By Marcello Cherchi, MD PhD
For patients
Here are answers to some of the most common questions about magnetic resonance imaging (MRI).
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What is this test? |
Magnetic resonance imaging (MRI) is a way of taking a special picture of the inside of the body. |
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What is this test looking for? |
This test is good at taking pictures of soft parts of the body. It is not so good at taking pictures of bones. |
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Is this test experimental or investigational? |
This test is approved by the Food and Drug Administration. It is neither experimental nor investigational. |
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What happens during this test? |
During this test you are usually lying on a table that slowly slides in and out of a donut-shaped machine. In some cases the radiology technician will inject a special dye into your veins during the test. |
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Is this test uncomfortable? |
The test does not hurt. The MRI machine is very noisy. |
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How long does this test take? |
The test takes about an hour. |
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Do I have to prepare for this test? |
You should not be wearing any metal objects. If you have any metal or devices inside your body, the radiology doctor will need to make sure that it is safe for you to have an MRI. |
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Are there any special instructions for what to do after the test? |
There are no special instructions for what to do after this test. |
For clinicians
Overview
Magnetic resonance imaging (MRI) is an excellent imaging modality for studying the anatomy and structure of soft tissues, including those of the nervous system. This can be especially helpful for certain disorders in otoneurology and neuro-otology. A common protocol is to check MRI of the brain and internal auditory canals without and with intravenous gadolinium contrast. The test is subject to artifact from metals. Contraindications include some metals and some implanted medical devices.
Introduction
There are a number of diseases in otoneurology and neuro-otology for which imaging of the soft tissues of the brain and internal auditory canals is helpful (Bulakbasi and Pabuscu 2007). MRI is currently the diagnostic modality of choice for this.
Equipment needed
MRI scanners are usually housed in a hospital radiology service. Some clinics also have MRI scanners.
How to perform the test
The specific protocol for an MRI depends on the differential diagnosis being considered.
When tumors are being considered — such as a vestibular schwannoma, intra-labyrinthine schwannoma, cerebellopontine angle meningioma, brainstem glioma — the study should be performed with and without intravenous gadolinium contrast. The most common imaging protocol used for otoneurology patients is probably MRI of the brain and internal auditory canals without and with intravenous gadolinium contrast.
When demyelinating disease is being considered, it is helpful to us a “multiple sclerosis” protocol, which often includes T2 sagittal and FLAIR sequences.
Literature has begun to explore whether MRI is helpful in the diagnosis of superior semicircular canal dehiscence (Beyazal Celiker et al. 2018), but most practitioners still rely on high resolution temporal bone CT for this purpose.
What this test assesses
MRI is an excellent tool for evaluating neural structures, which are soft tissues.
MRI is less useful for assessing bony structures.
How to interpret the test results
MRI of the brain and internal auditory canals is interpreted by a neuroradiologist.
Limitations
In order to obtain MRI images that are of good quality it is necessary for the patient to remain still for some time — typically 45 – 60 minutes.
Agitated patients often cannot perform this test because they cannot remain sufficiently still for this long.
Patients who are claustrophobic may not be able to tolerate this test. In some cases, sedation may make it possible, but this introduces additional logistical complexity.
MRI is subject to metal artifact, such as from dental fillings and braces.
Contraindications
Patients who have certain metals or medical devices implanted in their body cannot undergo MRI. The medical devices in question usually include various joint prosthesis, mechanical cardiac prosthetic valves, cardiac pacemakers, cardiac defibrillators, neural stimulators, and others. The device manufacturer should provide documentation to the radiology service of whether their device is compatible with MRI.
For some devices, such as cardiac pacemakers and defibrillators, it may be possible to turn the device off temporarily in order to undergo MRI. The device manufacturer should provide documentation to the radiology service of whether this is possible, and how to do it.
When is the test indicated
The indication for imaging depends on the differential diagnosis under consideration.
Diseases that may be diagnosed by this test
MRI is a very useful tool to study anatomical structure of soft tissues. It can be helpful in the diagnosis of a number of diseases in otoneurology and neuro-otology.
References
Beyazal Celiker F, Ozgur A, Celiker M, Beyazal M, Turan A, Terzi S, Inecikli MF (2018) The Efficacy of Magnetic Resonance Imaging for the Diagnosis of Superior Semicircular Canal Dehiscence. J Int Adv Otol 14: 68-71. doi: 10.5152/iao.2017.4103
Bulakbasi N, Pabuscu Y (2007) Neuro-otologic applications of MRI. Diagn Interv Radiol 13: 109-20.
