Introduction

Xe-129 in the barrier (TP) and red blood cells (RBC) could be separated by the dissolved-phase (DP) Xe-129 MRI with radial sampling strategy and Dixon methods^1,2. However, the number of the RF pulse was usually large and thus resulted in long acquisition time. An MRI strategy in the Cartesian coordinate has been used to for high-resolution rodent lung imaging of He-3 in the airspace (Gas)³, which could reduce the number of the RF pulse compared to the radial sampling strategy. The concept was introduced into fast acquisition of the DP Xe-129 in the human lung with the multi-point Dixon method.

Methods

The pulse sequence developed in this study was shown in Fig. 1. An optimized 3D FLASH sequence (BAMI) was used for data acquisition with compressed sensing¹. For each of the phase-encode step, the multi-echo data of the DP and Gas signals of Xe-129 were both acquired. A 1.2 ms sinc RF pulse (centered at +217 ppm relative to the resonance frequency of xenon in airspace) was used to excite the dissolved-phase xenon. And proton images were obtained in the same breath-hold with conventional 3D FLASH sequence. All the experiments were performed on a 1.5-T commercial whole-body imager (Avanto, Siemens Medical Solutions, Malvern, PA) using a homemade transmit-receive vest RF coil. Enriched xenon (86% 129-isotope) was polarized using a homemade xenon polarizer. One liter of xenon mixture (70% xenon + 30% N2) was inhaled from functional residual capacity before each measurement. Informed consent was obtained from each of 4 healthy young subjects (aged between 23 and 27, HY). The protocol was approved by the Ethics Committee of the Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences (WIPM, CAS). The multi-point Dixon method was used to separate the TP and RBC signals. And the ratios of DP/Gas, TP/Gas and RBC/Gas were calculated.

Results

The ratio maps of TP/Gas and RBC/Gas were presented in Fig. 2 with the relevant proton images. For the HY subjects, DP/Gas = 1.36% ± 0.20%, TP/Gas = 0.96% ± 0.16% and RBC/Gas = 0.40% ± 0.07%. These results agreed with the previous study¹.

Conclusion

Xe-129 in the airspace, barrier and red blood cells in the human lung were successfully obtained in a single breath-hold via hyperpolarized Xe-129 MRI. The method BAMI could reduce the number of the RF pulse compared to the radial sampling strategy, which is useful in the clinical practice.

Acknowledgements

We acknowledge the support by the Natural Science Foundation of China (81227902, 81625011, 81601491, 81771917) and National Program for Support of Eminent Professionals (National Program for Support of Top-notch Young Professionals).