What is MRI?
MRI stands for magnetic resonance imaging. It is a noninvasive test which measures blood flow through the brain using radio waves. The technique uses powerful magnets to create strong electric currents that are then reflected back from the brain. These currents are picked up by tiny coils placed all over the head and body, allowing them to pick up signals from specific areas of interest (areas of high or low electrical activity). These signals are then compared with those collected during normal brain function.
The results of the test can be very useful in diagnosing various conditions such as epilepsy, Alzheimer’s disease, multiple sclerosis, Parkinson’s disease and even depression. MRI scans have been shown to provide accurate results when performed correctly. They show changes in blood flow and oxygen levels within different parts of the brain. Changes in these areas may indicate problems ranging from mild cognitive impairment to dementia.
How Can MRI Detect Brain Problems?
The most common type of MRI used for detecting brain abnormalities is called diffusion tensor imaging (DTI). DTI is a noninvasive technique that measures how water molecules move through the brain. Water molecules carry chemical messages between cells in the brain. A change in water movement indicates a problem with cell communication, either due to damage or aging.
When compared to other types of brain scans, such as a CT scan or a PET scan, an MRI is able to detect changes over a longer period of time. This makes it a good tool for detecting brain abnormalities caused by diseases such as Alzheimer’s or other forms of dementia, tumors, and any other damage to different parts of the brain.
What is MRA?
MRA stands for magnetic resonance angiography. It is a specialized type of MRI that is used to detect potential problems in the blood vessels of the brain. These vessels supply oxygen and nutrients to different areas of the brain, making them very important for proper brain functioning.
The test works by injecting a harmless substance (contrast agent) into a blood vessel in the arm. The contrast agent contains water and radioisotopes (atoms that give off radiation). The contrast agent makes certain blood vessels show up brighter on the scan.
The injection is very quick and usually not very painful. Patients may experience a brief sensation of heat at the site of injection. A neurologist will perform the test in an MRI machine within a clinic or hospital. The entire test takes about 30-40 minutes per scan.
Some people may be allergic to the contrast agent, so your doctor will take certain precautions before the test. These may include testing you for allergies and performing a skin test with small amounts of the agent. A scan without the agent cannot provide as much detail, so it is important to receive the contrast injection for this type of MRI.
There are some risks with any type of medical test. These risks may be very low, but it is still important to be aware of them before proceeding. Your doctor will go over all the potential risks before performing the test.
The contrast injection may cause a brief burning or stinging sensation at the site of injection. Some people may also experience a small rash or itching. These symptoms can usually be treated with medication.
For some people, the contrast may cause nausea, vomiting, or an allergic reaction. These symptoms can usually be treated and are not life-threatening. It is also possible for the contrast to spread to other parts of the body and cause more serious reactions. If you have any reason to believe you may have an allergic reaction to the contrast you should tell your doctor before receiving the injection.
Some people with specific types of metal implants, such as an artificial joint, may not be able to have the test. Your doctor will be able to tell you if you have any issues that might prevent you from having an MRI.
In some cases, the contrast agent used for MRA may cause a small amount of kidney damage. This only happens in a very small percentage of cases and is usually temporary. If you experience any signs of kidney problems after the test, such as pain or a change in the amount of urine, let your doctor know as soon as possible.
MRI or MRA may be safe for most people, but it is always a good idea to speak with your physician if you have any concerns.
What to Expect
When you arrive at the location of your test, a technician will ask you to change into a gown and explain the procedures before beginning. You will then meet with a neurologist or other physician who will go over the details of the test and ask you some questions. They may ask why you are having the test done, whether you have any metal implants or other issues that may prevent you from having an MRI, etc.
After this, a technician will place a small mark on your leg to show the position for the scan. They will then take you to the MRI machine and ask you to lie down on the table inside. The technician will position your body and hold you in place while the scan is being completed.
During the scan, you may hear loud thumping or clanking noises coming from the machine. These are normal and should not be cause for concern. The test itself only takes a few minutes and is usually completely painless. After the scan is completed, you can get dressed and leave.
MRI results are available right away, but most people will tell you the results of the scan during a follow-up visit a few days after your appointment.
Sources & references used in this article:
MRI and MRA for diagnosis and follow-up of cerebral venous thrombosis (CVT) by F Lafitte, M Boukobza, JP Guichard, C Hoeffel… – Clinical radiology, 1997 – Elsevier
Thoracic outlet syndrome in a throwing athlete diagnosed with MRI and MRA by MD Esposito, JA Arrington… – Journal of Magnetic …, 1997 – Wiley Online Library
MRI-and MRA-guided therapy of carotid and vertebral artery dissections by A Jacobs, H Lanfermann, M Neveling, B Szelies… – Journal of the …, 1997 – Elsevier
MRI and MRA for evaluation of dissection of craniocerebral arteries: lessons from the medical literature by JM Provenzale – Emergency radiology, 2009 – Springer
Cerebral venous thrombosis: role of CT, MRI and MRA in the emergency setting by L Rizzo, SG Crasto, R Rudà, G Gallo, E Tola… – La radiologia …, 2010 – Springer