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Evaluation of Asthma With Hyperpolarized Helium-3 MRI^*

Correlation With Clinical Severity and Spirometry

Eduard E. de Lange, MD; Talissa A. Altes, MD; James T. Patrie, MS; John D. Gaare, MD; Jeffrey J. Knake, MD; John P. Mugler, III, PhD and Thomas A. Platts-Mills, MD, PhD

^* From the Departments of Radiology (Drs. de Lange, Altes, Gaare, Knake, and Mugler), Health Evaluation Sciences (Mr. Patrie), and Internal Medicine (Dr. Platts-Mills), Division of Asthma, Allergy, and Immunology, University of Virginia, Charlottesville, VA. Currently at the Department of Radiology, The Children’s Hospital of Philadelphia, Philadelphia, PA. Currently at Michigan State University, East Lansing, MI.

Correspondence to: Eduard E. de Lange, MD, University of Virginia Health Sciences System, Department of Radiology, HSC 800170, Charlottesville, VA 22908; e-mail: delange{at}virginia.edu

Abstract

Background: Accurate characterization of asthma severity is difficult due to the variability of symptoms. Hyperpolarized helium-3 MRI (H³HeMR) is a new technique in which the airspaces are visualized, depicting regions with airflow obstruction as "ventilation defects." The objective of this study was to compare the extent of H³HeMR ventilation defects with measures of asthma severity and spirometry.

Methods: Patients with a physician diagnosis of asthma and normal control subjects underwent H³HeMR. For each person, the number and size of ventilation defects were scored and the average number of ventilation defects per slice (VDS) was calculated. The correlations of the imaging findings with measures of asthma severity and spirometry were determined.

Results: There were 58 patients with asthma (mild-intermittent, n = 13; mild-persistent, n = 13; moderate-persistent, n = 20; and severe-persistent, n = 12) and 18 control subjects. Mean ± SE VDS for asthmatics was significantly greater than for control subjects (0.99 ± 0.15 vs 0.26 ± 0.22, p = 0.004). Among asthmatics, VDS was significantly higher for the group with moderate-persistent and severe-persistent disease than for the group with mild-intermittent and mild-persistent disease (1.37 ± 0.24 vs 0.53 ± 0.12, p < 0.001). VDS correlated significantly with FEV₁/FVC (r = – 0.51, p = 0.002), forced expiratory flow between 25% and 75% from the beginning of FVC (FEF_25–75%) percentage of predicted for height, sex, and race (%predicted) [r = – 0.50, p = 0.001], and FEV₁ %predicted (r = – 0.40, p = 0.002), but not with FVC %predicted (r = – 0.26, p = 0.057) and peak expiratory flow %predicted (r = – 0.16, p = 0.231). Many asthmatics had an elevated VDS, but their spirometric indexes, except FEF_25%-75%, were normal. Most ventilation defects were < 3 cm in size for all asthmatics. In the group of patients with moderate-to-severe persistant asthma, there were more defects 3 cm than in the group with mild-intermittent and mild-persistent disease (p = 0.021).

Conclusions: Regional changes of airflow obstruction in asthmatics depicted by H³HeMR correlate with measures of asthma severity and spirometry.

Key Words: airflow obstruction • airway • asthma • bronchial activity • hyperpolarized gases • hyperpolarized helium-3 • MRI • pulmonary function test • spirometry • ventilation defect