How does an MRI work?

How Does an MRI Work



Invention of MRI or magnetic resonance imaging was a revolution in medical diagnosis. This technique of imaging used in diagnosis of various ailments is based on the principles of nuclear magnetic resonance (NMR). It may all sound complicated, but with a little bit of interest, you will realize how an MRI machine generates images of our body.






MRI or magnetic resonance imaging, is a medical imaging technique, which facilitates detailed visualization of the internal structure of our body. It also helps in assessing some functions of the body to a certain extent. The technology, which was introduced in the last quarter of the 20th century, has undergone a dramatic change and gained immense popularity in the field of medicine today. The huge machine referred to as an MRI scanner is an object of fascination for many individuals, who are often left wondering how it works.






The Components of an MRI Machine






Before we move on to the working mechanism of MRI (Magnetic Resonance Imaging), let's take a brief look at the various components of the MRI scanner. The major components of an MRI machine include the primary magnet and the gradient magnets. The primary magnet, made from an electrical coil with power running through it, develops a magnetic field of around 1.5 to 3 Tesla. The gradient magnets, which are much smaller than the primary magnet, help in altering the magnetic field precisely. Other than these, the MRI scanner also includes the horizontal tube, wherein the person is made to lie for examination, and last, but the most important - the computer software and hardware components, which help in setting the parameters prior to the examination, and collecting the data in the form of multiple images.






How Does an MRI Scanner Work?






The MRI scanner is a giant cube, with a horizontal tube attached to it. The patient to be examined is made to lie on his back on this horizontal tube, and then, he is slowly slid into the machine. Whether the entire body of the individual will be sent in or just half of it, depends on which part of the body is to be examined. In case of brain MRI scan, sliding the upper torso of the patient inside the scanner would be enough for the diagnosis. As soon as the body part to be scanned reaches at the isocenter of the magnetic field, the scan begins.






How Does an MRI Generate Images of the Body?






A large part of the human body is composed of water molecules, each of which contains two hydrogen nuclei (or protons). When the patient is sent inside the scanner, the 'magnetic moments' of the protons present in the body align with the direction of the magnetic field. A radio frequency electromagnetic field is turned on for a few seconds, which makes the protons change their alignment relative to the field. As soon as the electromagnetic field is turned off, the protons return to their original alignment. The alterations in the alignment creates a signal which is detected by the scanner. The strength of the magnetic field determines the frequency at which the protons resonate.






Additional magnetic fields are created using the gradient magnets to determine the position of the protons, and the energy released by them. The damaged tissues can be detected as they take time in returning to the state of equilibrium. The parameters are set using the computer and contrast is created between different types of tissues. MRI with contrast is carried out by injecting contrast agents in the body, in order to enhance the appearance of the blood vessels, and to detect tumors and inflammation in the body. The computer takes a note of protons and the energy released by them to generate the image of the body part being examined.






Although MRI can be used to image any part of the body, it is most often used in neurological examinations, checking for tumors, abnormalities in blood vessels etc. MRI scan cost depends on which part of the body is being examined. A safe procedure owing to the exclusion of ionizing radiation, MRI has gained wide popularity in the medical field, across the world.