Today, read something on SPECT and PET scanners. These two are actually related to each other. Once became before the other, and they are similar in quite a few ways.
SPECT Scanners
Scientists have been looking for ways to use radioactive materials other than X-Rays to help them see inside the body. One year after X-Rays were discovered, radioactivity was discovered. Scientists figured out how to tag certain substances with radioactive materials that they made (like radioactive water or glucose; these made radioactive substances are called radioisotopes). Then they could use a Geiger Counter or a scanner to track the substance on its journey throughout the body.
Two scientists made the SPECT (Single Photon Emission Computed Tomography, according to the book) scanner. It traces the tagged materials throughout the body, and keeps an eye on it, mainly by detecting photons (very tiny traces/"packs" of light or energy or radioactivity) and making images from the photons released by the radioactively-tagged substance (according to the book). When using glucose (the body's main energy source, or "food") as a tagged material, areas that use a lot of energy--like growing and dividing cells--can be detected. Since tumors also use a lot of glucose while multiplying and growing their cells, SPECT scanners are good for spotting cancers. However, they do not make images of the body or inside it. Since they're relatively cheap, though, they're still highly commonly used.
PET Scanners
Years later, however, a scientist team in an university in St. Louis, Missouri, combined a couple of different technologies (CT Scanner included) to make a better version of the SPECT Scanner... the PET (Positron Emission Tomography) Scanner! The substance is tagged with a radioactive substance that emits particles called "positrons". However, this substance released two positrons at once... in opposite directions! While there was once a spiky-helmet device, now the person is put (a picture shows a person lying down, wearing a wired hair-net thing) into a tubular area. The scan work kind of like a CT Scanner... detectors pick up the released positrons and radioactivity, and then form an image. And it takes them from all angles too.
PET Scanners took a while to come out into the medical field. But even now, they're primarily used in research, not medical purposes. All though it is used to figure out different brain disorders in the medical field (one of the first patients was a 2-year-old named Ryan Peterson who had major problems in half of his brain, and only a PET Scanner could pick the problem up. He had major surgery, where the problem-half's outer "skin" was taken away, and was acting normal pretty soon! This happened in 1985), and some other stuff (like heart stuff & problems; and a PET Scanner is still highly useful for detecting tumors and their location), it is primarily used in research.
Now, there are some problems with using PET Scanners. To get the tagged substance inside the patients, the patients have to drink something with the tagged substance inside, and then the substance rides the bloodstream and blood cells... this and, the books says, just drinking the substance can make patients nervous (makes total sense! The same method is used for getting the substances inside patients for SPECT Scanners), since the material is radioactive (in fact, for a long time, people weren't sure if using radioisotopes were safe... once scientist only felt safe about figuring this out by using them on himself!!!). The radiation only lasts a short time, though. But this makes a problem for guys who use PET Scanners... the substance has to be made on-site or very close to the PET Scanner. Because of this, not every hospital or medical place has a PET Scanner.
Also, while glucose is the primary substance that's tagged, it's not always used. For checking out the heart and its problems, for example, a type of ammonia is used. The trip via the bloodstream through the heart doesn't affect the data sent by the substance, so that's what used. Glucose doesn't really help in this department, and doesn't get much data, so this other type of ammonia is used.
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