Quantifying Temperature-Dependent T1 Changes in Cortical Bone Using Ultrashort Echo-Time MRI

Purpose: To demonstrate the feasibility of using ultrashort echo-time MRI to quantify T-1 changes in cortical bone due to heating. Methods: Variable flip-angle T-1 mapping combined with 3D ultrashort echo-time imaging was used to measure T-1 in cortical bone. A calibration experiment was performed to detect T-1 changes with temperature in ex vivo cortical bone samples from a bovine femur. Ultrasound heating experiments were performed using an interstitial applicator in ex vivo bovine femur specimens, and heat-induced T-1 changes were quantified. Results: The calibration experiment demonstrated that T-1 increases with temperature in cortical bone. We observed a linear relationship between temperature and T-1 with a linear coefficient between 0.67 and 0.84 ms/degrees C over a range of 25-70 degrees C. The ultrasound heating experiments showed increased T-1 changes in the heated regions, and the relationship between the temperature changes and T-1 changes was similar to that of the calibration. Conclusion: We demonstrated a temperature dependence of T-1 in ex vivo cortical bone using a variable flip-angle ultrashort echo-time T-1 mapping method. (C) 2015 Wiley Periodicals, Inc.