Not implanted, just injected into a vessel with a needle or catheter. Any time you introduce something like this into the blood though, there are consequences. X-Ray contrast reactions can be lethal and MRI contrast (more similar to these since it’s metal-based) occasionally kills the arteries going to kidneys, which is bad. So, it’s easy to administer, but this is far too soon to claim it is safe at scale.
I had a CT scan after an accident, and no one told me what contrast is going to feel like, the nurse simply injected me without any explanation.
And omfg, that might’ve been one of the scariest 30 seconds of my life. It felt like I was injected with straight up lava. My whole body was burning from the inside, and I felt like I would just spontaneously combust any second. It very quickly subsided though and there was no negative reaction overall, just higher sensitivity than average. But holy shit, I would want to know about stuff like this beforehand.
