Passive elastography of the esophagus: from model to preliminary in-vivo experiments using diameter measurements

Numerous diseases alter the esophagus elasticity, such as eosinophilic esophagitis and esophageal motility disorders like achalasia. The possibility to measure these modifications using minimally invasive techniques is a key issue for the diagnosis of such pathologies. The commercially available EndoflipTM (endoluminal functional lumen imaging probe) can be used to measure the luminal cross-sectional diameter of the esophagus at different points and over time, and is used in clinical routine to assess esophageal distensibility. We used this probe to track the propagation of shear waves similar to those that are produced naturally by natural waves, to compute wavelength of the esophagus using passive elastography algorithms. To assess the feasibility of such measurements, we compared the wavelengths obtained with the probe in polyvinyl alcohol (PVA) gel tubes to those obtained for the same tubes with optical tracking of their edges using a camera. We first compared the wavelength obtained with homogeneous gel tubes with both techniques, and then used paired gel tubes of different elasticities to investigate the possibility to measure different wavelengths. Although, the wavelength computed using the probe and the camera showed some small differences, qualitative differentiation of the tubes was achieved when using paired tubes with different elasticities. Using the camera, a wavelength of 61 mm was measured for the hard tube, and 35 mm for the soft tube. Using the probe, wavelengths of 61 mm and 38 mm were measured, respectively. Therefore, we demonstrate here the feasibility of using this probe to track wave propagation and to determine the wavelengths in gel tubes of different stiffnesses. This analysis was also taken to a preliminary in-vivo study that allowed tracking of natural waves in the esophagus using the luminal probe, which indicates that this technique can also be used in vivo to measure the stiffness of the esophagus.