Evaluation of Structure-Function Relationships in Asthma using Multidetector CT and Hyperpolarized He-3 MRI

Abstract

Rationale and Objectives-While multiple detector CT (MDCT) and hyperpolarized gas MRI (HP MRI) have demonstrated ability to detect structural and ventilation abnormalities in asthma, few studies have sought to exploit or cross-validate the regional information provided by these techniques. The purpose of this work is to assess regional disease in asthma by evaluating the association of sites of ventilation defect on HP MRI with other regional markers of airway disease, including air trapping on MDCT and inflammatory markers on bronchoscopy.Materials and Methods-Both HP MRI using helium-3 and MDCT were acquired in the same patients. Supervised segmentation of the lung lobes on MRI and MDCT facilitated regional comparisons of ventilation abnormalities in the lung parenchyma. The percentage of spatial overlap was evaluated between regions of ventilation defect on HP MRI and hyperlucency on MDCT to determine associations between obstruction and likely regions of gas trapping.. Similarly, lung lobes with high defect volume were compared to lobes with low defect volume for differences in inflammatory cell number and percentage using bronchoscopic assessment.Results-There was significant overlap between sites of ventilation defect on HP MRI and hyperlucency on MDCT suggesting that sites of airway obstruction and air trapping are associated in asthma. The percent (r = 0.68; p = 0.0039) and absolute (r = 0.61; p = 0.0125) number of neutrophils on bronchoalveolar lavage (BAL) for the sampled lung lobe also directly correlated with increased defect volume.Conclusion-These results show promise for using image guidance to assess specific regions of ventilation defect or air trapping in heterogeneous obstructive lung diseases such as asthma.

Hyperpolarised 3He MRI versus HRCT in COPD and normal volunteers: PHIL trial

“…A recent study in an emphysema-induced canine model compared volumetric CT with 3 mm slice thickness and 3 He diffusion MRI and demonstrated very good correlation between the two modalities [41]. A further study in asthmatic patients also demonstrated good correlation between MDCT findings of airway morphology and expiratory air trapping and the presence of ventilation defects [42]. This discrepancy of our relative lack of agreement compared with this literature may well be related to the fact that we used traditional HRCT methods (with axial 1-mm slices and 1-cm gaps), thus reducing the ability to obtain better comparative images.…”

Regional Ventilation Changes in Severe Asthma after Bronchial Thermoplasty with3He MR Imaging and CT

“…Currently, ventilatory function cannot easily be extracted from CT alone (23,24); likewise, MR imaging cannot provide adequate structural information for segmental delineation (25)(26)(27). With the use of the anatomic information available from CT, we were able to quantify regional 3 He ventilation in healthy volunteers and patients with severe asthma (some of whom were treated by using bronchial thermoplasty and underwent imaging with 3 He a second time).…”

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.…”

“…Hyperpolarized 3 He magnetic resonance imaging (MRI) ventilation heterogeneity has been shown in patients with pulmonary diseases such as COPD (4,5), asthma (6,7), and cystic fibrosis (8). At the same time, however, preclinical or subclinical 3 He ventilation heterogeneity has also been observed in volunteers without clinical signs or symptoms of lung disease such as healthy elderly never-smokers (9), ex-smokers without airflow limitation (10), in second-hand smoke exposed adults (11), and current-smokers without disease (12).…”