There is ZERO risk to you or anyone around you. You don't need to stay away from anyone for that isotope. It's about the same exposure as a Cat scan. You will only get about 20-25 mCi which is a very small dose. I've injected thousands of patients with much more than that.the same exposure as a Cat scan. You will only get about 20-25 mCi which is a very small dose. I've injected thousands of patients with much more than that.

There will be a tiny portion of the population that should be no where near that small level of radiation. That is why all the warnings. And since you don't know which people these are generally, you are given a broad warnings.

If they deem it okay for you to have this procedure, you are fine. Most people can accept a certain dosage of radiation with no ill effects.

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Ian

Radiologist here. The radiotracer used for a regular bone scan is Technicium 99M-MDP. It's taken up by bone, not cartilage. A bone scan will not tell you anything about the cartilage in your knee (or anywhere else). You need an MRI to seen the cartilage. The bone scan might show reactive changes in the bone cortex and marrow around the joint, but so will an MRI. Just based on your original post and without other info, a bone scan is not indicated for you. I'd suggest you just get an MRI.

A bone scan uses very low level radiation that poses no health risk to you. We've been doing them for decades. The idea that you flush the toilet twice is because the radioisotope that is injected for the scan is excreted through your kidneys, so you pee it out. It's not really necessary for a bone scan. We do tell people to do that with other isotopes like Iodine-131 which we use to detect or treat thyroid cancer. But I-131 produces a much higher energy form of radiation that lasts many times longer in your body. Technicium 99M has a half life of 6 hours, so half is gone at 6 hours, 75% at 12, etc, and your body actually gets rid of it faster than that. You can be around other people, just don't piss on any little kids or pregnant women.

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Don't drown. Don't crash. Don't walk.

Physics guy here. :) I can't comment on the bio effects of a small dose. Looks like a Dr already did that. I have scanned CAT patients with a Geiger counter. They are hot for a few days, but the detectable range is only a couple of inches from their skin. The radiation is either alpha or beta. It is stopped by skin and clothes and a few inches of air. Radiation will overwhelmingly remain confined to within the body, and exit same way anything else ingested would exit. That's called biological half life, not to be confused with radiological half life of the isotope. Both will of course ensure that you are back to normal in a few days. So, don't worry about "irradiating" other people.

What happens within the body is complicated. Ionizing radiation can damage living cells. It doesn't always give people cancer. That's a misconception. What it does it raises risk of cancer. With a small dose, that risk is raised by a small amount. Study we just did showed that a trip to Mars, spending a year in a hostile environment of space, would raise cancer risk by 5-10%. What happens with a CAT isotope is again hard to predict. So best way to find out is to study the patients who have undergone the procedure.

I don't know this for a fact because it is not my area, but willing to bet there have been EXTENSIVE studies done on patients who have undergone this procedure, and data gathered on cancer rates for years after. Also willing to bet no statistically significant findings were discovered, or else the procedure would have been discontinued by now. If you want to assuage your worries, try finding some research papers online. Not sure what else to tell you.

Bottom line, it is not zero risk. But it is probably about as risky as a chest x-ray, or working as a flight attendant, or living somewhere near Hanford, Washington.

Thanks everyone for their responses. In relation to your comment about having an MRI. I already had it. According to it, besides a missing ACL which is old news, I have grade 4 chondropathy and subchondral geodes in the tibial condile. I guess this is what doc wants to check.

Unlike other doctors, my current doctor is in favor of not undergoing surgery for the ACL as I have a reasonable stability, provided I only do linear sports and avoid downhill running as much as possible. He wants to make sure my bones are not complaining too much.

Does this make sense to you?

My apologies for possible translation errors in medical jargon.

Another radiologist here. I still see no reason to do a bone scan, it seems like unnecessary radiation. It sounds like you have advanced degenerative changes in your knee joint, which will almost always demonstrate increased uptake on a bone scan. ACL repair is done for stability and to prevent degenerative disease, which it sounds like you already have...

Not sure if this will help your decision, but when there is a radiation dose comparison of your potential procedure to a CT scan, I would be very wary.

While CT scans make for some pretty pictures, many physicians are saying that CT scans are greatly overused. Then, another thing, CT scans can give you as much radiation as hundreds of chest xrays in one sitting, and that's no laughing matter. Plus, recent research has suggested that your chance of getting cancer from a single CT scan can be as much as 1 in 80.

I am not familiar with the dose of a knee bone scan, but if the total radiation dose is comparable to a CT scan, I would think very very hard before I got one.

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I presume they are planning a three phase bone scan to get an idea of how active the inflammation/arthritis is...not a very common indication for the test but an accepted one. The risk is very small particularly if you consider it in the context that it might inform decision making on an invasive procedure that would carry much higher risk. If the first two phases of the bone scan are negative it could indicate that the problems seen on MRI are chronic and you can keep on keepin on.

I don't think a bone scan would add any useful information for you. Again, this opinion is based solely on info you've provided here. Bone scans are very sensitive but not very specific. Meaning, if something is wrong with your knee, the bone scan will be abnormal. But it will not tell you what is abnormal with your knee. If you have arthritis, old injury, old healed fracture, or just about anything else, it will be positive. In that case the next step would be to do the more specific test, which would be an MRI. Since you've had that, I doubt a bone scan will tell you anything useful and would just be a waste of your time and money.

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Don't drown. Don't crash. Don't walk.

If it's a delayed phase bone scan only I'd agree with you but it's possible a 3-phase bone scan would provide useful formation on acuity of the process (i.e., answering the stated question of whether continuing to run is likely to cause further issues).

Just to update on this. Decided not to do it based on a UK government radiation equivalence that I found. A bone scan is equivalent to 500 thorax x-rays and 180 days of sun exposure. Although 180 days of sun exposure in the UK doesn't look like much 😀 the 500 thorax x-rays sounds scary.