Brain MRI – is a non-invasive diagnostic method that uses a strong magnetic field to produce very detailed images of the brain and surrounding structures. It’s the method of choice for imaging the brain which doesn’t use ionizing radiation, and if contrast agents are needed, they are less allergenic than contrasts used in other methods.
What you need to know before the exam
It is extremely important to tell your doctor about any health problems, recent surgeries, known allergies, and if you’re pregnant or planning a pregnancy. The last point is important because the FDA has not updated the status of fetal MRI risk from “has not yet been established.” Studies on animal models have shown that teratogenic (something that may damage the embryo or fetus) effects are present especially in early-term pregnancies. MRI exams for pregnant women are generally not recommended. Tell the technician about any implants, devices (like most pacemakers), or metal in your body. Leaving your jewelry at home isn’t necessary, but you will be asked to take it off before beginning, as any metal will interfere with the magnetic field.
Closed or open?
If the MRI machine is a closed type it will look like a tunnel with a circular opening. This type of machine may cause some discomfort for people who are claustrophobic or anxious. There are also obvious disadvantages to these types of machines for kids that are full of energy or may find it scary. If you feel you or your loved one will feel anxious during the procedure, you may ask for a mild sedative before.
There are also open MRI machines, which allow for free vision of your surroundings and won’t make you feel like you’re in a tomb. These types of machines are kid-friendly, because parents can sit next to their child while the exam is going on.
Get up, stand up or sit
MRI manufacturers have gone a step further in patient comfort. They have recently started developing upright and seated MRI machines. These types of exams are the perfect alternative for patients who find conventional machines unbearable. Although there won’t be much difference in brain images, images of the spinal cord may differ. This is explained by simple mechanics. In a seated or standing position, the intervertebral discs and soft tissues become weight-bearing which may or may not coincide with a prone position on MRI images.
Is MRI contrast necessary?
For certain brain MRI scans a contrast dye may be given through an IV. It helps highlight areas for a clearer image. This is where telling the doctor or technician about any known illnesses, especially kidney disease is of utmost importance because the contrast is excreted by the kidneys.
What else should I know about MRI?
The MRI technician monitors you from a separate room on a computer and communication with the tech is accomplished by an intercom system. The exam can take from 30 to 60 minutes or longer, depending on the purpose.
Remember that MRI doesn’t cause any side effects and is painless. Although the machine normally makes a lot of noise, some machines have active and/or passive noise reduction elements in place so that your experience isn’t so nerve-racking.
What can a brain MRI show?
MRI is the method of choice for scanning the brain and surrounding structures, and can be used to monitor and diagnose the following:
- Brain tumors
- Bleeding in the brain (traumas)
- Birth defects
- Brain infections
- Hydrocephalus (accumulation of fluid in the brain)
- Hormonal disorders (like Cushing’s syndrome)
- Chronic conditions (like multiple sclerosis)
- Disorders of the eye and inner ear
- Vascular problems (like aneurysms (localized expansion of a blood vessel), arterial occlusions (blockages) and venous thrombosis (blood clot))
In this case a magnetic resonance angiography (MRA) may be performed to evaluate blood vessels. Your doctor may send you for a brain MRI exam if you are having abnormal:
- Hearing, vision or speech problems
- Headaches accompanied by certain symptoms (for example if a headache gets progressively worse over the course of days or weeks)
- Muscle weakness or numbness and tingling
- Changes in thinking or behavior
How is a brain MRI performed?
To perform a brain MRI, you will be asked to first lie down on the table. The technician will then help you get in position and fasten a coil (a device that transmits and receives radio waves) around the head. If a contrast dye is required, it will be administered through an IV catheter before the exam. Allergic reactions to the contrast are possible, but rarely happen. The table will then be moved so that your head is in the field of the magnet. The exam usually includes running different sequences to highlight different areas of the brain.
Modern MRI facilities offer patients earplugs to cut down on noise or headphones with music to help pass the time. If you’re referred to a facility with a seated or standing MRI, you may even have the possibility of watching TV! You can tell when the exam has begun by either the technician’s cue or by a loud thumping or banging sound, which is normal.
What can be performed instead of an MRI?
A CT (computed tomography) scan is the preferred method in cases of acute trauma, suspected brain bleeds (<48 hours), early stroke symptoms and bone disorders. Other methods include PET (positron emission tomography) scan and skull X-ray.
What are the limitations of brain MRI?
MRI is well known for producing high-quality, high-resolution images of the brain, but it still has certain drawbacks. One of the most important is the need to lie still for an extended period of time. Clear images can only be received if you remain absolutely still during the exam. Overweight patients may not fit in the opening of some MRI machines or may exceed the table weight limit. Anything metallic will most definitely interfere with the magnetic field, thus causing blurry images, so patients with certain implants will not be allowed to get the exam.
By Dr. Yuriy Sarkisov, BiMedis staff writer
Pictures courtesy of Dr Frank Gaillard, Dr Mohammad A. ElBeialy, Radiopaedia.org, rID: 9878, 39578
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