Differentiation of Bone Metastases and Fractures using 24 hour / 3 hour Radio-uptake Ratio in Bone Scintigraphy

Han, Song Yee; Chun, Kyung Ah; Chung, Yong Ahn; Kim, Sung Hoon; Kim, Young Joo; Chung, Soo Kyo; Park, Seog Hee

Abstract

PURPOSE: We evaluated the usefulness of 24 hour/3 hour radio-uptake ratio, lesion to non-lesion ratio, in differentiating bony metastases from acute (<2 months) and healing ( 2 months) fractures.
MATERIALS AND METHODS
Sixty-three patients (age range: 26-81, 32 males, 31 females) having 90 lesions (30 bone metastases, 30 acute fractures, 30 healing fractures) were included. Bone scans were obtained 3 and 24 hours after administration of 740 MBq of 99mTc-MDP. The ratio of radio-uptake in the lesion to normal area was measured as 24/3 hour radio-uptake ratio ([lesion/non-lesion RUR at 24 hour]/[lesion/non-lesion RUR at 3 hour], 24/3 RUR) and analyzed clinical significance in differentiating bone metastases from acute or healing fractures.
RESULTS
Mean 24/3 RUR were 1.22+/-0.18 for bone metastases, 1.25+/-0.14 for acute fractures, and 0.99+/-0.15 for healing fractures. 24/3 RUR values of bone metastases and acute fractures were not significantly different. But 24/3 RUR values of bone metastases and healing fractures, and those of acute and healing fractures were found to be significantly different (p<0.001). When 24/3 RUR of 1.0 was considered as the cut off point separating metastases from fracture, a sensitivity of 100% (30/30) was obtained. The specificity was 0% (0/30) in separating metastases from acute fractures, and 47% (14/30) in separating metastases from healing fractures. When 24/3 RUR of 1.2 was considered as the cut off point, sensitivity of 53% (16/30) in the diagnosis of bone metastasis, and specificity of 37% (11/30) in separating metastases from acute fractures, and 100% (30/30) in separating metastases from healing fractures were obtained.
CONCLUSION
24/3 RUR is useful in differentiating bone metastases from healing fractures, but not in differentiating bone metastases from acute fractures. A 24/3 RUR of less than 1.0 suggests healing fractures. A 24/3 RUR of more than 1.2 suggests bone metastases or acute fractures.