What Is Magnetic Resonance Imaging (MRI), And How Does It Work?
Magnetic Resonance Imaging (MRI) is a structural and functional imaging technique that uses magnetism and radiofrequency (RF) waves to create tomographic (cross-sectional) images. A patient is placed into a scanner that contains a magnet that generates a very strong magnetic field. Atomic nuclei in the body, such as of hydrogen atoms, have a net magnetic moment and act like tiny magnets, aligning themselves with the main magnetic field. RF waves are turned on to knock the nuclear magnetic moments out of alignment. When the RF waves are then turned off, the nuclei realign themselves (i.e., relax) in the direction of the main magnetic field although at differential rates in different tissues. These differential relaxation rates lead to different signal properties of tissues that are detected by an RF coil placed around the patient. Magnetic gradients, controlled linear alterations of the magnetic field over distance in prespecified directions, are utilized to spatially localize the tissue signals so that MR images can be created. The process by which atomic nuclei undergo absorption or emission of RF energy is known as nuclear magnetic resonance (NMR).
When Was MRI Developed?
Isidor Rabi discovered the phenomenon of nuclear magnetic resonance in 1938 and received the Nobel Prize in Physics in 1944. Raymond Damadian discovered that the NMR signals of cancers appear different from those of normal tissues in 1971, proposed the concept of (and filed a patent for) the use of NMR for detecting cancer in the human body in 1972, and was the first to perform a human body MRI scan with the first full-body MRI scanner in 1977. In 1973, Paul Lauterbur produced the first tomographic MR image, and in 1976, Sir Peter Mansfield produced the first tomographic MR image of a human’s finger. Lauterbur and Mansfield received the Nobel Prize in Physiology or Medicine in 2003.
What Are Some Common Clinical Applications Of MRI?
MRI is commonly used to evaluate patients with neoplastic, infectious, and noninfectious inflammatory disorders and as a problem-solving tool to further characterize abnormalities detected on radiography, US, CT, or PET/CT. It is especially useful for evaluation of the brain and spinal cord, breasts, heart and vasculature, abdominal and pelvic organs, and musculoskeletal soft tissue structures including the bone marrow, as it provides excellent soft tissue contrast. Because MRI does not involve the use of ionizing radiation, it is also used during pregnancy and in the pediatric setting.
What Are Some Contraindications To The Use Of MRI?
In general, presence of metallic or electronic objects in the body such as orbital metallic foreign bodies, cerebral aneurysm clips, transvenous pacemakers, implantable cardioverter defibrillators, neurostimulators, and cochlear implants are contraindications for MRI, due to risks of device malfunction, device movement with tissue injury, or device heating with tissue injury. However, some patients with newer MRI-compatible versions of implanted metallic or electronic devices may be able to undergo MRI. Claustrophobia is also a relative contraindication to MRI but can be alleviated by using patient sedation, a wide bore short length scanner, or an open field scanner. Pregnancy is not a contraindication to MRI, but it is a contraindication for use of gadolinium-based contrast material.
What Do I Need To Do To Prepare For An MRI?
The magnetic resonance imaging (MRI) scanner uses strong magnets and radio wave signals that can cause heating or possible movement of some metal objects in your body. This could result in health and safety issues. It could also cause some implanted electronic medical devices to malfunction.
If you have metal-containing objects or implanted medical devices in your body, your healthcare provider needs to know about them before your MRI scan. Certain implanted objects may require additional scheduling arrangements and special instructions. Other items don’t require special instructions but may require an X-ray to check on the exact location of the object before your exam.
Please tell your provider and MRI technologist if you have any of the following:
— Heart pacemaker or defibrillator.
— Electronic or implanted stimulators or devices, including deep brain stimulators, vagus nerve stimulators, bladder stimulators, spine stimulators, neurostimulators and implanted electrodes or wires.
— Metallic joint prostheses.
–Cochlear implant or other ear implants.
–Implanted drug pumps, such as those that pump narcotic/pain medications or drugs to treat spasticity.
— Programmable shunt.
— Aneurysm clips and coils.
— Stents not located in your heart.
— Filters, such as blood clot filters.
— Metal fragments in your body or eye, such as bullets, shrapnel, metal pieces or shavings.
You won’t be able to wear the following devices during your MRI. Please coordinate your MRI appointment with the day you need to change your patch or device.
— Continuous glucose monitor (CGM).
— Insulin pump.
— Medication patches.
In addition, tell your provider if you:
— Are pregnant.
— Are not able to lie on your back for 30 to 60 minutes.
— Have claustrophobia (fear of enclosed or narrow spaces).
Leave all jewelry and other accessories at home or remove them before your MRI scan. Metal and electronic items aren’t allowed in the exam room because they can interfere with the magnetic field of the MRI unit, cause burns or become harmful projectiles. These items include:
— Jewelry, watches, credit cards and hearing aids — all of which can be damaged.
— Pins, metal hair accessories, underwire bras and metal zippers, which can distort MRI images.
— Removable dental work, such as dentures.
— Pens, pocketknives and eyeglasses.
— Body piercings.
— Cell phones, electronic watches and tracking devices.
FAQs.
Q. How long does an MRI scan take?
Depending on the type of exam and the equipment used, the entire exam usually takes 30 to 50 minutes to complete. Your healthcare provider will be able to give you a more exact time range based on the specific reason for your scan.
Q. What is MRI?
MRI stands for Magnetic Resonance Imaging, a non-invasive medical imaging technique used to visualize the internal structures of the body.
Q. How does MRI work?
MRI uses strong magnetic fields and radio waves to create detailed images of the body’s internal structures. It measures the behavior of hydrogen atoms in the body’s tissues.
Q. Is MRI safe?
Yes, MRI is generally considered safe as it does not use ionizing radiation. However, there may be safety concerns for individuals with certain metallic implants or devices.
Q. What can an MRI detect?
MRI can detect a wide range of conditions, including brain tumors, spinal cord injuries, joint problems, soft tissue injuries, and organ abnormalities.
Q. How long does an MRI scan take?
The duration of an MRI scan varies depending on the type of exam and the body part being imaged. It can range from 15 minutes to over an hour.
Q. Is MRI painful?
No, MRI is not painful. However, some people may find it uncomfortable due to the need to remain still inside the machine.
Q. Can I eat before an MRI?
In most cases, you can eat and drink normally before an MRI. However, for certain abdominal scans, you may be asked to fast for a few hours before the exam.
Q. Do I need contrast dye for an MRI?
Contrast dye may be used in some MRI exams to enhance the visibility of certain tissues or blood vessels. Your doctor will determine if contrast is necessary.
Q. Can I have an MRI if I’m pregnant?
MRI is generally considered safe during pregnancy, especially without contrast. However, it’s essential to inform your healthcare provider if you are pregnant or suspect you might be.
Q. Are there any risks associated with MRI contrast dye?
There can be risks associated with contrast dye, including allergic reactions or kidney problems. These risks are rare, and your healthcare team will assess your suitability for contrast.
Q. What should I wear for an MRI?
You should wear comfortable, loose-fitting clothing without metal zippers or buttons. In some cases, you may be asked to wear a hospital gown.
Q. Can I move during an MRI?
It’s crucial to remain as still as possible during an MRI scan to obtain clear images. Any movement can blur the images and may necessitate a repeat scan.
Q. Can I have an MRI if I have claustrophobia?
Some MRI machines are designed to accommodate claustrophobic patients, and sedation may be an option in extreme cases. Discuss your concerns with your healthcare provider.
Q. Are there open MRI machines for people who are claustrophobic?
Yes, open MRI machines offer a more spacious and open environment, which can be more comfortable for claustrophobic individuals.
Q. Can I talk to the MRI technician during the scan?
You will typically have communication with the MRI technician via an intercom system, allowing you to communicate any concerns or discomfort during the scan.
Q. Is there any age limit for getting an MRI?
There is no strict age limit for MRI. It can be performed on individuals of all ages, including infants and the elderly.
Q. Can I bring someone with me into the MRI room?
In most cases, you can have a friend or family member accompany you into the MRI room, but they must adhere to safety guidelines.
Q. What is an MRI with contrast, and why is it used?
An MRI with contrast involves the use of a contrast agent to enhance the visibility of specific tissues, blood vessels, or abnormalities. It’s used when additional information is needed.
Q. How long does it take to receive MRI results?
The time it takes to receive MRI results varies but is typically within a few days. Your healthcare provider will discuss the results with you.
Q. Can I have an MRI if I have metal implants?
It depends on the type of metal implant and its compatibility with MRI. Some implants are MRI-safe, while others may pose risks.
Q. Do I need a referral from a doctor for an MRI?
In many cases, you will need a referral from a healthcare provider to undergo an MRI, as it is often part of a diagnostic process.
Q. Can I have an MRI if I have a pacemaker?
Patients with pacemakers may not be eligible for MRI due to potential risks. However, some newer pacemaker models are MRI-compatible.
Q. What should I do to prepare for an MRI?
Preparation for an MRI varies depending on the type of exam. You may be asked to avoid eating or drinking certain things or to remove metallic items from your body.
Q. Can an MRI detect cancer?
Yes, MRI is a valuable tool for detecting and staging cancer, particularly in soft tissues like the breast, prostate, and brain.
Q. Are there any side effects from an MRI?
There are typically no side effects from the MRI procedure itself. However, some people may experience discomfort from lying still for an extended period.
Q. Can I receive an MRI if I have tattoos?
Tattoos are generally not a problem for MRI. Modern tattoo ink is usually safe in MRI environments.
Q. What is the difference between a closed and open MRI?
Closed MRI machines are more traditional and have a narrow, tube-like structure. Open MRI machines are more spacious and suitable for individuals with claustrophobia.
Q. Can I breastfeed after receiving contrast during an MRI?
It’s generally safe to breastfeed after an MRI with contrast. However, discuss any concerns with your healthcare provider.
Q. How is an MRI different from a CT scan?
An MRI uses magnets and radio waves to create images, while a CT scan uses X-rays. MRI is better for soft tissue imaging, while CT scans excel at visualizing bones and dense tissues.
Q. Can an MRI detect heart problems?
Yes, cardiac MRI is a specialized type of MRI that can assess the structure and function of the heart, helping diagnosis.
BOOK LINK :- Textbook of Radiology for X-ray, CT, MRI, BSc, BRIT and MSc Technicians