Effects of 99mTc-MIBI and 99mTc-MDP administration on dual-energy X-ray absorptiometry bone mineral density measurements.

Objective: Nuclear medicine procedures are often performed in close-time proximity to bone densitometry studies. The purpose of this study was to determine the effects of Tc-hexakis-2-methoxyisobutyl isonitrile (MIBI) and Tc-methylene diphosphonate (MDP) on the accuracy of bone mineral density (BMD) measurements performed using dual-energy X-ray density.

Methods: The effect of a diagnostic dose of Tc-MIBI on BMD estimations in the lumbar spine and the left total hip was assessed in 30 patients (19 female, 11 male; mean age: 55.5+/-10.5 years) by using a Lunar DPX-NT scanner. Thirty patients, admitted to the nuclear medicine department for bone scintigraphy (15 female, 15 male; mean age: 56+/-15.92 years), were included into the study. Each patient underwent dual-energy X-ray density assessment for which a Lunar DPX-NT scanner was used before and 2 h after intravenous injection of Tc-MDP (925 MBq) and Tc-MIBI (1110 MBq). BMD measurements were calculated from lumbar spine (including L2-4) and left hip (including femoral neck, trochanter, and total hip). For statistical analysis, the Wilcoxon test was used and a P value of less than 0.05 was accepted as statistically significant.

Results: According to Wilcoxon's statistical test, we found extremely significant changes on the measured BMD, T-score, before and 2 h after the injection of Tc-MIBI for lumbar spine and left hip in 30 patients. We found statistically significant decrement on measured BMD from lumbar spine and trochanter before and 2 h after the injection of Tc-MDP. Although MDP BMD values in femoral neck and total hip were decreased after the injection of Tc-99m, they did not reach a statistically significant value. The comparison of pre-T-score and post-T-score values showed a statistically significant decrease after the injection for only L2-4 lumbar spine (P = 0.002), but left hip of pre-T-score and post-T-score values did not reach a statistically significant value.

Conclusion: In this study, it was determined that measured BMD values are decreased in lumbar spine for all patients. The magnitude of the effect is dependent on the location of the activity. We assume that some radioactivity from Tc is counted by the densitometer's detector, thus resulting in a decrease in the measured BMD. Scintigraphy and bone densitometry should be performed on different days to avoid artifactual reduction in BMD measurements.