Have you ever received an MRI test? Do you know the contraindicaions for MRI scanning?
Let's tell you the introduction of Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging is a painless and safe diagnostic procedure that uses a powerful magnet and radio waves to produce detailed images of the body’s organs and structures, without the use of X-ray machine or other radiation. MRI is based on the principles of nuclear magnetic resonance, a technique used by scientists to obtain microscopic chemical and physical information about molecules.
The biggest and most important component in an MRI system is the magnet. The magnet in an MRI system is rated using a unit of measure known as a tesla. Another unit of measure commonly used with magnets is the gauss. The magnets is use today in MRI systems crate a magnetic field of 0.5 tesla to 2.0 tesla, or 5,000 to 20,000 gauss. When you realize that the Earth’s magnetic field measures 0.5 gauss, you can see how powerful these magnets are. Another part of the MRI system is a set of coils that transmit radiofrequency waves into the patient’ body. There are different coils for different parts of the body: knees, shoulders, wrists, heads, necks and so on. There cols usually conform to the contour of the body part being imaged, or at least reside very close to it during the exam. Other part of the machine include a very powerful computer system and patient table, which slides the patient into the bore. Whether the patient goes in head or feet first is determined by what part of the body needs examining. Once the body part to be scanned is in the exact center of the magnetic field, the scan can begin.
When patients side into an MRI machine, they take with them the billions of atoms that make up the human body. For the purposes of an MRI scan, we’re only concerned with the hydrogen atom,, which is abundant since the body is mostly made up of water. These atoms are randomly spinning on their axis, like a child’s top. All of the atoms are spinning in various directions around their individual magnetic fields.
But these hydrogen atoms have a strong magnetic moment,, which means that in a magnetic field, the atoms line up in the direction of the filed. If the nuclei of hydrogen atoms－single protons, all spinning randomly—are caught suddenly in s strong magnetic field, they tend to line up like so many compass needles. When radio frequency pulse is applied, the protons are ten hit with a short, precisely tuned burst of radio waves. They will absorb the energy, flip around, and spin again in da different direction. This is the “resonance” part of MRI. When the radio frequency is turned off, the hydrogen protons slowly return to their natural alignment within the magnetic filed and release the energy absorbed from the RF pulses. When they do this, they give off a signal that the coils pick up and send to the computer system. The computer receives the signal from the spinning protons as mathematical data; the data is converted into an image.
MRI is used to image every part of the body, and is particularly useful for showing soft tissues, such as the brain, muscle, connective tissue and most tumors. Another big advantage of MRI is that MRI does not use X-rays, so there is to exposure to radiation, such as pregnant women and babies.
MRI is usually a very safe procedure. However, the strong magnet used for scanning can attract any metal object containing iron. Patients who are having an MRI should be prescreened for the presence of any metal objects or accidental exposure to metal fragments.