Final answer:
A bone scan is the proper diagnostic tool to determine the involvement of Paget's disease, as it highlights areas of bone resorption that are characteristic of the disease.
Step-by-step explanation:
The proper tool to determine the involvement of Paget's disease is a bone scan. In this diagnostic method, a dye containing a radioactive ion is injected into the body, and areas undergoing bone resorption, which is characteristic of Paget's disease, will absorb these ions and light up on the scan, indicating the presence of the disease.
Alongside the bone scan, elevated levels of an enzyme called alkaline phosphatase in the blood are also indicative of Paget's disease. Though other imaging techniques like X-rays can show bone deformities and areas of resorption, and CT scans can provide cross-sectional views, the bone scan is the most revealing for this specific condition.