Magnetic Resonance Imaging (MRI)



A brief investigation into how MRI machines function, their purposes, and their risks. 

      Magnetic Resonance Imaging (MRI) machines use powerful, commercial grade magnets to take advantage of the body’s abundance of protons. All protons spin on their own axis, thus producing a slight magnetic field. An MRI can create a much stronger magnetic field in order to disrupt the proton’s natural position -- subsequently forcing the protons to align with the MRI’s field. A separate radio frequency is then introduced into the field. This disrupts the proton’s current alignment with the machine’s magnetic field -- either forcing the protons to spin ninety degrees perpendicular, or one hundred and eighty degrees parallel to the field. The technician then inhibits this radio frequency, consequently causing the protons to spin back into alignment with the magnetic field from the machine. This spinning motion causes the protons to release electromagnetic energy. The MRI machine is able to detect this energy and is even able to differentiate various types of tissues based upon how quickly it picks up the energy after the radial pulse is turned off.         

A singular hydrogen proton shifting out of alignment with the MRI's magnetic field (white pulse). The green pulse is the interrupting radio frequency. 

Image courtesy of the National Institute of Biomedical Imaging and Bioengineering.  

     MRI machines are used for disease detection, condition monitoring, and diagnosis. There are different types of MRI’s for different purposes, such as a functional MRI (fMRI). fMRI is a technique used to measure and map brain activity via differences in hydrogen ion nuclei in the cerebral blood vessels. MRI’s can be used to detect breast cancer, life threatening blood clots, and other venous conditions. Their non-invasive technology allows for effective diagnostic techniques before any other more invasive surgical actions or course of treatment.
     MRI’s do not emit ionizing radiation, yet they do use strong magnets and thus are not functional for some patients. Anyone with any sort of metal in their body, such as a pacemaker,  cochlear implants, interbody contraceptive devices, or certain prosthetics, may not use an MRI. In emergency medicine, any type of metal shrapnel must be removed as well before the patient can be assessed via MRI. Generally, MRI machines are extremely large and loud because of their many magnetic coils (MRI’s produce a magnetic field about 60,000 times stronger than the Earth’s natural magnetic field). Patients are often made aware of this beforehand in case anyone has claustrophobia (fear of tight spaces) or phonophobia (fear of loud noises). Ear protection is also recommended, as sounds can reach up to 125 decibels (anything above 80 decibels is risking permanent damage if proper protection is not utilized).
     Stanford's William PanLab for Precision Psychiatry and Transnational Neuroscience consistently use state of the art MRI's machines to observe and map brain activity. There, I had the opportunity to participate in a research study exploring the relationship between eating disorders and brain activity in female adolescents. The hour MRI scan was definitely worth the cool photos (below) and a hundred dollars too!  

Here's my brain from an fMRI I had done for a voluntary research study at Stanford University. 

     MRI imaging technology is fairly new to the field of internal medicine -- only about 40 odd years old. Despite the relatively young age, this imaging technique has made tremendous leaps in terms of scientific advancements. MRI machines have become a common sight in level one, two, and three trauma hospitals around the world. Its precision out rivals all other imaging techniques and continuous to make monumental discoveries via rapidly developing image sensors. The strength of MRI machines is measured in Teslas (T). Generally, the average machine runs around 1.5 T to 3 T. This means that they can resolve details in the brain as small as one millimeter. With new technology in the horizons, MRI machines of up to 14 T. The University of Minnesota houses one of only a handful of 10.5 T scanners available throughout the world (Minnesota's being the first of the bunch). With this kind of imaging power, the scans become much more clear and detailed, allowing details as small as .5 millimeters to be visible. This kind of precision is incredibly handy, allowing for virtually the same amount of detail as a neurosurgeon would achieve in the operating room. 
     The future of imaging technology is (almost) limitless. The higher the T, the more unstable the magnetic field becomes, thus increasing the risk of tissue overheating and nuerological side effects. Not to mention,  a 10.5 T machine costs about fourteen million dollars and weighs three times as much as a Boeing 737 air plane. While the future of MRI's is a promising one, it is also essential to take into account the limits of the human body, the elongated timeline of scientific research and advancement, and the consequential power of magnetic and radio waves. 

University of Minnesota's 10.5 T MRI. Image courtesy of the Center for Magnetic Resonance Research.

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© Lena Kalotihos 2020