Excess stannous ion in a 99mTc-MDP preparation leads to excess uptake in which organ?

In the context of a 99mTc-MDP (methylene diphosphonate) preparation, stannous ion (Sn2+) is used as a reducing agent during the radiopharmaceutical preparation process. However, if there is an excess of stannous ion present, it can impact the biodistribution of the radiopharmaceutical.

The liver has a significant role in the uptake of many radiopharmaceuticals due to its function in the body's metabolism and its ability to filter blood. Excess stannous ion can lead to increased uptake in the liver by enhancing the colloidal properties of the radiopharmaceutical or by altering its physiochemical properties, causing the liver to take up more of the agent than it normally would under optimal conditions.

Understanding the specific pathways of radiotracer uptake reveals that the liver tends to accumulate compounds that have altered physiochemical properties due to excess stannous ion. This is why, in this scenario, the correct answer is the liver, as it is the organ that experiences increased uptake in the presence of excess stannous ion during 99mTc-MDP preparations.