MRI

Q: Can you give some information on MRI scans?

Krishna: The full form of MRI is Magnetic Resonance Imaging. MRI is also known as NMRI (Nuclear Magnetic Resonance Imaging) or MRT (Magnetic Resonance Tomography).

The MRI scan is a medical imaging procedure that uses a magnetic field and radio waves to take pictures of your body's interior. It is used to investigate or diagnose conditions that affect soft tissue such as tumours or brain disorders.

MRI is a non-invasive imaging technology that produces three dimensional detailed anatomical images. It is often used for disease detection, diagnosis, and treatment monitoring. It is based on sophisticated technology that excites and detects the change in the direction of the rotational axis of protons found in the water that makes up living tissues.

MRIs employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. When a radiofrequency current is then pulsed through the patient, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field. When the radiofrequency field is turned off, the MRI sensors are able to detect the energy released as the protons realign with the magnetic field. The time it takes for the protons to realign with the magnetic field, as well as the amount of energy released, changes depending on the environment and the chemical nature of the molecules. Physicians are able to tell the difference between various types of tissues based on these magnetic properties (2).

There are a variety of different MRIs available. The most common MRIs include (1):

• Functional MRI A functional MRI (FMR) tests brain activity. The images indicate whether there are issues present that may predict or diagnose a stroke. A doctor also orders an FMR for brain mapping. Brain mapping is essential for brain surgery or for detecting epilepsy or tumors.
• Cardiac MRI A cardiac MRI produces detailed images of the heart. Your doctor will call for a cardiac MRI to diagnose your condition so that a treatment plan can be devised. In addition to the heart, the blood vessels surrounding it are also examined. The information gathered is used to determine heart function.
• MRI of the Breast Patients who are at high risk for breast cancer are candidates for an MRI. While it is a non-invasive procedure, doctors may order an MRI-guided needle biopsy of the breast. The MRI will detect breast cancer and provide information on progression and location of the tumor.
• Magnetic Resonance Venography Magnetic Resonance Venography (MRV) is combined with contrast dye to produce clear images of internal organs and other structures inside the body. The dye highlights the veins, so that they appear translucent and show up well in images. Magnetic Resonance Angiography (MRA) is similar to an MRV. It combines images with an intravenous contrast dye, but focuses on blood vessels instead of veins. The physician will be able to evaluate the blood vessels that run through the heart and soft tissues in the body.
• Non-Contrast MRA Some patients may be unable to tolerate contrast dye. This is especially true for patients who have renal problems. Historically, these patients could not get MRAs performed. However, it is now possible for all patients to get MRAs using advanced diagnostic technologies that eliminate the need for dye without compromising on clear images.
• Open, High-Field MRI Being closed-in is a fear that some patients have in regards to an MRI exam. Patients who are claustrophobic don’t like the design of an MRI machine that is enclosed. Other patients may be obese or suffer from post-traumatic stress syndrome, preventing them from feeling comfortable in the machine. For these patients, open, high-field MRIs are a better choice.

Drawbacks and Precautions to be taken while taking MRI scans (2)

When having an MRI scan, the following should be taken into consideration:

• People with implants, particularly those containing iron, — pacemakers, vagus nerve stimulators, implantable cardioverter- defibrillators, loop recorders, insulin pumps, cochlear implants, deep brain stimulators, and capsules from capsule endoscopy should not enter an MRI machine.
• Noise—loud noise commonly referred to as clicking and beeping, as well as sound intensity up to 120 decibels in certain MR scanners, may require special ear protection.
• Nerve Stimulation—a twitching sensation sometimes results from the rapidly switched fields in the MRI.
• Contrast agents—patients with severe renal failure who require dialysis may risk a rare but serious illness called nephrogenic systemic fibrosis that may be linked to the use of certain gadolinium-containing agents, such as gadodiamide and others. Although a causal link has not been established, current guidelines in the United States recommend that dialysis patients should only receive gadolinium agents when essential, and that dialysis should be performed as soon as possible after the scan to remove the agent from the body promptly.
• Pregnancy—while no effects have been demonstrated on the fetus, it is recommended that MRI scans be avoided as a precaution especially in the first trimester of pregnancy when the fetus’ organs are being formed and contrast agents, if used, could enter the fetal bloodstream.

Claustrophobia—people with even mild claustrophobia may find it difficult to tolerate long scan times inside the machine. Familiarization with the machine and process, as well as visualization techniques, sedation, and anesthesia provide patients with mechanisms to overcome their discomfort. Additional coping mechanisms include listening to music or watching a video or movie, closing or covering the eyes, and holding a panic button. The open MRI is a machine that is open on the sides rather than a tube closed at one end, so it does not fully surround the patient. It was developed to accommodate the needs of patients who are uncomfortable with the narrow tunnel and noises of the traditional MRI and for patients whose size or weight make the traditional MRI impractical. Newer open MRI technology provides high quality images for many but not all types of examinations.

Even though there are a few draw backs, MRI scan is completely safe for normal people.

Footnotes:

1. Different Types of MRI’s | Independent Imaging
2. Magnetic Resonance Imaging (MRI)