Find out more about MRI with Cobalt
What is an MRI scan?
Magnetic Resonance Imaging (MRI) produces high resolution pictures of any part of the body in any direction. The scanner uses a high-strength magnet, radio waves and computers to generate images. MRI does not use X-rays so it can be used repeatedly. It is considered to be a very safe way of producing images that can diagnose medical conditions.
- For a more scientific explanation click here
If you are interested in the mechanism behind MRI, it is a fairly complex concept, but essentially it relies on the fact that a human body contains a lot of hydrogen. About half of your body weight is due to the water content of your cells - slightly less in women and rather more in men. Water contains hydrogen and oxygen atoms and as a result approximately 62% of your body is made up from hydrogen atoms.
The importance of a hydrogen atom in MRI imaging is the fact that it is a tiny single particle which has its own microscopic magnetic field. When you are positioned for your scan, these magnetic fields naturally align themselves to the magnet inside the scanner. You will not feel anything because the human body is not sensitive to magnetic fields of this magnitude, so you can lie back and relax. Interestingly, even when you are keeping still, the magnetic fields of your atoms are in constant motion - rather than just pointing in a particular direction they wobble about! If you have ever seen a spinning top or gyroscope you will be able to picture this very well. A spinning top rotates very quickly, but in addition to this you will notice that it wobbles slowly around on its own axis in a circular path. In the case of your hydrogen atoms, the speed of wobble can be calculated according to the field strength used by the system.
The second part of the process involves the radio waves mentioned earlier. Every scanner has a built-in radio transmitter that is designed to "broadcast" radio waves at exactly the right frequency to match the wobbling magnetic fields of the hydrogen atoms. This is where the term "resonance" comes in. A great explanation for what happens is to imagine a musical tuning fork. If you have ever used a tuning fork you will know that when you strike it against something it vibrates at a certain frequency. This is the exact frequency required to tune your musical instrument. An interesting thing happens when you have two tuning forks of the same size. If you hold the vibrating fork close to the other - they start to vibrate in unison. This transfer of energy is defined as "resonance".
The scanner broadcasts a radio wave at the same frequency as the wobbling magnetic fields of your hydrogen atoms and transfers a small amount of energy to them. The amount of energy is fairly small and carefully calculated by the system for your personal body size (weight), so you should feel nothing. You may feel a little warm, but this is quite normal.
The final part of the process is what happens after the radio waves are momentarily switched off. The hydrogen atoms lose the energy that they have been given, and by placing a radio antenna close to the part of the body being examined the scanner can detect a very weak signal created by the billions of atoms inside the area being scanned. The receiver coils used don't look like radio aerials, in fact they are specially configured to fit the part of the body being examined. They come in all shapes and sizes, cylinder shaped for around the knee, cup-shaped to fit over the shoulder wrap-around designs for imaging the abdomen and long flat receivers that are built into the patient couch for imaging the spine.
MRI scanners are surprisingly noisy, some being louder than others. The sounds range from loud knocking to a rhythmic vibration during the acquisition of your images. This is simply due to the way the system works and is nothing to be alarmed about. The noise level is exactly equivalent to that experienced in an aircraft cabin during a flight - so just like on a plane you will be offered ear defenders for your comfort. Some scanners also offer music via headphones during the procedure. Don't be tempted to tap your feet along with the music - during your examination you will need to keep nice and still - just like when you have a photo taken. If you move about the images will be blurred and will lose their diagnostic value.
3.0 Tesla MRI
We have three 3.0 Tesla MRI Scanners in full time clinical use for patients. With a shorter bore and flared open ends it offers exceptional comfort and greatly reduces anxiety or claustrophobia. The majority of scanners in the UK are 1.5 Tesla (strength of the magnet used) a 3.0 Tesla MRI scanner uses a more powerful magnet which results in images of a higher quality. This means we can demonstrate and evaluate finer structures and vessels. Joint surfaces, cartilage, ligaments and muscles are seen in greater detail. Our two mobile 3.0 Tesla MRI scanners are still the first of their type in Europe.
We provide mobile MRI services to hospital sites around the country including Europe's first 3.0 Tesla mobile MRI scanner. This makes MRI accessible locally to many patients. The current clinical standard, our mobile 1.5 Tesla MRI scanners have short bores that are flared open at both ends. These scanners are comfortable and provide excellent image quality. If you are interested in hiring a mobile MRI unit from Cobalt please click here for more information.