Laser energy sealing systems have attracted much attention over the past decade given the general shift in surgical paradigm toward less invasive surgical approaches. Given this, it is paramount to have an objective method with which the quality of energy seals can be evaluated. Current methodologies used for this purpose can be problematic in the evaluation of small vessel seals. A methodology employing Doppler optical coherence tomography (DOCT) for the evaluation of energy seals is introduced. Avian chorioallantoic membrane vessels were subjected to thulium laser irradiation and were then scanned via OCT. Outcomes were classified based on several markers, predominantly the presence or absence of flow postirradiation. Vessel diameter and general morphology were also taken into consideration. Vessels were classified into four groups: seal (29%), rupture (30%), partial seal (19%), and unaffected (22%). All vessels were also evaluated visually by a trained neurovascular surgeon, and these visually classified outcomes were compared with DOCT evaluated outcomes. It was found that whether the vessel was considered sealed or not sealed was dependent on the evaluation method (p = 0.01) where visual classification resulted in 18% more seals than DOCT classification. Further, the specificity of visual classification was found to be strongly dependent on the number of partial seals (p < 0.0001). DOCT has shown to be an indispensable method for the evaluation of energy seals not only solely due to its high velocity resolution but also due to valuable microscopic morphological insight regarding the biological mechanisms responsible for energy sealing.
In this paper, beam-shifting optical coherence tomography (BSOCT) is presented for speckle reduction and flow rate measurement. The sample beam is rotated about the optical axis of the objective lens to modulate the incident angle on sample; 17 and 3 incident angles are respectively performed for speckle reduction and flow rate measurement. The performance of the proposed technique is investigated on both phantom and in vivo experiments. By combining a 2D micro-electro-mechanical system (MEMS) and a zigzag scanning protocol, the frame rates of 45.2 Hz for speckle reduction and 25.6 Hz for flow rate measurement are achieved. With beam-shifting angle of 4.76º, the speckle noise reduction of 91% and the flow rate measurement precision of 0.0019 μl/s are achieved.
Robot-guided laser ablation for surgical applications potentially offers many advantages compared to by-hand mechanical tissue cutting. However, given that tissue can be rough and/or uneven, ablation quality can be compromised if the beam waist deviates significantly from the target tissue surface. Therefore, we present a method that uses optical coherence tomography (OCT) for dynamic refocusing of robot-guided surgical laser ablation. A 7-DOF robotic manipulator with an OCT-equipped optical payload was used to simulate robotic guided laser osteotomy. M-mode OCT feedback is used for continuous surface detection to correct for axial deviations along the ablation path due to surface nonuniformity. We were able to show that such a correction scheme could maintain the beam waist within the depth of focus for surface variation as aggressive as 45 deg with feed rates up to 1 mm / s. Strategies for implementation in surgical and nonsurgical applications are examined.
Intraoperative characterization of blood flow and visualization of microvasculature can have a huge impact on surgical outcomes. Knowledge about vasculature can provide diagnostic leverage, reducing operating times and improving patient recovery. Currently used Doppler-based techniques suffer from various shortcomings such as poor spatial resolution, high susceptibility to motion artifacts, and the inability to detect longitudinal flows. Our aim is to develop a fast, non-invasive approach to intraoperative microvascular imaging of slow-moving blood. In this work, we present a spatio-temporal approach to detect blood flow in vessels on the order of 0.1 mm. Specifically, a speckle-variance flow processing algorithm is used to detect small changes in B-mode pixel intensity on a micro-ultrasound (μUS) system operating in the range of 22-70 MHz. Data used in this study was acquired intraoperatively for patients undergoing neurosurgical procedures. Microcirculation was clearly visible in various anatomical structures and the spatial resolution in flow detection was much superior in comparison to Doppler-based flow detection. Moreover, using infrared optical tracking (Northern Digital Inc., Waterloo, Canada), a three-dimensional reconstruction of the microvasculature was constructed. This 3D vessel map allows for better visualization of the vasculature in the surgical cavity – allowing surgeons to plan their incisions, minimizing blood loss and potentially improving patient outcomes. To our knowledge, this is the first implementation of a three-dimensional, intraoperative microcirculation imaging technique using statistical and optical methods, alongside a non-Doppler high frequency ultrasound.
In this paper, a multi-beam optical coherence tomography (OCT) was used to reconstruct the microvascular image of human skin in vivo with phase resolved Doppler OCT (PRDOCT), phase resolved Doppler variance (PRDV) and speckle variance OCT (svOCT), in which the blood flow image was calculated by averaging the four blood flow images obtained by the four beams. In PRDOCT method, it is difficult to detect the blood flow perpendicular to optical axis of the probe beam for single beam OCT, but the multi-beam scanning method can solve this because the input angles of the four probe beams are slightly different from each other. The proposed method can further improve the signal-to-noise ratio (SNR) of the blood flow signals extracted by the three methods mentioned above.
We present an imaginary part-based correlation mapping optical coherence tomography (IMcmOCT) technique for in vivo blood vessels imaging. In the conventional correlation mapping optical coherence tomography (cmOCT) method, two adjacent frames of intensity-based structural images are correlated to extract blood flow information and the size of correlation window has to be increased to improve the signal-to-noise ratio of microcirculation maps, which may cause image blur and miss the small blood vessels. In the IMcmOCT method, the imaginary part of a depth-resolved complex analytic signal in two adjacent B-scans is correlated to reconstruct microcirculation maps. Both phantom and in vivo experiments were implemented to demonstrate that the proposed method can provide improved sensitivity for extracting blood flow information in small vessels.
KEYWORDS: Blood vessels, Optical coherence tomography, Signal to noise ratio, Blood circulation, In vivo imaging, Tissue optics, Tissues, Optical engineering, 3D image processing, Associative arrays
We present a cube data correlation-based correlation mapping optical coherence tomography (cube-cmOCT) method to reconstruct small blood vessel maps. In the cube-cmOCT method, the two adjacent cube data are correlated to extract blood flow information. Both phantom experiments and in vivo experiments were performed to demonstrate the advantage of the proposed method in improving the SNR of blood vessel maps without increasing the window size in the xz plane and offering a clear image of the small blood vessels almost missed by the conventional cmOCT method.
A different real-time self-wavelength calibration method for spectral domain optical coherence tomography is presented in which interference spectra measured from two arbitrary points on the tissue surface are used for calibration. The method takes advantages of two favorable conditions of optical coherence tomography (OCT) signal. First, the signal back-scattered from the tissue surface is generally much stronger than that from positions in the tissue interior, so the spectral component of the surface interference could be extracted from the measured spectrum. Second, the tissue surface is not a plane and a phase difference exists between the light reflected from two different points on the surface. Compared with the zero-crossing automatic method, the introduced method has the advantage of removing the error due to dispersion mismatch or the common phase error. The method is tested experimentally to demonstrate the improved signal-to-noise ratio, higher axial resolution, and slower sensitivity degradation with depth when compared to the use of the zero-crossing method and applied to two-dimensional cross-sectional images of human finger skin.
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