In vivo endoscopic Polarization Sensitive Optical Coherence Tomography for the quantification of airway smooth muscle in severe asthma and healthy volunteers

Asthma is a chronic inflammatory disease characterized by airway remodeling, causing prominent thickening of the airway smooth muscle (ASM) [1], which may further compromise lung function [2]. Previous post mortem studies proved that thickening of the ASM is related to the severity of asthma [3]. Severe asthma patients may benefit from bronchial thermoplasty (BT), an endoscopic treatment that targets ASM reduction [4]. Unfortunately, no imaging modality is currently able to assess the ASM remodeling in vivo, other than invasive lung biopsies [2]. Conventional endobronchial optical coherence tomography (EB-OCT) has a sufficient resolution and depth of penetration to image the ASM fiber bundle, however the intensity of light scattered by the ASM does not provide sufficient contrast to distinguish it from other layers [2]. Polarization Sensitive Optical Coherence Tomography (PS-OCT) is an extension of conventional OCT that provides tissue-specific contrast by assessing tissue birefringence, which might enable ASM visualization and quantification. We previously performed in vivo endoscopic PS-OCT imaging in the lung periphery of three severe asthma patients before and after undergoing BT, which validated the use of PS-OCT to assess ASM mass [5]. Further to this we are performing in vivo endoscopic PS-OCT imaging in healthy subjects in order to provide a comparison with ASM mass in asthma subjects. This is the first instance of in vivo ASM quantification in healthy subjects.