MRI stands for “magnetic resonance imaging” and is a technique used to take images of the human body using a strong magnet and radio waves. Although it can be used to take images of any part of the body, it is commonly used to image soft tissue organs, such as the brain, lungs, or liver.MRI works by sending radio signals to a location of interest (e.g., brain) and receiving radio waves emitted back from that location within a large magnet. The properties of the received radio wave signals are different depending on the type of tissues being scanned.These signals are later transformed into a single grayscale image by a computer, in which different features of the organ (e.g., gray matter and white matter in the brain) can be identified.Learn moreWhen placed in the presence of the strong magnetic field found in an MRI machine, the spin (or magnetic moment) of hydrogen atoms align themselves in the direction of the magnetic field. In short, they “line up.” To create brain images using MRI, short bursts of radio waves “flip” the hydrogen atoms over, knocking them out of alignment with the magnetic field.Gradually, the hydrogen atoms line up again with the magnetic field, and as they do, they act as a small radio transmitter. Their signal is then picked up by the MRI machine.Different tissues in the body take different amounts of time to realign. Dense tissue, for example, takes longer to realign than soft tissue.To create a 3-D image as is commonly required for MRI studies of the brain, magnetic gradients of different strengths and different directions are applied on top of the main magnetic field and are turned on and off during the scan.Thus, an MRI image is the result of a complicated interplay between radio frequency pulses and intermittently activated gradient fields, all of which are under computer control. Later, a mathematical technique called "Fourier transform" is used to translate the values obtained by the MRI machine into grayscale images.MRI has a wide range of applications in medical diagnosis and over 25,000 scanners are estimated to be in use worldwide.[1] MRI has an impact on diagnosis and treatment in many specialties although the effect on improved health outcomes is uncertain.[2] Since MRI does not use any ionizing radiation, its use is generally favored in preference to CT when either modality could yield the same information.[3] (In certain cases, MRI is not preferred as it can be more expensive, time-consuming, and claustrophobia-exacerbating).
Medical uses
MRI is in general a safe technique but the number of incidents causing patient harm has risen.[4] Contraindications to MRI include most cochlear implants and cardiac pacemakers, shrapnel and metallic foreign bodies in the eyes. The safety of MRI during the first trimester of pregnancy is uncertain, but it may be preferable to other options.[5] The sustained increase in demand for MRI within the healthcare industry has led to concerns about cost effectiveness and overdiagnosis