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MRI 101

What is an MRI?

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Magnetic resonance imaging (MRI) uses a powerful magnetic field, radio waves and computers to produce detailed pictures of the body’s internal structures – especially the soft tissues. MRI images are clearer, more detailed and more likely in some instances to identify and accurately characterize disease than other imaging methods. It is used to evaluate the body for a variety of conditions, including identifying and classifying; tumours throughout the body, abnormalities in the brain, spine and nervous system, injuries to the muscles and joints, abnormalities in the large blood vessels in the body, gynaecologic abnormalities and diseases of the liver, biliary system, heart, and bowel. It may also be used to monitor an unborn child in the womb. MRI is non-invasive and does not use ionizing radiation.

Common uses of MRI:

  • Any abnormalities in the brain –including tumours, multiple sclerosis, aneurysms, cysts, internal bleeding and stroke name a few.

  • Evaluating all joints including the ankle, shoulder, knee, hip, TMJ, sacroiliac joint, elbow and wrist.

  • Comprehensive breast imaging including screening and staging for breast cancer and evaluating implants.

  • Complete evaluation of the spine and spinal cord including disc herniation, spinal cord compression, spinal AVM, spinal fractures and bone metastases

  • Organs of the chest and abdomen—including the heart, liver, kidneys, spleen, bowel, pancreas and adrenal glands.

  • Pelvic organs including the bladder and the reproductive organs such as the uterus and ovaries in females and the prostate gland in males.

  • Blood vessels throughout the body – including aortic aneurysms, coarctation of the aorta, dissections, congenital malformations, blockages and inflammation.

  • Tumour response to therapy.

  • Lymph node metastases.

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During a Magnetic Resonance Imaging (MRI) scan, magnetic fields along with pulses of radio waves are used to generate images of the internal body structures. It is a painless procedure wherein individuals undergoing the test can relax and have a few MRI images done each taking not more not more than a couple of minutes. MRI scans are proven to be helpful in cases where other diagnostic tests such as X-ray, ultrasound or CT scanning do not yield definitive results. MRI gives a comprehensive insight into the internal body organs which can be used to diagnose illness and plan treatment. The images generated through the MRI scan can accurately pinpoint to the cause of disease or prove the absence of disease.

As is the case with all medical procedures it is quite natural to feel anxious if you have to undergo the procedure. However, as mentioned above MRI scans are painless. By following few simple guidelines you can go ahead with the scan and be done in few minutes.

Advantages of MRIs

An MRI scan has many advantages but it is usually only used when other less costly tests fail to provide the exact cause of disease. There is no radiation involved in the process which makes it safe for children or pregnant ladies.  Since it is also capable of visualising blood circulation, it can be used for detecting blockages or abnormalities in blood vessels.

An MRI scanner digitally collects 3D information about the structures being imaged. This data can then be manipulated to get cross-sectional or slice images in any direction of the scanned body part.  This is very useful for doctors to precisely examine the anatomy being imaged.

How MRIs work

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The human body is made up of billions of water molecules and other hydrocarbons which contain hydrogen atoms. Each hydrogen atom contains one proton at its center which is magnetic and is therefore sensitive to a strong magnetic field very much like the needle of a compass. This is the exact principle that MRI uses to create an image of the large number of hydrogen atoms in our body.

The MRI unit is basically a very powerful magnet that is used to align the hydrogen protons in the area being imaged.   Due to a physical phenomenon known as resonance once the hydrogen protons are aligned they will absorb radio waves of a very particular frequency.  This is the same type of radio waves that we use to listen to music in our cars!   Once the protons absorb the radio waves we say that the protons are in an “excited” state.   Once we stop transmitting the radio frequency then the “excited” protons “relax” and in this process emit the same frequency radio waves which we can then detect using an antenna (like we do in our car) which is placed close to the body part being imaged.   It is this detected radio signal coming back from the protons that we use to create the very detailed MRI image of the body.

Smaller magnetic fields are also applied on and off during the scanning process to give us the prcise location of each proton so as to create the 3D image.  The knocking noise that is heard during the MRI scan is caused by the interaction of the strong main magnetic field and these smaller fields being turned on and off.

Because MRI uses harmless magnetic fields and radio waves instead of radiation like an X-ray or CT scan it is called a non-invasive procedure.   However because of the strong magnetic fields, extreme care must be taken to avoid any ferromagnetic metals from coming into the room and we must be aware of any metal in your body (eg implants or clips) or any electronic devices like pacemakers.   While many metal implants and even some newer pacemakers are safe under certain conditions in the MRI unit there are many older pacemakers and some implants that cannot come in the MRI unit under any condition.

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