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MRI is a method of creating images inside our body by utilizing radio frequency waves and a strong magnetic field. This method eliminates the risks of harmful x-ray radiation. Recently, MRI has become increasingly popular since the procedure is noninvasive1; currently, there are no known side effects. In addition, the image quality is much improved, providing more clear and detailed images of the internal organs and tissues. MRI technology has become so advanced that we are able now to detect heart disease, strokes and cancer and other conditions.
Let’s begin with the basic structure of the MRI scanner. A typical MRI scanner is a 7 feet high by 7 feet wide by 10 feet long. It is cylindrical in structure with an automated and protruding bed. The subject is placed on their back on the MRI bed which slides into the bore, the hollow inside of the cylindrical tube.
The most important feature of the MRI is the magnet. The magnets are quite strong (typically 0.5 tesla2 to 2 tesla) which is why many precautions are taken during MRI scans (See Safety Precautions below). The magnet, however, does not have an effect on the body but rather helps image quality. The typical magnets found in MRI scanners are as follows: resistive magnets, permanent magnets, and super conducting magnets. Resistive magnets are simply coils of wire around the bore. In order to generate a magnetic field, electricity is passed into these coils. Once electricity is passed into these coils, all of the coils turn to produce a north pole and south pole similar to the ends of a typical bar magnet. Different contours of coils are needed to scan different parts of the body; so, cardiac MRI utilizes coils that are different in shape from ones scanning the brain. Permanent magnets are basic magnets that do not require any energy. Like resistive magnets, super conducting magnets also have coiled wires with one major difference: the wire used is immersed in liquid nitrogen or liquid helium at very low temperatures and well-insulated so as not to affect the temperature within the hollow bore.
The magnets align hydrogen protons in the area of interest, such as the heart. A radio frequency pulse is directed to these protons to “energize” them. Once energized, these protons spin. Once the radio frequency pulse is shut off, the protons release energy. The energy released activates the coils and sends information to the computer. The computer, using a mathematical analysis through Fourier transform, translates the information to an image.
The MRI is best for quantitative studies; MRIs can let doctors know the volume of the left ventricle, or the ejection fraction. The ejection fraction is the percent of the blood squeexed out of each ventricle after a contraction (usually around 60%). The MRI can measure myocardial mass, or the rate of blood flow.
In the lab...
Magnetic Amount: The magnetic amount of a MRI machine is from 0.5 to 2 tesla.
Safety Precautions: Due to the use of magnets, all metal items are removed from the area. Credit cards and other types of bank cards are also removed since magnets will erase the magnetic encoding embedded in the cards. In addition, people with pacemakers, dental or orthopedic implants or any such metallic implants are prohibited to be near the scanner at all times. Although there have been no known side effects, pregnant women are generally preferred not to be scanned; the effects on the developing fetus are currently unknown.
Orientation of Patient: Depending on the injury and type of MRI scanner, patients lay face up or down on a suspended bed. In a cardiac MRI, patients are typically placed in a supine manner. The patient feels nothing during the scan but may feel somewhat claustrophobic due to the limited amount of space. The patient must also lie still since movements may distort the images produced.
Length of Scan: MRI scanning is a long process requiring a patient to lie still anywhere from half an hour to an hour and a half.
1941 - Yevgeni K. Zavoisky discovers the electron spin resonance phenomenon. However, his attempts to detect and measure magnetic resonance fail.
1946 - Felix Bloch and Edward Purcell work independently and create the first instruments that could perform magnetic resonance imaging with bulk material.
1970 - Raymond Damadian demonstrates that the time taken by a proton to release energy differs between abnormal and normal tissues. In other words, the relaxation period, or the time it takes a proton to release its energy, would determine the normality of the tissues being studied.
1973 - Up until this point, the image produced lacks spatial information. The image is only one dimensional. Paul Lauterbur discovers a new imaging technique that was able to produce two-dimensional images. He coins his technique Zeugmatography.
1975 - Unlike Lauterbur’s technique, Richard Ernst discovers a new technique that is the basis of today’s magnetic resonance imaging scanners. Richard Ernst also used the Fourier transformation.
1977 - The first MRI images are presented. Peter Mansfield and Andrew Maudsley show a cross section through a finger. Also during this year Raymond Damadian founds the FONAR corporation that manufactures MRI scanners and receives FDA approval in 1981.
Pathologies Detected by EKG
The MRI scanner, though a non-invasive procedure, can accurately detect defective tissues of the heart. The MRI can diagnose heart attacks, inflammations, and regurgitations. The MRI scanner is typically used for diagnosing the following pathologies.
Aortic Dissection - MRI detects the location of the tear and where treatment needs to be directed.
Aortic Aneurysm – MRI images a wider vessel, a telling irregularity.
Congenital Heart Disease – MRI is typically used for diagnosing congenital heart disease.
Aortic Regurgitation - MRI gives a good picture of this problem.
Atherosclerosis – MRI can provide a non-invasive procedure for detection of atherosclerosis by an analysis of the tissue.
Cardiomyopathy – MRI can provide visualization of the cardiac chambers.
Valvular abnormalities- MRI can detect the irregularity of the valve movements
Pericarditis - MRI detects a thickening of the pericardial lining.
Since the main component is a magnet, people with pacemakers must not be near such a machine. In addition, these machines are incredibly noisy: Patients and operators must use earplugs to muffle the loud noise. Scannng can take up to half an hour in a small cylindrical tube and claustrophobic people cannot tolerate the wait. The procedure is expensive.