This is a picture of a slice right down the middle of a human brain.

And so is this.

And this.

And this.

And these all happen to be of the same brain, my brain.

It turns out there's nothing wrong with it.

But that's not why I had these pictures taken.

These were taken in an fMRI machine, that is, a functional MRI, which is a giant magnet used to look at activity in the brain.

These pictures were part of cognitive studies trying to figure out how the human brain works.

And I obviously did a lot of them.

So should I have been worried about the effects of so many sessions in a giant magnet on my brain?

Well, let's figure out how an MRI works first.

And we're going to do that by using an MRI.

I'm here with Dr. Meg Richman at the Center for Translational Imaging and Precision Medicine.

At UCSD.

And-- at UCSD.

And she's giving us the wonderful opportunity of imaging some fruits and vegetables.

Yep, I brought fruits to MRI.

In our magnetic resonance imaging session, we start by putting the fruit in the center of a giant magnet.

This magnet is strong enough to align the hydrogen atoms of anything we put inside.

And by measuring how those atoms respond to magnetic pulses, we can peer inside the fruit.

The machine is still scanning right now.

MEG RICHMAN: Absolutely.

Yeah, right?

Look, there's your pineapple.

DIANNA COWERN: Oh, that's so cool!

Are you scanning for brain tumors?

The first thing we're looking for is dark and light contrast to differentiate tissues.

Oh, my gosh, look at all the detail on this.

MEG RICHMAN: Yeah, look at the-- DIANNA COWERN: That's amazing.

MEG RICHMAN: That is the pomegranate.

Look at the seeds in the pomegranate.

DIANNA COWERN: Oh, that's the pomegranate next to it.

The base magnetic field in an MRI is produced by an electromagnet at a strength of usually around 3 tesla.

That's 100,000 times stronger than Earth's magnetic field.

MEG RICHMAN: The magnetic force is always on.

DIANNA COWERN: I did not realize that.

So-- Because I thought it was an electromagnet that's pulsed.

It turns out the base superconducting electromagnets are always on, even between patients.

They're only turned off for maintenance.

That base magnetic field aligns all of the tiny hydrogen nuclei, or protons, in your body, which have a magnetic moment.

Which means they act like tiny magnets.

Then radiofrequency magnetic pulses are sent from the machine, which causes those tiny magnets in your body to move out of alignment temporarily.

As they relax back into alignment with the magnetic field, they induce a current in the magnet, which is detected as a signal from the hydrogen atoms in different tissues.

MEG RICHMAN: So again, it's all based on hydrogens, hydrogen molecules.

And they operate differently depending on what tissue they're in.

They relax, if you will, into their native state at different times.

And so we use that by comparing different sequences to say, this thing is very dense and it's bone.

This thing is water.

DIANNA COWERN: So with those differing relaxation times, and depending on which imaging sequence you ran, the different tissues look different.

MEG RICHMAN: Typically, when things are bright on T2, they have more water in them.

DIANNA COWERN: OK. MEG RICHMAN: So I would have predicted that the center would have had less water and more fibrous tissue rather than the meat too.

DIANNA COWERN: I just grabbed a bad pineapple.

No, no, no.

The machine images and slices through the entire object.

What do these lines do?

Like, what do you have to align while you're imaging?

That just tells you where your slices are going to be.

DIANNA COWERN: So you can look right into the middle of a body and get a 3-D image of its structure.

Combining the results of contrast on various scan sequences with the area's anatomic structure, MRI can be used to diagnose numerous medical issues.

But are there any dangers associated with this giant magnet?

Luckily not here.

But there have been instances where people have brought in oxygen tanks because they're trying to revive someone.

And then they get sucked right into the bore of the magnet.

If you have any credit cards, it'll erase your credit cards.

So you don't want to bring credit cards into the magnet.

Don't bring your credit cards.

And let's say that you say, oh, I am a metal worker.

And so they might have little shards of metal in their eye.

We can get them an x-ray and see, is there any metal in that eye?

Because if there's little shards of metal, that will move, and that can cause corneal problems to the surface of the eye.

DIANNA COWERN: So you have to be careful with ferrous metals.

This is what a decommissioned MRI machine did to a stapler.

Whoa!

DIANNA COWERN: And a chair.

TECHNICIAN 1: 700 pounds.

TECHNICIAN 2: Oh, it's about-- oh, oh, oh!

TECHNICIAN 3: It's plastic.

You put a lot of plastic there.

DIANNA COWERN: But the technicians make sure you don't enter the MRI room with any metals on.

MRI is great for showing tissues and the structure of your body.

So then how can it show you what your brain is doing?

This is a pretty amazing technology.

fMRIs can show you what parts of your brain are being used for different tasks.

And they use no ionizing radiation like x-rays or CT scans do.

No studies have linked MRIs to any adverse health effects.

So I'm not too worried about my noggin after all these photos.

I think it looks pretty good, thanks to physics.

And thanks to you for watching this video.

And I hope you learned something.

And if you want to keep on learning physics, hit subscribe.

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