A Complete Guide to MRI Scans from a Radiologist
Written for Doctify by Dr Russell Young
Radiologist Dr Russell Young tells us what you can expect when you go into the hospital for an MRI scan.
What are the origins of MRI scanners?
In 1937 nuclear magnetic resonance was discovered and this phenomenon was developed into magnetic resonance imaging (MRI) in 1971. The first MRI scanner was built in 1977, with rapid improvements in the imaging of soft tissues than previously seen with x-rays.
What is an MRI scan?
An MRI scanner is a tube surrounded by a large circular magnet, and the patient is placed on a moveable bed that is inserted inside the tube. The strong magnetic field aligns the protons of hydrogen atoms in the body, which are then exposed to radio waves. This spins the protons, which produce a faint signal that is detected by a receiver. This information is processed by a computer, and a detailed image is produced. For some procedures, contrast agents (gadolinium) are used to increase the accuracy of the images.
When should an MRI scan be used?
MRI scans are very good for assessing orthopaedic, sports, neurological, vascular and other conditions. For example, assessing the brain, spinal cord, intervertebral discs, bone, muscles, joints, soft tissues, and blood vessels. MRI scans are better than ultrasound for imaging larger and deeper structures
As there is no radiation involved, MRI scans are very safe and can be widely used in research, for example, screening for chronic traumatic brain injury in contact sports, measuring the brain activity of video gamers, meditating monks, and jazz musicians.
Do you have any facts and figures about the machines themselves?
In 1882, Nikola Tesla discovered the rotating magnetic field, and his name is used to calibrate its strength. A stronger magnetic field increases the number of radio signals emitted from atoms in the body. Most MRI scanners use a 1.5 Tesla strength magnet, but now some use three Tesla magnets, which can give higher quality images or reduce scanning times. Cobalt Health operates the only 3 Tesla mobile MRI scanner in Europe.
The magnetic field of an MRI scanner is up to 4000 times stronger than the earth’s magnetic field. Using liquid helium, the magnet is cooled close to absolute zero, to enable superconducting. At this temperature, the MRI scanner will always be working, but in an emergency, the liquid helium can be released, turning off the magnetic field within a few seconds. This “quench” is a big deal, as the scanner will be offline for a week or more, the magnet can be damaged, and it will cost at least £30,000 to replace the liquid helium!
Every year about 20 million patients now get an MRI scan, and over 1 billion MRI scans have been performed in total since the 1970s.
What are the risks of having an MRI scan?
MRI scans are painless and one of the safest medical procedures currently available, as there is no radiation exposure. There are no known harmful effects from the magnetic field.
However, patients who may have any metallic material within their body must notify their doctor and the radiographers before the scan. Metallic materials can significantly distort the images obtained by the MRI scanner.
What are the contra-indications for an MRI scan?
The powerful magnet may affect any item or medical device that contains iron. Any loose metal object may cause damage or injury if it gets pulled rapidly toward the strong magnet.
Patients who have metallic fragments or clips in or around the eyes, artificial heart valves, metallic ear implants, neurostimulators, implantable cardiac defibrillators, arterial clips, aneurysm clips, programmable hydrocephalus shunts, and chemotherapy or insulin pumps should not enter the MRI scanner room, as these items may move or break. Some pacemakers are now MRI safe, but you should always check first with your cardiologist.
What is it like having an MRI scan?
During the scan, you will lie on a bed, which will move into the scanner either head first or feet first, depending on the scan. You are given headphones for listening to music, and to reduce the noise from the scanner. You can also hear instructions from the MRI radiographer, who will keep an eye on you and you can contact them too.
Sometimes the scanner can feel enclosed, but now more spacious “open” and “wide bore” MRI scanners are available, with ambient themes viewed from a mirror above. Sometimes patients prefer “wide bore” scanners, as there is more space above your head. Relaxation and stress relief techniques can also work well, and mild sedation is also available if needed. For more information on “open” MRI scanners, and on relaxation techniques, visit http://www.cotswolddiagnosticclinic.co.uk/open-mri.
A scan usually lasts between 15 and 60 minutes, and there are segments of up to 6 minutes, when you will need to keep reasonably still, to help get the best images possible.
What are some recent developments in MRI?
Functional MRI can be used to show the location of mental processes in the brain, and how the brain responds to outside events.
Smaller more portable MRI scanners are in development, mostly for imaging the limbs. Multiband imaging is also in development, which significantly reduces scanning times.
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