The diagnostic capabilities of today’s hospitals are nothing short of amazing, especially when viewed in contrast to the tools in use just 50 years ago (believe me, 50 years is far shorter than it sounds when discussing scientific advancement). Much of this progress has been enabled by the hard work of scientists & engineers who continually develop innovative science & technology to aid medical professionals in their duties. Perhaps once of the most revolutionary techniques to arise from this evolution is that of Magnetic Resonance Imaging (or, as you might be more familiar with, MRI). MRI was developed starting in the early 1970s & MRI machines hit the commercial market in the 80s; since that time, the technique has enjoyed a steady rise to prominence & has become just about as close as a medical imaging technique can to being a household abbreviation today. This is not without reason. The functional capabilities of MRI are vast and can provide radiologists & other medical professionals with a great deal of anatomical & physiological information on basically any part of the body for the purpose of medical diagnosis of everything from heart disease to tumors to common sports injuries to even prostate cancer. Alright, so now that we fully understand the importance of MRI, it’s time to ask the question of how MRI works. To give a simplistic answer to this question, we will purely look at the fundamentals.
As you may have heard at some point in your life, the human body (on average) is about 60% water (by weight). Water, as you may remember from virtually any chemistry or biology class you’ve ever taken, is a fluid whose molecules have the chemical formula H2O, meaning that each water molecule contains 2 Hydrogen atoms & 1 Oxygen atom. Each of these atoms has a nucleus at its center, which contains positively charged protons & neutral charge neutrons. Under general conditions, the Hydrogen atoms in these water molecules tend to be oriented randomly in your body as they spin about their axes. Once you enter the MRI machine & it boots up, the machine creates a magnetic field which tends to align the spin axes of these Hydrogen atoms with the magnetic field lines (which run along the length of the MRI machine) due to the interaction between the impressed magnetic field & the positively charged protons in the nuclei of the Hydrogen atoms. Most of the Hydrogen atoms either align their axes pointing toward your feet, or towards your head, but there is a small percent that remain unmatched with atoms facing in the opposite direction. When multiplied by the crazy number of Hydrogen atoms in your body, this small percentage becomes quite significant. At this point, the machine begins to emit a Radio Frequency (RF) pulse that excites these unmatched atoms at their resonant frequencies, causing them to align in a specific direction & spin at a certain frequency. When the pulse is discontinued, the unmatched atoms revert to their previous state, releasing energy in the process, & thus emitting a “signal”. This signal is sent to a computer, which uses mathematical formulas (i.e. Fourier Transforms) to translate the signal into a piece of the final image. The greater degree to which the atoms were disturbed by the pulsed energy, the darker those atoms appear in the final image, thus leading to an image of varying contrast. Another major factor in the final appearance of the image is the relaxation rate of the various tissues, or how quickly these atoms revert to their undisturbed states in the various tissues.
By utilizing this technology, medical professionals can help to identify health issues & diseases in their early stages, thus helping to save lives. Pretty cool, right?