Evaluating bronchodilator effects in chronic obstructive pulmonary disease using diffusion-weighted hyperpolarized helium-3 magnetic resonance imaging

Abstract

The objective of this study was to evaluate the regional effects of bronchodilator administration in chronic obstructive pulmonary disease (COPD) using hyperpolarized helium-3 ((3)He) MRI apparent diffusion coefficient (ADC). Ten COPD ex-smokers provided written, informed consent and underwent diffusion-weighted, hyperpolarized (3)He MRI, spirometry, and plethysmography before and 25 ± 2 min after bronchodilator administration. Pre- and postsalbutamol whole-lung (WL) ADC maps were generated and registered together to identify the lung regions containing the (3)He signal at both time points, and mean ADC within those regions of interest (ROI) was determined for a measurement of previously ventilated ROI ADC (ADC(P)). Lung ROI with (3)He signal at both time points was used as a binary mask on postsalbutamol WL ADC maps to obtain an ADC measurement for newly ventilated ROI (ADC(N)). Postsalbutamol, no significant differences were detected in WL ADC (P = 0.516). There were no significant differences between ADC(N) and ADC(P) postsalbutamol (P = 1.00), suggesting that the ADC(N) lung regions were not more emphysematous than the lung ROI participating in ventilation before bronchodilator administration. Postsalbutamol, a statistically significant decrease in ADC(P) (P = 0.01) was detected, and there were significant differences between ADC(P) in the most anterior and most posterior image slices (P = 0.02), suggesting a reduction in regional gas trapping following bronchodilator administration. Regional evaluation of tissue microstructure using hyperpolarized (3)He MRI ADC provides insights into lung alterations that accompany improvements in regional (3)He gas distribution after bronchodilator administration.

Ventilation Heterogeneity in Ex-smokers without Airflow Limitation

“…Eighteen subjects (18 of 60 = 30%) reported normal VDP and 42 (42 of 60 = 70%) subjects reported abnormally elevated VDP. As shown in Figure 1 for three representative subjects, volunteers with normal VDP showed small or no ventilation defects along the periphery of the lung, whereas (16) 27 (14) 28 (17) .86 (1.0) Years quit smoking 19 (15) 13 (12) 21 (15) .06 (1.0) BMI, kg/m 2 29 (4) 29 (5) 30 (4) .5 (1.0) FVC, % pred 97 (13) 100 (10) 95 (14) .18 (1.0) FEV 1 , % pred 104 (13) 106 (12) 102 (14) .28 (1.0) FEV 1 /FVC 80 (6) 80 (6) 80 (6) .78 (1.0) RV/TLC, % pred 103 (15) 104 (12) 103 (16 ADC, apparent diffusion coefficient; BMI, body mass index; BSA, body surface area; DL CO , diffusing capacity for carbon monoxide; FEV 1 , forced expiratory volume in 1 second; FVC, forced vital capacity; LA, mean fifth generation airway lumen area; 6MWD, six-minute walk distance; RA 950 , relative area of the lung parenchyma with attenuation #À950 HU; RV, residual volume; SD, standard deviation; SGRQ, St. Georges Respiratory Questionnaire; TLC, total lung capacity; VDP, ventilation defect percent; WA%, mean fifth generation airway wall area percent.…”

“…Therefore, ex-smokers with VDP <4.3% were classified as normal, whereas ex-smokers with VDP $4.3% were classified as having abnormally elevated VDP. 3 He MRI apparent diffusion coefficients (ADCs) were generated as previously described (16).…”

Effects of Bronchodilators on Regional Lung Sound Distribution in Patients with Chronic Obstructive Pulmonary Disease

“…Kirby et al [9 ]used magnetic resonance imaging with inhaled hyperpolarized 3 He to evaluate regional structure-function measurements in COPD subjects, and they reported a change in gas distribution following bronchodilator administration. Kirby et al suggested that the newly ventilated lung regions were not more emphysematous than the lung regions of interest that participated in ventilation prior to bronchodilator administration.…”

Clinical highlights from the 2013 ERS Congress in Barcelona

“…Using oxygen enhancement at MRI, ZHANG et al [63] found a heterogeneous pattern of decreased lung oxygenation in severe asthmatics in response to salbutamol due to the so-called ventilation/perfusion imbalance. KIRBY et al [64] found similar results using hyperpolarised 3 He with diffusion-weighted MRI.…”