the history of MRI - World Today News

When NASA sent the Ranger probes to the moon in the mid-1960s, they wanted to bring back photos of the terrain. The task was not entirely easy, and the images they produced were distorted and skewed. Not satisfied with this result, NASA got down to work trying to improve the images obtained. The first step was to make them digital, and this is how digital image processing came about. Thanks to him, they managed to straighten the images and make them sharper. The technique took little time to spread and even reach our pockets: it is the same one behind the Instagram filters.

But digital image processing has also had another perhaps more unsuspected application: magnetic resonance imaging. It is a safe test and used to detect a multitude of diseases, but It would not have come true had it not been possible to transform analog images into digital ones.

Protons: calling rows

As its name suggests, the key to this medical test is magnetism. The machine is a huge magnet with about 600 times the power of a kitchen magnet, and 60,000 times greater than Earth’s magnetic field. Magnetic resonance imaging takes advantage of the fact that our body contains a large amount of water. The water molecule, H2O, has two hydrogen atoms, which are the ones that react to the magnet.

And it is that hydrogen atoms have a single proton in their nucleus, which rotates on its own axis. This movement is called precession and is also experienced by a spinning top when it wobbles. Normally, the protons that we have in the body are not coordinated at all, each one points in one direction and rotates on its axis without knowing anything about the others.

But if we put all these protons in one big magnet, they line up. The effect is the same as that of the compass: the needle aligns itself with the Earth’s magnetic field, indicating the North pole of the huge magnet that is also our planet. The magnet of the resonance makes the axes of the protons all point in the same direction. Well, some in one direction (up, say) and others in the opposite (down), but all parallel. Turns out that there are always a few more protons pointing up than down, so the effect of some is not completely canceled out with that of others: the excess of atoms pointing upwards creates a small magnetic field. This is exactly what we want to measure.

Of course, this small magnetic field is very difficult to distinguish from the large magnetic field that the resonance machine creates. But all is not lost: we can take advantage of the fact that the rotation speed is the same for all protons. We know how many rotations per minute they make, that is, we know their frequency. If we send out a radio wave that vibrates at the same frequency (i.e. It’s in resonance with protons), this distorts all the protons at the same time, which are no longer aligned with the large magnet of the machine. By pointing in a different direction, we can already measure this small magnetic field.

If we turn off the radio wave, the protons re-align themselves with the big magnet, and in this process they emit some energy. This energy is what interests us: it is emitted more or less depending on the tissue, so that if we measure this energy we can know if the tissues we have inside the body are altered, and thus diagnose pathologies.

Drawing the fabric

It is time to close the circle, because this is where digital image processing comes in– This is essential to generate an image from energy measurements. This energy, which is detected as an analog electrical signal, has to be transformed into a digital signal that makes up the image.

In fact, the mechanism of aligning protons and distorting them with a radio wave was invented in the 1930s, but it was not until 1977 (after the advent of digital image processing) that the first machine to generate images of the human body was built. by magnetic resonance imaging.

The technique is full of advantages: there are no known risks associated with MRI. No side effects have been found associated with either radio waves (which have low energy and are not ionizing, unlike X-rays) or magnetic fields. It is true that the metal inside the body is the great enemy of resonances, because the large magnet could move it and alter the image or, worse still, be dangerous. For this reason, the situation is studied in detail before performing this test in patients with pacemakers, metal valves, prostheses, etc. What’s more, magnetic resonance imaging allows the detection of many pathologies, from multiple sclerosis to heart attacks or tumors in almost any part of the body.

A predictable chance

It is clear that we would not have magnetic resonance imaging without digital image processing. And good, Would this processing have existed without the space race? Probably yes. The way to invent it would have been different, perhaps, and perhaps it would have developed later. But it is not uncommon to find stories of inventions or discoveries arising independently in two different places. Just a related technique, nuclear magnetic resonance spectroscopy, was invented by two different teams at the same time, and its leaders shared the 1952 Nobel Prize in Physics.

Science is full of these seeming coincidences. That a technological need fuels the scientific search, that it results in an invention or a discovery, and that it later has applications in very disparate areas is the order of the day. That is why it is essential to keep exploring. Even if we do not know what we are going to find or when.

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