WEBVTT - 3D Printing and Tomography 0:00:04.240 --> 0:00:07.240 Welcome to tex Stuff, a production of I Heart Radios, 0:00:07.320 --> 0:00:14.040 How Stuff Works. Hey there, and welcome to tex Stuff. 0:00:14.120 --> 0:00:17.480 I'm your host, Jonathan Strickland. I'm an executive producer with 0:00:17.560 --> 0:00:20.360 I Heart Radio and a love of all things tech. Now, 0:00:20.360 --> 0:00:23.680 before I jump into this episode, I want to address 0:00:23.800 --> 0:00:28.800 an error I made multiple times in a recent episode, 0:00:29.440 --> 0:00:34.479 and it's a very Jonathan kind of mistake. So in 0:00:34.520 --> 0:00:38.640 the episode I did about smoke detectors, I talked about 0:00:38.640 --> 0:00:44.000 the radioactive element ama sirium to forty one. Here's the problem. 0:00:44.040 --> 0:00:47.239 I inserted an extra syllable there, and even in my 0:00:47.280 --> 0:00:51.120 notes I had it spelled correctly. It's a marasium to 0:00:51.360 --> 0:00:54.280 forty one. So in other words, I I kind of 0:00:54.320 --> 0:00:59.600 pulled a classic Homer Simpson goof, like a Saxoma phone uh, 0:00:59.680 --> 0:01:02.720 several times in one episode. So thanks to Twitter user 0:01:02.840 --> 0:01:06.800 Ken Waldrop for pointing it out. It is incredibly embarrassing. 0:01:07.120 --> 0:01:11.240 It is all my mistake. It's totally me. It's kind 0:01:11.240 --> 0:01:15.520 of an insight into how Jonathan's brain works, which is 0:01:15.520 --> 0:01:19.679 not all that great sometimes. I don't know why I 0:01:19.760 --> 0:01:24.280 inserted an extra syllable multiple times throughout that episode, but 0:01:24.720 --> 0:01:27.160 thank you Ken for letting me know, so that I 0:01:27.200 --> 0:01:30.560 could correct that error in this episode. Let's move on 0:01:30.600 --> 0:01:34.520 to another episode where I'm sure I will mispronounce multiple things. 0:01:35.680 --> 0:01:38.520 But it's a fascinating topic, or at least I find 0:01:38.520 --> 0:01:42.360 it fascinating. So I was looking through tech news recently 0:01:42.800 --> 0:01:45.440 and I saw a really interesting article. It was covered 0:01:45.440 --> 0:01:47.320 in a lot of places. The first place I saw 0:01:47.319 --> 0:01:50.480 it was engadget, but I read about it elsewhere as well, 0:01:50.880 --> 0:01:54.680 and on engadget it has the title Researchers find a 0:01:54.720 --> 0:01:59.240 way to three D print whole objects in seconds. Now 0:01:59.280 --> 0:02:02.880 that immediately got my attention because typically three D printing 0:02:02.880 --> 0:02:06.440 takes a while, sometimes a long while to create an object, 0:02:06.440 --> 0:02:10.640 because it typically does it layer by layer. The answer 0:02:10.680 --> 0:02:14.160 in this case lies in the technique called tomography. So 0:02:14.200 --> 0:02:16.560 this episode is going to cover a few different topics 0:02:16.840 --> 0:02:19.520 so that I can explain as best I can how 0:02:19.560 --> 0:02:24.240 this methodology works. So let's start talking first about just 0:02:24.400 --> 0:02:28.639 three D printing in general. It's a type of additive manufacturing, 0:02:28.880 --> 0:02:32.639 which means you're making something by adding to it rather 0:02:32.720 --> 0:02:37.440 than taking unwanted stuff away. So with traditional sculpture, the 0:02:37.480 --> 0:02:40.960 sculptor might take a block of some material like marble 0:02:41.200 --> 0:02:44.320 and then carve it and cut away tons of it. 0:02:44.520 --> 0:02:51.279 There's an undoubtedly apocryphal quote attributed to Michaelangelo who allegedly 0:02:51.320 --> 0:02:54.800 described his process as you just chip away the stone 0:02:54.800 --> 0:03:00.400 that doesn't look like David. Now, Mikey probably never said that, 0:03:01.040 --> 0:03:03.560 but you get the point of the quote. You're removing 0:03:03.720 --> 0:03:07.720 material and whatever is left after you're done is the 0:03:07.760 --> 0:03:12.959 finished piece. Additive manufacturing goes the opposite way. You add 0:03:13.000 --> 0:03:16.360 material bit by bit until you have the thing you 0:03:16.400 --> 0:03:19.360 wanted to make. So it's kind of like how potters work, 0:03:19.480 --> 0:03:22.560 you know, you add clay until you've got enough mass 0:03:22.600 --> 0:03:26.880 to shape it into whatever final form they have in mind. 0:03:27.400 --> 0:03:30.000 And three D printers work in a similar way. They 0:03:30.080 --> 0:03:35.200 lay down thin layers of material one after another until 0:03:35.320 --> 0:03:38.200 layer by layer they have completed a print job, and 0:03:38.240 --> 0:03:42.400 typically the bottom surface would be whichever one is the 0:03:42.520 --> 0:03:46.000 largest of the finished three D object, So it might 0:03:46.000 --> 0:03:48.680 not necessarily be the bottom of the three D object, 0:03:49.040 --> 0:03:51.880 but the bottom of the print job, because a larger 0:03:51.920 --> 0:03:54.200 surface area means it's going to support the rest of 0:03:54.200 --> 0:03:58.440 that physical structure much more easily. There are three D printers. 0:03:58.640 --> 0:04:01.560 They can work with all sorts of materials. The kind 0:04:01.600 --> 0:04:05.320 of average person would have access to. Uses plastic, one 0:04:05.360 --> 0:04:08.800 of two types, and a typical three D printer uses 0:04:08.920 --> 0:04:12.760 spools of plastic cable as printing material. So the cable 0:04:12.840 --> 0:04:16.760 gets pulled into a piece called the extruder, which heats 0:04:16.800 --> 0:04:20.120 the plastic to make it sort of a semi liquid 0:04:20.200 --> 0:04:23.800 before depositing layers of this plastic, usually mixed with some 0:04:23.880 --> 0:04:28.640 sort of binding agent, onto the printing surface, or after 0:04:28.839 --> 0:04:32.839 the first layer, onto the last layer that was laid down. 0:04:33.160 --> 0:04:35.520 This process tends to take a while, and you have 0:04:35.600 --> 0:04:38.919 to get the temperature and speed just right, or you 0:04:38.960 --> 0:04:42.120 get problems with layers not adhering to each other properly, 0:04:42.360 --> 0:04:45.680 or peeling away or sticking to the extruder as it 0:04:45.680 --> 0:04:48.520 moves through its path. I say this from experience. We 0:04:48.600 --> 0:04:51.000 have a three D printer in the office. We have 0:04:51.440 --> 0:04:55.839 successfully printed on it perhaps four times. We have run 0:04:55.880 --> 0:04:59.800 it many more times than that. But however, it does 0:04:59.839 --> 0:05:03.200 me you can actually make whatever the object is relatively 0:05:03.279 --> 0:05:08.360 quickly compared to more traditional forms of manufacturing, and there 0:05:08.400 --> 0:05:10.560 are lots of benefits with three D printing. One is 0:05:10.640 --> 0:05:14.320 that it makes the prototyping process much faster. So let's 0:05:14.320 --> 0:05:16.320 say you got an idea for the body shape of 0:05:16.360 --> 0:05:19.160 a car. You could build a three D model of 0:05:19.200 --> 0:05:21.520 the shape. Then you could use a three D printer 0:05:21.720 --> 0:05:24.800 to create a small physical model of what you had 0:05:24.800 --> 0:05:27.279 in mind, and you could test that and say a 0:05:27.279 --> 0:05:29.719 wind tunnel, to make sure it would work the way 0:05:29.760 --> 0:05:33.120 you planned before you moved further into the process. But 0:05:33.279 --> 0:05:36.560 maybe you discover that your design has some unexpected quality, 0:05:36.600 --> 0:05:40.360 like increased air resistance, so the extra drag would mean 0:05:40.400 --> 0:05:42.640 the car would not be as fuel efficient, so you 0:05:42.680 --> 0:05:44.440 need to go back to the drawing board. You could 0:05:44.440 --> 0:05:47.480 go make some quick adjustments to your model and then 0:05:47.600 --> 0:05:49.760 send that to the printer again and print up a 0:05:49.760 --> 0:05:53.359 new prototype and would go pretty quickly. You don't have 0:05:53.400 --> 0:05:56.159 to carve away its stuff over and over, and another 0:05:56.200 --> 0:05:59.880 big benefit is that you have less waste overall. You're 0:06:00.160 --> 0:06:02.640 taking material and then only using a small part of 0:06:02.680 --> 0:06:05.400 the overall mass and throwing the rest away. So lots 0:06:05.440 --> 0:06:08.839 of companies that manufacture physical goods use three D printing 0:06:09.160 --> 0:06:12.279 for the prototyping phase, and several are using three D 0:06:12.360 --> 0:06:16.400 printing in the actual manufacturing process for finished items, whether 0:06:16.440 --> 0:06:19.719 it's for a small component that goes into a bigger 0:06:19.760 --> 0:06:23.560 product or a complete product from top to bottom. And 0:06:23.680 --> 0:06:26.360 while we've heard predictions that three D printing would bring 0:06:26.360 --> 0:06:29.960 about the end two mass manufacturing as we know it, 0:06:30.520 --> 0:06:33.000 the future in which everyone either has a three D 0:06:33.080 --> 0:06:36.360 printer or has easy access to a business that owns 0:06:36.360 --> 0:06:40.239 a three D printer. Thus far, that has not happened. 0:06:40.279 --> 0:06:41.880 We have not seen a world where we all just 0:06:42.000 --> 0:06:44.200 print whatever we need on demand, where I sit there 0:06:44.200 --> 0:06:46.160 and think, oh, I need a new chair, so I'm 0:06:46.160 --> 0:06:47.880 gonna go down to the three D printers down the 0:06:47.880 --> 0:06:50.640 block and get one printed out. That has not yet happened. 0:06:51.120 --> 0:06:53.560 Maybe one day that will change, but for now the 0:06:53.600 --> 0:06:58.039 process isn't quite as convenient or as reliable as more 0:06:58.040 --> 0:07:03.080 traditional manufacturing methods. But that's traditional three D printers, and 0:07:03.120 --> 0:07:06.039 I've done episodes to go further into detail about their 0:07:06.080 --> 0:07:08.560 history and how they work. So you can go and 0:07:08.600 --> 0:07:10.920 listen to those classic episodes if you want to hear 0:07:10.960 --> 0:07:12.920 more about that. But that's not what we're going to 0:07:12.920 --> 0:07:15.200 focus on for the rest of this episode. Now it's 0:07:15.240 --> 0:07:18.880 time to switch over to tomography, which is not the 0:07:18.920 --> 0:07:22.920 science of how tom works. It's that has nothing to 0:07:22.960 --> 0:07:25.880 do with tom and my space. Now, this relates to 0:07:26.000 --> 0:07:28.960 radiography and the use of stuff like X rays. Those 0:07:29.000 --> 0:07:32.040 we'll learn. It's not exclusively limited to X rays. And 0:07:32.080 --> 0:07:33.800 I know I've talked a lot about X rays in 0:07:33.800 --> 0:07:36.680 recent episodes, but bear with me here. So early on, 0:07:37.280 --> 0:07:41.760 physicists learned about how X rays could penetrate solid material 0:07:42.280 --> 0:07:45.480 much more effectively than visible light could, and that if 0:07:45.480 --> 0:07:48.960 these X rays hit a sheet of photoreactive material, it 0:07:49.000 --> 0:07:51.840 would cause that material to react, so it reacted as 0:07:51.880 --> 0:07:54.840 if visible light had hit it. So if you put 0:07:54.880 --> 0:07:59.000 something like, I don't know your wife's hand between an 0:07:59.160 --> 0:08:02.680 X ray emitter and a sheet of photographic paper, you 0:08:02.720 --> 0:08:06.840 would end up with an image of your wife's skeletal 0:08:06.880 --> 0:08:10.160 hand on that paper. I say wife because runt Jen 0:08:10.320 --> 0:08:14.240 Vilham run Jen, who discovered X rays, used his wife 0:08:14.240 --> 0:08:16.800 as a photographic subject for a lot of early X 0:08:16.880 --> 0:08:21.080 ray photographs, exposing her two ridiculous amounts of radiation in 0:08:21.120 --> 0:08:24.200 the process. At the time, he didn't know any better. 0:08:24.800 --> 0:08:28.000 But that's why I use that specific example. Now, why 0:08:28.360 --> 0:08:32.760 do you get the skeleton hand in the finished image. Well, 0:08:32.800 --> 0:08:36.880 it's because X rays can pass through different materials with 0:08:36.960 --> 0:08:39.959 different levels of ease, so they can pass through less 0:08:40.000 --> 0:08:44.040 dense material more easily than the denser stuff, and that 0:08:44.080 --> 0:08:47.320 follows common logic. That just makes sense, right. So X 0:08:47.400 --> 0:08:51.319 rays can pass through muscle tissue far more readily than 0:08:51.360 --> 0:08:54.920 they can pass through bone, and bone is just much 0:08:54.960 --> 0:08:58.520 more dense. They can pass even less easily through something 0:08:58.559 --> 0:09:02.000 like metal. So if you were to take an X 0:09:02.120 --> 0:09:06.520 ray photo of a typical person's hand, the bone would 0:09:06.520 --> 0:09:10.239 block more X rays from hitting the paper than the 0:09:10.280 --> 0:09:13.280 soft tissues would. The soft tissues would allow more X 0:09:13.360 --> 0:09:15.680 rays to come through. So the result is that the 0:09:15.720 --> 0:09:17.680 image on the photographic paper would be kind of like 0:09:17.720 --> 0:09:20.680 a negative. The skeletal hand would show the spots on 0:09:20.720 --> 0:09:23.160 the paper where X rays were blocked from hitting it, 0:09:23.800 --> 0:09:27.880 and that meant that it would be relatively unexposed to light, 0:09:28.600 --> 0:09:31.160 and the softer tissues would allow it to go through, 0:09:31.200 --> 0:09:33.600 and thus you would have a greater exposure. So you 0:09:33.600 --> 0:09:36.559 can see that skeletal hand because the contrast between these 0:09:36.559 --> 0:09:40.360 two sections where the rays were blocked versus where they 0:09:40.400 --> 0:09:43.600 passed through. Now, the discovery of X rays came at 0:09:43.640 --> 0:09:47.840 the very end of the nineteenth century. The medical establishment 0:09:48.080 --> 0:09:51.240 quickly saw the potential for this technology. They saw that 0:09:51.440 --> 0:09:54.319 this could be really valuable. You can see stuff like 0:09:54.360 --> 0:09:59.520 broken bones very easily. They immediately recognized its usefulness. They 0:09:59.600 --> 0:10:04.720 also over time recognized some of the dangers of X rays, 0:10:04.760 --> 0:10:07.400 such as radiation exposure, which was really more of a 0:10:07.400 --> 0:10:10.680 problem for doctors than it was for patients. Patients would 0:10:10.720 --> 0:10:13.880 get small exposures whenever they would get an X ray 0:10:14.679 --> 0:10:17.160 done on them, but the doctors who were performing the 0:10:17.280 --> 0:10:20.320 X rays, we're getting exposures time and time again, and 0:10:20.360 --> 0:10:22.559 they were the ones who were really sorry to develop 0:10:22.880 --> 0:10:27.160 serious problems because X rays are a form of ionizing radiation, 0:10:27.400 --> 0:10:29.920 which means they can do cellular damage, and that in 0:10:29.960 --> 0:10:33.960 turn can manifest in different ways from radiation poisoning to 0:10:34.920 --> 0:10:40.679 higher risk of contracting cancer. So uh, they also saw 0:10:41.000 --> 0:10:45.800 a limitation of this technology, namely that X ray photos 0:10:45.840 --> 0:10:49.800 have the same problem as any traditional photo has. They 0:10:49.840 --> 0:10:54.360 produced two dimensional images of three dimensional objects. So in 0:10:54.400 --> 0:10:57.839 medical schools, it was pretty standard practice for students to 0:10:57.880 --> 0:11:03.240 work with or even produce cross sections of organs. Essentially 0:11:03.280 --> 0:11:06.880 involves cutting organs into thin slices like a loaf of bread, 0:11:07.320 --> 0:11:10.439 and then examining each of those slices carefully, and it's 0:11:10.440 --> 0:11:13.600 an effective way to teach medical students about anatomy and 0:11:13.840 --> 0:11:17.360 organ structures as well as learning what is and isn't typical, 0:11:17.679 --> 0:11:20.679 so that if one were to encounter an atypical scenario, 0:11:21.360 --> 0:11:24.440 the doctor would be able to recognize that as such. Now, 0:11:24.480 --> 0:11:26.200 if you put all the slices together, it looks like 0:11:26.240 --> 0:11:28.720 the original organ. Of course, the big problem with this 0:11:28.800 --> 0:11:31.679 method is that it usually requires the original owner of 0:11:31.679 --> 0:11:37.720 that organ to be, you know, not alive anymore, making 0:11:37.720 --> 0:11:41.600 it a little difficult to apply medical knowledge to their case. 0:11:42.040 --> 0:11:45.280 So it's a useful educational tool, but not great for 0:11:45.360 --> 0:11:49.160 diagnosing a patient, at least not in a timely manner. 0:11:49.559 --> 0:11:51.800 So doctors at the time were hopeful that there would 0:11:51.800 --> 0:11:54.160 be a new technology that would make it possible to 0:11:54.240 --> 0:11:58.320 create images of three dimensional objects in an accurate way, 0:11:58.400 --> 0:12:02.880 specifically organs showing their volume metric property, so that you 0:12:02.920 --> 0:12:05.400 could do things like look at them in perspective, as 0:12:05.400 --> 0:12:08.040 opposed to looking at what amounted to a series of 0:12:08.040 --> 0:12:10.560 silhouettes of organs and bones. If you took an X 0:12:10.640 --> 0:12:13.800 ray of someone's torso the rib cage would obscure a 0:12:13.800 --> 0:12:17.240 lot of your your view. And then your lungs in 0:12:17.280 --> 0:12:21.280 your heart are located in an area where it's hard 0:12:21.320 --> 0:12:25.800 to see them individually because they're overlapping each other, so 0:12:25.840 --> 0:12:27.640 they wanted to find a way to create a three 0:12:27.640 --> 0:12:31.920 dimensional representation of this. Doctors at the time, we're hopeful 0:12:32.000 --> 0:12:34.800 that they could come up with a way of doing 0:12:34.800 --> 0:12:37.720 this in a practical manner, but they weren't really sure 0:12:37.920 --> 0:12:41.440 how that would happen now. One person whose work would 0:12:41.520 --> 0:12:45.640 contribute to achieving this goal, though that was not his 0:12:45.880 --> 0:12:49.120 particular aim at the time, was a mathematician in the 0:12:49.120 --> 0:12:55.280 early twentieth century named Johann Raydon. In nineteen seventeen, Raydon 0:12:55.440 --> 0:13:00.240 produced a mathematical transform, a specifically an integral trans form, 0:13:00.360 --> 0:13:03.960 which means you add up basic elements until you get 0:13:04.040 --> 0:13:07.480 the full thing you're looking for. There are a lot 0:13:07.480 --> 0:13:10.800 of different versions of integral transforms, and he also discovered 0:13:10.840 --> 0:13:14.920 its inverse. So this transform described mathematically a process that 0:13:14.960 --> 0:13:18.079 could be realized in a practical setting, namely that one 0:13:18.120 --> 0:13:22.280 could take the result of projections of an object and 0:13:22.400 --> 0:13:26.520 reconstruct an image in real space based on those projections. 0:13:26.559 --> 0:13:28.840 It all has to do with geometry, and again into 0:13:28.840 --> 0:13:32.880 further detail would require someone far more educated in mathematics 0:13:32.880 --> 0:13:36.000 than i am, but there are some great videos online 0:13:36.240 --> 0:13:39.000 about the Radon transform that give it a good explanation 0:13:39.040 --> 0:13:42.760 of it, including one from Rich rad k It's titled 0:13:42.960 --> 0:13:47.560 d I P Lecture eighteen Reconstruction from Parallel Projections and 0:13:47.600 --> 0:13:50.319 the Radon transform. You can find that on YouTube if 0:13:50.360 --> 0:13:54.120 you want to see a really detailed mathematical explanation of 0:13:54.160 --> 0:13:56.520 this that is far beyond what I can give you. 0:13:57.080 --> 0:13:59.400 Radon's work was interesting, but at the time there wasn't 0:13:59.440 --> 0:14:02.280 really any practical way to put it into actual use. 0:14:03.120 --> 0:14:06.040 One early step in getting to the goal was the 0:14:06.080 --> 0:14:11.160 development of linear tomography, or the ability to take radiographic 0:14:11.240 --> 0:14:15.360 images of a specific plane or cross section in a 0:14:15.440 --> 0:14:19.200 solid object like a human being. So, in other words, 0:14:19.200 --> 0:14:21.160 you could create a cross section of a human being 0:14:21.400 --> 0:14:24.680 without having to cut the human being open. It was 0:14:24.720 --> 0:14:28.800 a miracle. So this relates to that mathematical transform I 0:14:28.880 --> 0:14:32.320 just mentioned, and interestingly, in the early days of tomography 0:14:32.520 --> 0:14:36.680 they that actually would predate Radon's transformers. Physicists were thinking 0:14:36.680 --> 0:14:39.840 about how to take X ray images from multiple angles 0:14:39.880 --> 0:14:43.200 to get a more complete picture of a specific internal 0:14:43.360 --> 0:14:48.120 organ as early as nineteen fourteen. For actual implementations, there 0:14:48.160 --> 0:14:50.920 was a period from around nineteen twenty one to nineteen 0:14:50.960 --> 0:14:55.400 thirty four in which multiple people all working independently, all 0:14:55.440 --> 0:14:59.360 not knowing about each other, started to build systems capable 0:14:59.360 --> 0:15:04.560 of producing what would be called tomographic images. They didn't 0:15:04.600 --> 0:15:08.040 know about the other's work for a very long time, 0:15:08.080 --> 0:15:10.480 and when they found out. Can you guess what happened? 0:15:11.160 --> 0:15:14.200 If your guess was, I bet they all rushed to 0:15:14.240 --> 0:15:17.280 be the one to claim credit for it, you'd be right, 0:15:17.360 --> 0:15:20.600 because that was a very human reaction to say I'm 0:15:20.640 --> 0:15:23.600 the reason why this works. But that was put on 0:15:23.640 --> 0:15:27.240 hold because a little thing called World War two happened. 0:15:27.920 --> 0:15:31.720 The basic idea was the same from one instance to 0:15:31.760 --> 0:15:34.120 another instance that all these people were coming up with, 0:15:34.160 --> 0:15:37.200 but the actual details were different, such as the angles 0:15:37.240 --> 0:15:40.360 of motion for the X ray emitter and the detectors 0:15:40.360 --> 0:15:42.920 which would be on the opposite side of the patient, 0:15:43.480 --> 0:15:46.520 or the speed at which these components should move with 0:15:46.560 --> 0:15:49.960 each other. Also, the word tomography itself was coined around 0:15:50.040 --> 0:15:53.400 nineteen thirty five and comes from the Greek word thomas, 0:15:53.920 --> 0:15:58.480 meaning section, and the suffix graphy from the Latin word 0:15:58.880 --> 0:16:02.800 graphia mean study of So it's the study of sections 0:16:02.840 --> 0:16:05.480 and it combines Greek and Latin. So I have friends 0:16:05.520 --> 0:16:10.040 who hate this word. They would say, stick with one 0:16:10.240 --> 0:16:14.160 or the other, um, one of them sitting right across 0:16:14.200 --> 0:16:17.840 from me, but never mind that anyway. So imagine you've 0:16:17.880 --> 0:16:22.040 got a person standing in front of you, and you 0:16:22.080 --> 0:16:26.080 are somehow able to produce an image of a slice 0:16:26.400 --> 0:16:30.200 of that person from head to toe, and their shoulders 0:16:30.200 --> 0:16:32.000 are facing you. So it's like it's like you just 0:16:32.280 --> 0:16:34.760 are able to look at a slice of them right 0:16:34.840 --> 0:16:38.080 from the middle of that person, but you're able to 0:16:38.080 --> 0:16:40.360 do it without, you know, actually physically slicing them. So 0:16:40.360 --> 0:16:42.640 how does it work. Well, I'm gonna do my best 0:16:42.640 --> 0:16:45.040 to try and explain this process. So this is gonna 0:16:45.080 --> 0:16:47.920 be an example. They don't all have to look this way, 0:16:47.920 --> 0:16:50.400 but this is a way for me to explain how 0:16:50.440 --> 0:16:53.800 this could happen. Imagine that we've got a patient laying 0:16:53.840 --> 0:16:57.520 down on an X ray table, and above this patient 0:16:57.680 --> 0:17:00.880 there is a track that's in an kind of like 0:17:00.920 --> 0:17:04.920 a rainbow above the patient, starting from around the head 0:17:05.000 --> 0:17:09.639 and ending somewhere around let's say the knees. Uh On 0:17:09.800 --> 0:17:13.840 this arc is mounted an X ray emitter, So this 0:17:13.920 --> 0:17:16.960 is the tube that will shoot out X rays at 0:17:16.960 --> 0:17:20.960 the patient. On the opposite side are X ray detectors. 0:17:20.960 --> 0:17:23.920 This is underneath the table and the two can move 0:17:23.960 --> 0:17:29.119 with each other, So you start UH make moving the 0:17:29.119 --> 0:17:33.399 the emitter along this track. It moves gets in motion 0:17:34.080 --> 0:17:37.080 once it starts. Shortly after it started to move, it 0:17:37.119 --> 0:17:41.120 begins to emit X rays, and then it nears the 0:17:41.240 --> 0:17:43.879 end of its arc, it stops emitting X rays and 0:17:43.920 --> 0:17:47.320 then it comes to a physical stop. And you're aiming 0:17:47.359 --> 0:17:49.760 this at a specific point on the patient. Perhaps you 0:17:49.800 --> 0:17:53.400 want to image this patient's liver, so you've aimed the 0:17:53.440 --> 0:17:56.400 emitter at the patient's liver, and as it goes through 0:17:56.400 --> 0:18:00.360 this entire arc, it still stays focused on a liver, 0:18:00.840 --> 0:18:03.359 so that point of focus does not change as it 0:18:03.400 --> 0:18:08.679 goes through this arc. UH. That liver will then become 0:18:08.880 --> 0:18:14.240 the pivot point for this particular scan. The ends of 0:18:14.320 --> 0:18:17.920 the seesaw of this pivot point would be the X 0:18:18.040 --> 0:18:20.600 ray tube on one side and the X ray receptors 0:18:20.640 --> 0:18:22.920 on the other side. So if you think of a 0:18:22.960 --> 0:18:25.359 seesaw going up and down, in this case, it's not 0:18:25.400 --> 0:18:27.440 really going up and down, it's just going through an arc. 0:18:27.880 --> 0:18:30.280 Then one end of the seesaw is the emitter, the 0:18:30.280 --> 0:18:33.119 other end of the seesaw is the receiver, and the 0:18:33.160 --> 0:18:39.120 middle is the liver. The pivot point the The angle 0:18:40.000 --> 0:18:42.960 from the top of the arc to the bottom of 0:18:43.000 --> 0:18:47.040 the arc is called the tomographic angle. The angle at 0:18:47.040 --> 0:18:50.360 which the X ray emitter starts to admit X rays, 0:18:50.480 --> 0:18:52.840 and the angle at which are and when it stops 0:18:53.480 --> 0:18:56.159 is called the exposure angles. There are two different angles 0:18:56.160 --> 0:18:58.560 in here. The exposure angle is always going to be 0:18:58.600 --> 0:19:03.760 smaller than the tomographic angle because of that. So how 0:19:05.200 --> 0:19:08.119 why why would you go through all this? What? What's 0:19:08.160 --> 0:19:20.240 the end result? I'll explain after we take a quick break. Okay, 0:19:20.280 --> 0:19:23.840 I just described this weird process of an X ray 0:19:23.840 --> 0:19:27.160 emitter going across an arc aimed at a patient. Why 0:19:27.200 --> 0:19:30.520 would you do that? Well, it's because the image produced 0:19:30.560 --> 0:19:33.560 at the end of this process creates a very sharp 0:19:33.680 --> 0:19:38.640 picture of everything within the exposure angle along the focal 0:19:38.760 --> 0:19:42.960 plane of the pivot point. So let's say you're looking 0:19:43.000 --> 0:19:45.080 at this patient from the side the patient's laying on 0:19:45.119 --> 0:19:48.080 the table, you're off to an observation area off to 0:19:48.119 --> 0:19:52.520 the side. The focal plane is the horizontal slice of 0:19:52.560 --> 0:19:55.960 that patient that runs through the pivot point. So let's 0:19:55.960 --> 0:19:58.479 say that you've determined that you wanted to aim at 0:19:58.480 --> 0:20:01.320 a point that's about eight centim ter's up from the 0:20:01.320 --> 0:20:04.480 surface of the table. That means that at that eight 0:20:04.520 --> 0:20:08.919 centimeters height along that entire horizontal slice of the patient, 0:20:09.400 --> 0:20:13.879 you're gonna get a very clear X ray image. The 0:20:14.000 --> 0:20:16.560 further out you are from the focal plane, so the 0:20:16.600 --> 0:20:21.920 further towards the patient's front or anterior and back or posterior, 0:20:22.359 --> 0:20:25.400 then the fuzzier the image is going to be. Now, 0:20:25.400 --> 0:20:28.119 in this way, a radiologist could produce a sharp image 0:20:28.119 --> 0:20:31.240 of a specific slice inside a person. You would get 0:20:31.280 --> 0:20:34.240 that cross section, but you still have to deal with 0:20:34.240 --> 0:20:36.280 other issues, such as the fact that bone is more 0:20:36.280 --> 0:20:39.080 effective in blocking X rays than soft tissues or water. 0:20:39.480 --> 0:20:41.439 So if the area you wanted to look at was 0:20:41.760 --> 0:20:44.560 below bone, such as within the rib cage, the bones 0:20:44.560 --> 0:20:47.280 would still present something of a problem, but you would 0:20:47.280 --> 0:20:50.399 still get a better look within a specific depth of 0:20:50.440 --> 0:20:52.960 a person, if that makes sense. So it was definitely 0:20:53.040 --> 0:20:56.320 an evolution of the science of radiology. Now you can 0:20:56.400 --> 0:20:59.360 repeat this process, and you could adjust the pivot location 0:21:00.160 --> 0:21:03.520 further up or further down to get sharp images along 0:21:03.600 --> 0:21:06.800 different depths. But that also means you're also exposing the 0:21:06.840 --> 0:21:10.880 patient to multiple, you know, exposures of X ray radiation. 0:21:11.359 --> 0:21:15.840 A little exposure presents relatively low risk, but the more 0:21:15.960 --> 0:21:18.040 you're exposed to X rays, the greater the risk of 0:21:18.080 --> 0:21:21.520 adverse effects like damage to yourselves, right, so you want 0:21:21.520 --> 0:21:25.040 to be careful with this. Over time, advances in technology 0:21:25.160 --> 0:21:29.480 created the possibility of axial tomography, which was introduced in 0:21:29.480 --> 0:21:32.280 the nineteen seventies. So in this version, instead of having 0:21:32.320 --> 0:21:36.359 an arc above the patient, the X ray emitter and 0:21:36.480 --> 0:21:40.439 receivers are mounted on a ring that goes around a table. 0:21:40.760 --> 0:21:43.760 So think of a table that passes through a ring 0:21:43.880 --> 0:21:46.680 and the patient lays on the table. The emitter and 0:21:46.720 --> 0:21:48.920 the receivers are mounted on opposite sides of this ring, 0:21:49.359 --> 0:21:51.280 and the patient and table are at the center of it. 0:21:51.680 --> 0:21:55.040 And with axial tomography, you take a series of images 0:21:55.119 --> 0:21:58.240 with the X ray tube along different points of the ring, 0:21:58.320 --> 0:22:00.320 moving in a full circle around the patient it on 0:22:00.359 --> 0:22:03.080 the table, So you get above, below, and on either 0:22:03.160 --> 0:22:06.159 side and every angle you can really imagine, and the 0:22:06.200 --> 0:22:09.560 machines typically take a ton of quick images as the 0:22:09.600 --> 0:22:12.760 machine rotates around the table very very fast. You can 0:22:12.800 --> 0:22:17.199 actually find videos of a cat scan because this is 0:22:17.440 --> 0:22:21.640 what this is a computer axial tomography scan. You can 0:22:21.640 --> 0:22:25.840 find videos of this equipment rotating where the cover is 0:22:25.880 --> 0:22:28.760 off so you can see how the internal structure rotates 0:22:28.800 --> 0:22:33.480 within this this machine. It's amazing how fast it goes. 0:22:33.960 --> 0:22:36.760 Uh I found it almost alarming how fast it goes, 0:22:36.840 --> 0:22:39.240 because these machines also are very big, and to think 0:22:39.240 --> 0:22:42.000 that something is spinning that fast around you is a 0:22:42.040 --> 0:22:44.960 little unsettling. But the result of all this fuss is 0:22:45.000 --> 0:22:48.000 you get a cross section image of the subject, and 0:22:48.000 --> 0:22:50.800 the table can be moved further in or out of 0:22:50.800 --> 0:22:53.480 the ring, and another series of images can be taken, 0:22:53.680 --> 0:22:55.760 and that gives you another cross section, and you could 0:22:55.800 --> 0:22:58.600 do it again and take another cross section. You do 0:22:58.680 --> 0:23:01.280 this no off and you eventually end up with images, 0:23:01.440 --> 0:23:04.440 three dimensional images of the stuff you want to take 0:23:04.480 --> 0:23:08.520 pictures of, and you're able to put that together through 0:23:08.560 --> 0:23:12.920 the help of computers. Engineers would call these CATS scans, 0:23:12.920 --> 0:23:16.080 and later just CT scans. A bit later, in the 0:23:16.160 --> 0:23:19.800 nineteen seventies, you had Dr Raymond Damedian who created a 0:23:19.840 --> 0:23:24.320 device capable of imaging internal body scans using magnetic resonance 0:23:24.600 --> 0:23:27.359 rather than X rays. The major benefit of this technology 0:23:27.400 --> 0:23:30.040 is that, unlike X rays, m r I machines do 0:23:30.119 --> 0:23:34.879 not emit ionizing radiation, so you don't get that radiation 0:23:35.119 --> 0:23:38.320 damage to yourselves with an MRI machine. There are other 0:23:38.400 --> 0:23:41.520