ABSTRACT
Nuclear medicine personnel employ a variety of devices to detect radioactive decay. Generally, the result of this effort is a set of images at various levels of organization. At the largest scale, entire systems are imaged using agents that target to those tissues. For example, using sulfur colloid labeled with 99mTc, the radiologist is able to image the reticuloendothelial system (RES). Here, one is involved with cells found in liver, spleen, and bone marrow. At the next level of organization, specific cell types within an organ are made visible. Galactosylated chitosan, tagged with 99mTc, may be used to image hepatocytes within the patient’s liver (Kim, Jeong, et al. 2005). The smallest scale level of targeting involves finding molecules within the patient’s body. For example, the surgeon may wish to find possible metastatic sites in the liver due to a primary colon cancer. In this last case, an antibody to carcinoembryonic antigen (CEA) labeled with 111In may be a useful tracer. Note that such cancer-associated targets can, in principle, be in any tissue so that the first and second levels of targeting are now not relevant as the observer is looking for a specific molecule. The last strategy is of primary interest in contemporary nuclear medicine and is the featured topic in this text.
