Magnetic Resonance Imaging (MRI)

August 8, 2011

Magnetic Resonance Imaging (MRI) is a safe and non-invasive scanning technique. Instead of using X-rays, MRI is based on nuclear magnetic resonance. This means all atoms have nuclei with their own resonant frequency. If you disturb them, they sing like tuning forks.

The different structural components of the brain have atoms with nuclei that have their own unique song. The MRI scan sends a high frequency alternating magnetic field through the brain via electromagnets surrounding the brain, thereby disturbing the various nuclei. The magnetic sensors in the scanner pick up the activity of the nuclei.

A computer then generates a two- or three-dimensional image of the brain. This detailed picture of brain structures (not brain functions) helps physicians locate possible causes of seizures and identify areas that may generate seizures. No X-rays or radioactive materials are used. As such, this procedure is not known to be harmful.

MRI offers doctors the best chance of finding the source of seizures. Because epilepsy can arise from scar tissue in the brain, MRI can show scar tissue and allow doctors to determine the nature of it. The images produced from MRI are extremely precise. The information provided by MRI is valuable in the diagnosis and treatment of individuals with epilepsy and to determine whether surgery would be beneficial.

Before an MRIExpand Before an MRI Section

  • Prior to the test, your child should eat and drink normally unless instructed otherwise by the doctor.
  • If your infant or child will be taking a sedative, s/he should not eat or drink for approximately four  hours prior to the exam.
  • Your child should take all prescribed medication(s) as usual.
  • To gain the most cooperation from your child, it is best if s/he is tired or hungry.
    • Keep your child up late the night before the MRI. Do not let him/her nap prior to the examination.
    • Bring a bottle to feed your infant upon arrival of the examination.
  • It will be easier for your child to relax during the exam if you refrain from giving him/her too much liquid, especially caffeinated drinks.
  • Dress your child in loose, comfortable clothing.
  • All jewellery, hairpins, glasses, hearing aids, certain dental work or any metal objects should be removed before the examination. Metals can cause a bright or blank spot on the images.
  • If your child is claustrophobic (fear of closed-in spaces), you should inform the doctor before taking the test.
    • Some children who are not usually claustrophobic may become anxious inside an MRI machine. In this case, you should talk to the doctor and ask about appropriate medication.

During an MRIExpand During an MRI Section

  • The technologist will ask you about your child’s medical history.
  • The technologist will help your child to lie down on a cushioned table.
  • When your child is in a comfortable position for the exam, the table will slide towards the machine so his/her head is inside its circular opening. It is important for your child to lie flat and still as s/he moves through a narrow cylinder.
  • The technologist will step into the control area. Your child will be able to speak to the technologist through an intercom at all times. The technologist will talk with your child frequently during the scan, explaining the procedure each step of the way.
  • You may stay with your child during the procedure as there are no known risks to those in the room with the machine.
  • To help your child relax and to reassure him/her of your presence, you may want to give gentle foot and leg massages.
  • Your child may take a nap during the procedure, if s/he wishes.
  • The technologist will remind him/her to stay still as the images are taken. Any movement during this time will blur the picture.
  • Your child may hear thumping sounds from the machine and may feel a slight vibration, which is normal. It is important to inform your child of these noises so s/he will not panic but remain still during the examination.
  • In some cases, the physician may request a Magnetic Resonance Angiography (MRA) in addition to your MRI exam.
    • This exam will provide an analysis of your child’s vascular system and major blood vessels.
    • Usually, the MRI and MRA are completed in the same visit.
  • The MRI procedure usually takes 30 to 90 minutes.

After an MRIExpand After an MRI Section

 

  • There are no harmful side effects after the examination. Your child can resume normal activities and diet immediately after the scan.
  • If a sedative is administered, your child will be monitored until the effects of the sedative subside.
  • The radiologist will review the MRI scan and send a report to your physician.
  • After the physician receives the results of the test, s/he will confirm a diagnosis or prescribe further tests and treatments.

PersonnelExpand Personnel Section

 

MRI Technologists

  • operate the MRI machines using giant magnets and radio waves to create an image
  • take patients’ medical histories
  • prepare patients for the MRI examination
  • prepare data for doctors to interpret

Radiologists

  • interpret images and sends report to the referring physician

Doctors

  • interpret the results

PaymentExpand Payment Section

 

An MRI examination is covered by the Ontario Health Insurance Plan (OHIP).

EquipmentExpand Equipment Section

 

The MRI machine is a cylindrical magnet in which the patient must lie still. For patients that feel claustrophobic, there are new MRI systems that are wider and shorter and do not fully enclose the patient. Some newer units are open on all sides, but the image quality may vary.

Additional Types of MRIs

Expand Functional MRI (fMRI) SectionFunctional MRI (fMRI)


An fMRI is a non-invasive technique that provides both an anatomical and functional view of the brain. Similar to the MRI, the fMRI uses magnetic fields instead of X-rays to produce detailed pictures of the brain. This technique allows us to localize specific areas of brain function by imaging patients while they perform specific tasks.

An fMRI can identify regions of the brain that are active during cognitive, sensory, and other tasks by detecting changes in the flow of blood to particular areas of the brain. This information is often very useful to the neurosurgeon. It helps physicians identify the exact location of the source of the seizures.

One benefit of using an fMRI is it can still measure blood flow without using radioactive tracers. Instead, the fMRI takes advantage of an iron molecule with magnetic properties contained in hemoglobin, an oxygen-carrying molecule in the blood. When a magnetic field is presented to the brain, the hemoglobin molecules line up like tiny magnets.

An fMRI indicates the presence of brain activity because hemoglobin molecules in areas of high activity lose some of the oxygen they are transporting. This makes the hemoglobin more magnetic, thereby responding more strongly to the magnetic field. The fMRI machine determines the relative activity of various areas of the brain by detecting changes in the magnetic response of hemoglobin.

Advantages of fMRI:

  • It can look at discrete areas of brain activation.
  • The final image depicts more detail than CT scans.
  • It can measure fast-changing physiology better then the PET scan.

Expand Magnetic Resonance Spectroscopy (MRS) SectionMagnetic Resonance Spectroscopy (MRS)

The MRS gives information about the chemical and physiological information about certain structures in the brain.

Expand Open MRI SectionOpen MRI

The “open” MRI is a new design with an extra large opening. This allows more airflow and an open view around you during the examination, an open design that minimizes anxiety for those who are claustrophobic. Because of the open view, this system provides enough room to image patients weighing more than 500 pounds (about 227 kilograms). In addition, the “open” MRI allows a family or staff member to accompany patients throughout the examination.

Important ConsiderationsExpand Important Considerations Section

The strong magnetic field used for MRI will pull on any ferromagnetic metal object implanted in the body. If you have ever been a metal worker, you may be required to have your eyes X-rayed before having the MRI scan. Fillings in your teeth, dental braces, and permanent bridges may distort images of the facial area or brain, but will not cause harm to you or the MRI equipment.

Notify the doctor or nurse prior to the examination if you have any of the following metal implants or objects:

  • aneurysm clips,
  • artificial heart valve,
  • bullets,
  • cardiac pacemaker,
  • ear implants,
  • eye/orbital prosthesis,
  • hip or knee prosthesis,
  • insulin pump implant,
  • intracranial bypass graft clips,
  • intrauterine device (IUD),
  • neurostimulators (vagus nerve stimulation device),
  • shrapnel,
  • sternal wire,
  • sutures, or
  • tantalum mesh.

A small number of people have experienced skin irritation, swelling, discomfort or burning/heating sensations at the site of any type of permanent colourings (tattooing, cosmetic applications such as eyeliner, lip-liner, lip colouring, etc.). Certain ferrous pigments used in tattoos and permanent colouring can interact with the electromagnetic fields used in the MRI procedure. Large or very dark tattoos can cause “artefacts” or false shadows to appear on the image. Inform the technologist or doctor of any unusual sensations in area of the tattoo or permanent colouring during the examination.

Patients may not have an MRI scan if they are:

  • pregnant (whether suspected or confirmed)
  • critically ill (The strong static magnetic field interferes with the proper function of the usual life-support equipment, which may make it difficult or impossible to examine some critically ill patients.
  • uncooperative (It is essential that the patient lie still.)

Consider “open” MRI systems for:

  • claustrophobic patients
  • obese patients who may not fit in the scanner

Click here to learn about other types of diagnostic tests.

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