Final answer:
The second phase of a 4-phase bone scan occurs 2-4 hours after injection, which allows for the visualization of areas with increased bone cell activity potentially indicating bone growth, repair, or abnormalities such as cancer. Option b.
Step-by-step explanation:
The second phase in a 4-phase bone scan typically takes place 2-4 hours after injection. This phase is crucial because it allows for the detection of areas with increased metabolic activity, which may suggest bone growth or repair, and in some cases, abnormal conditions such as bone cancer. The radiopharmaceuticals used in these scans often have varying half-lives, and their behavior in the body (e.g., how quickly they pass through the digestive system or become lodged) is an important aspect of obtaining a clear and useful image. In a bone scan, a short-lived radioactive substance selectively locates itself in areas of high bone cell activity, and the emitted gamma radiation is measured with an external detector. This is especially relevant when understanding the image provided in Figure 31.6 in the context of a bone scan.
The use of radiopharmaceuticals with specific half-lives is optimized to allow for sufficient time to measure the radiation externally while minimizing the patient's exposure to the radioactive substance. Understanding the dynamics of bone repair is also essential. Soon after a fracture, bone repair begins with the formation of a fracture hematoma approximately six to eight hours post-injury, which can be visualized during the scan.