Combined helium‐3/proton magnetic resonance imaging measurement of ventilated lung volumes in smokers compared to never‐smokers

Abstract

Purpose: To use a combination of helium-3 (3-He) magnetic resonance imaging (MRI) and proton single-shot fast spin echo (SSFSE) to compare ventilated lung volumes in groups of "healthy" smokers, smokers diagnosed with moderate chronic obstructive pulmonary disease (COPD), and never-smokers. Materials and Methods:All study participants were assessed with spirometry prior to imaging. 3-He images were collected during an arrested breath hold, after inhaling a mixture of 200 mL of hyperpolarized 3-He/800 mL of N 2 . Proton SSFSE images were acquired after inhaling 1 liter of room air. The ventilated volume for each study participant was calculated from the 3-He images, and a ratio was calculated to give a percentage ventilated lung volume.Results: Never-smokers exhibited a 90% mean ventilated volume. The mean ventilated lung volumes for healthy smokers and smokers diagnosed with COPD were 75.2% and 67.6%, respectively. No correlation with spirometry was demonstrated for either of the smoking groups. Conclusion:Combined 3-He/Proton SSFSE MRI of the lungs is a noninvasive method, using nonionizing radiation, which demonstrates ventilated airspaces and enables the calculation of ventilated lung volumes. This method appears to be sensitive to early obstructive changes in the lungs of smokers. HYPERPOLARIZED HELIUM-3 (3-He) magnetic resonance imaging (MRI) is an emerging technique, which has been shown to produce high-resolution images of ventilated human airspaces (1,2). Proton MRI of the lungs has long been regarded to be of limited use in lung imaging due to cardiac motion artifacts, low proton density, and large magnetic susceptibility gradients associated with lung tissue. However, with ongoing development of fast imaging sequences, proton MRI of the lungs is now enjoying somewhat of a renaissance (3,4). In this work single-shot fast spin echo (SSFSE) breathhold images of the lungs were used to calculate a thoracic volume (5), and 3-He ventilation images were used to calculate a ventilated volume (6 -8) for each study participant. A ratio of ventilated volume to thoracic volume was calculated to give a percentage ventilated lung volume. MATERIALS AND METHODSThe local research ethics committee gave approval, and written informed consent was obtained from each study participant. The lungs of 13 volunteers (5 male, 8 female; mean age ϭ 51; range ϭ 40 -62) and 5 patients with chronic obstructive pulmonary disease (COPD) (2 male, 3 female; mean age ϭ 53; range ϭ 47-61) were imaged using proton SSFSE MRI and 3-He MRI in the coronal plane. All participants were assessed with spirometry prior to imaging and assigned to three groups: eight healthy never-smokers, five "healthy" smokers with a smoking history of Ͼ10 pack years, and five smokers with moderate COPD as demonstrated by spirometry and clinical history. Thus, COPD was defined as a subject who is symptomatic (chronic cough and shortness of breath), and the spirometric indices are 30% Ͻ forced expiratory volume in one second (FEV1) Ͻ 80% of the predicted value in comb...

Ventilation Heterogeneity in Ex-smokers without Airflow Limitation

“…At the same time, we were surprised that these same measurements showed no significant differences between subjects with elevated VDP compared to subjects with normal VDP. Previous work (10) in ''healthy'' smokers showed significantly different MRI ventilation measurements as compared to never-smokers and COPD smokers and our findings build on this previous work by showing that ex-smokers with abnormally elevated VDP also showed significantly greater whole-lung and apical lung 3 He ADC. In this regard, it is important to note that 3 He ADC provides a surrogate measure of microstructural emphysema (21) and was previously shown to be sensitive to very mild emphysematous changes by detecting differences in subjects exposed only to second-hand smoke (11).…”

“…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). To evaluate the underlying anatomic and structural determinants of ventilation heterogeneity, thoracic x-ray computed tomography (CT) has been used to help determine the spatial relationship of airways disease and emphysema with ventilation abnormalities.…”

Assessment of hyperpolarized 3He lung MRI for regional evaluation of interventional therapy: A pilot study in pediatric cystic fibrosis

“…Each child was accompanied into the scanner room by one or both parents and a member of the CF team, after all parties had satisfactorily completed a safety questionnaire. The total imaging exam typically lasted about 35 minutes per session, including a 10-minute period for the acquisition of anatomical 1 H MRI with a HASTE sequence as described previously (21). Between sessions every attempt was made to ensure patients adopted the same position in the scanner for both sets of images but no restraints were used in the interest of patient comfort.…”

Functional lung imaging using hyperpolarized gas MRI

“…Various studies have used different subjective ventilation defect scores (68) and semiquantitative measures using mean defect counts per slice (72), heterogeneity (73), and defect volume (74,75). Although in obstructive lung diseases, ventilation measures correlate well with FEV 1 (68,73), and correlate spatially with regions of decreased parenchymal density on CT for patients and smokers with COPD and BO syndrome in lung transplant (71,76), little progress has been made toward quantifying the gradations of signal density to true quantitative ventilation.…”