What’s that knocking?

MRI technology is one of the great achievements of medical technology - discover 12 things that are barely known. 

Philipp Grätzel von Grätz
Published on November 26, 2020

Magnetic resonance imaging (MRI) has been part of routine medical practice for years. The big tubes produce fascinating images. No wonder that MRI is seen as the crowning glory of diagnostics. But how exactly does it work? What’s so special about it? We answer twelve questions to give a better idea.

1) What does an MRI machine do?

Major fields of application of MRI include visualizing the brain, inflammation, cancer, muscles and joints, blood vessels and the heart.

2) What are MRIs used for? And what not?

3) Is MRI better or worse than computer tomography (CT)?

4) Does MRI involve contrast agents?

When you place a person in the extremely strong magnetic field of an MRI machine, hydrogen nuclei with their mini magnetic fields align with the MRI´s magnetic fields and spin in step.

5) How exactly is an MRI image produced?

An MRI is structured like a Russian doll: the superconducting magnetic coil is placed on the very outside of the MRI machine. Then come the gradient coils. And on the inside are the body coils.

6) Can you explain further how it works?

7) So this is what produces the precise images?

A 3-tesla MRI machine produces a magnetic field around sixty thousand times stronger than the earth’s.

8) How strong are these MRI magnets? Aren’t they dangerous?

9) Are there patients who can’t have an MRI scan?

10) On the subject of claustrophobia: Why do the tubes have to be so narrow?

With the magnetic coils, the cooling system, and all the equipment required to stabilize the machine, a scanner ends up weighing between six and seven tons.

11) Do MRI machines always have to be kept in a basement?

MRI scanners certainly make plenty of noise. Depending on the machine and the sequence used, the noise can easily reach aircraft volume levels.

12) Last question: an MRI scan can be incredibly loud. It makes creaking and sawing noises, and sometimes there’s a kind of knocking like a tumble dryer that’s unevenly loaded. Why?

By Philipp Grätzel von Grätz

Philipp Grätzel von Grätz lives and works as a freelance medical journalist in Berlin. His specialties are digitalization, technology, and cardiovascular therapy.