What is an MRI (magnetic resonance imaging) scan?
This scan is performed with magnetism. A very large magnet aligns and realigns the molecules of the body and a computer then interprets the signals that are received and turns them into images. These images are really very clear and all the tissues in the body can be seen in great detail. As with CT scans, contrast can be used to give greater detail to blood vessels and also to indicate inflammation and cancer.
Since this technology works with a large magnet, patients who have certain metal implants cannot undergo this test.
When you undergo this test you will be placed in a machine that has a narrow tunnel and claustrophobic patients frequently need some form of sedation for this procedure. The machine makes quite a lot of metallic banging and clattering noises and you will usually be offered earphones to block out the noise and in some institutions soft music is piped through these.
Several types of pictures are taken. The most frequently used images are T1-weighted and T2-weighted scans. This is a description of the different ways that the scan manipulates the magnetic field of the tissue that is being examined. It is not important to know anything about the difference between these different types of MRI pictures that are taken.
It is, however, useful to know that there are several cuts (planes in which the body is examined) that are done. The most frequently used cuts are the sagittal images. These are images that are taken of your body from a side-on view. They are very useful in giving an overview of the spine in its entirety.
The images that are more important for depicting the finer detail of the pathology are the axial cuts or planes that are taken straight through the spine and are like slices taken of a sausage. The nerves that are leaving through the foramina are seen side-on and look like little worms as they leave the spinal canal. This way your specialist can see a lot of detail about the nerves and any compression of the nerves.
There are other cuts as well, such as coronal cuts where the body is viewed from front to back. Both coronal cuts and sagittal cuts are useful for revealing the alignment of the spine. The coronal cuts demonstrate scoliosis well. Scoliosis is where the spine is bent (has an abnormal curve) when viewed from the front. The normal curve of the spine can be evaluated on the sagittal views.
When the curve is more pronounced to the front, it is called kyphosis and when it is more curved towards the back, it is called lordosis. The coronal cuts are also useful for evaluating the nerve roots as they leave the spinal canal through the foramina and can demonstrate extraforaminal (outside of the foramen of the spinal canal) disc compression of the spinal nerves.
This is a picture of an MRI scan machine. The section that generates the magnetic field is a tubular structure and patients are moved into this cave-like tube on the table, which has an electric motor. The room is devoid of loose metallic objects, as these would become airborne when the machine is activated because of the magnetic field, which is extremely powerful. Objects such as the magnetic strips on bank cards are rendered useless by the machine, so make sure that you leave these outside the room.
These machines tend to be quite noisy on the inside with all manner of tapping and banging noises. These are perfectly normal and you should not be alarmed by them. Some institutions will have earphones with music available to reduce the noise.