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  • [♪ INTRO]

  • When doctors need to quickly identify tumors,

  • diagnose heart diseases and even watch our brains at work,

  • they use the by-products of something called radioactive decay.

  • The decay comes from specific radioactive isotopes that emit a certain type

  • of antimatter particle called a positron, the counterpart to electrons.

  • Normally, when the positron gets in contact with things like electrons,

  • they destroy each other.

  • By carefully sneaking in radioactive molecules that emit positrons,

  • doctors can see what's happening inside your body.

  • But here's the catch...these molecules need to be made fresh every day,

  • against the clock, in the basement of a hospital.

  • Doctors measure the positrons emitted by the decay of a radioactive atom

  • with a technology called Positron Emission Tomography, or PET.

  • And it works by sensing gamma rays,

  • a type of photon emitted when positrons and electrons come into contact.

  • To accomplish this feat, physicists and chemists must work quickly

  • to incorporate radioactive isotopes into chemical compounds called radiotracers.

  • They do this by swapping a normal part of the molecule

  • for something radioactive that releases positrons.

  • Now you may be thinking, radioactivity sounds bad,

  • but it's commonly used in different things in medicine like X-rays.

  • And these radioactive molecules only emit very small amounts of radiation for a short

  • period.

  • The way the radiotracers work is by accumulating in specific areas of our bodies.

  • For example, tumors have a faster metabolism compared to normal cells.

  • So when tumors use chemical compounds, like radiotracers,

  • instead of normal sugar, they'll accumulate faster compared to normal cells.

  • Which is why tumors are more visible on a scan.

  • When injected, the radiotracer will travel through the entire body

  • and accumulate in things like tumors.

  • And the difference of where the tracer is hoarded compared to the rest of the body

  • will create a contrast in radioactive decay picked up by the PET instrument.

  • But making radiotracers is a race against the clock

  • because the very thing that makes them work,

  • radioactivity, also means they won't last long.

  • A common radiotracer used for PET scans is fluorodeoxyglucose, or FDG, for short.

  • And its half-life is about 110 minutesjust under two hours.

  • Half-life is the time it takes for half of a radioactive sample to decay.

  • As soon as FDG is made in a lab,

  • the clock starts to tick to get the molecule purified from reaction by-products,

  • tested to ensure its safety, prepared in a solution, and into the patient.

  • Because in two hours, only half of what was made will be useful.

  • The journey of these radioactive molecules starts with a

  • compact particle accelerator called a cyclotron,

  • usually housed in a well-shielded room in the basement of a hospital

  • or at a specialized facility nearby.

  • The main job of the cyclotron is to create a beam of

  • positively charged hydrogen atoms, also called protons.

  • Scientists use the magnets inside the cyclotron to speed up and steer

  • negatively charged hydrogen atoms creating the proton beam.

  • To make FDG, scientists use oxygen-18,

  • which has two extra neutrons compared tonormaloxygen-16.

  • The process starts by displacing one neutron from oxygen-18 and

  • adding one proton using the beam from the cyclotron.

  • By displacing that neutron, scientists create the isotope fluorine-18.

  • This change is possible because the identity of an atom is defined by

  • how many protons it has.

  • So, if one of these particles loses or gains a proton,

  • it can become an entirely different element.

  • But fluorine-18 is unstable.

  • Meaning that eventually,

  • that extra proton decays into a neutron and emits that extra energy as a positron.

  • Making the atom back into stable oxygen-18.

  • But a pile of radioactive fluorine isn't very useful because it's so reactive.

  • So one way to use fluorine-18 as a radiotracer is to incorporate it into molecules like the

  • sugar FDG.

  • To make FDG, chemists take the radioactive fluorine from the cyclotron and then

  • subject the sugar to a series of chemical reactions to substitute radioactive fluorine

  • on an area of the molecule.

  • Next, purified and tested FDG has to make its way to the patient,

  • which can be as simple as taking it upstairs in the hospital

  • r as complicated as driving it across a state.

  • Once the FDG is injected into the patient's body,

  • the sugar starts to get used by different parts of the body, including tumors,

  • which doctors can image with the PET scanner after a few minutes.

  • And the scanner can be used by doctors to diagnose things like cancer,

  • heart disease, or Alzheimer's.

  • So while it might seem strange to have a small particle accelerator in a hospital,

  • it's a critical piece in the puzzle to image your body.

  • A critical piece in the puzzle to your intelligence is today's sponsor:

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  • [♪ OUTRO]

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What’s a Particle Accelerator Doing in a Hospital?

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    joey joey に公開 2021 年 07 月 02 日
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