How MRIs Work

on to a little listener mail. This listener mail comes from Brad, and Brad says, how about a series of podcasts that explain the technologies of medicine between the diagnostics like m R I X ray, CT scans and nuclear medicine to read habilitative therapies like ultrasound and electrical stimulations. There are a lot of different possibilities. Well, Brad, we

agree with you. Now, granted those are that's a lot of topics, so we can't really, we definitely cannot tackle them all in one go because we would be here for five hours and I am exhausted, So we are

going to just do one of those. However, it is one of the more technically difficult ones to talk about in a way it's magnetic resonance imaging or m r I. S Yeah, you know, it's funny that you just said five hours, because the very first m r I, which was conducted on July third, seven, took about five hours. That's right. It took almost five hours to get one image. And what was weird was the image was of a

man waving. No, that's that parts a lie. Well, the that that image was from a graduate student because the original um, well one hesitates to use the word victim, but subject, The original subject of the first m r I was supposed to be the fellow who was kind of the driving force behind inventing the m r I machine, Raymond Domedian. Yes, now, Raymond was not able to be the first subject of the first m r I because he didn't fit. Yeah, he was. He had a little

too much junk in the trunk. That's that's never mind. Get in there, dude, My my trunk has got so

much junk in it. I'm just saying so, yeah, do Median was not able to He was disappointed when he first used his machine because it didn't work, and at first he thought that perhaps all this work he had been putting into developing this device was for not and then someone suggested that perhaps a slightly thinner subject might be better suited for the first test, and so one of the graduate students that was working with him stepped up to the plate and said that they would take

the place. And indeed it worked. It did take about five hours. Um, that's it's a long time to be in an MRI machine. Yes, and another just another trivia act for those of you who like to play trivia games. The very first machine was called the Indomitable. Yes. And you can actually see the Indomitable Yes, it's at the Smithsonian. Yes. So I wonder if the Abominable Snowman could be have an m r I in the in the Abdomitable. I am almost certain that the Abominable Snowman has even more

junk in the trunk than the median. Probably probably does. I'll ask my sister. She knows him. Okay, yeah, actually, no, you're right, that's true. I'm not making it up. So so, yeah, there there's a very small space in an m r I machine. Um. And do you think we should mention before we get into the technology behind it, what you would use an m r I for sure? Sure? Why don't you Why don't you illuminate? Okay, well, there there are lots of different things that you can use an

m r I for. Now, what it does is it basically captures an image of your insides. Um. I was going to say sort of like an X ray, But I don't really like an X ray at all, because X rays are really good for things like bone structure and but damage to bones, whereas m r I s are really good for soft tissue like organs. Yes, and Uh, if you ever have the opportunity to see pictures that have come from an m I, U might be worth looking up online. But um, it's it's really fascinating. You

could see a whole lot of detail. Um. And speaking of of detail, I mean I could tell you a little bit about that. I actually had an m r I this year. We'll get into that in a minute. But you can look for things like tumors for different signs of disease, torn ligaments or damaged tendons. Um, just irregularities and organs. Someone might have an enlarged heart or things of that nature. You have damage to blood vessels. Uh,

you know, if you have anything wrong with your abdominal area. Um, you know, you could you could look to see if there's something that's uh that's available, and the technology is is amazing to me. The things the report that I got back from the doctor when it was all done, it's going, how did you see as they sent the entire thing? So I saw all the other stuff, the um the person who did it catalog pretty much everything

was visible, even things that they weren't looking for. So it was going, that's a little creepy, yeah, but it's amazing. You think the back scatter X ray machines at the airport are are really detail oriented. Well. Also, I found the key to my back door. It was it was, it was inside there all the time, and I wondered what happened to it? Apparently it fell in my burrito. Okay, I was wondering if that was a euphemism. Now, actually, actually we'll get into this. If there had been a key,

that would have been extremely bad. All right, Yeah, so let's let's talk a little bit about m ris of why they are important. Besides the fact that they look at your squishy bits as opposed to your skeletal system like all the uh, your lungs and liver and all that kind of stuff that they're really good for that. Um, it's a scientific term squishy bits. Yeah, well I'm not

I'm no adicition. Um, I don't have my my discinal degree. Uh. The it's it's non invasive, so that means it doesn't there's no there's no incisions that have to be made. And also unlike X rays, it is uh, it's not an ionizing form of radiation. Right now, X rays are uh, that is a form of ionizing radiation, which means that when the X rays hits you, they can create ions, which you know, it's essentially it's stripping electrons away from from atoms and this can cause cells to be damaged.

It can cause mutations, which is why you hear about you know, it's it's it's why anyone who works in an X ray laboratory laboratory, I could hear it. I don't know why that has every now and then I oratory. My schedule has me in the laboratory this afternoon. They but anyone who works in one of those they they usually have to be behind like a protective barrier for whenever they're running the machines. It's why when you get

an X ray done of your teeth. You may have to wear out like the lead apron because too much exposure to too too many X rays can cause damage. Well, m r I s do not use that kind of radiation. There is radiation that's involved, but it's not that it's not that ionizing radiation. So it's there's no real damage, um, that that could happen on that on that in that way. There are ways to get damaged getting an m r I, and you alluded to one of them earlier. So, um,

what exactly is going on here? The m r I. We said that that stands for magnetic resonance imaging. That magnetic, of course, is the really big part of this. There's a an enormous magnet that is um uh generating a very powerful magnetic field. Yes, extremely powerful. In fact, um uh. They measure the field in in tesla, not in gaus, which is typical of measuring magnetic fields, right right, gals is a is a unit that's much smaller than a tesla. Yeah. As a matter of fact, a tesla is equal to

ten thousand cows and uh typical m r I machine. Um. By the way, it's a very excellent article on this website. That you mentioned earlier, right, how stuff works dot com. Yeah, yeah, there is a great article on our m R I machines on there. But according to that article, um, we do uh there there is an field of about to tesla going on. So that's twenty thousand gaus if you are inside the machine and um, and it is a long machine. It's long enough to uh you know, stick

a whole human in there. Um. But yeah, so it's it's got very very powerful magnets in their most frequently their permanent magnets. Yeah, superconduction magnets. There are some that do use permanent magnets, you're right, but the majority superconduct Now, a superconductor is an interesting thing. They in order to get a it's essentially a electro magnet. But to really reach superconductivity, they have to lower the resistance within the

wires that create the magnetic field. Now if you I'm sure you all remember, but an electro magnet is essentially a coil of wire. You run an electric current through this coil of wire and that generates a magnetic field. Well, all wires have a certain amount of resistance. It's dependent upon the material of the wire and the gauge of the wire and resistance just that that that's going to inhibit the strength of the magnetic field. So to lower

the resistance, you actually lower the temperature. And with superconductive magnets you do this using liquid helium, which is incredibly cold. This is the same stuff they used to cool the Large Hadron Collider at CERN. That's point four degrees below zero if you're talking fahrenheit, or about to sixty nine point one below zero celsius, or as I call it on my scale, really really really really cold. Yeah, you're approaching absolute zero zero kelvin and um and of course

zero kelvin absolute zero. What that means is you've reached a point where there is no molecular movement. So really, when you think about temperature in a way, you're talking about how fast molecules move. That's that's kind of a way of thinking about it, right. Well, so this this way, you're reducing the movement of those molecules as much as possible. You run the electric current through it generates a very

powerful magnetic field. Now why do you create this magnetic field? Well, to do to really understand that, you have to understand that the the whole basis of m R I is uh is on the principles of nuclear magnetic resonance. Now, first of all, when you hear the word nuclear, you start to freak out right because you know, yeah, well it's nuclear power plants, nuclear bombs. You think about these

things that are potentially really powerful and devastatingly dangerous. But really it just means that it we're dealing with nuclei here, yes, the nucleus of an atom, and we're talking specifically about hydrogen. Hydrogen nucleus is a proton. You've got a proton an electron that's hydrogen, so you're nucleus is just proton. Now. Nuclear magnetic resonance is a spectroscopic technique that gets information about chemical and physical properties of a material at the

microscopic level. And it was developed it was actually discovered by Felix Block and Edward Purcell at the same time, independently. In why is it always? It seems like big advances in science are always there are always two people that figured out about the same time. I don't know. It is pretty interesting when you sit there and you think, well, you know what driving forces inspired two people in different parts of the world to study the same thing and

come to the same conclusion. Now, what I would argue is that that shows that science is good, because it means that if you follow the scientific method, you will reach the proper conclusion in time. Alright, then, so I figured there was some kind of bond between them. Science as good as the alternative title of this episode of tech stuff. Um. So, at any rate, they both actually were awarded the Nobel Prize in ninety two. Domedian did who invented the m R A machine, did not win

the Nobel Prize. But at any rate, you've got this this principle, and the principle essentially essentially states that there's this feature of of atoms called spines nuclear spin. Um. It's a little interesting and a little difficult to explain, but but atoms are spinning in a particular direction all right, independently of other materials. But if you introduce a magnetic field that's strong enough to the to the atoms, their

spin will align with that magnetic field. So it's kind of like when you think of iron filings and a magnet. If you have the magnet in a certain way, the iron filings will actually start to align themselves in the in the same direction as the magnetic field around that magnet. So first you create this magnetic field, a powerful magnetic field that's using the superconductor magnet, and you start to align these proton uh well, I'm starty, not just protons,

but these hydrogen nuclei in the proper alignment. Then you use a radio frequency that's a tune specifically to those nuclei, and you hit the nuclei with a frequency. When you do that, you excite some of the nuclei to a higher state uh of energy. And then when you stop, when you remove that radio frequency, the nuclear returned to their relaxed state. They go back to what they were

doing before, right. And by measuring this different difference, you can you can sort of see you know where the protons are, where the nuclear are, But you have to you have to get a little more specific than that. If you were just using the superconductor magnet and just using radio frequency, you would know that there were protons there, but you wouldn't really have a map, you wouldn't have an image that you could look at. It would just

tell you that there were nuclei there. So what you have to do is you have to actually add more magnets to the mix and create a gradiated magnetic field. So this this gradation, this variable magnetic field, gives you more information and you can actually map out what the the inside of something looks like based upon the position of hydrogen uh atoms just through blasting it with radio frequencies and putting this magnetic field around them. It's it's

pretty interesting stuff. And it's a little complicated. Um, actually it's a lot complicated. But because we're talking about really we're talking about nuclear physics when we get down to it, and um, of course, when you ever you talk about magnetism, eventually you get to a point where I'm just like, Okay, we're well beyond what I can easily explain. Nonetheless, they really like magnets, and you know what a super cool but um, and they're actually uh, I believe there are

actually three gradient magnets in an MR machine. Um, and they're not as powerful as the superconductor magnet, but they don't need to be right. Um, But let's see the U the tunnel. There's basically it's if you think about it, it it kind of looks like a donut on a stand, a very long donut, and you the the hole. In this case, it is called the bore b o r E. Yes, I also get that term when I go to parties, but we won't go there now, or sometimes when our

podcast goes long. But what happens when you go to UH to sit in for an m R I uh you are asked to basically leave everything behind. You don't wear your clothes. You have to you know, strip down and wear a hospital gown. They ask you things like, you know, do you have any metal in your body right?

Any screws or metal plates or if you have like a pacemaker, anything like that could be um, well, that would definitely be a problem, yes, because what what can happen during the m R I process is depending on the kind of metal that maybe inside, say it's a screw, um, uh, steel screw it would it could heat up and because internal burns, which are bad. Yeah, and you can't have any metal in the room because it's gonna fly right at that MR machine once you turn it on. That

would be fun. No, it's not fun. No, I mean that was sarcasm um and it's sadly it is. It has actually contributed well, it's contributed to a few pretty well publicized accidents in in m R I labs um, including I almost did again, Yeah, and you almost spit coffee all over me. Um. So I don't know what do with laboratory aluminium. Yes, aluminium, I think is you're you're pretty safe. It's not magnetics. And I have I have actually some some titanium inside and I was kind

of wondering about that. What's your key was made out of? Yeah, yes it is. No, I had, uh yeah, some clips from a previous surgery. You know. It's kind of concerned because I knew they were made of metal and they said, no, no, that's titanium. You're fine. No, I honestly did not know this. But apparently Mr Palette is the bionic man. Well you know that sixty million dollars doesn't buy what it used to. This is this is becoming all that more more and

more apparent. Actually was six million, it wasn't sixty adjusting for inflation. That's fair enough. But yeah, so they what they do is they have you lie down on this um. It's sort of like a long like you might see a gurney, except it's attached to the machine. You lie down and they there are motors attached to the underside of that and they when you are comfortably lying back on this device, they uh, the motors wheel you in and they don't necessarily have to put your entire body

in the machine, which is good for people who are claustrophobic. Right, they don't have to look at your head. It's probably better not to just you can actually go in feat first if if that's the case, I mean, um, and there are there are times where people have been sedated to uh in order to calm down enough to be able to go through an m r I. But that's tricky too because one of the other parts about getting an m r I done is you have to stay

very very still. That is the truth, because if you move at all, then you're going to distort the image because you're going to change the position of those those nuclei everything that happens to be inside you. By the way, in case you're wondering, we happen to have a lot of hydrogen in our bodies. Um, it's stored mostly in water and fat. But uh, one figure I read said that about oh of us is hydrogen, so uh, you know it's it's measuring where that is that we can

make the the images to to show what's happening. So yeah, when you go in and uh the magnet kicks on and the radio frequency starts to blast you, what's that like? Um? Well, one of the things that I have to say that the technician who administered the m R I that that I had earlier this year was very very patient. Um, and although I'm not claustrophobic, I was a little concerned that I might uh feel a little uncomfortable being in such a tight space. Uh. They did put me all

the way inside the bore of the m R I machine. Um. But one nice thing that they did, Uh they gave me a set of headphones and uh they had you know, gave me a variety of music to choose from, and I picked a station that I thought would be calming. Did you choose the Magnetic Fields Book of Love? No? I did not, but that is an excellent a series of records. Um. But uh no, that's funny. I'm sorry,

I'm just kind of funny. Um. But that and they put a towel over my eyes, you know, and had me lay back, and uh, they can actually talk to you from the booth so that you know, what are you doing now? You are you feeling okay? Um? You know, are you concerned? Um? What they didn't tell me was it makes a whole lot of noise. And I didn't read this article, uh, nor do any other research before

I went in. Uh so when this sounds, and I didn't hear a loud knocking, so this isn't uh you know, I've heard that some machines there is a loud knocking noise. Now I did not hear that. I heard sounded like a warning class in from a nineteen seventy two science fiction movie. And I'm going, well, either the bombing has started and they're leaving me here to die, or this is normal. Yeah, either the m I R I is going as planned, or the Klingons have have materialized off

the starboard bell exactly. I'm not kidding. It was me, and I'm going interesting, I assume that this is part of the normal functioning of the machine. And as it turned out, the Klingons left the hospital pretty much, uh you know, untouched. So that's good, that's good. But yeah,

it's it's a little it's a little disconcerting. But I didn't really I didn't really feel a lot, now, you know they that was up until that was probably the two thirds of the way through the m r I. And then they stopped and came in the room and had to move my body back out of the bore of the m r I. And I'm sure you probably know why that is. We got to the next phase of the m r I process because the m or I can only do so much by itself. At one point they ask you if you're willing to be injected

with a die, yes, a contrast die. Yes. The thing is it's it's from what I understand, it's radioactive and can cause some problems. Some people can have an allergic reaction to it. That is one of the dangers of the m r I is that you can you can actually suffer an allergic reaction to the contrast material. Yea, they gave me a nice long form to sign saying you really won't be angry at us if we kill you, right, I'm kidding. It was yes, and they were They explained

it in great details. So they were very many nice people. But um, but it's funnier to see it the other way. But yeah, and so they injected me with a die, which felt very weird and uh kind of kind of a cold feeling. Actually, yeah, I've I've had I've had various dyes injected into me, both on purpose and on accident. Hey, let's see if we can turn the more in. She's a weird your college experience. Anyway, Then they put me back inside the machine and ran the machine for another

fifteen minutes. The whole thing for me only took probably about an hour. Yeah, the they tend to be between fifteen and forty five minutes, but some can be a little longer. It all depends on the equipment, the technician, and exactly why you need to have the the m r I done because you know, if it's just one where you have to scan one little part of your body, then obviously that's not gonna take as long as if

you need, you know, like a full body scan. Um when when you're being put through the boar, or when anyone really is being put through the boar, the part of the body that needs to be scanned has to be in the center of it, which is called the ISO center of the boar um. And like I said that those radio frequencies start to excite the hydrogen atoms in your body flipping them making them go to a

higher energy state. And then when what happens is when they go to that lower energy state, they actually give off radio frequencies the atoms do. The nuclei give off these radio frequencies, which you use. The m r I machine picks up those radio frequencies and that's what provides the information to UH to locate where the nuclei are and thus build the picture of what's inside you. It's

actually pretty cool now, UM. Now, a lot of people kind of freak out because they or some people I'm sure do, because they hear the words radiation and they immediately think of ionizing radiation. But we're talking about radio frequencies here, not X rays or gamma raise or anything that would give you the power of super stretching abilities. So it was really disappointed. Yeah, I gotta admit I was a little disappointed to UM. But there are other things that can happen through an m r I that

can some interesting side effects that are possible. Well, first of all, not everyone can have an m r I because if you have any materials in you that would caught would interfere, obviously, that would be a bad idea. Um. But also beyond that, there's the you know, if you're too large, you couldn't have an m r I UM. And the boar is very very narrow. Yeah, it's like two ft in diameter. So uh but yeah. One of the other possible side effects I've heard about are called

magneto phosphenes. I'm impressed but that I was able to say magneto phosphines. Practiced that for about a minute before you. Yeah, I just I got to magneto and then I would say I'll crush you x men. But magneto phosphenes. The phosphene kind of gives it away. It's it's it's a visual phenomena. You get these visual sensations. It's like, um, it's like flashes of light, like you're like someone's taking photographs of you, which kind of they are, except it's

not really photograph um. But you're getting these flashes of light. And what's happening is it's it's not entirely understood, but it's it's these induced electrical currents that are occurring inside your retina when you move through the magnetic field. UM

or that the or a magnetic field is changing around you. UM. It's it doesn't happen with everyone, and it's not gonna happen on It's not gonna happen every time you get an m r I or even if you have experienced them before, there's no guarantee that you're going to experience them again if you have another m r I and Uh, they're harmless, but I'm sure that's very disorienting. Apart from these, there really aren't that many hazards to having an m

r I done. Uh. And there are other potential uses of m r I s that we're just starting to kind of develop now, like the the functional m r I s, which are really interesting. It's kind of making a map of the human brain, and it can be a real time map. You're actually looking at the images as someone is being subjected to various stimuli, and then you look at the patterns that are occurring in the

brain and you start to map functions that way. And the way this works is when you get someone to think about something like think about moving your hand, or think about the color blue or whatever, you know, whatever

the criteria are. Um oxygen goes to the brain and the level of oxy as the level of oxygen increases in the regions where there's brain activity that actually affects that magnetic field because oxygen is paramagnetic, and by measuring the differing levels of oxygen in the brain, you can kind of see brain activity. Interesting. Yeah, there's it's I mean, just the idea that you could you could do that,

I wonder how long. It seems like that would be sort of impractical though, well, because you'd have to I mean, you can't use you wouldn't. You would be limited in what you could offer the subject in stimuli because it had to it would have to fit in the more and not interfere with the machines. Involve a lot of

thinking and what you can do. But there's one one potential, uh use I've heard that's kind of scary and interesting at the same time, which is to use an f m R I as a new and improved lie detector. That's true, where you ask the subject questions and you observe the brain activity and look for attempts to be subversive or to elude the the question asker, person, interrogator.

That's a good word. We'll use that one. Hey, whatever, man, I've been up for a really long time, so um, yeah, that's that's kind of the the overall statement about m R eyes and how they work. It's it's really a very fascinating subject and if you really want to delve into the science. Um Dr Joseph P. Hornack h O r in A k of Rochester Institute of Technology, has

a hypertext textbook on m R eyes onlines free. You can read all about everything the science behind MR eyes, the math behind it, the math behind electron spins and and nuclei spins. It's really fast, sinating reading and it goes into way more detail and um you may need most of the most of the text is pretty understandable to someone who's got, you know, a good grounding in math and science, but some of it's going to go

beyond that. So you know, if you are interested in this sort of thing, I do recommend it, and also our article if you want to have kind of the general overview, and you know, we dive into the science, but we don't get so far down that you need a degree in science or mathematics in order to understand it. Our article at how stuff words dot com is also great, So I do recommend that. So that wraps up this discussion on m r I s if you have any

questions or suggestions for topics. We do plan on hitting some of these other medical topics in the future, so keep an ear out for those. Maybe we'll even have another like we've got our movie making series or medical series focus on series denystifying series. We could be called this demystifying the m R. I. I guess, but if you have any suggestions for similar topics, let us know. You can let's know on Twitter and Facebook are handled.

There is text stuff h s W or you can email us and that address is tech stuff At how stuff works dot com, Chris and I will talk to you again really soon for moral this and thousands of other topics. Is it how stuff works dot com. To learn more about the podcast, click on the podcast icon in the upper right corner of our homepage. The how Stuff Works iPhone app has arrived. Download it today on iTunes. Brought to you by the reinvented two thousand twelve camera. It's ready, are you