Magnetic Resonance Imaging (MRI)

Overview

MRI is a non-invasive technique, advanced medical imaging technique that uses magnetic fields and computers to generate images of the various parts of the body. It is a painless procedure used to create clear 3-dimensional images that can be viewed from different angles. 

Indications

MRI can be used to detect a disease, diagnose it, plan a treatment, and monitor the treatment. It is for various disorders of various internal organs. It can be used to identify disorders like stroke, tumors, damage to the organs due to trauma, analyze the size and functions of the heart chambers, structural deformities in the valves or heart, inflammation, heart blockages, joint trauma, disk problems, infections, and cancers. Functional MRI helps to study the anatomy and functions of a particular body part by using images of blood flow. 

Contraindications

MRI cannot be taken in individuals who have functional devices like cardiac pacemakers, metallic joint prostheses, cochlear implants, clips used in conditions of brain aneurysms, vagal nerve stimulators, or insulin pumps. Magnetic radiation can disturb the functionality of these devices. Hence, computed tomography scans are preferable for such patients. It is not indicated in the first trimester of pregnancy as it can cause damage to the growing fetus. 

MRI Principle

MRI works on the principle of nuclear spinning and the reactions of nuclei to external magnetic fields. Strong magnets produce a powerful magnetic field that pushes the protons in the body tissues to align according to the magnetic force. As the radiofrequency (RF) current passes, the protons absorb the energy, spin, and align in the direction of the force. When the RF current is turned off, these protons release energy, which is captured by the MRI sensors. The amount of energy released and the time taken for the protons to align varies depending on the type and the chemical nature of the tissue. The machine sends the signals to the computer, where sectional images similar to the loaves of bread are generated. 

Advantages of MRI

• MRI has many advantages. They include the following: 
• MRI is a non-invasive technique. 
• It does not use ionizing radiation like X-rays, which are used in conventional radiography and computed tomography images.
• It creates clear images of non-bony or soft-tissue parts better than any imaging modality. Hence, it is used for brain, spinal cord, muscles, ligaments, and tendon imaging. It can also differentiate between white and grey matter in the brain. Hence it is used for aneurysms and tumors of the brain and spinal cord. 
• It is the preferred imaging treatment when frequent imaging is required for either diagnosis or monitoring therapy. 
• Functional MRI is a special kind of MRI that can produce images of blood flow to certain areas of the brain helping in understanding the functions of certain areas of the brain while preparing for surgery. It also detects brain damage in injuries and degenerative diseases like Alzheimer's. 
• MRI Contrast: To obtain better quality images, MRIs are taken by injecting contrast-like gadolinium into the body. Gadolinium is a rare metal found on earth that can change the magnetic properties of the water molecules in the cells and tissues to produce a better-quality image. This increases the visualization of tumors, infections inflammation, and blood vessels. 
• MR Elastography: It is a technique of combining MRI and elastography principles to assess the stiffness of tissues. It creates a visual map of the stiffness and is mainly used for screening liver disorders. 

 MRI Machines

There are two types of MRI machines. They are Open bore and Closed bore machines. The open-bore MRI machine has two flat magnets placed above and below a table. Closed-bore MRI machines are made of a ring of magnets with an open hole or tube in the center. Closed-bore MRI machines can cause anxiety due to their structure, and in such cases, open-bore MRI machines are preferrable. Closed-bore MRI machines produce much clearer images than open-bore MRI machines. Based on the procedure, MRI is of different types like: 

Before the procedure

An individual undergoing an MRI procedure can have their regular diet and medications. As there is a magnetic field involved, one should remove metals present on the body. Metal things like jewelry. Watches, hairpins, spectacles, dentures, wigs, hearing aids, wired bras, and cosmetics with metal particles. If contrast is injected, one has to give information about allergies to contrast materials to the healthcare providers. Information regarding the presence of any metal prostheses should be given to the healthcare provider. 

During the procedure

An individual getting an MRI scan is made to lie on the table. In case of anxiety or claustrophobia, anxiety-reducing drugs will be given. The procedure is painless and one does not feel any radio waves or electromagnetic waves around them. MRI machine has huge magnets and they produce loud repetitive noises. Hence, it is advisable to wear earplugs or listen to music that can reduce the background noise and calm the person.  

When a functional MRI is taken, one has to make small movements like tapping with fingers, rubbing on paper, speaking, or replying to some questions. One has to remain still without moving to reduce the disturbance or blurring of the images. 

After the procedure

MRI scan takes about 30 minutes. One can resume normal activities after the scan unless a contrast is injected. 

Risks and complications

MRI uses huge magnetic fields, and hence, it is risky if any metal objects are influenced by the magnetic field inside or outside the body. The sound intensity in MRI is up to 120 decibels; hence, special ear protection should always be used. Rapid switching of magnetic fields can cause nerve twitching. Contrast agents used in MRI can cause allergies in some individuals. Claustrophobia is a complication in individuals with anxiety disorders. 

Conclusion

MRI is an advanced and non-invasive diagnostic imaging method that provides detailed images of the internal organs. It can detect various conditions ranging from complex neurological disorders to musculoskeletal diseases. It is an invaluable diagnostic tool that helps in the detection, diagnosis, planning, and monitoring of treatments.