## 3 Doppler OCT for Otology Applications
### In Vivo Experiments
#### 3.3.2 In Vivo Human Experiments  
As a first approach to measure the Doppler OCT signal of the live human middle ear, highly phase-stable Vernier-tuned distributed Bragg-reflector laser with a graphics processing unit were utilized by [PERSON] et al. [49]. As shown in Figure 7, representative cross-sectional image and 3D reconstructed volume data were clearly obtained with vibration displacement on the sub-nanometer scale in vivo. The results of this study suggested the clinical applicability of Doppler OCT to detect the vibrating motion of tissues. In addition, the clinical results for distinguishing normal, otosclerosis TM using Doppler OCT was presented in [PERSON] et al. (2017). Following the condition of the TM (i.e., normal and otosclerosis), the ratio of umbo to incus vibration level was well-distinguished by comparing the obtained data of each group. This study demonstrated the feasibility of Doppler OCT as a clinical tool of diagnosis and investigation of the status of the middle ear non-invasively. Moreover, in terms of the scanning range of endoscopic Doppler OCT, an endoscopic phase-resolved Doppler OCT with a wide field-of-view, which allows 3D visualization of the nearly entire TM and measurement of the vibrating motion, was presented in [PERSON] et al. (2015). As shown in Figure 8, distinctive oscillating patterns were measured according to the externally induced sound frequencies. This study demonstrated the imaging capability of Doppler OCT as a promising tool of diagnosis in otology. As an aspect of the clinical application of Doppler OCT, [PERSON] et al. (2017) demonstrated the comparison results between normal control and ears with an otosclerotic stages fixation. By combining the cross-sectional structural imaging with vibration measurement, the reduction of vibration motion with otosclerosis was measured at umbo. The results of this study verified the clinical feasibility of Doppler OCT compared to laser Doppler vibrometry, which has been a widely utilized method in otology. Figure 6: Three-dimensional reconstruction images of the detected phase shift on the contact area between tympanic membrane (TM) and malleus in (**A**) normal TM and (**B**) simulated effusion condition stimulated by 1 kHz, 2 kHz, and 4 kHz pure tone stimuli. Reprinted with permission from Ref. [66]. In addition to the clinical applications with Doppler OCT as a diagnostic tool, [PERSON] et al. [79] presented the highly phase-stable OCV, which was attached to a surgical microscope as an accessory to apply for clinical diagnosis and surgeries in the operation room. The phase sensitivity of this system is under five picometers, which sufficiently exploits the tuning curve of the human TM according to the threshold of hearing. This study demonstrated the possibility of Doppler OCT for providing vibrational information with simultaneous monitoring. Figure 7: In vivo, real-time functional imaging of a normal left ear’s response at 1030 Hz. (**A**) A 1 \(\times\) 1 cm\({}^{2}\) 2D cross-section of the middle ear in the transverse plane. (**B**) A 1 \(\times\) 1 \(\times\) 1 cm\({}^{3}\) 3D volume render of the middle ear as seen from the perspective of the ear canal with the TM digitally removed, and (**C**) from an inferior-posterior perspective with the TM in place showing the axis of Doppler measurement along the yellow line passing through the incus at the stapedius tendon. Functional measurements of the TM and incus’ peak-to-peak vibrational response at 1 kHz (**D**) with a 100 dB SPL tone applied to the ear and (**E**) without a stimulus. (**F**) Plot of the displacement response versus the sound pressure level showing excellent linearity from 80 dB SPL to 100 dB SPL. Error bars represent \(\pm\) one standard deviation of the response over the pixels along the axial length of the incus. Tympan membrane (TM), malleus (M), incus (IN), incudo-stapedial joint (IS), stapedius tendon (ST), chorda tympani nerve (CT), cochlear promontory (CP), round-window niche (RW). Reprinted with permission from Ref. [49]. © The Optical Society.