Rapid 3-D mapping of hyperpolarized ~3He spin-lattice relaxation times using variable flip angle gradient echo imaging with application to alveolar oxygen partial pressure measurement in rat lungs

摘要

Objective: The purpose of this work was to develop a rapid 3-D, variable flip angle (VFA) method for measurement of hyperpolarized ~3He T _1 which accounts for the effects of radiofrequency (RF) pulses without the need for additional flip angle information. Materials and methods: The 3-D, VFA method was validated in vitro over a range of oxygen partial pressures ranging from 0.04 to 0.52 atm. The approach was also tested in vivo in five healthy rats as a function of increasing number of wash-out breaths. The T _1 accuracy of the VFA method in the presence of flip angle mis-setting and RF field non-uniformity was compared with the CFA method using simulations and experiments. Results: T _1 measurements were found to provide p_AO_2 estimates, both in vitro and in vivo consistent with those predicted based on gas dilution and/or ventilation para- meters. For the RF pulse mis-setting (4%) and RF field non-uniformity (3%) used here, the VFA method provided a T _1 accuracy of better than 5% compared to 12% for the CFA method. Conclusion: With sufficient RF field homogeneity (3%) and proper calibration (4%), the VFA approach can provide rapid and reliable 3-D T _1 mapping of hyperpolarized ~3He without the need for additional flip angle information.