Determination of regional pulmonary parenchymal strain during normal respiration using spin inversion tagged magnetization MRI

Abstract

In clinical practice, the assessment of lung mechanics is limited to a global physiological evaluation, which measures, in the aggregate, the contributions of the pulmonary parenchyma, pleura, and chest wall. In this study, we used an MR imaging methodology which applies two-dimensional bands of inverted magnetization directly onto the pulmonary parenchyma, thus allowing for the quantification of local pulmonary tissue deformation, or strain, throughout inhalation. Our results showed that the magnitude of strain was maximal at the base and apex of the lung, but was curtailed at the hilum, the anatomical site of the poorly mobile bronchial and vascular insertions. In-plane shear strain mapping showed mostly positive shear strain, predominant at the apex throughout inhalation, and increasing with expanding lung volume. Anisotropy mapping showed that superior-inferior axial strain was greater than medial-lateral axial strain at the apex and base, while the opposite was true for the middle lung field. This study demonstrates that localized pulmonary deformation can be measured in vivo with tagging MRI, and quantified by applying finite strain definitions from continuum mechanics.