## 4 Discussion
Compared with the collagen fibre, the elastic fibre is more flexible [43], which means the elasticity of the elastic fibre should be lower than the collagen fibre. By comparing the histology results (see Figure 3b), the distribution of the collagen fibre and elastic fibre are clearly shown. Those main elements significantly contribute to the mechanical behaviour of the tissue. By evaluating the layers' mechanical propertiesthroughout 52 samples, the OCE results represent the same phenomenon depending on the fibre composition of each layer. The different elements' distribution in the tissue leads to big differencesin the elastic properties which can be observed in Figure 8. The fact that the samples were obtained from different human cadavers, as well as the preservation conditions, could potentially lead to a variation in the elasticity value. However, a clear trend was found, which is that the submuc layer has the highest elasticity, muscularus mucosa has the lowest elasticity and the lamina propria has the middle value. This quantitative elasticity of the oesophagus layers could be used as a parameter to characterize the pathological conditions. It is noticed that the silicone reference material shows an appearance of inhomogeneity in OCE results, which can be observed in Figure 7b. The yellow arrow in Figure 7a indicates the boundary between the sample and the silicone reference material. The silicone reference material region shows an unsmooth, plaque pattern. This phenomenon may affect the sample elasticity evaluation. In practice, the commercial silicone material (Ecoflex, 00-30; Smooth-on Inc., Macungie, PA, USA) was fabricated via an aqueous emulsion process. From the technical data, there is no information supplied regarding the silicone particle size, whereas the study investigated the silicone elastomeric particle size in silicone rubber and demonstrated that the mean size of the silicone particle is 2 \(\upmu\)m to 10 \(\upmu\)m [44]. Due to the resolution of the OCE result being in micro-metre scale, the relatively large particle size caused the pattern to appear in the reference material region. As the mean strain value of the reference material is obtained for the elasticity evaluation, the impact of the reference material's inhomogeneous appearance is minimized. We performed both OCT and OCE results for 52 specimen samples from 7 different human Thiel-embalmed cadavers. By comparing the corresponding histology results, the boundaries between layers were clearly observed within OCT/OCE results. Optical, structure and elastic properties were quantitatively evaluated and summarized. The results demonstrated the clinical feasibility of OCT/OCE in the investigation of oesophageal tissue. By way of the OCT/OCE results which indicate the clear differences between layers in quantitative data, the characterizing of layers and monitoring of tissue abnormality can be achieved. Studies have shown that ultrasound elastography can be easily included in clinical diagnosis of oesophageal cancer, and the staging of oesophageal cancer can be improved [45; 46]. Compared with ultrasound elastography imaging, OCT/OCE could offer higher resolution results in both structure and elasticity images which could potentially contribute to the future diagnosis and staging of oesophageal cancer. However, the imaging depth may limit the application of OCT/OCE in clinical practice. Even the literature indicates that OCT/OCE can reach the depth of 4 mm to 5 mm [47]. Based on the system setup in this study and practice with human Thiel-embalmed oesophageal tissue, the actual imaging depth is around 1.5 mm to 2 mm. To scan the entire oesophagus wall, multiple scanning can be considered to solve this limitation. Another limitation of this study is that there was no control group of fresh human tissues used. The Thiel-embalmed oesophageal tissue was obtained from bodies that had been previously used for teaching. Therefore, cadaveric tissue was exposed to air for periods of time.