How X-rays see through your skin – Ge Wang


In 1895, a physicist named
Wilhelm Roentgen was doing experiments
with a cathode tube, a glass container in which a beam of
electrons lights up a fluorescent window. He had wrapped cardboard around the tube to keep the fluorescent
light from escaping, when something peculiar happened. Another screen outside the tube
was glowing. In other words, invisible rays
had passed through the cardboard. Wilhelm had no idea what those rays were,
so he called them X-rays, and his discovery eventually won him
a Nobel Prize. Here’s what we now know was happening. When high energy electrons
in the cathode tube hit a metal component, they either got slowed down
and released extra energy, or kicked off electrons
from the atoms they hit, which triggered a reshuffling
that again released energy. In both cases, the energy was emitted
in the form of X-rays, which is a type
of electromagnetic radiation with higher energy than visible light,
and lower energy than Gamma rays. X-rays are powerful enough
to fly through many kinds of matter as if they are semi-transparent, and they’re particularly useful
for medical applications because they can make images of organs,
like bones, without harming them, although they do have a small chance of causing mutations
in reproductive organs, and tissues like the thyroid, which is why lead aprons are often
used to block them. When X-rays interact with matter,
they collide with electrons. Sometimes, the X-ray transfers all of its
energy to the matter and gets absorbed. Other times, it only transfers
some of its energy, and the rest is scattered. The frequency of these outcomes depends on how many electrons
the X-rays are likely to hit. Collisions are more likely
if a material is dense, or if it’s made of elements
with higher atomic numbers, which means more electrons. Bones are dense and full of calcium,
which has a relatively high atomic number, so they absorb X-rays pretty well. Soft tissue, on the other hand,
isn’t as dense, and contains mostly lower
atomic number elements, like carbon, hydrogen, and oxygen. So more of the X-rays penetrate tissues
like lungs and muscles, darkening the film. These 2-D pictures are only useful
up to a point, though. When X-rays travel through the body, they can interact with many atoms
along the path. What is recorded on the film reflects
the sum of all those interactions. It’s like trying to print 100 pages
of a novel on a single sheet of paper. To see what’s really going on, you would have to take X-ray views
from many angles around the body and use them to construct
an internal image. And that’s something
doctors do all the time in a procedure called a CT,
Computed Tomography scan, another Nobel Prize winning invention. Think of CT like this. With just one X-ray, you might be able to see the density
change due to a solid tumor in a patient, but you wouldn’t know how deep
it is beneath the surface. However, if you take X-rays
from multiple angles, you should be able to find
the tumor’s position and shape. A CT scanner works by sending
a fan or cone of X-rays through a patient to an array of detectors. The X-ray beam is rotated
around the patient, and often also moved down
the patient’s body, with the X-ray source tracing
a spiral trajectory. Spiral CT scans produce data
that can be processed into cross sections detailed enough to spot
anatomical features, tumors, blood clots, and infections. CT scans can even detect
heart disease and cavities in mummies buried thousands of years ago. So what began as Roentgen’s happy accident
has become a medical marvel. Hospitals and clinics now conduct over
100 millions scans each year worldwide to treat diseases and save lives.

100 thoughts on “How X-rays see through your skin – Ge Wang

  1. As a rad tech student, I can personally tell you several things: one, your video broke radiography down perfectly, two, bones are bones not organs and three your video was great

  2. Doctors do not take CT scans. Radiologic Technologists registered in Computed Tomography take CT scans. Doctors order the scans, but they do not perform them.

  3. The cathode ray depicted is wrong. (He most likely used a "Lenard tube" which you covered but he also had other tubes but none of them had a cross in it with a hinge) Also, as he was creating x-rays from bombarding either aluminum or glass with beams of electrons he was not making "characteristic x-rays" (I think they put it as "rearranging the electrons in the atom and producing x-rays" as glass and aluminum and other low mass items tend to absorb that x-ray and produce another electron instead, called an Auger electron (if you type in Auger electron you can see a nice graph of it).

  4. Good news, we found the Tumor with the CT scan,
    Bad news, the CT scan caused significant mutations, and thus now might get more tumors. Pray physics isnt correct, and no DNA damage occurs.

  5. One thing is clear from extensively reading the comments, half of the commenters did not understand it or were confused/ mislead. It's a difficult subject and this is as basic as it gets.

  6. I remember getting an X-Ray at 5 because a doctor thought I had athsma. I don't remember a lead apron but I'm above average in height so I think I'm fine.

  7. I love how back in the day people could make groundbreaking nobel prizeworthy discoveries just by carrying out everyday chores . Good times

  8. Its pity that the medical monster in Nepal uses this kind of dangerous testing to earn money even if it is not required for the patients.

  9. Well explained! 🙂 Small correction: Gamma rays and X rays overlap in energies (you can have X rays with higher energies than some gamma rays). The difference between gamma rays and X-rays is how they are produced (gamma rays: emitted from the nucleus, X-rays produced in the "electron cloud").

  10. The moment when you have to prepare a prasentation for your class about X-Rays, which has to be minimum 5 minutes, but Ted-Ed explains everything in 4 and a half minutes…

  11. That's why I don't understand why abortion is legal. What if that baby you are carrying will invent a cure to solving the never ending deaths with cancer and HIV/AIDS? What if that baby you wanted to abort have the capacity in the future to make a huge difference or impact to the world.

  12. In india, there is no concept of apron for protection. They do it without any such precautions. Is it safe ??
    I guess no!!

  13. Finally someone that knows rads I have a massive interest in Rads and election advisement and so on. I am still young as in middle school young but I have been studying Rads and of corse electrical engineering on my own outside of school and I like the amount of true facts in this vid I would 50/10 recommend this to people. Thanks for this vid 😄

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