Transbronchial cryobiopsy, updated guidelines for chronic cough in children, PD-1 inhibition

Pulmonary Physiology, Function, and Rehabilitation

Functional imaging of the lung

Quantifying heterogeneity of ventilation and gas exchange in lung diseases remains a clinical challenge. Conventional pulmonary function test is insensitive to regional changes. The multiple inert gas elimination technique can quantify ventilation-perfusion distribution, but it requires invasive instrumentation (eg, pulmonary artery catheterization) and is not practical for clinical use. Computed tomography (CT) scans delineate spatial changes in lung structures but do not directly measure changes in ventilation and gas exchange. With its radiation, it is difficult to apply CT scanning repeatedly in patients. More recently, MR imaging techniques have been developed to directly “visualize” and quantify regional lung function (Kruger SJ, et al. J Magn Reson Imaging. 2016;43(2):295; Roos JE, et al. Magn Reson Imaging Clin N Am. 2015;23(2):217). These techniques employ inhalation of gases, such as oxygen, perfluorinated gases, and hyperpolarized ³He and ¹²⁹Xe. Hyperpolarized ³He has been studied the most; however, the dwindling supply of ³He gas and its rising cost have prevented its further development. ¹²⁹Xe has abundant supply and has emerged to be the inert gas of choice for MR imaging. Hyperpolarized ¹²⁹Xe can measure ventilation, like hyperpolarized ³He. In addition, Xe diffuses into alveolar barrier (interstitium and plasma) and red blood cells, where it exhibits distinct resonant frequency shifts that can be captured by MR. Therefore, in one test, information on pulmonary ventilation and gas transfer can be obtained. To date, the results from MR imaging studies have provided new insights into the pathophysiology of obstructive and restrictive lung diseases. With continuous development, MR imaging of the lung could become a clinically useful tool in the near future.

Yuh-Chin T. Huang, MD, MHS, FCCP

Steering Committee Member