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Technetium 99m

- Discussion:
    - over the course of several hours, half or more of the dose accumulates in bone, and the remainder is excreted in urine;
    - images obtained over 2-4 hours (half life of technetium is 6 hours);
    - increased uptake in immature bone and metabolically active bone, or where large numbers of osteoblasts are present;
    - intensity of the characteristic "hot" lesion reflects the degree of reative new bone formation as well as increased blood flow;
    - in children the epiphyseal growth plates display the most activity, and non-ossified bone is not visualized;
    - in elderly, degenerative dz is common and shows typical distribution of increased, often focal, joint activity at the sternocostal junction, 
           shoulders, spine, knees, hips, hands, & feet;
    - since bone scan agents and Ga are usually both positive at fracture sites, they may have limited value, even in combination;
    - triphasic bone scan is procedure of choice if suspected osteomyelitis is not superimposed on another disease that causes increased bone 
           remodeling (i.e., findings on the radiograph are normal);
           - photopenic (cold) scans may indicate early osteomyelitis

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