Lung Function Measurement of Single Lungs by Lung Area Segmentation on 2D Dynamic MRI

Rationale and Objectives

Most lung disease is inhomogeneously distributed but diagnosed by global spirometry. Regional lung function might allow for earlier diagnosis. Dynamic two-dimensional magnetic resonance imaging (2D-MRI) can depict lung motion with high temporal resolution. We evaluated whether measurement of lung area on dynamic 2D-MRI has sufficient agreement with spirometry to allow for lung function testing of single lungs.

Material and Methods

Ten healthy volunteers were examined in a 1.5 T MRI scanner with a Flash 2D-sequence (8.5 images per second, sagittal and coronal orientation) with simultaneous spirometry. The lung area was segmented semiautomatically and the area changes were compared with spirometric volume changes.

Results

Segmentation of one time series took 191 seconds on average. Volume-time and flow-volume curves from MRI data were almost congruent with spirometric curves. Pearson correlation of MRI area with spirometry was very high (mean correlation coefficients >0.97). Bland-Altman plots showed good agreement of lung area with spirometry (95% limits of agreement below 11% in each direction). Differences between lung area and spirometry were significantly smaller for sagittal measurement of the right lung than sagittal measurement of the left lung and coronal measurement. The relative forced expiratory volume in the first second differed less than 5% between MRI and spirometry in all but one volunteer.

Conclusions

Measurement of lung area on 2D-MRI allows for functional measurement of single lungs with good agreement to spirometry. Postprocessing is fast enough for application in a clinical context and possibly provides increased sensitivity for lung functional measurement of inhomogeneously distributed lung disease.

Most pulmonary diseases alter pulmonary mechanics by changes in tissue elasticity, airflow resistance, or a combination of both. The most frequently applied test to assess such changes is spirometry. A common spirometric parameter is the volume expired in the first second of forced expiration (FEV1). It is used for grading of chronic obstructive pulmonary disease (global initiative for chronic obstructive lung disease [GOLD classification]) , monitoring of asthma , or follow-up after lung transplantation .

Because spirometry is an inherently global measurement, it can only measure the combined air flow from both lungs. In disease with regional inhomogeneous distribution favoring a single lung, pathological changes of lung function might pass unnoticed because of averaging with the less affected lung. A spirometric test for single lungs would be able to detect such changes and thus improve functional pulmonary assessments. This is relevant in single-lung transplantation, for example. Here, alteration in FEV1% is taken as indication of organ rejection–induced bronchiolitis obliterans syndrome, but changes in the transplanted lung can be covered by the remaining contralateral lung . Better sensitivity of regional functional changes might also improve treatment in chronic obstructive pulmonary disease, where the GOLD classification recently dropped the GOLD stage 0 because there was no clear evidence that these patients progress to stage 1 . Yet, a subpopulation of the patients with clinical symptoms but normal lung function does progress to Stage I and might profit from preventive treatment. A spirometric test for single lungs might be able to identify some of these patients and help to improve long-term outcome.

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Material and methods

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Data Acquisition

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Image Analysis

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Data Analysis

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Results

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Table 1

Product Moment Correlation Coefficients of Magnetic Resonance Imaging Area Changes with Spirometric Volume Changes for Sagittal and Coronal Image Orientation of the Left and Right Lung

Volunteer Right Sagittal Left Sagittal Right Coronal Left Coronal 01 0.99 1.00 0.97 0.98 02 1.00 1.00 1.00 0.99 03 0.98 0.99 0.99 0.98 04 0.99 0.99 0.99 0.98 05 0.99 0.99 0.98 0.98 06 0.97 0.96 0.86 0.84 07 0.99 0.98 1.00 1.00 08 0.99 0.99 0.98 0.99 09 0.99 0.98 0.99 0.99 10 0.97 0.97 1.00 0.99 Mean (SD) 0.99 (0.01) 0.98 (0.01) 0.98 (0.04) 0.97 (0.05)

The large correlation coefficients show that the respiratory volume changes are well captured by measurement of the lung area on dynamic two-dimensional magnetic resonance imaging.

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Table 2

FEV1% Calculated from Spirometric and MRI Measurement for Sagittal and Coronal Imaging of Both Lungs (the Values for Spir and MRI are Rounded, the Values for Diff are Calculated from the Original Data and are Rounded to the First Decimal)

Sagittal Right Sagittal Left Coronal Vol. Spir MRI Diff Spir MRI Diff Spir MRI R Diff R MRI L Diff L 01 79 78 1.3 81 77 3.1 78 72 6.4 70 8.6 02 82 79 2.6 82 83 0.3 80 83 3.2 80 0.3 03 86 89 2.8 82 81 0.8 84 85 0.5 84 0.2 04 76 73 2.5 75 74 1.5 74 76 1.1 75 0.1 05 73 72 0.8 73 73 0.4 73 78 4.7 77 3.4 06 75 71 4.7 75 68 7.7 74 74 0 67 6.3 07 80 79 0.7 77 81 3.4 80 76 4.4 82 2 08 69 70 0.2 69 65 3.7 69 84 14.4 69 1 09 73 65 8.4 73 73 0.4 71 75 4.4 73 2.1 10 68 68 0.6 68 72 4.6 68 65 3.1 64 4.5 Mean (SD) 2.45 (2.5) 2.59 (2.39) 4.2 (4.1) 2.84 (2.88)

FEV1%, first second of forced expiration; Vol., volunteer; Spir, spirometric FEV1%; MRI, FEV1% as determined from magnetic resonance imaging; Diff, Spir – MRI; R and L, left and right lung.

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Discussion

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Conclusion

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Lung Function Measurement of Single Lungs by Lung Area Segmentation on 2D Dynamic MRI

Rationale and Objectives

Material and Methods

Results

Conclusions

Material and methods

Data Acquisition

Image Analysis

Data Analysis

Results

Discussion

Conclusion

References

Further Reading

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