Measurement of alveolar oxygen partial pressure in the rat lung using Carr‐Purcell‐Meiboom‐Gill spin–spin relaxation times of hyperpolarized ³He and ¹²⁹Xe at 74 mT

Abstract

Regional measurement of alveolar oxygen partial pressure can be obtained from the relaxation rates of hyperpolarized noble gases, 3 He and 129 Xe, in the lungs. Recently, it has been demonstrated that measurements of alveolar oxygen partial pressure can be obtained using the spin-spin relaxation rate (R 2 ) of 3 He at low magnetic field strengths (<0.1 T) in vivo. R 2 measurements can be achieved efficiently using the Carr-Purcell-Meiboom-Gill pulse sequence. In this work, alveolar oxygen partial pressure measurements based on Carr-PurcellMeiboom-Gill R 2 values of hyperpolarized 3 He and 129 Xe in vitro and in vivo in the rat lung at low magnetic field strength (74 mT) are presented. In vitro spin-spin relaxivity constants for 3 He and 129 Xe were determined to be (5.2 6 0.6) 310 26 Pa 21 sec 21 and (7.3 6 0.4) 310 26 Pa 21 s 21 compared with spin-lattice relaxivity constants of (4.0 6 0.4) 310 26 Pa 21 s 21 and (4.3 6 1.3) 3 10 26 Pa 21 s 21 , respectively. In vivo experimental measurements of alveolar oxygen partial pressure using 3 He in whole rat lung show good agreement (r 2 5 0.973) with predictions based on lung volumes and ventilation parameters. For 129 Xe, multicomponent relaxation was observed with one component exhibiting an increase in R 2 with decreasing alveolar oxygen partial pressure. Magn Reson Med 64:1484-1490,

Measurement of 129Xe gas apparent diffusion coefficient anisotropy in an elastase‐instilled rat model of emphysema

“…Although three washout breaths were applied for each acquisition to minimize residual air in the lung, any differences in the gas composition present in the lungs between the S and the S 0 measurement would change the diffusion coefficient of 129 Xe, as well as introduce an undesirable difference in T 2 decay for the echo measurements which would be expected to be more problematic at longer Δ. Furthermore, T 2 decay has been shown to behave biexponentially for 129 Xe in rats (8). With the use of enriched 129 Xe, higher polarization levels, or both, S and S 0 could both be acquired during the same breath hold, ensuring proper relaxation normalization.…”

“…A trapezoidal diffusion‐sensitized PGSE experiment (Fig. 1) was performed (43) during 4‐s 129 Xe breath holds (one per b ‐value, for each Δ) to allow the inflated lung to relax and time for the operator to initiate the sequence, preceded by three 129 Xe washout breaths to remove residual air (e.g., oxygen) in the lungs (8) thereby maximizing signal. The animals were ventilated with medical air for 60–90 s between measurements.…”

“…3 He ventilation maps have proven to be a useful tool for investigating asthma (2, 3) and chronic obstructive disease (4, 5). In addition, by measuring the T 1 and T 2 relaxation of hyperpolarized gases in the lungs, regional alveolar oxygen partial pressure can be quantified (6–8). Microstructural changes in the terminal airways can be detected by measuring the apparent diffusion coefficient (ADC) of 3 He (9), which is smaller than the self‐diffusion coefficient of 3 He due to restrictive diffusion in the lung.…”

Signal‐to‐noise ratio, T2, and for hyperpolarized helium‐3 MRI of the human lung at three magnetic field strengths

“…They found the optimum field strength for hyperpolarized helium-3 ( 3 He) MRI to be 0.1T-0.6T. Several studies have experimentally investigated the properties of hyperpolarized-gas MRI at relatively low field strengths (6,(8)(9)(10)(11)(12)(13)(14), but to our knowledge the lung imaging characteristics at the commonly used field strength of 1.5T have not been compared systematically with those for field strengths below 1.5T. The purpose of this study was to perform hyperpolarized 3 He MRI of the human lung at field strengths between 0.4T and 1.5T using the same MR scanner and to evaluate the associated T 2 , T Ã 2 , and SNR values as a function of field strength (15).…”

A variability study of regional alveolar oxygen tension measurement in humans using hyperpolarized 3He MRI

“…The use of 3 He gas in particular has enabled imaging of both structural and functional aspects of the lung. Specifically, p A O 2 imaging using hyperpolarized 3 He MRI has the potential to provide a quantitative and regional map of lung function , which can be a valuable tool for investigating the physiological changes in lung disease, the response to stress in the healthy lung, and innate differences among individuals . The p A O 2 changes linked to disease state have been previously observed; with the aim of defining the significance of these changes and those of future investigations, this study presents a systematic short‐term and repeat‐visit variability measurement of p A O 2 in the human lung.…”