History of MRI - Foundation
MRI is based on a physics phenomenon discovered in the1930s,called nuclear magnetic resonance or NMR, in which magnetic fields and radio waves cause atoms to give off tiny radio signals. Felix Bloch, working at Stanford University, and Edward Purcell, from Harvard University, discovered NMR. NMR spectroscopy was then used as means to study the composition of chemical compounds.
History of MRI - Paul Lauterbur and Peter Mansfield
The 2003 Nobel Prize in Physiology or Medicine was awarded to Paul C Lauterbur and Peter Mansfield for their discoveries concerning magnetic resonance imaging.Paul Lauterbur, a Professor of Chemistry at the State University of New York at Stony Brook wrote a paper on a new imaging technique which he termed zeugmatography (from the Greek zeugmo meaning yoke or a joining together). Lauterbur imaging experiments moved science from the single dimension of NMR spectroscopy to the second dimension of spatial orientation - the foundation of MRI.
Peter Mansfield of Nottingham, England, further developed the utilization of gradients in the magnetic field. He showed how the signals could be mathematically analyzed, which made it possible to develop a useful imaging technique. Peter Mansfield also showed how extremely fast imaging could be achievable. This became technically possible within medicine a decade later.
Raymond Damadian - First Patent in the Field of MRI
In 1970, Raymond Damadian, a medical doctor and research scientist, discovered the basis for using magnetic resonance imaging as a tool for medical diagnosis. He found that different kinds of animal tissue emit response signals that vary in length, and that cancerous tissue emits response signals that last much longer than non cancerous tissue.Less than two years later he filed his idea for using magnetic resonance imaging as a tool for medical diagnosis with the U.S. Patent Office, entitled "Apparatus and Method for Detecting Cancer in Tissue." A patent was granted in 1974, it was the world's first patent issued in the field of MRI. By 1977, Dr. Damadian completed construction of the first whole-body MRI scanner, which he dubbed the "Indomitable."
Rapid Development within Medicine
The medical use of magnetic resonance imaging has developed rapidly. The first MRI equipment in health were available at the beginning of the 1980s. In 2002, approximately 22 000 MRI cameras were in use worldwide, and more than 60 million MRI examinations were performed.HOW MRI WORKS
Magnetic resonance imaging (MRI) is a diagnostic imaging technique for obtaining digitized visual images representing the internal structure of objects (such as the human body) having substantial populations of atomic nuclei that are susceptible to nuclear magnetic resonance (NMR) also known as magnetic resonance (MR) phenomena. Magnetic resonance imaging (MRI) is also known as magnetic resonance tomography (MRT). Magnetic resonance imaging has been developed as an imaging technique adapted to obtain both images of anatomical features of human patients as well as some aspects of the functional activities and characteristics of biological tissue. These images have medical diagnostic value in determining the state of the health of the tissue examined. Magnetic resonance imaging is a diagnostic imaging modality that does not rely on ionizing radiation. Instead, it uses strong (ideally) static magnetic fields, radio-frequency (RF) pulses of energy and magnetic field gradient waveforms. MR imaging is a non-invasive procedure that uses nuclear magnetization and radio waves for producing internal pictures of a subject. Medical diagnostic imaging has evolved as an important non-invasive tool for the evaluation of pathological and physiological processes. Presently, nuclear magnetic resonance imaging (MRI) and computerized tomography (CT) are two of the most widely used imaging modalities. In medical diagnostics, MRT is particularly distinguished as a tomographic imaging method as being a "non-invasive" examination with a versatile contrast capability. Due to the excellent presentation of soft tissue, MRT has developed into a method that is often superior to X-ray computer tomography (CT). Magnetic resonance imaging (MRI) apparatuses are widely used especially in medical applications because of their capability of capturing a tomographic image of a subject using the nuclear magnetic resonance (NMR) phenomenon. Magnetic resonance imaging has proven to be an enormously useful technology both for the detection and diagnosis of human disease as well as for research into the understanding of basic animal physiology. MRI is well suited to the visualization of soft tissues and is primarily used for diagnosing disease pathologies and internal injuries.
In general, magnetic resonance imaging (MRI) is a technique of applying a gradient magnetic field and an RF (radio frequency) wave to a subject in a static magnetic field, and producing an image based on magnetic resonance signals emitted as an echo from protons in a region to be examined. Magnetic resonance imaging (MRI) systems typically include a super conducting magnet capable of producing a strong, homogenous magnetic field around a patient or portion of the patient; a radio frequency (RF) transmitter and receiver system, including transmitter and receiver coils, also surrounding or impinging upon a portion of the patient; a gradient coil system also surrounding a portion of the patient; and a computer processing/imaging system, receiving the signals from the receiver coil and processing the signals into interpretable data, such as visual images. Magnetic resonance imaging systems utilizing a superconductive electromagnetic device include tunnel-type and open-type systems when categorized according to the contours of vacuum containers for incorporating superconductive coils and the like. For the magnets of the MRI apparatus, permanent magnets, normal conducting magnets and superconducting magnets have been put into practical use. The superconducting magnets, which can achieve higher magnetostatic field strength, are finding wider applciations than permanent magnets and normal conducting magnets. Magnetic resonance imaging (MRI) utilizes hydrogen nuclear spins of the water molecules in the human body or other tissue, which are polarized by a strong, uniform, static magnetic field generated by a magnet. The magnetically polarized nuclear spins generate magnetic moments in the human body. The magnetic moments point in the direction of the main magnetic field in a steady state, and produce no useful information if they are not disturbed by any excitation. MRI involves the interrogation of the nuclear magnetic moments of a subject placed in a strong magnetic field with radio frequency (RF) magnetic fields. Typically, a high frequency magnetic field is applied to the subject placed in homogeneous static magnetic field to obtain a tomographic image of the region from nuclear magnetic resonance signals induced thereby. Radio frequency energy is applied to this region of the patient by a transmitter and antenna. The RF energy excites atomic nuclei within the patient's tissues. The excited nuclei spin at a rate dependent upon the magnetic field. As they spin, they emit faint RF signals, referred to herein as magnetic resonance signals. In order to select a specific region, a gradient magnetic field is applied together with the high frequency magnetic field and further, in order to provide correct positional information for the echo signals measured, it is necessary to correctly control the application time and intensity of the gradient magnetic field. By applying small magnetic field gradients so that the magnitude of the magnetic field varies with location within the patient's body, the magnetic resonance phenomenon can be limited to only a particular region or "slice" of the patient's body, so that all of the magnetic resonance signals come from that slice. Moreover, by applying additional magnetic field gradients, the frequency and phase of the magnetic resonance signals from different locations within the slice can be made to vary in a predictable manner depending upon the position within the slice. A magnetic resonance imaging system is equipped with a radio frequency oscillator. This oscillator is used to adjust the carrier frequency of a radio-frequency excitation pulse for selective excitation, depending on a slice-directional position of a specified section (single slice) to be imaged of an object, in cases where imaging is carried out while the object is moved.
Magnetic resonance imaging (MRI) detects the faint nuclear magnetic resonance (NMR) signals given off by protons in the presence of a strong magnetic field after excitation of the protons with a radio frequency signal. The NMR signals are detected using loop antennas termed coils. Magnetic resonance imaging (MRI) collects data in the Fourier domain, typically referred to as k-space, from the magnetic signals of protons processing in a magnetic field. The spin frequency, also referred to as the resonance frequency, is a function of a material's gyromagnetic ratio and the strength of the magnetic field. Magnetic resonance imaging (MRI) can be used to generate chemical shift specific images because protons in different chemical species may have different resonance frequencies. The chemical shift artifact (CSA) presents a significant barrier to the quantitative MR image analysis of small features, in which the amount of shift is comparable to the dimension of the object. The CSA appears as a "shadowing" effect in the read direction of MR images. In magnetic resonance image scanning (MRI scanning), images of a subject, usually a patient's body, are produced through the interaction of a magnetic field applied to the patient's body and the magnetic moment of protons. Each proton behaves as small bar magnet, and the strength of the bar magnet is referred to as the "magnetic moment" of the proton. The protons are the nuclei of hydrogen atoms. The hydrogen is chemically bonded in compounds of the patient's tissue. Magnetic resonance imaging (MRI) provides excellent soft tissue contrast with arbitrary scan-volume orientations, thus making MRI an extremely useful medical imaging modality. Magnetic resonance imaging offers a powerful, non-intrusive 3D imaging technique for various medical, engineering and scientific studies. This is achieved by spatially coding the precessing frequencies or phases of nuclear magnetic moments of a sample under study under a bias magnetic field and using radio frequency (RF) coils to excite and detect emitted signals with a certain sequence. A three-dimensional (3D) image is then reconstructed after signal processing with a processor. The MRI systems can be divided into two general categories mainly in terms of a magnetic field application method. One is a horizontal magnetic field apparatus in which an imaging volume is placed in an internal space of a group of coils arranged coaxially in multiple layers, and the other is a vertical magnetic field apparatus (open type) in which an imaging volume is sandwiched between opposing coil groups. Because of its openness the vertical magnetic field apparatus reduces a psychological burden on a patient and significantly improves an accessibility to the patient by an inspector.
Information for patients having an MRI scan
This web tells you about having a magnetic resonance imaging (MRI) Scan. It explains what is involved and what the possible risks are. It is not meant to replace informed discussion between you and your doctor, but can act as a starting point for such a discussion.
Whether you are having an MRI scan as a planned or an emergency procedure, you should have sufficient explanation before you sign the consent form.
The radiology department
The radiology department may also be called the x-ray or imaging department. It is the facility in the hospital where radiological examinations of patients are carried out, using a range of x-ray equipment, such as a CT (computed tomography) scanner, an ultrasound machine and a MRI scanner.
Radiologists are doctors specially trained to interpret the images and carry out more complex examinations. They are supported by radiographers who are highly trained to carry out x-rays and other imaging procedures.
What is an MRI
MRI (magnetic resonance imaging) is the name given to a technique which builds up pictures of an internal cross-section of the part of the body under investigation. The large machine contains a ‘tunnel’, about four feet long, through which a patient lying on the attached couch can pass.
It uses a magnetic field and radio waves, together with an advanced computer system to build up a series of images, each one showing a thin slice of the area being examined.
These images are very detailed can show both bones and soft tissues in the body and can therefore give a great deal of information. By means of the computer, the ‘slices’ can be also be obtained in any direction.
Detailed MR images allow physicians to better evaluate parts of the body and certain diseases that may not be assessed adequately with other imaging methods such as x-ray, ultrasound, or computed tomography (also called CT or CAT scanning).
Are there any risks?
As far as is known at present, this is an extremely safe procedure. It does not involve the use of x-rays. You are placed in a very powerful magnetic field, and consequently if you have any small pieces of metal inside your body, you should inform the radiographer as in some cases you may not be able to have the examination.
If you have had a history of metal fragments in your eyes, it is necessary to have an ordinary x-ray done to prove there are no bits left. If you have a pacemaker, metal heart values or metallic clip on an artery at the base of your brain, then there is a risk that these may move during an MR scan, and a different examination will need to be arranged instead. However, any shrapnel or metal sutures, such as stitches, that have been in place for a long time may not create a problem.
For female patients, if you are or might be pregnant, you must make sure the doctor referring you or a member of staff in the radiology department knows as soon as possible in advance. MR scans may not be advisable in early pregnancy, unless there are special circumstances.
ring, cash, keys, credit cards and watches etc. This is because anything containing metal may interfere with the magnetic field of the MRI unit. Metal and electronic objects are not allowed into the examination room.
You may be asked to put on the surgical gown and dressing gown provided, but you may wish to bring your own dressing gown. You should place your clothes and personal belongings either in a basket, which you will keep with you, or in a secure locker.
Who will you see?
You will be cared for by a small team including a radiographer who will perform the examination. The radiologist may be look at the results on the computer screen, as it is happening, or may simply look at a recording of the images later, before writing a report.
What happens during the MRI?
You will be taken into the special room and made comfortable lying on the couch. Straps and pillows may be used to help you stay still and maintain your position during imaging. You may be given a contrast medium (a dye) which helps to produce a more detailed image.
The contrast medium would be injected into a vein in your arm, which occasionally causes a warm feeling for a short while.
The couch will be moved slowly to position the part of your body under investigation within the ‘tunnel’. The radiographers will retire to the control room but you will be able to talk to them via an intercom, and they will be watching you all the time. It is important that you remain completely still while the images are being recorded. During the scan, you may well find the machine very noisy and you will probably be given ear plugs and/or earphones. If you feel uncomfortable or worried, do mention it immediately to the radiographer.
Upon completion you may put on any clothes you have taken off, but may be asked to wait a little longer while the radiologist is satisfied that the scans have been successfully completed.
Will it be uncomfortable?
Apart from any machine noise you will not be aware of anything happening. Most patients do not mind lying with their body within the ‘tunnel’, but some find it claustrophobic. If this makes you feel worried
do tell the radiographer straight away. However, if you suffer badly from claustrophobia, you should talk to the radiology department as soon as possible ahead of your appointment.
How long will it take?
The process of taking the images on the screen usually takes about 20–30 minutes and unless you are delayed by such as emergency patients, your total time in the department is likely to be about 45 minutes.
Are there any side-effects?
No. You can drive home afterwards and return to work as necessary.
Can you eat and drink afterwards?
Yes, do so normally.
When will you get the results?
After the scan, the images will be examined further by the radiologist, who will prepare a report on their findings. This may take some time to reach your referring doctor, but is normally less than 14 days. You
could ask the radiographer or radiologist for some indication of timing.
Preparing for your Scan
In general, there are no special preparations to follow before your exam. Because MRI uses a strong magnetic field, metal objects may interfere with the scan. For your convenience, we provide a locker to store your keys, jewelry and other valuables during the exam. We ask that you wear comfortable, loose-fitting clothing, but you may be asked to change into a hospital gown for image quality and safety reasons.
Please check the following list carefully. All metallic/surgical implants must be assessed for safety before undergoing any MRI procedure. Common implants that may not be safe for MRI procedures include the following:
- Pacemaker
- Aneurysm clips in the brain
- Inner ear (cochlear) implants
- Implanted spinal cord stimulator
- Metallic implants
- Metal fragments in one or both eyes
Also, please alert our staff if you:
- Have dental bridges
- Wear a hearing aid(s)
- Have ever been a metal worker
- Are pregnant or think you might be
Because a paramagnetic agent (a type of contrast media) may be used, please tell your physician if you:
- Are pregnant or think you might be
- Are breastfeeding
- Have anemia or any diseases that affect red blood cells
- Have asthma or other allergic respiratory disorders
If you have any questions about your eligibility to have an MRI scan, consult with your physician.
Finally…
Some of your questions should have been answered by this leaflet, but remember that this is only a starting point for discussion about your treatment with the doctors looking after you. Make sure you are satisfied that you have received enough information about the procedure, before you sign the consent form.
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