00:00This syringe contains a radioactive form of glucose known as FDG.
00:14The doctor will soon inject its contents into her patient's arm,
00:18whom she's testing for cancer using a PET scanner.
00:21The FDG will quickly circulate through his body.
00:24If he has a tumor, cancer cells within it
00:27will take up a significant portion of the FDG,
00:30which will act as a beacon for the scanner.
00:33Pet tracers such as FDG are among the most remarkable tools in medical diagnostics,
00:39and their life begins in a particle accelerator, just hours earlier.
00:45The particle accelerator in question is called a cyclotron,
00:48and it's often housed in a bunker within hospitals.
00:51It uses electromagnetic fields to propel charged particles like protons
00:57faster and faster along a spiraling path.
01:00When the protons reach their maximum speed, they shoot out onto a target.
01:05That contains a few milliliters of a type of water with a heavy form of oxygen,
01:10called Oxygen 18.
01:12When a proton slams into one of these heavier oxygen atoms,
01:16it kicks out another subatomic particle called a neutron.
01:20This impact turns Oxygen 18 into Fluorine 18,
01:24a radioactive isotope that can be detected on a PET scan.
01:28In a little under two hours,
01:30about half the fluorine will be gone due to radioactive decay,
01:34so the clock is ticking to get the scan done.
01:37So how can Fluorine 18 be used to detect diseases?
01:41Radiochemists at the hospital can use a series of chemical reactions
01:45to attach the radioactive fluorine to different molecules creating radiotracers.
01:52The identity of the tracer depends on what doctors want to observe.
01:56FDG is a common one because the rate at which cells consume glucose
02:00can signal the presence of cancer, the location of an infection,
02:04or the slowing brain function of dementia.
02:07The FDG is now ready for the patient's scan.
02:11When a radio-labeled tracer enters the body,
02:14it travels through the circulatory system and gets taken up by its target,
02:18whether that's a protein in the brain, cancer cells, or otherwise.
02:22Within a few minutes,
02:24a significant amount of the tracer has found its way to the target area,
02:28and the rest has cleared from circulation.
02:30Now the doctors can see their target using a PET,
02:33or positron emission tomography, scanner.
02:37The radiation that the tracer emits
02:40is what makes this possible.
02:41The isotopes used in PET decay by positron emission.
02:46Positrons are essentially electrons with positive charge.
02:50When emitted, a positron collides with an electron from another molecule in its surroundings.
02:56This causes a tiny nuclear reaction,
02:59in which the mass of the two particles is converted into two high-energy photons,
03:04similar to X-rays, that shoot out in opposite directions.
03:08These photons will then impact an array of paired radiation detectors in the scanner walls.
03:15The software in the scanner uses those detectors to estimate where inside the body the collision occurred,
03:21and create a 3D map of the tracer's distribution.
03:25PET scans can detect the spread of cancer before it can be spotted with other types of imaging.
03:31They're also revolutionizing the diagnosis of Alzheimer's disease by allowing doctors to see amyloid,
03:37the tell-tale protein buildup that otherwise couldn't be confirmed without an autopsy.
03:43Meanwhile, researchers are actively working to develop new tracers,
03:47and expand the possibilities of what PET scans can be used for.
03:51But with all this talk of radiation and nuclear reactions inside the body,
03:56are these scans safe?
03:57Even though no amount of ionizing radiation is completely safe,
04:01the amount of radiation the body receives during a PET scan is actually quite low.
04:06One scan is comparable to what you're exposed to over two or three years from natural radioactive sources,
04:12like radon gas,
04:13or the amount a pilot would rack up from cosmic radiation after 20 to 30 transatlantic flights.
04:20Most patients feel that those risks are acceptable for the chance to diagnose and treat their illnesses.
04:27If you think scanning the human body is as fascinating as we do, check out this lesson.
04:32Otherwise, here's a playlist on other fascinating technologies that'll spark your curiosity.
04:43I'll see you next time.
04:45Bye.
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