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Publish Date: 12/1/2017
Author: Steve Leung

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With advances in medical technology, there are many non-invasive methods of assessing a person’s body.  Several of these techniques requires the use of ionizing radiation such as x-rays, CT scan, nuclear scans, and fluoroscopy (e.g. heart cath).  High enough doses can cause radiation damage to the tissue, from erythema to tissue necrosis.  Exposure to ionizing radiation can also increase a patient’s risk of developing cancer long term.  Thus, radiology societies (RSNA) encourage best practice or appropriate use to minimize the risk by only performing these tests that are deemed necessary, and to only use as low dose of radiation as possible to still obtain useful images (the ALARA principle: As Low As Reasonably Achieved).

Cardiac MRI does not use ionization radiation to obtain images.  The technology utilizes changes in magnetic fields along with radiofrequency pulse (radio waves) to form images.  These radiofrequency pulses do not increase the risk of cancer development.  The combination of the magnetic field changes and radiofrequency pulse does deposit a very small amount of energy into the tissue and cause slight increase in temperature (SAR – specific absorption rate).  Many of the imaging sequences used in cardiac MRI does not raise the temperature enough for the patient to feel the temperature change, and especially not enough to cause damage to the tissue.  However, certain types of metal can heat up significantly in this environment, and cause burns.  This is the reason technologists go through a screening form to ensure that the patient does not have any dangerous metals that can cause harm.

Orthopaedic implants, coronary stents, heart valves (with the exception of ball and cage valves) are generally MRI safe.  For a more comprehensive list, you can visit www.mrisafety.com.

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