Search Results (4)

The fiber-optical current transformer (FOCT) is the core measuring equipment of the flexible DC converter station, which affects the operation control of the system. In order to solve the problem of the influence of the abnormal FOCT on the operation of the converter valve being unclear, the common fault modes of temperature and optical path of the FOCT are analyzed in this paper. Then, based on the traditional optical current transformer (OCT) model and considering the influence of temperature parameters on the FOCT, the FOCT dynamic model considering multiple factors is constructed. Finally, the simulation analysis is carried out on the MATLAB 2021b/Simulink platform, and the results show that (1) when the FOCT temperature compensation is abnormal, the transmission power of the converter valve increases with the increase in temperature, but the increase in temperature change is small; (2) when the FOCT light source compensation is abnormal, the light source attenuates, the converter valve active power decreases, and the reactive power increases; and (3) when the optical fiber sensing ring is broken, the transmission power increases and seriously deviates from the preset value (the active power increases by about 87.5% and the reactive power increases by about 90%). It can be seen that the abnormal FOCT in the converter station has a serious influence on the operation of the converter valve. Full article

Background: Although visual field (VF) defects are common in compressive pituitary adenoma (CPA), their pathophysiology has not been fully elucidated. The mechanical theory (i.e., direct compression of the optic chiasm by the CPA) and the vascular theory (i.e., compression of the vessels supplying the visual path by the CPA) or their association could explain the visual impairment. The aim of this study was to determine whether the vascular density (VD) improved after surgical decompression of the optic chiasm in CPA patients and whether OCT-A could help to identify predictive factors for postoperative visual recovery. Methods: A prospective controlled study was conducted in patients who underwent transsphenoidal pituitary adenoma surgery. Patients were divided into two groups: with CPA and without CPA (NCPA). All patients underwent a neuro-ophthalmological examination, VF testing, macular and optic disc structural OCT [retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) thicknesses] and OCT-A before and then 1 and 6 months after surgery. Results: Twenty-four eyes and fourteen eyes were included, respectively, in the CPA and NCPA groups. None of the VD parameters assessed by OCT-A were significantly improved after surgery in the CPA group. In the CPA group, the mean macular superficial VD was significantly decreased at 6 months. The multivariate analysis failed to identify any preoperative parameters predictive of postoperative VF improvement. Conclusions: Our preliminary findings suggest that the visual impairment observed in CPA patients could not be explained by the vascular theory. None of the preoperative OCT-A parameters allowed a postoperative VF recovery assessment. Trial registration number NCT04074642, ID-RCB 2019-A01186-51 date of registration 30 July 2019. Full article

The measurement of the biomechanical properties of the skin is of great interest since these properties play an important role in the development of several diseases such as skin cancer and systemic sclerosis. In this direction, several diagnostic tools have been developed to analyze the mechanical properties of the skin. Optical coherence elastography (OCE) is one of the emerging imaging techniques used for the characterization of the mechanical properties of the tissue quantitatively. In systemic sclerosis patients, the measurement of the mechanical properties of the deeper skin layers is desirable compared to the superficial layers. There are several variants of OCE that exist, but it is still not clear which method is more suitable for the measurement of the mechanical properties of the deeper tissue. In this work, we tested three common methods, the pulsed excitation method, the continuous wave excitation method, and the resonant frequency method, for the measurement of the mechanical properties of the deeper layers in the tissue. We found out that the pulsed wave excitation method provides the most reliable measurements in the shortest possible time compared to the other two methods. Full article

In this paper, we present the development of a handheld common-path swept source optical coherence tomography (CP-SSOCT) guided microinjector system and demonstrated its utility by precisely injecting fluorescein dye in the subretinal layer of ex vivo bovine eyes. The system enables precise subretinal injection with micron-level injection depth control. This was achieved by using a high-resolution CP-SSOCT distal sensor and signal processing using a graphics-processing unit (GPU), which made a real-time smart motion control algorithm possible. The microinjector performance was first evaluated using a gelatin phantom in terms of its ability for dynamic depth targeting and injection depth. This is followed by using an ex vivo bovine eye model to perform multiple consecutive subretinal injections of fluorescein dye. The results validated the OCT guided injector’s ability to precisely guide and lock in the needle tip to the target depth during injection. The ex vivo evaluation tests demonstrate that an OCT-guided injector can consistently guide the injecting needle to the desired depth and is able to maintain the position with 9.38 μm average root mean square error during the injections. Full article