Quantification of bone metabolic activity in the natural course of fractural lesions measured by quantitative SPECT/CT

Objective(s): While increased uptake at the bone fractural site gradually decreases over time on bone scans, the rate of change has not been quantitatively evaluated. The purpose of this study was to quantify the extent of bone metabolic changes in fractural lesions on bone SPECT/CT. Methods: We reviewed bone scans acquired by dedicated SPECT/CT and chose those scans in which quantitative SPECT/CT of the same range was acquired twice or more. We set the region of interest on lesions of bone fracture and degeneration, and measured the maximum standardized uptake value (SUVmax). From the SUVmax of lesions and the interval between scans, a value for 30-day change in SUVmax was calculated as DSUVmax30d. The relationship between preSUVmax, SUVmax for the first scan of the comparison, and DSUVmax30d was evaluated utilizing a linear least-squares method. Furthermore, we assessed the ability to differentiate between fracture and degeneration using receiver operating characteristics (ROC) analysis and the Mann-Whitney U test. All cases were then categorized into five groups according to preSUVmax. Values of p <0.05 were considered statistically significant. Results: We investigated 175 scans from 60 patients and analyzed scan combinations for 157 fractural lesions and 266 degenerative lesions. The relationship between preSUVmax of fractural lesions and DSUVmax30d was approximated as DSUVmax30d =-0.15×preSUVmax +1.35 (R2=0.60, p<0.0001). Area under the curves for all cases, 30≤ preSUVmax, 20≤ preSUVmax <30, 15≤ preSUVmax <20, 10≤ preSUVmax <15, and preSUVmax <10 were 0.73, 0.89, 0.86, 0.80, 0.91, and 0.59, respectively. Median DSUVmax30d was significantly lower at fractural lesions than at degenerative lesions (-0.62 vs -0.04; p <0.0001). As for analyses of groups divided by preSUVmax, all median DSUVmax30d for fractural lesions were significantly lower than those of degenerative lesions except for the group with preSUVmax <10. Conclusion: The increased uptake at the fractural bone lesion observed in the quantitative bone SPECT/CT gradually decreased at the rate of SUV 0.15 per month, which showed a different trend with degenerative change