## 3 Doppler OCT for Otology Applications
### Ex Vivo Studies
#### 3.2.2 Human Cadaveric Experiments  
[PERSON] et al. [62] initially employed phase-sensitive OCT to detect the micro-vibrations in the TM and ossicular chain of the cadaveric temporal bone. This study demonstrated the possibility of Doppler OCT to diagnose the middle ear abnormalities by comparing the corresponding vibrating pattern of normal and ossicle-fixed cadavers. In addition to the obtained 2D vibration data in [62], the 3D vibration patterns of a human cadaver using Doppler OCT with repeated sound stimuli was presented in [PERSON] et al. [48]. As shown in Figure 4, different characteristic of each typical point (e.g., umbo and manubrium of malleus) was measured according to the applied external sound pressure, which is one of the factors to distinguish the normal and abnormal condition. Based on these results, the feasibility of Doppler OCT as a promising technique to investigate and diagnose in otology was verified. Moreover, in terms of detecting the effusions in the tympanic cavity, which is required to choose the appropriate therapeutic strategies, [PERSON] et al. (2018) demonstrated the possibility of Doppler OCT as a tool to indirectly measure the scattering and transparent fluids. Since non-invasive detection of the fluid in the tympanic cavity is difficult when using otoscopy and tympanometry, the selection of proper therapeutic strategy depends on the expertise of the physician. In contrast, by applying Doppler OCT, oscillation of the TM is able to be non-invasively measured, which enables to detect the scattered and transparent fluids of the tympanic cavity. This study showed the possibility of Doppler OCT as a tool for classifying the effusion in the tympanic cavity. To provide the functional movement information using otoscopy, the new probe, combining otoscopy with phase-sensitive OCT, was presented in [PERSON] et al. (2018). Otoscopy has been widely utilized as a conventional diagnostic tool in otology providing superficial information of the middle ear with limited range. The results of this study obtained using a cadaveric human temporal bone model demonstrated the capability of visualizing the middle ear anatomy on a micro-scale and measuring the vibration on a sub-nanometer scale. Figure 3: Projection view of the ossicular chain at 500 Hz (100 dB SPL), 6.4 kHz (108 dB SPL), and 15 kHz (103 dB SPL). (**a–c**) Axial velocity maps. (**d–f**) Phase maps relative to the umbo. (**g–l**) Phase maps of the manubrium (dashed box in d) relative to the umbo. The range of the colormap is reduced to help visualize phase gradients along the manubrium. Labels: manubrium (M), incus (I), stages (S), lateral process (LP), and umbo (U); * shows the umbo location used as phase reference. Reprinted with permission from Ref. [47]. © The Optical Society. To verify the effect of the moisture degree on the TM, and to understand how it relates to chronic otorrhea and abnormal TM, [PERSON] et al. (2018) analyzed the dependency of the moisture degree with the vibrating phase. As shown in Figure 5, the homogenously moisturized cadaveric TM was exposed and the Doppler signal to each frequency was measured every 30 min. This study revealed a depth-dependent vibration tendency of the applied frequencies according to the declined moisture level on the TM. Figure 4: The upper left image shows the projection (average intensity) of the OCT stack. The quantitative evaluation in Figure 4 was carried out for the red marked points A–H. Point A represents the umbo, the line along A–B–C corresponds to the manubrium of malleus (MM), D indicates the pars flaccida, and E–F–A–G–H show the orientation perpendicular to the MM. The other images present the instantaneous displacement for five characteristic frequencies, where prominent patterns became visible. The scale of the patterns varies between each plot, because of a variation of the amplitude in the order of one magnitude over the whole frequency range. Reprinted with permission from Ref. [48].