MOXE: A model of gas exchange for hyperpolarized ¹²⁹Xe magnetic resonance of the lung

Abstract

We present a model of gas exchange for hyperpolarized (129)Xe in the lung, which we refer to as the Model of Xenon Exchange. The model consists of two expressions and characterizes uptake of dissolved xenon in the lung at two different resonance frequencies. The two expressions are governed by the following five critical pulmonary parameters that characterize both lung function and structure: the surface-area-to-volume ratio, barrier-to-septum ratio (ratio between air-blood barrier thickness and septal thickness), hematocrit, gas-exchange time constant, and pulmonary capillary transit time. The model is first validated by computer simulation. We show that Model of Xenon Exchange can be used to measure the pulmonary parameters mentioned above under various pathological or physiological conditions and is robust against moderate noise. Model of Xenon Exchange is further used to fit an existing data set of xenon uptake, thereby we demonstrate that the data can be well interpreted with Model of Xenon Exchange and reasonable parameters from the fitting routine. The good results obtained in both simulation and fitting to real data indicate that the model is sensitive to various functional and structural changes of the lung, and that it will allow for screening for a variety of pulmonary diseases by using hyperpolarized (129)Xe of the lung.

Reproducibility of quantitative indices of lung function and microstructure from 129 Xe chemical shift saturation recovery (CSSR) MR spectroscopy

“…In each case, a gas dose of 350–400 mL xenon (86% 129 Xe, polarized to ∼25% ), balanced to 1 L with nitrogen, was inhaled from a Tedlar ® bag (Jensen Inert Products, Coral Springs, FL) from functional residual capacity (FRC) before a 10–15‐s breath‐hold. CSSR data were fitted with the model of xenon exchange (MOXE) , using a xenon diffusion coefficient in the dissolved phase of D = 3.0 x10 ‐10 m 2 s ‐1 and an Ostwald solubility coefficient of xenon in tissue of 0.1 , to estimate whole‐lung alveolar septal thickness (ST) and surface‐area‐to‐volume ratio (S/V).…”

Quantitative evaluation of radiation-induced lung injury with hyperpolarized xenon magnetic resonance

“…The exchange time constant ( T ), the barrier‐to‐septum ratio ( δ/d ), the scaling factor ( b ), the fraction of RBC xenon in blood ( η ), and the pulmonary capillary transit time ( t X ), which is defined as the average time an RBC spends in the exchange zone, can be obtained from the fitting directly. Using the diffusion coefficient for xenon in lung tissue D ∼ 3.3 × 10 −6 cm 2 /s and the average Ostwald solubility of xenon in the entire lung (λ = 0.2) in the plasma (λ p = 0.09) and in the RBC (λ RBC = 0.19) in Equations , the relevant physiological parameters of the lung, such as the total septal thickness ( d ), the blood hematocrit ( Hct ), the surface area to volume ratio (SVR), and the air–blood barrier thickness ( δ ) can be calculated.…”

Magnetic resonance imaging with hyperpolarized agents: methods and applications

“…Compartmental modeling of these components has advanced relatively rapidly [148]. Simple and robust single voxel MR spectroscopy readily resolves tissue and blood fractions and enables the calculation of the blood-to-tissue ratio as a possible biomarker of “diffusion block” [149, 150].…”

“…Quantitative measures such as “saturation transfer time” allow the kinetics of 129 Xe recovery to be modeled. These more advanced methods can provide direct [29–31, 151] or indirect [147, 152] estimates of average septal wall thickness and alveolar surface area-to-volume ratio [147, 148, 153]. Both single-voxel [153, 154] and spectroscopic imaging methods [30, 31] are feasible.…”