Quantitative Studies of Bone in Postmenopausal Women Using ¹⁸F-Fluoride and ^99mTc-Methylene Diphosphonate

Results of compartmental model analysis for K_bone and k₄ for ¹⁸F-fluoride (A), ^99mTc-MDP assuming no protein binding of MDP in ECF space (B), and ^99mTc-MDP assuming protein binding in ECF space is same as that in plasma (C). In each plot, values for K_bone are normalized to values determined using AUC approximation. Stippled bands show range of allowed values of K_bone and k₄ based on assumption that bone tracer in plasma reaches equilibrium with ECF space by 2 h after injection. Four thumbnail plots show ECF space curves (Eq. 1) at points A–D. Points on upper boundary of stippled bands correspond to solutions where ECF spaces are equal at 2 and 4 h after injection, whereas points on lower boundary correspond to 10% increase in ECF space between these times. Solutions to right of D are excluded by nonphysiologic behavior of ECF space at times earlier than 2 h.

Scatter plot of values of ¹⁸F-fluoride skeletal clearance (K_bone) determined using compartmental model method for k₄ = 0.0018 min⁻¹ compared with values determined using AUC (area under plasma clearance curve) approximation. Although values of K_bone for k₄ = 0.0018 min⁻¹ are 1.5 times larger than AUC approximation values, 2 sets of values are highly correlated (r = 0.989). Correlation coefficients for other values of k₄ are indicated.