It is a common misunderstanding that nuclear medicine is mainly about tumor imaging. In fact, we search for tumors in about half of all investigations. Unfortunately, we do not have a single optimal method for tumor imaging; how­ever, the methods of nuclear medicine are particularly powerful for many tumor types and able to answer many questions. Today, the PET/CT study of glucose

metabolism is considered the most effective for a wide range of tumors (see Section 12.6).

For many decades, the most common imaging method in the field of nuclear medicine worldwide has been bone scintigraphy. Radiolabeled diphosphonates accumulate in the bones proportionally to bone formation (osteoblast activity). As a consequence, bone metastases of various tumors show an increased uptake of Tc-99m-labeled diphosphonates (see Figure 12.10). Detecting bone metastases is very important since many of the most common tumors (e. g., lung, breast, and prostate) often have their metastases in the bones, and their early detection may influence the method and prognosis of the therapy applied substantially. Bone scintigraphy may visualize metastases in an earlier phase, months before X-ray images, as the latter detect only an abnormality that has already caused significant changes in the structure and calcification of the bones.

Note that gamma camera images from the anterior and posterior views are different (see Figure 12.10), resulting from the attenuation of radiation inside the body. (For example, the half-value layer of the 141 keV gamma radiation of Tc-99m is 4.6 cm in body tissue.) In bone scintigrams, the bones closer to the back surface of the body (e. g., the spine and back ribs) are better seen (brighter) from the posterior, while those closer to the frontal surface (e. g., the sternum and the frontal edge of the hip bone) are more prominent from the anterior view.