Abstract
Noble gas pulmonary magnetic resonance imaging (MRI) is transitioning away from 3He to 129Xe gas, but the physiological/clinical relevance of 129Xe apparent diffusion coefficient (ADC) parenchyma measurements is not well understood. Therefore, our objective was to generate 129Xe MRI ADC for comparison with 3He ADC and with well‐established measurements of alveolar structure and function in older never‐smokers and ex‐smokers with chronic obstructive pulmonary disease (COPD). In four never‐smokers and 10 COPD ex‐smokers, 3He (b = 1.6 sec/cm2) and 129Xe (b = 12, 20, and 30 sec/cm2) ADC, computed tomography (CT) density‐threshold measurements, and the diffusing capacity for carbon monoxide (DLCO) were measured. To understand regional differences, the anterior–posterior (APG) and superior–inferior (∆SI) ADC differences were evaluated. Compared to never‐smokers, COPD ex‐smokers showed greater 3He ADC (P = 0.006), 129Xe ADCb12 (P = 0.006), and ADCb20 (P = 0.006), but not for ADCb30 (P > 0.05). Never‐smokers and COPD ex‐smokers had significantly different APG for 3He ADC (P = 0.02), 129Xe ADCb12 (P = 0.006), and ADCb20 (P = 0.01), but not for ADCb30 (P > 0.05). ∆SI for never‐ and ex‐smokers was significantly different for 3He ADC (P = 0.046), but not for 129Xe ADC (P > 0.05). There were strong correlations for DLCO with 3He ADC and 129Xe ADCb12 (both r = −0.95, P < 0.05); in a multivariate model 129Xe ADCb12 was the only significant predictor of DLCO (P = 0.049). For COPD ex‐smokers, CT relative area <−950 HU (RA950) correlated with 3He ADC (r = 0.90, P = 0.008) and 129Xe ADCb12 (r = 0.85, P = 0.03). In conclusion, while 129Xe ADCb30 may be appropriate for evaluating subclinical or mild emphysema, in this small group of never‐smokers and ex‐smokers with moderate‐to‐severe emphysema, 129Xe ADCb12 provided a physiologically appropriate estimate of gas exchange abnormalities and alveolar microstructure.
Highlights
Magnetic resonance imaging (MRI) using hyperpolarized noble gases 3He and 129Xe provides high spatial and temporal resolution images of pulmonary gas distribution (Kauczor et al 1997; de Lange et al 1999; Moller et al 2002)
There were no significant differences in age, sex, or BMI, the never-smokers and chronic obstructive pulmonary disease (COPD) ex-smokers were significantly different with respect to FEV1 (P = 0.01), FEV1/FVC (P = 0.002), TLC (P = 0.02), RV (P = 0.02), functional residual capacity (FRC) (P = 0.01), and DLCO (P = 0.006)
Previous studies (Kaushik et al 2011; Kirby et al 2013, 2012d) reported 129Xe apparent diffusion coefficient (ADC) based on a b value of 12 sec/ cm2, it is still unclear how to provide the optimal balance between sensitivity to the lung microstructural abnormalities in emphysematous patients and feasibility with respect to image quality
Summary
Magnetic resonance imaging (MRI) using hyperpolarized noble gases 3He and 129Xe provides high spatial and temporal resolution images of pulmonary gas distribution (Kauczor et al 1997; de Lange et al 1999; Moller et al 2002). The first demonstrations of inhaled hyperpolarized gas MRI used 129Xe gas (Albert et al 1994; Mugler et al 1997), until recently, most examinations in subjects with chronic obstructive pulmonary disease (COPD) used 3He gas mainly due to the nearly threefold higher gyromagnetic ratio and higher polarizations – both of which independently contribute to greater image quality for 3He MRI These previous studies showed that 3He ADC values are reproducible in emphysematous subjects (Morbach et al 2005; Diaz et al 2008; Mathew et al 2008), sensitive to lung microstructure and airspace size (Saam et al 2000; Salerno et al 2002), and correlate with spirometry (Salerno et al 2002; Diaz et al 2009), diffusing capacity of carbon monoxide (DLCO; Fain et al 2006), and x-ray computed tomography (CT) measurements of emphysema (Diaz et al 2009). There is considerable interest in transitioning to 129Xe MRI
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