Illustration of a person in the MRI tube. Lying on their back, head tilted to the side, the person wears a pink-colored robe. Darkness is all around the body.

INTO THE TUBE

TEXT NILS WISCHMEYER
ILLUSTRATION MICHAŁ BEDNARSKI

—— To look at, an MRI scanner isn’t much more than a large tube that makes loud clicking noises and somehow ends up producing images. But how does the device actually allow doctors to see inside the human body? A simplified explanation.

WHAT DOES “MRI” STAND FOR?

MRI is an acronym for magnetic resonance imaging, a medical imaging technique that makes it possible to create layer-by-layer images of the human body. MRI is used for examinations of what are known as soft tissues, which can include the brain, breasts or kidneys. Doctors can also look at joints or spinal disks, for instance in cases when they suspect the patient might have a herniated disk. Unlike other imaging methods, such as X rays, MRI doesn’t use radiation to create images.

Illustration of spheres, through each of which a line runs, symbolizing an axis. On the side of each sphere is an arrow indicating the direction of rotation of the particles.

STARTING POINT:

An adult’s body consists of about 60 percent water. These water molecules ­contain hydrogen protons that rotate around their own axes, meaning they have a measurable “spin.” As long as they aren’t subject to some external magnetic source, these numerous subatomic particles move around in a completely random manner, pointing in completely different directions as they continue spinning.

Illustration of two groupings of spheres. The upper group of spheres each has an arrow pointing in one direction and the lower group of spheres each has arrows pointing in the opposite direction. The groups are separated by a horizontal bar.

STEP 1:

The MRI scanner generates a strong external magnetic field. As a result, all the protons align themselves along this magnetic field, either in the same direction, or in the exact opposite direction. To put it simply, imagining the protons as passengers on a train: they are all facing either in the direction the train is going or they are facing backwards, but they aren’t facing up, down, or to either side.

Illustration of two groupings of spheres. In the upper group of spheres there are spheres of different size. Two of them are green. Their arrows point in different directions than the rest of the group, and an arrow is drawn on the side marking a rotational motion. The lower group of spheres consists of different-sized spheres, whose arrows all point in one direction.

STEP 2:

In the second step, a high-frequency pulse of energy is sent through the person’s body, what is known as a radio frequency impulse. This is generated by magnetic coils inside the MRI scanner. This pulse causes some of the protons to absorb the energy and tip to one side, in a manner of speaking.

Illustration of two groupings of spheres. In the upper group of spheres there are spheres of different sizes. Two of them are green. There are jagged lines going from them, and an arrow is drawn on the side marking a rotational movement. The lower group of spheres consists of spheres of different sizes, all of which have arrows pointing in the opposite direction to the upper group.

STEP 3:

As the energy pulse is turned off, the protons then realign themselves with the initial magnetic field. This realignment causes the protons to emit a small amount of energy in the form of high-frequency signals, which are then crucial for the final step.

Illustration of a screen on which a head is in profile.

THE FINALE:

An antenna captures these signals, which are then compiled by a computer to form an image for the attending doctor. In this way, a layer-by-layer image of the person is created, according to the part of the body and its composition.

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