Large production system for hyperpolarized 129Xe for human lung imaging studies

RATIONALE AND OBJECTIVES: Hyperpolarized gases such as (129)Xe and (3)He have high potential as imaging agents for functional lung magnetic resonance imaging (MRI). We present new technology offering (129)Xe production rates with order-of-magnitude improvement over existing systems, to liter per hour at 50% polarization. Human lung imaging studies with xenon, initially limited by the modest quantity and quality of hyperpolarized gas available, can now be performed with multiliter quantities several times daily. MATERIALS AND METHODS: The polarizer is a continuous-flow system capable of producing large quantities of highly-polarized (129)Xe through rubidium spin-exchange optical pumping. The low-pressure, high-velocity operating regime takes advantage of the enhancement in the spin exchange rate provided by van der Waals molecules dominating the atomic interactions. The long polarizing column moves the flow of the gas opposite to the laser direction, allowing efficient extraction of the laser light. Separate sections of the system assure full rubidium vapor saturation and removal. RESULTS: The system is capable of producing 64% polarization at 0.3 L/hour Xe production rate. Increasing xenon flow reduces output polarization. Xenon polarization was studied as a function of different system operating parameters. A novel xenon trapping design was demonstrated to allow full recovery of the xenon polarization after the freeze-thaw cycle. Delivery methods of the gas to an offsite MRI facility were demonstrated in both frozen and gas states. CONCLUSIONS: We demonstrated a new concept for producing large quantities of highly polarized xenon. The system is operating in an MRI facility producing liters of hyperpolarized gas for human lung imaging studies.     

Diffusion‐weighted hyperpolarized 129Xe MRI in healthy volunteers and subjects with chronic obstructive pulmonary disease

Given its greater availability and lower cost, ¹²⁹Xe apparent diffusion coefficient (ADC) MRI offers an alternative to ³He ADC MRI. To demonstrate the feasibility of hyperpolarized ¹²⁹Xe ADC MRI, we present results from healthy volunteers (HV), chronic obstructive pulmonary disease (COPD) subjects, and age‐matched healthy controls (AMC). The mean parenchymal ADC was 0.036 ± 0.003 cm² sec^?1 for HV, 0.043 ± 0.006 cm² sec^?1 for AMC, and 0.056 ± 0.008 cm² sec^?1 for COPD subjects with emphysema. In healthy individuals, but not the COPD group, ADC decreased significantly in the anterior–posterior direction by ～22% (P = 0.006, AMC; 0.0059, HV), likely because of gravity‐induced tissue compression. The COPD group exhibited a significantly larger superior–inferior ADC reduction (～28%) than the healthy groups (～24%) (P = 0.00018, HV; P = 3.45 × 10^?5, AMC), consistent with smoking‐related tissue destruction in the superior lung. Superior–inferior gradients in healthy subjects may result from regional differences in xenon concentration. ADC was significantly correlated with pulmonary function tests (forced expiratory volume in 1 sec, r = ?0.77, P = 0.0002; forced expiratory volume in 1 sec/forced vital capacity, r = ?0.77, P = 0.0002; diffusing capacity of carbon monoxide in the lung/alveolar volume (V_A), r = ?0.77, P = 0.0002). In healthy groups, ADC increased with age by 0.0002 cm² sec^?1 year^?1 (r = 0.56, P = 0.02). This study shows that ¹²⁹Xe ADC MRI is clinically feasible, sufficiently sensitive to distinguish HV from subjects with emphysema, and detects age‐ and posture‐dependent changes. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Direct imaging of hyperpolarized 129Xe alveolar gas uptake in a mouse model of emphysema

MRI of hyperpolarized ¹²⁹Xe dissolved in pulmonary tissues, and blood has the potential to offer a new tool for regional evaluation of pulmonary gas exchange and perfusion; however, the extremely short T and low magnetization density make it difficult to acquire the image. In this study, an ultrashort echo‐time sequence was introduced, and its feasibility to quantitatively assess emphysema‐like pulmonary tissue destruction by a combination of dissolved‐ and gas‐phase ¹²⁹Xe lung MRI was investigated. The ultrashort echo‐time has made it possible to acquire dissolved ¹²⁹Xe images with reasonably high spatial resolution of 0.625 × 0.625 mm² and to obtain T of 0.67 ± 0.30 ms in a spontaneously breathing mouse at 9.4 T. The regional dynamic alveolar gas uptake as well as subsequent transport by pulmonary blood flow was also visualized. The ratio of ¹²⁹Xe magnetization that diffused into the septa relative to the gas‐phase magnetization F was regionally evaluated. The mean F value of elastase‐treated mice was 2.28 ± 0.46%, which was significantly reduced from that of control mice 3.41 ± 0.48% (P = 0.0052). This reflects the reduced uptake efficiency due to alveolar tissue destruction and is correlated with the histologically derived alveolar surface‐to‐volume ratio. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Measurement of xenon diffusing capacity in the rat lung by hyperpolarized 129Xe MRI and dynamic spectroscopy in a single breath-hold.

We used the dual capability of hyperpolarized 129Xe for spectroscopy and imaging to develop new measures of xenon diffusing capacity in the rat lung that (analogously to the diffusing capacity of carbon monoxide or DLCO) are calculated as a product of total lung volume and gas transfer rate constants divided by the pressure gradient. Under conditions of known constant pressure breath-hold, the volume is measured by hyperpolarized 129Xe MRI, and the transfer rate is measured by dynamic spectroscopy. The new quantities (xenon diffusing capacity in lung parenchyma (DLXeLP)), xenon diffusing capacity in RBCs (DLXeRBC), and total lung xenon diffusing capacity (DLXe)) were measured in six normal rats and six rats with lung inflammation induced by instillation of fungal spores of Stachybotrys chartarum. DLXeLP, DLXeRBC, and DLXe were 56 +/- 10 ml/min/mmHg, 64 +/- 35 ml/min/mmHg, and 29 +/- 9 ml/min/mmHg, respectively, for normal rats, and 27 +/- 9 ml/min/mmHg, 42 +/- 27 ml/min/mmHg, and 16 +/- 7 ml/min/mmHg, respectively, for diseased rats. Lung volumes and gas transfer times for LP (TtrLP) were 16 +/- 2 ml and 22 +/- 3 ms, respectively, for normal rats and 12 +/- 2 ml and 35 +/- 8 ms, respectively, for diseased rats. Xenon diffusing capacities may be useful for measuring changes in gas exchange associated with inflammation and other lung diseases.     

一种基于原型体模的宝石能谱CT成像的质量保证检测方法

目的：探讨宝石能谱 CT 成像(GSI)的质量保证检测方法。方法以纯净水和碘帕醇300对比剂为原料,配制9种不同浓度溶液,形成原型体模,在 GE Discovery CT750 HD 扫描仪上,采用常用头部 GSI 方案进行扫描,并在 GE AW4.6图像后处理工作站上进行图像后处理。结果基于等效原子序数直方图、基质散点分布图和 CT 值随射线能量变化的能谱曲线图,GSI 能够区分不同浓度碘溶液,并能定量分析其水和碘的含量。结论通过碘溶液原型体模检测 GSI 的定量分析能力是可行的。