Human pulmonary imaging and spectroscopy with hyperpolarized 129Xe at 0.2T

Rationale and Objectives: Using a novel Xe-129 polarizer with high throughput (1-2 L/hour) and high polarization (similar to 55%), our objective was to demonstrate and characterize human pulmonary applications at 0.2T. Specifically, we investigated the ability of 129Xe to measure the alveolar surface area per unit volume of gas, S-A/V-gas. Materials and Methods: Variable spin echo time (TE) gradient and radiofrequency (RF) echoes were used to obtain estimates of the lung's contribution to both T-2* and T-2. Standard multislice ventilation images were obtained and signal-to-noise ratio (SNR) determined. Whole-lung, time-dependent measurements of Xe-129 diffusion from gas to septal tissue were obtained with a chemical shift saturation recovery (CSSR) method. Four healthy subjects were studied, and the Butler et al CSSR formalism (J Phys Condensed Matter 2002; 14:L297-L304) was used to calculate S-A/V-gas. A single-breath version of the xenon transfer contrast (SB-XTC) method was implemented and used to image Xe-129 diffusion between alveolar gas and septal tissue. A direct comparison of CSSR and SB-XTC was performed. Results: T-2* = 135 +/- 29 ms amd T-2 = 326.2 +/- 9.5 ms. Maximum SNR = 36 for ventilation images from inhalation of IL 86% Xe-129 and voxel volume = 0.225 mL. CSSR analysis showed S-A/V-gas decreased with increasing lung volume in a manner very similar to that observed from histology measurements; however, the absolute value of S-A/V-gas was similar to 40% smaller than histology values. SB-XTC images in different postures demonstrate gravitationally dependent values. Initial comparison of CSSR with XTC showed fairly good agreement with expected ratios. Conclusions: Hyperpolarized Xe-129 human imaging and spectroscopy are very promising methods to provide functional information about the lung.