The difference in ventilation heterogeneity between asthmatic and healthy subjects quantified using hyperpolarized ³He MRI

Abstract

In this pilot study, algorithms for quantitatively evaluating the distribution and heterogeneity of human ventilation imaged with hyperpolarized (HP) (3)He MRI were developed for the goal of examining structure-function relationships within the asthmatic lung. Ten asthmatic and six healthy human subjects were imaged with HP (3)He MRI before bronchial challenge (pre-MCh), after bronchial challenge (post-MCh), and after a series of deep inspirations (post-DI) following challenge. The acquired images were rigidly coregistered. Local voxel fractional ventilation was computed by setting the sum of the pixel intensity within the lung region in each image to 1 liter of inhaled (3)He mixture. Local ventilation heterogeneity was quantified by computing regional signal coefficient of variation. Voxel fractional ventilation histograms and overall heterogeneity scores were then calculated. Asthmatic subjects had a higher ventilation heterogeneity to begin with (P = 0.025). A methacholine challenge elevated ventilation heterogeneity for all subjects (difference: P = 0.08). After a DI postchallenge, this heterogeneity reversed substantially toward the baseline state for healthy subjects but only minimally in asthmatic subjects. This difference was significant in absolute quantity (difference: P = 0.007) as well as relative to the initial increase (difference: P = 0.03). These findings suggest that constriction heterogeneity is not a characteristic unique to asthmatic airway trees but rather a behavior intrinsic to all airway trees when provoked. Once ventilation heterogeneity is established, it is the lack of reversal following DIs that distinguishes asthmatics from non-asthmatics.

Airway Smooth Muscle in Asthma Symptoms: Culprit but Maybe Innocent

“…In accordance to the computational models discussed above, this is indicative of a heterogenous pattern of constriction that includes randomly distributed airway closures or near closures (138). These observations are supported by ventilation imaging studies such as hyperpolarized 3 He MRI (39,207,234), single-photon emission computed tomography (116) and positron emission tomography (169). These studies showed that asthmatics have increased ventilation heterogeneity at baseline and, even if heterogeneous airway response to a spamogen is also observed in non-asthmatics, the level of ventilation heterogeneity achieved is greater in asthmatics (39,207,234).…”

Using hyperpolarized 3He MRI to evaluate treatment efficacy in cystic fibrosis patients

“…The forced expiratory volume in the first second of expiration (FEV 1 ) and the forced vital capacity (FVC) were measured on the days of both the pretreatment and posttreatment MRI scans. In addition, we created color-coded maps that represented fractional ventilation per pixel normalized to the trachea signal, which is the maximum value, as per the methodologies described in Tzeng et al (25).…”

A View on Imaging in Drug Research and Development for Respiratory Diseases

“…5), and COPD (van Beek et al, 2004). Patients with asthma demonstrated ventilation defects both before and after a challenge with methacholine or exercise (Samee et al, 2003;Tzeng et al, 2009), and a significant overlap of 3 He defects and hyperlucency on HRCT was found (Fain et al, 2008). In patients with COPD, primarily 3 He diffusion MRI has been applied to examine alveolar air space size as mentioned previously (see Emphysema).…”