I got my quantum spin measured in an MRI

0:00 I'm about to do an MRI and have it

0:03 measure the quantum spin of the protons in my body,

0:07 except I don't understand how that's possible.

0:10 When I was studying physics in university,

0:12 they told us that no one understands quantum spin.

0:16 So how come I could just walk into a hospital

0:20 and have them measure the spin of all of my protons?

0:24 And then use that to tell me how messed up my organs are.

0:26 I'll tell you about my MRI results later.

0:30 But first I really want you to see this.

0:34 Oh.

0:35 This is an MRI, and as you can see, an MRI is basically a massive magnet.

0:43 This is the reason that they made me swear up

0:46 and down that I wasn't wearing any metal jewellery or anything because

0:49 the strongest MRIs that you can get at a hospital are

0:53 about as strong as the magnets in the Large Hadron Collider,

0:57 and there are research grade MRIs that are way stronger.

1:01 So firstly, how is it even safe to put yourself inside such a massive magnet?

1:06 Like for example, shouldn't we be worried about iron?

1:09 There's iron in our blood and iron is attracted to magnets.

1:14 Well, thankfully in our blood,

1:15 the form iron is in hemoglobin isn't actually attracted to magnets.

1:20 So we don't have to worry about iron being

1:22 ripped out of us when we're in an MRI.

1:25 But there is another important source of magnets in your body.

1:30 And that's your protons to explain.

1:32 Let me show you this experiment.

1:34 I've got some normal copper wire here, and as you can see, this is not magnetic.

1:39 If it were, you could use it to pick up these pins,

1:42 but now I'm gonna attach it to a battery and you can see

1:45 that this is gonna form a circuit because

1:48 we'll get some tiny little littles box there.

1:50 And suddenly it is a magnet.

1:53 This is one of the most surprising things people ever discovered in physics

1:58 because it shows that there's a link between magnets and charged particles.

2:03 Here's why this wire loop is full of electrons,

2:07 but at first, each of them is just sitting there.

2:10 But when you put a battery on, it forces the charge particle to rotate around,

2:15 and now suddenly this is a magnet.

2:18 So the rule we discovered is whenever you have

2:22 a positive or negatively charged particle rotating around, it's a magnet.

2:27 But let's shrink this loop until the proton here is just spinning around.

2:33 This should still be a magnet.

2:35 So if a proton is a ball spinning on its axis,

2:40 this rule would say that it must be magnetic.

2:43 In the early 19 hundreds,

2:45 they realized that protons are always magnetic, and same with electrons.

2:49 So naturally they assumed that they must be spinning,

2:52 and that is what's making them magnetic.

2:55 This is where the term quantum spin was coined.

2:58 But it turns out that this picture of spin is oversimplified

3:02 and we will come back and correct that a bit later.

3:06 So for now, let's just say that protons and electrons are spinning balls,

3:10 and that's what makes them magnetic.

3:12 But if all of the electrons and protons inside of me are magnetic,

3:17 then how come I'm not a magnet overall?

3:21 For electrons.

3:22 The answer is that misery loves company.

3:25 Electrons in your body tend to pair up in molecules

3:28 where each member in the pair is spitting in opposite directions.

3:32 So they're like magnets pointing in exactly

3:35 the opposite direction to each other,

3:37 so they cancel out and overall, your electrons aren't magnetic.

3:41 But if we look at a proton, that's all alone in a H2O molecule.

3:47 It's not paired.

3:49 And there's many, many of these unpaired protons in your body.

3:54 So why don't they make us magnetic?

3:57 It's because each individual proton is facing a random direction.

4:01 So for example, this proton cancels out that proton,

4:05 and in the end, you're not magnetic.

4:08 Overall, that changes inside an MRI though remember that in an MRI,

4:13 you're lying inside a massive magnet where this is north and this is south.

4:18 I've simulated this by putting some north facing magnets

4:21 along this side and south facing ones on this side.

4:25 So now let's see what one randomly oriented proton will do.

4:29 When it's in the MRI.

4:31 You can see how quickly it aligned itself to the field.

4:36 So if each individual proton actually did align itself

4:39 to the field like this, you would become a super strong magnet.

4:44 But don't worry, not all your protons can align.

4:48 There's loads of energy in your body that knocks around

4:51 each proton that stops them aligning even though they want to.

4:54 An estimate I've heard is that only a one in about

4:57 a million protons can actually end up aligning to the field.

5:01 So your magnetic inside of an MRI, but not that magnetic.

5:05 And as soon as you're out of the MRI,

5:07 all of that jostling is going to just randomize the direction of your protons.

5:12 So they're not going to on net be aligned anymore.

5:14 And so you're not gonna be magnetic as soon as you're out of the MRI.

5:19 Well, that's reassuring that you don't walk out of an MRI

5:21 with magnets sticking to you for the rest of your life.

5:24 But let's think about a spinning proton when it's in the MRI.

5:28 Again, when they spin like this, they're like magnets facing this way.

5:32 So in the MRI, which way will a proton want to spin?

5:36 Well, since the MRI magnet looks like this, the protons

5:40 will want to have its north facing down.

5:43 That means that if your proton is like this spinning top,

5:47 then it's in its most relaxed state when it's allowed to just hang like this.

5:51 And so this is how they start out in the MRI.

5:54 But we can't just let the protons relax, right?

5:57 The actual point of the MRI is that we give them

6:01 a jolt and then we see how they react to that jolt.

6:04 The idea is that if we give this jolt to all parts of your body at once,

6:09 the protons in this part of your body are going

6:12 to react differently than the protons in that part of your body,

6:15 and that's because in this part of your body, the proton might be surrounded by.

6:20 Bone, but in this part it's surrounded by tissue

6:23 and that makes both of them react a little bit differently.

6:27 So telling the difference between how all of these protons react

6:30 will let you map out what's happening in the whole body.

6:36 But how is this jolt administered exactly?

6:40 Well, after they slid me into the MRI borehole,

6:45 suddenly everything started vibrating.

6:48 And the sounds were so bizarre.

6:51 There was this bit that was like pew, pew, pew, DUUUSH, DUUUSH, DUUUUSHH.

7:01 It felt like being in an intergalactic space battle.

7:06 It was like the wave.

7:09 It was honestly so confusing, but it turns out that all that they

7:14 were doing was shining radio frequency light on me,

7:18 and I couldn't see that because radio

7:20 frequency light is invisible to the human eye,

7:22 but I could hear it because to make that light,

7:25 you had to turn on and off some like very noisy coils quite quickly.

7:29 And so apparently that's where the sounds were coming from.

7:32 But honestly, at the time it was quite scary.

7:35 But what's that light gonna do to my relaxed protons?

7:39 Well, the light is at exactly the right frequency for those protons to absorb,

7:44 and after that, they're in a high energy state.

7:47 So as an example, let's look more closely at this spinning top.

7:51 So it looks really fancy, but there's actually nothing to it.

7:54 It's very similar to just like a regular spinning top.

7:56 The only difference is that when I pull this string,

7:59 it makes the middle bit rotate,

8:00 so it's like the middle bit really that's rotating.

8:02 Now, if the top isn't spinning and I start it in a high energy state,

8:07 then it will just fall back down.

8:09 But watch what happens when instead,

8:13 I start it spinning and then put it into its high energy state.

8:23 The why doesn't it just fall straight down?

8:26 It's 'cause spinning objects are honestly so weird.

8:30 And this particular phenomena is called lamore procession,

8:34 and it is one of the hallmarks of spin.

8:37 So if you watch this video, you can see how this object,

8:41 instead of just dropping at some point,

8:44 like you kind of expect it gracefully, spirals down.

8:48 You might think that it fell here, but let's replay that really slowly.

8:52 Look how it gradually loses height and eventually

8:56 it's nearly vertical and it still hasn't fallen.

9:00 If this table didn't get in the way here,

9:03 it would've gracefully spiraled all the way down.

9:06 So a spinning object like this will realign to its most relaxed

9:10 state by slowly and gracefully circling

9:13 around until eventually it's pointing downwards.

9:16 And incredibly, this is what protons do as well.

9:19 But the question that matters medically is how long will it take

9:24 the proton to go from its excited state down to its relaxed state.

9:29 Well, this all depends on the environment of the proton

9:32 and how easily it can transfer energy from itself to that environment.

9:37 So, for example, look at these two spinning tops.

9:39 I've added some tape to one,

9:41 to add friction and make it easier for it to lose energy more quickly.

9:46 And as you can see, that one drops more quickly than the other one.

9:50 That's because it was able to more

9:53 effectively transfer its energy to the environment.

9:55 And in a similar way, a proton that's surrounded by, let's say blood will

10:00 take longer to relax than one that's surrounded by fat.

10:04 Because fat more readily absorbs the energy from the proton relaxation.

10:08 Time is the time it takes for a proton to go back into its relaxed state.

10:13 And since we know the relaxation times

10:16 of the different environments in the body.

10:18 If you are able to measure the average

10:21 relaxation time for a particular part of the body,

10:24 you would be able to tell what's there,

10:26 but how do you actually measure the relaxation time?

10:29 Well, it turns out that protons are actually emitting

10:32 radio frequency light the whole time while they're spiraling down.

10:36 And so if you are able to actually

10:38 measure the radio frequency light coming from those protons,

10:41 then you can just time how long that signal goes,

10:44 and that's the relaxation time.

10:46 And actually that's exactly what they did.

10:49 They had this sheet that they put on top

10:51 of me in the MRI and they called it a camera, and I guess it was a camera,

10:56 just wasn't a camera in the regular frequency of light.

10:59 It was a camera in the invisible radio frequency,

11:02 and the images I got out was so incredibly helpful.

11:05 I have a condition called endometriosis that causes these growths to pop

11:11 up in my abdomen and they have this unfortunate side effect of, um,

11:17 gluing together my organs, but I also have a fair bit of scar tissue

11:23 from previous surgeries and it also can cause some adhesion.

11:27 And so sometimes in some scans it can be a bit hard to tell those two apart.

11:31 But not in an MRI because it turns out that scar tissue and, uh,

11:37 endometriosis growths have quite different relaxation times,

11:40 so they're very easy to tell apart.

11:43 And MRIs don't just measure relaxation time either.

11:46 There are all kinds of different ways that an MRI pokes

11:51 and prods these protons to figure out exactly what their environment is.

11:55 So it gives a super detailed picture of what's going on inside.

11:59 Which is why I can't believe that all

12:02 of this comes from quantum spin because here's the crazy thing,

12:06 protons aren't actually spinning.

12:08 I don't understand this because in every other way,

12:12 protons act like they really are spinning charge balls.

12:16 Like why do they do lamore procession?

12:18 Lama procession is such a specific thing to spinning objects.

12:22 So why does quantum mechanics decide to mimic

12:25 that even though nothing is actually spinning?

12:28 Honestly, I don't get it,

12:30 but I am so grateful to the people who took this esoteric

12:36 idea from the quantum world and used it to help patients like me.

12:41 I mean, I went in for a completely routine MRI,

12:44 and I really wasn't expecting to see anything because

12:47 I thought we were kind of on top of it.

12:50 But the MRI scan revealed that, you know,

12:53 these growths had kind of aggressively started growing

12:55 into some of my organs in a way that.

12:59 Would've become irreversible pretty quickly.

13:01 So yeah, I am very grateful that getting my K

13:07 spin measured meant that they caught that in time.

13:12 I.