Question about PET scans (Positron emission tomography)

In summary: They need to know how it works and what the potential risks and benefits are.In summary, PET scans are potentially harmful but the risks are largely outweighed by the benefits.
  • #1
riodice
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Why there are no free radicals formed with PET scan?
I understand that a PET scan will produce Positrons which will come into contact with an electron and produce Gamma rays in the area where there is a high uptake of sugar (assume glucose). In this process of annihilating an electron, some poor atom will lose an electron which I assume would produce a free radical(s). I assume would produce a large number of free radicals.
So what is the real story? PET scan is supposedly safe but I don't understand how!
thanks
 
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  • #2
The radionucleotide used when mimicking glucose is Florine-18. Its decay products include Oxygen and a positron. So there is not much ionization due to the electron it absorbs - because going from Florine to Oxygen yields a "spare" electron.

It is ionizing, and some free radicals can be created - but not exactly by the mechanism you describe.

According to this article: http://www.radioactivity.eu.com/site/pages/Doses_Diagnostics.htm
The positron emission tomography (PET) is still rare compared to scintigraphy. Most of these tests use as a marker 18F-FDG whose irradiating character is estimated by the ICRP – for an adult - to 19 µSv / MBq. For a standard PET (injected activity of 10 millicuries or 370 MBq), the resulting dose is 7 mSv, about the same as for a scanner. If tomography is performed in conjunction with a scanner (PET-SCAN) the dose from the scanner must be added.
That would be the same radiation damage you would expect to get in about 2 years from natural background radiation.

Whether or not it is "safe" depends on what you are comparing it to. In most cases, someone getting a PET scan has more serious conditions to worry about than 7 mSv.
 
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  • #3
.Scott said:
there is much ionization due to the electron it absorbs - because going from Florine to Oxygen yields a "spare" electron

I think you mean there is not much ionization, because the positron emitted in the nuclear reaction will most likely meet up with the electron that now no longer has an atomic orbital because oxygen has one less atomic electron than fluorine. To a first approximation this should produce zero ionization; the complete reaction is fluorine + 9 electrons -> oxygen + 8 electrons + positron + spare electron -> oxygen + 8 electrons (i.e., a neutral oxygen atom) + gamma rays.
 
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  • #4
PeterDonis said:
I think you mean there is not much ionization, because the positron emitted in the nuclear reaction will most likely meet up with the electron that now no longer has an atomic orbital because oxygen has one less atomic electron than fluorine. To a first approximation this should produce zero ionization; the complete reaction is fluorine + 9 electrons -> oxygen + 8 electrons + positron + spare electron -> oxygen + 8 electrons (i.e., a neutral oxygen atom) + gamma rays.
Yes, that is what I meant. I have corrected the post.
 
  • #5
Thanks for such a rapid response. So, since the reactions take place where there is more uptake there is most likely a canceling out with positron and the spare electron. I didn’t know about the decay that produces Oxygen.

The reason I asked this was that I had a PET scan a couple of years ago and found it like SIFI!

I need to do lots of reading to further understand everything. I did have Chemistry back in Junior high and then again in High School but that was back in 1965. It seems that Chemistry has become a branch of Physics.

As a Social Implications of Technology, I think that the public needs to have a better understanding and appreciation of Technology.
 

1. What is a PET scan?

A PET scan, or positron emission tomography, is a medical imaging technique that uses a radioactive tracer to produce 3D images of the body's organs and tissues. It is commonly used to diagnose and monitor various medical conditions, including cancer, heart disease, and brain disorders.

2. How does a PET scan work?

During a PET scan, a small amount of radioactive material is injected into the body. This tracer travels to the area being examined and emits positively charged particles called positrons. As the positrons collide with negatively charged particles in the body, they produce gamma rays, which are detected by a scanner. The scanner then creates images based on the distribution of the tracer in the body.

3. What are the benefits of a PET scan?

PET scans provide detailed images of the body's tissues and organs, allowing for the detection of abnormalities that may not be visible on other imaging tests. They can also help doctors determine the stage and severity of a disease, as well as monitor the effectiveness of treatments.

4. Are PET scans safe?

PET scans are generally considered safe, as the amount of radiation exposure from the tracer is minimal. However, pregnant women and individuals with certain medical conditions may need to avoid or postpone a PET scan. It is important to discuss any potential risks with your doctor before undergoing the procedure.

5. How do I prepare for a PET scan?

Prior to a PET scan, you may be asked to fast for a certain period of time and avoid caffeine and strenuous exercise. It is also important to inform your doctor of any medications you are taking, as they may interfere with the results of the scan. Your doctor will provide specific instructions based on your individual situation.

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