Technetium -99 can travel though the blood stream. A detector outside the patient's body detects gamma rays, and uses this to form a picture of a flow of blood. Technetium has a half life of 6 hours. Why do radiologists use technetium -99 to image patient's blood flow, and not ruthenium-106 which decays via beta decay with a half life of 372 days.
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$\begingroup$ I think you wand to have something that is short-lived but not too short-lived. You do not want your patients to go around radioactive for several weeks after their examination. $\endgroup$– Mikael FremlingCommented Jun 15, 2015 at 11:50
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$\begingroup$ @MikaelFremling Please convert your comment to an answer. $\endgroup$– rob ♦Commented Jun 15, 2015 at 11:53
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$\begingroup$ You do not want beta radation as it has a shorter free path length in tissue than gamma radiation (and not a sharp spectrum, which might be impractical for detection). Furthermore, beta particles will do more radiation damage (as more energy is absorbed). $\endgroup$– Sebastian RieseCommented Jun 15, 2015 at 12:06
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$\begingroup$ Additional Note: Wikipedia answers your question very nicely and extensively: en.wikipedia.org/wiki/Tc-99m#Medical_uses (see especially the discussion of radiation side-effects). $\endgroup$– Sebastian RieseCommented Jun 15, 2015 at 20:55
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$\begingroup$ I'm voting to close this question as off-topic because it is about medical choices and not physics. $\endgroup$– Kyle KanosCommented Jun 19, 2015 at 1:48
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2 Answers
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I think you want to have something that is short-lived but not too short-lived. You do not want your patients to go around radioactive for several weeks after their examination.
Regarding the precise choice of of radioactive material, that is likely a medical question. Different compounds will move around in the body in different ways and affect your organs differently as well.
Also, you have to think of the effects of the decay products. For instance, are they toxic or dangerous?
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$\begingroup$ Another important point are chemical properties. You want something you can bind to diverse molecules, so it will be absorbed in the desired tissues. Tc even has the nice property of being accumulated in the thyroid without begin bound to some molecule. $\endgroup$ Commented Jun 15, 2015 at 12:22
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The Technetium-99 gamma ràys are long and more easily detectable. It's Gamma radiation waves exit the body quicker ie. 6hrs and does no cellular damage compared to the Beta radiation (which are particles) in ruthenium-106 with a half life of 371.5 days.
