Learn how nuclear magnetic resonance is used to look inside the human body when a knee injury sustained while playing sports leads to an MRI scan. We’ll also explore how MRI works, its advantages and disadvantages, and how scientific discoveries have impacted medical diagnosis.
I was exercising when the sole of my shoe caught in the grass and my knee stopped following my body. There was a momentary pain, but I didn’t think much of it. The next day, my knee swelled up and I couldn’t bend my leg, but the doctor told me it was a sprain and to rest for a couple of days. After two days of compresses, I was back to running, stopping, sitting down, and standing up without much difficulty. However, during intense workouts, my knee would sometimes feel like it was giving out, and on those days, it would swell up. I would take a break and wait for it to get better, but I became increasingly aware that it wasn’t working. Finally, after a year of procrastinating, I went to see a doctor, who recommended a magnetic resonance imaging (MRI) scan.
As I waited in the waiting room for my turn, I was filled with anxiety, wondering if there was something seriously wrong with my knee. Even as the doctor explained the procedure to me, I couldn’t help but think that it could be something serious. I went into the examination room, removed my belt, watch, and other metallic objects, and lay down on the examination table with earplugs in. After 30 minutes of lying on the conveyor belt in a claustrophobically narrow circular passageway, listening to the loud thumping of the machine, the shooting was complete. The series of photos the doctor showed me afterward were like slices of pressed meat made from my leg. As I smirked at the thought that I was made of bone and flesh like that, that the machine knew me better than I knew myself, the doctor pointed to a blurry spot on the image and said to me.
“Your anterior cruciate ligament is almost gone.”
Hearing these words, my head went white. As an avid athlete, this news came as a shock. He explained the treatment options, but I was already thinking in my head that I might not be able to do the sports I normally enjoy anymore.
The Nuclear Magnetic Resonance Phenomenon
Magnetic resonance imaging devices like this one allow us to see deep inside the body, and they are playing an important role in detecting not only internal injuries that don’t cause many symptoms, but also in the location and malignancy of various tumors. How is this possible? The answer lies in the phenomenon of nuclear magnetic resonance.
Matter is composed of atoms, which can be divided into nuclei and electrons. The nucleus and electrons each rotate and have angular momentum, which we call spin. Just as there are north and south poles on the rotating Earth, nuclei and electrons with spin also have N and S poles, so with a bit of exaggeration, we could say that our bodies are actually made up of countless magnets. But our bodies don’t work as magnets. The axes of rotation of the countless atomic nuclei and electron “magnets” are aligned in different directions so that the sum of their magnetic properties is zero. Only when a strong magnetic field is applied from the outside in a certain direction do the nuclei and electrons’ axes of rotation turn to face the same direction, like a compass. But even after alignment, the axis of rotation wobbles with a certain periodicity, like the axis of a spinning top spinning around a cone as its speed decreases. This staggering motion of a spinning object as it turns on its axis is called precession, and it can be observed not only in the rotation of atomic nuclei or electrons, but also in physical phenomena ranging from spinning tops to planets.
It is noteworthy that the spin frequency (spin speed) of an atomic nucleus in a magnetic field is uniquely determined by the strength of the magnetic field and the type of atom, and that when electromagnetic waves of the same frequency as the spin frequency are emitted from the outside, the electromagnetic waves are absorbed by the material, causing a phenomenon called resonance.
In 1945, American Edward Purcell, who discovered this phenomenon, laid the foundation for nuclear magnetic resonance analysis, an experiment in which electromagnetic waves of various frequencies are bombarded with a sample placed in a magnetic field to determine the frequency of the sample’s spin and thus the atoms of which it is composed, and was awarded the Nobel Prize in 1953 for his work. However, early nuclear magnetic resonance methods were too insensitive to determine which atoms were in which positions, which limited their versatility. Swiss chemist Richard Ernst developed high-resolution nuclear magnetic resonance analysis in two and three dimensions, which paved the way for the development of magnetic resonance imaging (MRI) devices. Ernst was awarded the 1991 Nobel Prize in Chemistry for his work.
Hydrogen atoms and magnetic resonance imaging
Hydrogen is a great atom for nuclear magnetic resonance analysis. With an atomic number of 1, hydrogen has only one electron, which is often not entirely its own due to covalent bonding or ionization. This makes it easy to apply nuclear magnetic resonance analysis to the nucleus of an atom, which has the advantage of low error and high sensitivity. In addition, as a member of water (H20), which is 70% of our body, it has a wide distribution range and a large number.
So how does a magnetic resonance imaging (MRI) device obtain information about the inside of the human body from hydrogen? In the circular passage of a magnetic resonance imaging device, the human body is subjected to a uniformly sized magnetic field, which causes the hydrogen atoms in the body to align in the direction of the magnetic field and undergo a washing motion. However, not all parts of the body experience the same level of alignment and scavenging.
In organs with a high concentration of water, such as the brain, there are more aligned hydrogen nuclei. In contrast, airy organs, such as the lungs, have relatively fewer aligned hydrogen nuclei. The distribution of hydrogen nuclei in organs, as well as in bones and ligaments, can be altered by physical trauma. Cell-specific characteristics must also be considered. A normal cell and a tumor cell are likely to have a different distribution of hydrogen nuclei.
Therefore, when electromagnetic waves are bombarding the human body in a uniform magnetic field, the amount of electromagnetic waves absorbed in the form of energy will vary depending on whether the organ, skeleton, ligament/tendon, or cell is diseased or not. Magnetic resonance imaging devices use sensors to measure the amount of energy absorbed and released by different parts of the body. Based on this, it creates a picture of the inside of the body.
Advantages and disadvantages of magnetic resonance imaging
Anyone who’s ever had an X-ray or computed tomography (CT) scan in a hospital has seen the radiation danger zone warnings painted in front of the room. But with magnetic resonance imaging, which uses magnetic fields and electromagnetic waves, you don’t have to worry about radiation at all. In particular, the electromagnetic waves used in nuclear magnetic resonance analysis of hydrogen nuclei are in the frequency range of radio waves (RF) that we use for radio, television, and cell phones.
The results are also excellent. X-rays provide blurry information about a single cross-section, and computed tomography (CT) can only take cross-sectional images, but MRI provides information in three dimensions, so you can section in any direction for high-resolution results. The downside is that the equipment is expensive, noisy, and requires the patient to be in a confined space for a long time. Patients with metallic materials inside the body, such as artificial hearts, should not be imaged due to the possibility of magnetic field distortion or electromagnetic induction.
Since its inception, magnetic resonance imaging has allowed us to see inside the body and has contributed to the early diagnosis of many diseases. As the saying goes, you can see through water ten ways, but you can’t see through people, and now it seems to be easier than ever to see through people. But what the heck, magnetic resonance imaging is probably one of the few human inventions where only the good guys stand out.
