fetus’ organs are being formed and contrast agents, if used, could enter the fetal bloodstream.
-== Claustrophobia and MRI ==
+[[Category:Medical imaging]]
-*Claustrophobia—people with even mild claustrophobia may find it difficult to tolerate long scan times inside the machine. Familiarization with the machine and process, as well as visualization techniques, sedation, and anesthesia provide patients with mechanisms to overcome their discomfort. Additional coping mechanisms include listening to music or watching a video or movie, closing or covering the eyes, and holding a panic button. The open MRI is a machine that is open on the sides rather than a tube closed at one end, so it does not fully surround the patient. It was developed to accommodate the needs of patients who are uncomfortable with the narrow tunnel and noises of the traditional MRI and for patients whose size or weight make the traditional MRI impractical. Newer open MRI technology provides high quality images for many but not all types of examinations.
+[[Category:Radiology]]
+[[Category:Magnetic resonance imaging]]
-==What are examples of NIBIB-funded projects in MRI?==
+{{medicine-stub}}
-''Replacing Biopsies with Sound''
+<gallery>
+File:Structural MRI animation.ogv|Magnetic resonance imaging
-Chronic liver disease and cirrhosis affect more than 5.5 million people in the United States. NIBIB-funded researchers have developed a method to turn sound waves into images of the liver, which provides a new non-invasive, pain-free approach to find tumors or tissue damaged by liver disease. The Magnetic Resonance Elastography (MRE) device is placed over the liver of the patient before he enters the MRI machine. It then pulses sound waves through the liver, which the MRI is able to detect and use to determine the density and health of the liver tissue. This technique is safer and more comfortable for the patient as well as being less expensive than a traditional biopsy. Since MRE is able to recognize very slight differences in tissue density, there is the potential that it could also be used to detect cancer.
+File:Mri scanner schematic labelled.svg|Magnetic resonance imaging
+File:Glebefields Health Centre - 2020-03-22 - Andy Mabbett - 03.jpg|Magnetic resonance imaging
-=='''New MRI just for Kids'''==
+File:TR TE.jpg|Magnetic resonance imaging
+File:T1t2PD.jpg|Magnetic resonance imaging
-MRI is potentially one of the best imaging modalities for children since unlike [[CT scan|CT]], it does not have any ionizing radiation that could potentially be harmful. However, one of the most difficult challenges that MRI technicians face is obtaining a clear image, especially when the patient is a child or has some kind of ailment that prevents them from staying still for extended periods of time. As a result, many young children require anesthesia, which increases the health risk for the patient. NIBIB is funding research that is attempting to develop a robust pediatric body MRI. By creating a pediatric coil made specifically for smaller bodies, the image can be rendered more clearly and quickly and will demand less MR operator skill. This will make MRIs cheaper, safer, and more available to children. The faster imaging and motion compensation could also potentially benefit adult patients as well.
+File:Spin Orientations During Relaxation.jpg|Magnetic resonance imaging
+File:Siemens Magnetom Aera MRI scanner.jpg|Magnetic resonance imaging
-Another NIBIB-funded researcher is trying to solve this problem from a different angle. He is developing a motion correction system that could greatly improve image quality for MR exams. Researchers are developing an optical tracking system that would be able to match and adapt the MRI pulses to changes in the patient’s pose in real time. This improvement could reduce cost (since less repeat MR exams will have to take place due to poor quality) as well as make MRI a viable option for many patients who are unable to remain still for the exam and reduce the amount of anesthesia used for MR exams.
+File:Radiologist interpreting MRI.jpg|Magnetic resonance imaging
+File:White Matter Connections Obtained with MRI Tractography.png|Magnetic resonance imaging
-=='''Determining the aggressiveness of a tumor'''==
+File:PAPVR.gif|Magnetic resonance imaging
+File:mra1.jpg|Magnetic resonance imaging
-Traditional MRI, unlike PET or SPECT, cannot measure metabolic rates. However, researchers funded by NIBIB have discovered a way to inject specialized compounds (hyper polarized carbon 13) into prostate cancer patients to measure the metabolic rate of a tumor. This information can provide a fast and accurate picture of the tumor’s aggressiveness. Monitoring disease progression can improve risk prediction, which is critical for prostate cancer patients who often adopt a wait and watch approach.
+File:Real-time MRI - Thorax.ogv|Magnetic resonance imaging
+</gallery>
-==Summary==
-A procedure in which radio waves and a powerful magnet linked to a computer are used to create detailed pictures of areas inside the body. These pictures can show the difference between normal and diseased tissue. Magnetic resonance imaging makes better images of organs and soft tissue than other scanning techniques, such as computed tomography (CT) or x-ray. Magnetic resonance imaging is especially useful for imaging the brain, the spine, the soft tissue of joints, and the inside of bones. Also called MRI, NMRI, and nuclear magnetic resonance imaging.
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-[[Category:Magnetic resonance imaging| ]]
-[[Category:1973 introductions]]
-[[Category:20th-century inventions]]
-[[Category:American inventions]]
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-[[Category:Biomagnetics]]
-[[Category:Cryogenics]]
-[[Category:Discovery and invention controversies]]
-[[Category:Radiology]]
-[[Category:Diagnostic studies]]