The images made by MRI scan is different from that of a Ultrasound scan, CT scan or X-ray in a way that it provides clearer images of tissues like tendons, ligaments, fat and cartilages that are not clearly visible with the help of other scans. Sometimes a contrast medium that is magnetically active is used during a MRI scan to highlight more clearly the internal structures and abnormalities.
A brief history of MRI scan
The works of many notable scientists laid the foundation of MRI scan technology and helped in the perfection of MRI scan technology to be used as a medical imaging machine.
The MRI scan technology for medical imaging was perfected in the 1970s. Peter Mansfield and Paul Lauterbur shared the 2003 Nobel Prize in Physiology or Medicine for their contribution on the MRI (Magnetic Resonance Imaging).
The technology was perfected based on the initial works numerous scientist like Isidor Isaac Rabi who was awarded the Nobel Prize in Physics in 1944.
I think physicists are the Peter Pans of the human race. They never grow up and they keep their curiosity.
- Isidor Isaac Rabi
The contributions made in 1946 by Felix Bloch and Edward Purcell were also important developments in this direction. They were awarded the 1952 Nobel Prize in Physics for their independent works that lead to the discovery of magnetic resonance phenomena.
It is also important to note the works of Raymond Damadian who demonstrated that tumors and normal tissues could be differentiated using nuclear magnetic relaxation times.
How does a MRI scan work?
The technology behind the working principles of a MRI machine is very complex. Let’s try to quickly simplify this process to get a quick grasp of the inner working of the machine.
MRI scanners produces a strong magnetic field inside the "eye" or tunnel of the donut shaped scanner using three differently aligned sources of magnetic field that works at various phases of the machine operation
A patient is placed on a bed that can be moved and aligned inside the tunnel of the scanner during the scanning process. The machine produces sounds of varying intensity while it goes through its various phases of examination process. Patients may be offered Ear plugs or headphones to help them relax and keep the machine noise out. A patient may have to wear a special type of "helmet" (head coil) if the brain is to be scanned. This helmet does not touch the patient and is fixed over the head. It helps in producing more refined images of the brain.
When the machine is working, it creates a strong and steady magnetic field using the first set of magnets and by placing the human body inside this field, it activates the “biological magnets” inside the body by acting on the protons in the hydrogen molecule inside the water molecules.
These protons have a normal random orientation inside the body under normal conditions. When inside the steady magnetic field of a MRI scanner these protons are aligned in either north or south position.
The second set of coils when switched on produces an electromagnetic pulse (RF pulse). At the correct frequency the RF pulse causes the water molecules to change its orientation after it gains enough energy from the RF pulse. Once the second source is switched off the molecules return to its previous state quickly. In this process the molecule emits a small amount of energy that is registered by the antenna inside the machine. By repeating this process the machine makes the characteristic knocking sound while the machine is working. The coil which creates the magnetic field when electricity is passed through it vibrates and this causes the buzzing sound the machine produces while it’s working.
The rate at which the energy is released by the water molecules when they return to their pre RF pulse stimulated state is unique for different types of tissues in the human body. This difference in rate is the key for creating an image that can differentiated between various body tissues.
There is also a third source of magnetic field and this source produces a gradient of magnetic field to determine from where the energy was emitted, thus help the computer to figure of how the image should be assembled.
The data received is transferred to computers that processes the information and create a visual image on the computer screen of the area being examined.
MRI scanner’s power is rated using a tesla unit like 1 T, 1.5T, 3T which signifies the strength of the magnetic field inside the MRI scanner. The stronger the magnetic field inside the MRI scanner, the more better images it produces.
What are the most common uses of MRI scan?
- MRI scan are used as a very efficient detection tool for diagnosing certain diseases inside the body when other medical imagining technologies like ultrasound, CT scan and x-ray fail to provide enough conclusive results.
- MRI scanners are very popular with Neurosurgeons (brain surgeons) due to the ability to of the machine to produce images that can distinguish between various soft tissues, structures in the brain. Abnormalities of the brain and conditions like stroke, tumors, and swellings can be easily detected
- It is also good in checking the integrity of the spinal cord after an accident or in cases of persistent back pains.
- MRI scans can help in assessing the general health of the cardiovascular system. It is good at detecting structural abnormalities of the heart and blood vessels.
- Orthopedic surgeons (bone surgeons) due to the ability to distinguish between various connective tissues in the joints and other parts.
- Organs in the abdominal area and below can be evaluated for abnormalities. It can easily distinguish between various organs and tissues in the area.
What are the advantages of MRI scanner?
- It is a painless and noninvasive medical imaging technique that can produce some very detailed internal images of the human body.
- MRI scanners use magnets and radio waves and it is considered as a much safer alternative in comparison to CT scans and X-rays that emit electromagnetic radiation.
- It can be safely used for pregnant women and small children without risk of being exposed to radiation.
What are the disadvantages of MRI scanner?
- Some people may find it bit uneasy inside the internal tunnel of the machine due to their fear (Claustrophobia) of confined areas. The good news is that the scanners are open in both ends. The rooms are usually well lit and there is always some medical staff near the patient. A panic button is also offered to the patient to stop the machine in case of feeling uneasy or panicking during the examination process.
- People with certain older pacemakers and other types of metal implants cannot undergo a MRI scan because of the effect of magnets on metal.
- MRI scanners are comparatively much slower than CT scanners at producing the images. The whole test may take anywhere from 10 minutes to over 2 hours. It’s important to remain perfectly still during the scanning process for the machine to produce perfectly clear pictures. Fortunately, the scanning process is broken down into many smaller sections of few minutes of scanning accompanied with a pause.
- In some cases, an contrast medium is used and there is slight risk of having an allergic reaction to the contrast medium
- People with tattoos or permanent eyeliner may also experience some allergic reaction during the MRI scan. The type of dye used in these kinds of cosmetic procedures play a major role in such indents.