Value of a 24-hour image (four-phase bone scan) in assessing osteomyelitis in patients with peripheral vascular disease.

The delayed images of the four-phase 99mTc phosphonate bone scan are compared with the delayed images of the three-phase study in patients with diabetes mellitus and/or peripheral vascular disease and suspected osteomyelitis. Three-phase bone imaging includes an immediate postinjection radionuclide angiogram, a blood-pool image, and delayed static images to 7 hr. The four-phase study adds a 24-hr static image. The scan is positive for osteomyelitis if images show progressively increasing lesion to background activity ratios over time. The results of analyzing 21 three- and four-phase bone scans in 17 patients were correlated with clinical course, cultures, and/or x-rays, gallium scans, and CT scans. The accuracy of four-phase bone imaging for diagnosing osteomyelitis was 85%; for three phase, 80%. Sensitivity for four phase was 80%; specificity was 87%. Sensitivity for three phase was 100%; specificity was 73%. Since overall accuracy of the four-phase study is slightly better than three phase, in these patients with diabetes mellitus and/or peripheral vascular disease, the addition of a 24-hr image, creating a four-phase bone scan, is recommended.