Magnetic Resonance Imaging (MRI):
- MRI is an indispensable tool to look inside the human body without surgery. It is used to obtain images of soft tissues within the body. Soft tissue is any tissue that has not become harder through calcification.
- It is a non-invasive diagnostic procedure widely used to image the brain, the cardiovascular system, the spinal cord and joints, various muscles, the liver, arteries, etc.
- MRI scans do not pose any threats; once the magnetic fields are taken away, the atoms in the scanned part do not remain affected. There is no long-term harm associated with scans.

Applications:
- Brain imaging: MRI can help identify abnormalities such as tumours and track neurological conditions including Alzheimer’s, dementia, epilepsy, and stroke etc. Functional MRI (fMRI) is a specialised technique that measures brain activity by detecting changes in blood flow, providing insights into brain function and mapping brain networks.
- Cardiovascular imaging: MRI can produce detailed images of the heart and blood vessels without using ionising radiation. It helps diagnose heart conditions such as coronary artery disease, cardiac tumours, and congenital heart defects.
- Spinal cord imaging: MRI is effective in visualising the spinal cord and various structures like joints, ligaments, tendons, and muscles.
- Abdominal and pelvic imaging: MRI is used to examine abdominal and pelvic organs, including the liver, pancreas, kidneys, uterus, ovaries, and prostate. It can detect tumours, cysts, infections, and other abnormalities, and it is often employed when other imaging methods like ultrasound or computed tomography (CT) provide inconclusive results.
- Cancer detection: Its use is particularly important in the observation and treatment of certain cancers, including prostate and rectal cancer.

How does MRI work?
- An MRI procedure reveals an image of a body part using the hydrogen atoms in that part. A hydrogen atom is simply one proton with one electron around it. These atoms are all spinning, with axes pointing in random directions. Hydrogen atoms are abundant in fat and water, which are present almost throughout the body.
- The MRI machine itself looks like a giant doughnut. The hole in the centre, called the bore, is where the person whose body is to be scanned is inserted. Inside the doughnut is a powerful superconducting magnet whose job is to produce a powerful and stable magnetic field around the body. Once the body part to be scanned is at the centre of the bore, the magnetic field is switched on.
- Each hydrogen atom has a powerful magnetic moment, which means in the presence of a magnetic field, the atom’s spin axis will point along the field’s direction. The superconducting magnet applies a magnetic field down the centre of the machine, such that the axes of roughly half of the hydrogen atoms in the part to be scanned are pointing one way and the other half are pointing the other way. This matching is almost exact: in around a million atoms, only a handful remain unmatched — that is, a small population of ‘excess’ atoms pointing one way or the other.
- The machine has a device that emits a radiofrequency pulse at the part under the scanner. When the pulse is ‘on’, only the small population of ‘excess’ atoms absorbs the radiation and gets excited. When the pulse goes ‘off’, these atoms emit the absorbed energy and return to their original, lower energy states.
- Finally, a detector receives the emissions and converts them to signals, which are sent to a computer that uses them to recreate two- or three-dimensional images of that part of the body.
Limitations:
- Because of the MRI technique’s use of strong magnetic fields, individuals with embedded metallic objects (like shrapnel) and metallic implants, including pacemakers, may not be able to undergo MRI scans.
- MRI machines are expensive: Depending on the specifications, including the strength of the magnetic fields and the imaging quality, they cost from a few tens of lakh rupees to a few crores. Diagnostic facilities pass this cost on to its patients. Based on the clinical requirements, scans often cost ₹10,000 or more each — a sizable sum in India.
- Discomfort: Inside the machine, the individual is expected to lie still for tens of minutes, until the scan is complete. If the individual moves, the resulting image will be distorted and the scan will have to be repeated. The problem is exacerbated if the individual is claustrophobic (although some ‘open-bore’ MRI machine designs can alleviate this issue).











