Abstract
Purpose:To optimize 19F imaging pulse sequences for perfluoropropane (C3F8) gas human lung ventilation MRI considering intrinsic in vivo relaxation parameters at both 1.5T and 3T.Methods:Optimization of the imaging parameters for both 3D spoiled gradient (SPGR) and steady‐state free precession (SSFP) 19F imaging sequences with inhaled 79% C3F8% and 21% oxygen was performed. Phantom measurements were used to validate simulations of SNR. In vivo parameter mapping and sequence optimization and comparison was performed by imaging the lungs of a healthy adult volunteer. T1 and T2 * mapping was performed in vivo to optimize sequence parameters for in vivo lung MRI. The performance of SSFP and SPGR was then evaluated in vivo at 1.5T and 3T.Results:The in vivo T2 * of C3F8 was shown to be dependent upon lung inflation level (2.04 ms ± 36% for residual volume and 3.14 ms ± 28% for total lung capacity measured at 3T), with lower T2 * observed near the susceptibility interfaces of the diaphragm and around pulmonary blood vessels. Simulation and phantom measurements indicate that a factor of ~2‐3 higher SNR can be achieved with SSFP when compared with optimized SPGR. In vivo lung imaging showed a 1.7 factor of improvement in SNR achieved at 1.5T, while the theoretical improvement at 3T was not attained due to experimental SAR constraints, shorter in vivo T1, and B0 inhomogeneity.Conclusion:SSFP imaging provides increased SNR in lung ventilation imaging of C3F8 demonstrated at 1.5T with optimized SSFP similar to the SNR that can be obtained at 3T with optimized SPGR.
Highlights
MRI of lung ventilation with inhaled inert hyperpolarized (HP) gases has a proven sensitivity for the assessment of lung ventilation changes in obstructive airways disease.[1]
Fluorinated gases may be mixed with oxygen (O2) and continuously breathed, possibly allowing simpler investigation of dynamic lung physiology, such as the measurement of fractional ventilation by multi‐breath washout[3,4,5] without the complication of gas depolarization observed with HP gas
We demonstrate the application of steady-state free precession (SSFP) sequences for 19F lung ventilation imaging using C3F8/O2 gas at 1.5T and 3T
Summary
MRI of lung ventilation with inhaled inert hyperpolarized (HP) gases has a proven sensitivity for the assessment of lung ventilation changes in obstructive airways disease.[1]. Past strategies of fluorinated gas MRI have focused on the use of short TE spoiled gradient (SPGR) sequences with TR relatively close to T1. The optimization of SSFP imaging parameters[20] has been investigated for the imaging constraints of HP gas ventilation MRI with both 3He and 129Xe.[21] Sequence optimization for perfluorocarbon emulsions has been performed previously,[22,23] but in this instance the T2 and T1 relaxation parameters are significantly longer than for gas phase perfluorocarbons. Optimization of SSFP and SPGR imaging parameters was carried out by simulation with the specific relaxation parameters of C3F8/O2 gas as found in phantoms. The mean in vivo T1 has been reported as 12.4 ms at 3T.14 the intrinsic T2 of C3F8 gas within the lungs has not been reported, but is expected to remain comparable to T1.17,34 the mean in vivo T2* relaxation constant of C3F8 has been reported as ∼2.2 ms at 3T.14
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