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, 252 (2), 386-93

Pulmonary Perfusion and Xenon Gas Exchange in Rats: MR Imaging With Intravenous Injection of Hyperpolarized 129Xe

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Pulmonary Perfusion and Xenon Gas Exchange in Rats: MR Imaging With Intravenous Injection of Hyperpolarized 129Xe

Bastiaan Driehuys et al. Radiology.

Abstract

Purpose: To develop and demonstrate a method for regional evaluation of pulmonary perfusion and gas exchange based on intravenous injection of hyperpolarized xenon 129 ((129)Xe) and subsequent magnetic resonance (MR) imaging of the gas-phase (129)Xe emerging in the alveolar airspaces.

Materials and methods: Five Fischer 344 rats that weighed 200-425 g were prepared for imaging according to an institutional animal care and use committee-approved protocol. Rats were ventilated, and a 3-F catheter was placed in the jugular (n = 1) or a 24-gauge catheter in the tail (n = 4) vein. Imaging and spectroscopy of gas-phase (129)Xe were performed after injecting 5 mL of half-normal saline saturated with (129)Xe hyperpolarized to 12%. Corresponding ventilation images were obtained during conventional inhalation delivery of hyperpolarized (129)Xe.

Results: Injections of (129)Xe-saturated saline were well tolerated and produced a strong gas-phase (129)Xe signal in the airspaces that resulted from (129)Xe transport through the pulmonary circulation and diffusion across the blood-gas barrier. After a single injection, the emerging (129)Xe gas could be detected separately from (129)Xe remaining in the blood and was imaged with an in-plane resolution of 1 x 1 mm and a signal-to-noise ratio of 25. Images in one rat revealed a matched ventilation-perfusion deficit, while images in another rat showed that xenon gas exchange was temporarily impaired after saline overload, with recovery of function 1 hour later.

Conclusion: MR imaging of gas-phase (129)Xe emerging in the pulmonary airspaces after intravenous injection has the potential to become a sensitive and minimally invasive new tool for regional evaluation of pulmonary perfusion and gas exchange.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/2513081550/DC1.

Figures

Figure 1:
Figure 1:
Dissolution of hyperpolarized (HP) 129Xe into saline, injection of the xenon (Xe)-saturated solution, and excretion of hyperpolarized 129Xe into the alveoli. 1, Saline is degassed by evacuation, and gas-phase hyperpolarized 129Xe is then introduced to the container. 2, The container is manually shaken for 20 seconds to dissolve the hyperpolarized 129Xe into the saline, and the saturated fluid is then withdrawn into an attached syringe. 3, Saline is injected into venous blood, where it is transported to the lungs and excreted from the capillaries into the alveolar space. Hyperpolarized 129Xe in the pulmonary airspaces has a substantially different resonance frequency than dissolved 129Xe, which enables the gas phase to be selectively detected and imaged.
Figure 2:
Figure 2:
Graph of time course of 129Xe signals during injection of 129Xe-saline mixture in the tail vein depicts the dynamics of the three resonances corresponding to 129Xe in blood (215 ppm), 129Xe in plasma or saline (195 ppm), and gaseous 129Xe in the airspaces (0 ppm). These resonances are shown in the inset spectrum, which was obtained by averaging the signals from 8 to 12 seconds. These spectral dynamics clearly illustrate that the airspace 129Xe peak is dramatically larger (and narrower) than that of the dissolved 129Xe resonances and is the most favorable peak for imaging. The dynamics were probed during a 30-second period at a repetition time of 250 msec, with the injection starting at frame 0 and lasting 16 seconds. Arb = arbitrary units, RF = radiofrequency.
Figure 3:
Figure 3:
Graphs of dynamics of the gaseous 129Xe signal acquired at various flip angles (α) during and after 129Xe-saline injection. Injection started at 0 seconds, simultaneously with data collection, and ended at 19 seconds, as indicated by the dashed line. These data were collected every 125 msec. All experiments showed that signal appeared roughly 3.3 seconds after injection and continued after injection with a decay that was driven by the flip angle.
Figure 4:
Figure 4:
High-spatial-resolution ventilation MR image (left) and MR image acquired with gaseous 129Xe signal emerging in the airspaces after 129Xe-saline injection (right). The injected image shows hypointense region (arrow) in the area of the right descending mainstem bronchus where there is no gas exchange and hence no emerging airspace 129Xe. Both images show gaseous 129Xe; only the delivery method was different.
Figure 5:
Figure 5:
Ventilation (left) and injected (right) 129Xe MR images acquired with an identical sequence and imaging parameters (1 × 1-mm resolution). This particular rat showed reduced ventilation in the right cranial lobe of the lung and matching signal intensity reduction on the injected 129Xe image (circled areas); this likely resulted from reduced perfusion in the same area.
Figure 6:
Figure 6:
MR images show changes in perfusion and gas exchange caused by saline overloading in 200-g rat. The images are a ventilation image, a baseline injected 129Xe image, and an injected 129Xe image obtained after the rat had received 10 mL of saline in a 2-minute period. This overloading likely caused vascular congestion resulting from hypervolemia and created substantial impairment of xenon exchange in the right lung and the base of the left lung. However, a subsequent perfusion image obtained 1 hour later shows almost complete recovery of perfusion and xenon exchange.

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