Dataset Information

Hyperpolarized 3He magnetic resonance imaging ventilation defects in asthma: relationship to airway mechanics.

ABSTRACT: In patients with asthma, magnetic resonance imaging (MRI) provides direct measurements of regional ventilation heterogeneity, the etiology of which is not well-understood, nor is the relationship of ventilation abnormalities with lung mechanics. In addition, respiratory resistance and reactance are often abnormal in asthmatics and the frequency dependence of respiratory resistance is thought to reflect ventilation heterogeneity. We acquiredMRIventilation defect maps, forced expiratory volume in one-second (FEV1), and airways resistance (Raw) measurements, and used a computational airway model to explore the relationship of ventilation defect percent (VDP) with simulated measurements of respiratory system resistance (Rrs) and reactance (Xrs).MRIventilation defect maps were experimentally acquired in 25 asthmatics before, during, and after methacholine challenge and these were nonrigidly coregistered to the airway tree model. Using the model coregistered to ventilation defect maps, we narrowed proximal (9th) and distal (14th) generation airways that were spatially related to theMRIventilation defects. The relationships forVDPwith Raw measured using plethysmography (r = 0.79), and model predictions of Rrs>14(r = 0.91,P < 0.0001) and Rrs>9(r = 0.88,P < 0.0001) were significantly stronger (P = 0.005;P = 0.03, respectively) than withFEV1(r = -0.68,P = 0.0001). The slopes for the relationship ofVDPwith simulated lung mechanics measurements were different (P < 0.0001); among these, the slope for theVDP-Xrs0.2relationship was largest, suggesting thatVDPwas dominated by peripheral airway heterogeneity in these patients. In conclusion, as a first step toward understanding potential links between lung mechanics and ventilation defects, impedance predictions were made using a computational airway tree model with simulated constriction of airways related to ventilation defects measured in mild-moderate asthmatics.

SUBMITTER: Leary D

PROVIDER: S-EPMC4831329 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Hyperpolarized 3He magnetic resonance imaging ventilation defects in asthma: relationship to airway mechanics.

Leary Del D Svenningsen Sarah S Guo Fumin F Bhatawadekar Swati S Parraga Grace G Maksym Geoffrey N GN

Physiological reports 20160401 7

In patients with asthma, magnetic resonance imaging (MRI) provides direct measurements of regional ventilation heterogeneity, the etiology of which is not well-understood, nor is the relationship of ventilation abnormalities with lung mechanics. In addition, respiratory resistance and reactance are often abnormal in asthmatics and the frequency dependence of respiratory resistance is thought to reflect ventilation heterogeneity. We acquiredMRIventilation defect maps, forced expiratory volume in ...[more]

PMID: 27053294

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Project description:Regions of diminished ventilation are often evident during functional pulmonary imaging studies, including hyperpolarized gas magnetic resonance imaging (MRI), positron emission tomography, and computed tomography (CT). The objective of this study was to characterize the hypointense regions observed via (3)He MRI in a murine model of acute lung injury. LPS at doses ranging from 15-50 μg was intratracheally administered to C57BL/6 mice under anesthesia. Four hours after exposure to either LPS or saline vehicle, mice were imaged via hyperpolarized (3)He MRI. All images were evaluated to identify regions of hypointense signals. Lungs were then characterized by conventional histology, or used to obtain tissue samples from regions of normal and hypointense (3)He signals and analyzed for cytokine content. The characterization of (3)He MRI images identified three distinct types of hypointense patterns: persistent defects, atelectatic defects, and dorsal lucencies. Persistent defects were associated with the administration of LPS. The number of persistent defects depended on the dose of LPS, with a significant increase in mean number of defects in 30-50-μg LPS-dosed mice versus saline-treated control mice. Atelectatic defects predominated in LPS-dosed mice under conditions of low-volume ventilation, and could be reversed with deep inspiration. Dorsal lucencies were present in nearly all mice studied, regardless of the experimental conditions, including control animals that did not receive LPS. A comparison of (3)He MRI with histopathology did not identify tissue abnormalities in regions of low (3)He signal, with the exception of a single region of atelectasis in one mouse. Furthermore, no statistically significant differences were evident in concentrations of IL-1β, IL-6, macrophage inflammatory protein (MIP)-1α, MIP-2, chemokine (C-X-C motif) ligand 1 (KC), TNFα, and monocyte chemotactic protein (MCP)-1 between hypointense and normally ventilated lung regions in LPS-dosed mice. Thus, this study defines the anatomic, functional, and biochemical characteristics of ventilation defects associated with the administration of LPS in a murine model of acute lung injury.

Project description:Two magnetic resonance specific ventilation imaging (SVI) techniques, namely, oxygen-enhanced proton (OE-1H) and hyperpolarized 3He (HP-3He), were compared in eight healthy supine subjects [age 32 (6) yr]. An in-house radio frequency coil array for 1H configured with the 3He transmit-receive coil in situ enabled acquisition of SVI data from two nuclei from the same slice without repositioning the subjects. After 3?×?3 voxel downsampling to account for spatial registration errors between the two SV images, the voxel-by-voxel correlation coefficient of two SV maps ranged from 0.11 to 0.63 [0.46 mean (0.17 SD); P < 0.05]. Several indexes were analyzed and compared from the tidal volume-matched SV maps: the mean of SV log-normal distribution (SVmean), the standard deviation of the distribution as a measure of SV heterogeneity (SVwidth), and the gravitational gradient (SVslope). There were no significant differences in SVmean [OE-1H: 0.28 (0.08) and HP-3He: 0.32 (0.14)], SVwidths [OE-1H: 0.28 (0.08) and HP-3He: 0.27 (0.10)], and SVslopes [OE-1H: -0.016 (0.006) cm-1 and HP-3He: -0.013 (0.007) cm-1]. Despite the statistical similarities of the population averages, Bland-Altman analysis demonstrated large individual intertechnique variability. SDs of differences in these indexes were 42% (SVmean), 46% (SVwidths), and 62% (SVslopes) of their corresponding overall mean values. The present study showed that two independent, spatially coregistered, SVI techniques presented a moderate positive voxel-by-voxel correlation. Population averages of SVmean, SVwidth, and SVslope were in close agreement. However, the lack of agreement when the data sets were analyzed individually might indicate some fundamental mechanistic differences between the techniques. NEW & NOTEWORTHY To the best of our knowledge, this is the first cross-comparison of two different specific ventilation (SV) MRI techniques in the human lung (i.e., oxygen-enhanced proton and hyperpolarized 3He). The present study showed that two types of spatially coregistered SV images presented a modest positive correlation. The two techniques also yielded similar population averages of SV indexes such as log-normal mean, SV heterogeneity, and the gravitational slope, albeit with some intersubject variability.

Dataset Information

Hyperpolarized 3He magnetic resonance imaging ventilation defects in asthma: relationship to airway mechanics.

Publications

Hyperpolarized 3He magnetic resonance imaging ventilation defects in asthma: relationship to airway mechanics.

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