Estimation of the absolute shear stiffness of human lung parenchyma using ¹H spin echo, echo planar MR elastography

Abstract

Purpose To develop a rapid proton MR Elastography (MRE) technique that can quantify the absolute shear stiffness of lung parenchyma, to investigate the ability to differentiate respiration-dependent stiffness variations of the lung, and to demonstrate clinical feasibility. Methods A spin-echo echo planar imaging MRE sequence (SE-EPI MRE) with a very short echo time was developed and tested in a series of 5 healthy volunteers at 3 different lung volumes: 1) residual volume (RV), 2) total lung capacity (TLC), 3) and midway between RV and TLC (MID). At each volume, lung density was quantified using a MR-based density mapping sequence. For reference, data was acquired using the previously described spin-echo lung MRE sequence (SE-MRE). MRE data was also acquired in a patient with proven Idiopathic Pulmonary Fibrosis (IPF) to test clinical feasibility. Results The SE-EPIMRE sequence reduced total acquisition time by a factor of 2 compared to the SE-MRE sequence. Lung parenchyma median shear stiffness for the 5 volunteers quantified with the SE-EPI MRE sequence was 0.9 kPa, 1.1 kPa and 1.6 kPa at RV, MID and TLC, respectively. The corresponding values obtained with the SE-MRE sequence were 0.9 kPa, 1.1 kPa and 1.5 kPa. Absolute shear stiffness was also successfully measured in the IPF patient. Conclusion The results indicate that stiffness variations due to respiration could be measured with the SE-EPIMRE technique and were equivalent to values generated by the previously described SE-MRE approach. Preliminary data obtained from the patient demonstrates clinical feasibility.

Quantitative assessment of lung stiffness in patients with interstitial lung disease using MR elastography

“…Although MRE has been shown to be sufficiently sensitive to assess the shear stiffness of normal lung parenchyma in vivo, our study demonstrated that MRE‐derived shear stiffness can quantitatively discriminate between healthy individuals and patients with lung disorders, specifically ILD. Additionally, our results also demonstrate that lung stiffness increases with increasing transpulmonary pressure (ie, from RV to TLC).…”

“…MRE is also being investigated in a variety of other clinical applications including brain, heart, and lung . Recent work has demonstrated that, despite the low signal‐to‐noise ratio of 1 H MRE within the lung, this technique can be used to delineate stiffness distributions within lung parenchyma under clinically feasible conditions …”

Hepatic MR Elastography: Clinical Performance in a Series of 1377 Consecutive Examinations

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Experimental and computational studies of sound transmission in a branching airway network embedded in a compliant viscoelastic medium

“…An FE model could be used to calculate and visualize vibroacoustic pressure and motion inside the lung and its airways caused by the acoustic input. Lung structural and mechanical property changes can also be simulated and their influence on sound transmission in the lung could aid in the interpretation of wave images that are acquired using, for example, magnetic resonance elastography [10, 11, 37], to reconstruct a quantitative map of variation in mechanical properties that can correlate with injury, the progression of disease and/or the response to therapy.…”