If you are a fan of movies or medical drama, then you have definitely watched scenes where a patient is laid on a bed-like structure and slid into a typically large circular tube with a movable table in the middle. This large tube is called an MRI scanner.
Magnetic Resonance Imaging (MRI) is a non-invasive and painless radiology technique that uses magnetism, radio waves and a computer to produce detailed images of internal human body organs.
MRI scans can be used as a very accurate method of detecting diseases throughout the body and are mostly requested by surgeons after other tests fail to provide adequate information to confirm a patient’s diagnosis.
How it is done
Neurosurgeons use MRI scans to get images of anomalies in the brain before conducting surgery. They are used for breast cancer screening or to provide valuable information about abnormalities like strokes, tumours, aneurysms, spinal cord injuries, multiple sclerosis and eye or inner ear problems. MRI scans can also be used to check certain types of heart problems.
The results of an MRI scan are often used by surgeons to accurately direct how an operation will be done or in some cases suspend it altogether.
The human body is mostly water, which contains hydrogen and oxygen atoms. The scanner creates a strong magnetic field that aligns the protons of hydrogen atoms, which are then exposed to a beam of radio waves. This spins the various protons of the body, and they produce a faint signal that is detected by the receiver portion of the MRI scanner. A computer processes the receiver information, which produces an image.
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Apart from a patient being asked to wear a gown before being inserted in the machine, very little preparation is required to conduct the test. The patient will be advised to stay still during the scan to avoid distorting clarity of the images being produced.
To ensure as much comfort as possible during the procedure, a patient may be given a blanket to cover themselves and headphones to block out the noise coming from the scanner. Music may be played to children to relieve them of anxiety during the test.
Patients who have any metallic implants in the body must notify their physician or radiologist prior to the examination because these materials can significantly distort images produced by the scanner.
Devices like heart pacemakers, metallic implants or clips in the eyeball cannot be scanned with an MRI to avoid the risk of the magnet moving the metal in these areas. Patients with artificial heart valves, cochlear implants, and chemotherapy or insulin pumps should also not have MRI scanning.
However “most implants now come with information on MRI compatibility which the surgeon should inform a patient of at the time of surgery,” says Dr Sheila Waa, a consultant radiologist at the Aga Khan University Hospital Nairobi. “If the patient does not have information on MRI compatibility of an implant, we consider how long after surgery the scan is being performed.”
MRI scans can last 20 to 60 minutes, depending on the part of the body being analysed and how many images are needed. The images are usually ready for reporting immediately after scanning whereas others may require post-acquisition processing depending on the condition being investigated.
For instance, “a patient with a possible stroke is one whose scans the radiologist will want to review quickly and issue a report promptly whereas staging of cancer will probably take more time due to its complexity,” says Dr Waa.
What happens if a patient is claustrophobic?
A mild sedative is given before the scan to reduce anxiety and relax a patient who is likely to develop a claustrophobic sensation. A radiologist can also communicate with them using a buzzer until the procedure is complete. This helps to take away the patient’s thoughts from the scan if they cannot tolerate it.
In Kenya, an MRI scan costs between Sh16,000 and Sh33,000, although the test can be as cheap as Sh10,000 in public facilities.
In addition to structural imaging, MRI can also be used to visualise functional activity in the brain. Functional MRI, or fMRI, measures changes in blood flow to different parts of the brain.
It is used to observe brain structures and to determine which parts of the brain are handling critical functions.
Functional MRI may also be used to evaluate damage from a head injury or Alzheimer’s disease.