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What I have learned

The detectors of the PET actually measure the photons, which are caused by the radioactive tracer injected into the patient. Then, with the help of backprojection, we get the photon count for each voxel. I hope I understood these processes right, please correct me if this is not the case.

But as final result, we get the radioactivity concentration in kBq/mL.

Question

How can the scanner convert the counted photons into radioactivity concentration?

My guess would be, that a phantom of known volume is used, with an inserted radiotracer of known radioactivity concentration.

Carl Witthoft
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LynxLynx
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1 Answers1

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I happen to be a cancer patient and have had the PET-CT.

The way they explained it to me is after giving you a rapidly decaying radioactive sugar with a half-life of about one hour which has one carbon switched with fluoride.

Then the hungry cancer cells break the sugar, positrons are released which in a deadly collision with electrons release two gamma rays which are colinear and in opposite direction.

The machine is counting only these colinear gamma rays and will trace them back to their origin's x,y,z. This point will be shown as a red dot superposed on a regular ct of patients body that is used as a reference to his/her anatomy.

Problem is because of ethnicity and nutrition and diet some false positive shadows may show up.

kamran
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