Exercise-induced bronchoconstriction: reproducibility of hyperpolarized 3He MR imaging

Abstract

Purpose: To quantitatively evaluate interday, interreader, and intersite agreement of readers of hyperpolarized helium 3 (HPHe) MR images in patients with exercise-induced bronchoconstriction.

Materials and methods: This HIPAA-compliant, institutional review board approved study included 13 patients with exercise-induced bronchoconstriction. On two separate days, HPHe MR imaging of the lungs was performed at baseline, immediately after a 10-minute exercise challenge (postchallenge), and 45 minutes after exercise (recovery). Patients were imaged at two sites, six at site A and seven at site B. Images were analyzed independently by multiple readers at each site. Lung volume, ventilation defect volume, ventilated volume, and the number of defects were measured quantitatively, and the location of defects was evaluated qualitatively at site A. Interday and interreader agreement were evaluated by using the intraclass correlation coefficient (ICC), and intersite agreement was evaluated by using a modified Bland-Altman analysis.

Results: The ICC between days for ventilation defect volume, ventilated volume, and number of defects was at least 0.74 at both sites. The ICC for lung volume was greater at site B (0.83-0.86) than at site A (0.60-0.65). Defects seen in the same location in the lung on both days included 19.7% of those seen on baseline images and 29.2% and 18.6% of defects on postchallenge and recovery images, respectively. Interreader ICC for each measurement was at least 0.82 for each site. Analysis of intersite agreement showed biases of 612 mL for lung volume, -60.7 mL for ventilation defect volume, 2.91% for ventilated volume, and -6.56 for number of defects.

Conclusion: The reported measures of reproducibility of HPHe MR imaging may help in the design and interpretation of single- and multicenter studies of patients with exercise-induced bronchoconstriction.

Figure 1:

Timeline of exercise challenge and HPHe MR imaging examinations during each visit.

Figure 2a:

Coronal images of lungs show examples of segmentation steps performed at each site. (a) Segmentation of V_L from proton image acquired in patient at site B. (b) Segmentation of V_L from HPHe image of patient at site A. Ventilation defects appear as dark regions. (c) Segmentation of V_D from HPHe image.

Figure 2b:

Coronal images of lungs show examples of segmentation steps performed at each site. (a) Segmentation of V_L from proton image acquired in patient at site B. (b) Segmentation of V_L from HPHe image of patient at site A. Ventilation defects appear as dark regions. (c) Segmentation of V_D from HPHe image.

Figure 2c:

Coronal images of lungs show examples of segmentation steps performed at each site. (a) Segmentation of V_L from proton image acquired in patient at site B. (b) Segmentation of V_L from HPHe image of patient at site A. Ventilation defects appear as dark regions. (c) Segmentation of V_D from HPHe image.

Figure 3:

Typical coronal HPHe MR images acquired at baseline (left), postchallenge (middle), and recovery (right) time points for one patient on the, A, first and, B, second visits at site A and one patient on the, C, first and, D, second visits at site B. Defects (arrows) appear with similar size and location during each visit.

Figure 4:

Box-and-whisker plots show percentage of defects observed in the same location in lung at both visits. Whiskers indicate largest and smallest values within 1.5 times interquartile range, and median values are indicated by horizontal lines in boxes. Significant differences (*) were observed between baseline and postchallenge values and between postchallenge and recovery values.