MAGNETIC RESONANCE IMAGING (MRI)

• Magnetic Resonance Imaging (MRI) is a non-invasive diagnostic procedure utilized to generate images of soft tissues within the body. Soft tissue, devoid of calcification, encompasses organs, muscles, blood vessels, and more.
• MRI serves as a crucial tool in medical diagnostics, offering detailed images of various body parts including the brain, cardiovascular system, spinal cord, joints, liver, and arteries. It plays a vital role in cancer diagnosis and treatment, particularly for prostate and rectal cancers. Moreover, MRI aids in tracking neurological conditions such as Alzheimer's disease, dementia, epilepsy, and stroke.
• Researchers leverage MRI technology to observe changes in blood flow, providing insights into brain activity—a technique known as functional MRI (fMRI).
• However, MRI poses limitations for individuals with embedded metallic objects or implants, such as pacemakers, due to its reliance on strong magnetic fields. Even everyday items like credit cards can be affected, as the magnetic fields can erase their magnetic strips.

MRI operates by harnessing the properties of hydrogen atoms present in the body, specifically their magnetic properties.

• Hydrogen atoms, consisting of a single proton and electron, are abundant in fat and water throughout the body. Within an MRI machine, a powerful superconducting magnet generates a stable magnetic field around the body. When exposed to this magnetic field, hydrogen atom spins align with the direction of the field.
• A radiofrequency pulse is emitted towards the body part being scanned. This pulse causes only a small population of hydrogen atoms, known as 'excess' atoms, to absorb the radiation and become excited. The frequency of this pulse, called the Larmor frequency, depends on the strength of the magnetic field and the type of tissue.
• When the radiofrequency pulse ceases, the 'excess' atoms release the absorbed energy and return to their original state. These emissions are detected by a receiver within the MRI machine, which converts them into signals. These signals are then processed by a computer to generate two- or three-dimensional images of the scanned body part.
• An MRI machine consists of four essential components: the machine itself, resembling a giant doughnut with a central bore for inserting the patient; a powerful superconducting magnet generating the magnetic field; a device emitting radiofrequency pulses; and a detector receiving emissions and converting them into signals for computer analysis.

MRI imaging offers several advantages over other diagnostic techniques, making it a valuable tool in medical diagnostics

• MRI machines utilize gradient magnets to highlight specific portions of the body, allowing for precise imaging of targeted areas. By controlling the gradient magnets, MRI scans can focus on regions just a few millimetres wide without requiring the patient to move.
• The design and organization of magnets within the MRI machine enable imaging of the body from various directions and in small increments. This versatility allows clinicians to obtain comprehensive and detailed images of the patient's anatomy.
• MRI exploits the different T1 relaxation times of hydrogen atoms in water within different tissues, resulting in images that depict various tissues in shades of grey. Contrast agents, such as gadolinium-based compounds, further enhance tissue visibility by altering T1 times, aiding in the diagnosis of certain conditions.
• Extensive research has demonstrated the safety of MRI scans, as the magnetic fields used do not pose long-term harm to the body. Once the scan is complete, the atoms in the scanned area return to their original state without any lingering effects. Additionally, MRI imaging is non-invasive, eliminating the need for invasive procedures like surgery.
• While MRI scans are generally safe, their effects on pregnant women are not as extensively studied. As a precautionary measure, many scanning facilities may refuse appointments for pregnant women to ensure their safety and that of their unborn child.

While Magnetic Resonance Imaging (MRI) technology offers valuable diagnostic capabilities, several limitations and challenges accompany its usage:

• MRI machines entail substantial upfront costs, ranging from several tens of lakhs to crores of rupees, contingent upon factors such as magnetic field strength and imaging quality. These expenses are ultimately transferred to patients, with individual scans often commanding fees upwards of ₹10,000. Such financial burdens can pose significant challenges, particularly for uninsured individuals or those requiring multiple scans.
• Despite the advantage of minimal patient movement during scanning, MRI procedures necessitate prolonged periods of stillness, often lasting tens of minutes. Any involuntary movement during this time can distort the resulting image, necessitating scan repetition. This requirement for immobility can be particularly challenging for individuals who experience claustrophobia, although some "open-bore" MRI designs aim to alleviate this issue.
• Generating magnetic fields exceeding 1 tesla requires substantial energy consumption and maintenance efforts. Superconducting coils cooled with liquid helium facilitate the creation of these fields, but their operation remains energy-intensive and costly. Additionally, the sequential switching of heavy currents within the machine, as dictated by the operation of gradient coils, generates loud noises, further contributing to patient discomfort.