With OCT, for the first time, the urothelial thickness change induced by water transport was observed in situ under OCT. The percentage of the change is proportional to the osmolarity of the NaCl applied to the urothelium, and different degrees of damage can be observed in histology and SEM. The observation may reveal the etiology of some highly prevalent diseases, such as interstitial cystitis/bladder pain syndrome (IC/BPS) and overactive bladder (OAB).
To image the underlying structures of a scattering medium, raster scanning imaging technologies capture least scattered photons (LSPs) and reject multiple scattered photons (MSPs) in backscattered photons. However, MSPs can still squeeze into the images, resulting in limited imaging depth, degraded contrast, and significantly reduced lateral resolution. Great efforts have been made to understand how MSPs affect imaging performance through modeling, but how the backscattered photons are distributed in a scattering medium during imaging remains a conceived picture base on simulations. Here, we demonstrate a method of reconstructing BSPP using beam-offset optical coherence tomography (OCT), where OCT images are acquired at offset positions from the illumination beam. By separating LSPs and MSPs, we can quantify imaging depth, contrast, and lateral resolution and access the depth-resolved modulated transfer function (MTF). This approach presents great opportunities for better retrieving tissue optical properties, correctly interpreting images, or directly using MTF as the feedback for adaptive optical imaging.
OCTSharp is a versatile open-source OCT software that aims to support real-time OCT imaging development in research labs. For high-speed imaging, OCT demands high-performance real-time data processing and visualization. However, hardware control and sophisticated memory management prevent agile prototyping. The proposed OCTSharp allows users to tailor OCT for specific purposes in a short development cycle. This software is based on managed C# environments with accessible hardware control, minimal memory management, and GPU support. We demonstrate that OCT software based on C# is highly efficient and can satisfy most research-level OCT applications.
Newts have a remarkable ability to regrow organs, providing key insights into the mechanisms of tissue regeneration. Lens regeneration in newts only initiates from the dorsal iris, and the underlying mechanism remains unknown. Understanding this process is critical for triggering non-competent adult tissues to support somatic cellular plasticity. Studies have focused on the difference in morphological and genetic variations between dorsal and ventral iris during the lens regeneration process using endpoint ex vivo tissue imaging and analysis, however, lens regeneration is a dynamic process. Therefore, this study aims to characterize the lens regeneration process in vivo with OCT and OCTA to non-invasively visualize the morphological variation of the anterior chamber and vasculature injury responses in the iris. Our results demonstrate that OCT is an ideal platform for in vivo monitoring lens regeneration in newts and provides a dynamic insight into this process.
Significance: Speckle variation induced by intracellular motion (IM) in the urothelium was observed in optical coherence tomography (OCT) images. IM can be used as a dynamic contrast to segment the urothelium by comparing two sequential OCT images. This method opens the possibility of specifically tracking the distribution of urothelial cancerous cells for identifying the microinvasion of bladder tumors.
Approach: OCT images were acquired ex vivo with fresh porcine bladder tissue. IM was analyzed by tracking speckle variation using autocorrelation function, then quantified with constrained regularization method for inverting data (CONTIN method) to identify the decorrelation time (DT) of the speckle variations. Variance analysis was also conducted to show IM amplitude and distribution in the urothelium. The segmentation of the urothelium was demonstrated with OCT images with a visible urothelial layer and OCT images with an invisible urothelial layer.
Results: Significant speckle variation induced by IM was observed in the urothelium. However, the distribution of the IM is heterogeneous. The DTs are mostly concentrated between 1 and 30 ms. With the IM as a dynamic contrast, the urothelium can be accurately and exclusively segmented, even the urothelial layer is invisible in normal OCT images.
Conclusions: IM can be used as a dynamic contrast to exclusively track urothelial cell distribution. This contrast may provide a new mechanism for OCT to image the invasion depth and pattern of urothelial cancerous cells for accurately substaging of bladder cancer.
Intracellular motion (IM) is originated from the motion of molecules and organelles in the cytoplasm of eukaryotic cells. IM is essential for the proper functioning of cells. Instead of tracking specific molecules, coherent gated methods measure the speckle variation induced by IM. Initially, holographic optical coherence imaging was used to image the IM of tumor spheroids and drugs' responses1,2 . Later on, with optical coherence tomography (OCT), IM has been used as an endogenous contrast to reveal the cellular and subcellular structures with freshly excised tissue. The uniqueness of the coherent gated method is that it can detect IM at different depths without requiring fluorescence tagging. Therefore, the imaged objects can stay at a more natural status.
Newts have the exceptional capability of regenerating the lens through their lifetime. The transparency of the anterior chamber makes OCT an idea imaging technology to track the entire process of the lens regeneration in vivo without interruptions. We demonstrated, for the first time, that OCT can capture not only essential morphological changes similar to the changes observed in histology but some fine structures, like zonular fibers, which are not visible in histology. Our initial results warrant the future research of tailoring OCT for dynamically imaging the lens regeneration in newts.
Laser interstitial thermal therapy (LITT) has received increased interest in recent years, especially for treating neurological disorders such as gliomas and epilepsy. In LITT, monitoring tissue temperature is critical. For hyperthermia treatment of tumors, temperature must be controlled between 43 – 45°C to kill cancer cells through apoptosis. Heating tissue to higher temperatures between 50 – 80°C will quickly coagulate the tissue through necrosis. The success of LITT depends on accurate real-time temperature feedback. The advance of magnetic resonance imaging (MRI) thermometry has greatly enabled LITT for neurosurgery. However, the FDA has recently warned that MRI thermometry has a slow response time, which may lead to overtreatment. Here, we report our progress in developing a thermal sensing system based on blackbody radiation in the short-wave infrared range (SWIR, 1 μm – 2.5 μm) through a 2 m silica fiber to monitor temperatures as low as 40°C. In the SWIR range, water absorption and silica fiber attenuation are relatively low, making tissue temperature measurement feasible during LITT. We demonstrate the feasibility of using SWIR blackbody radiation for real-time temperature monitoring through bench-top studies and ex vivo tissue studies. This new thermal sensing technology could be seamlessly integrated with current MRI thermometry to improve response time. It could also be used standalone during LITT for applications when use of MRI thermometry is not feasible.
Laser vaporization is a surgical procedure which utilizes a high power laser to quickly heat and vaporize tissue. Laser vaporization can be conducted on internal organs, such as breast or prostate, through a fiber catheter. Compared with other surgical technologies, it has excellent hemostasis capability with minimal collateral tissue damage, which may reduce hospitalization time and postoperative complications. Accurately monitoring tissue temperature during laser vaporization procedures provides important feedback to surgeons to improve surgical outcomes. Tissue cannot be vaporized if the temperature is lower than the boiling point, while high temperatures may lead to carbonization over the tissue surface, which not only reduces vaporization efficiency but also leads to postsurgical complications. However, until now, no sensing technologies have been developed to monitor tissue temperature during routine laser vaporization in clinics. Here, we report the use of blackbody radiation in the short-wave infrared range (SWIR) for tissue temperature monitoring during laser vaporization. Although blackbody radiation in SWIR is very weak for temperatures less than 100°C, the relatively low water absorption and silica fiber attenuation may allow temperature sensing in vivo. We successfully detected blackbody radiation in SWIR down to 80°C through a 2 m silica fiber. We then proved the feasibility of using blackbody radiation in SWIR to monitor tissue temperature during laser vaporization through an ex vivo tissue study. The developed technology is low-cost and can be seamlessly integrated with the fiber catheter used in laser vaporization.
The bladder urothelium is usually considered as an impermeable barrier to urine, but recent reports pointed that it was not only a passive impermeable membrane but also has some sensory and signaling functions. While aquaporin expression has been found in the urothelium, which implicits water transportation through the urothelium, it has never been observed directly the process of water transportation through the urothelium. We describe here for first time how water is transported through the urothelium through osmosis.
The calibration of a spectrometer is a critical step to obtain high-quality images in SDOCT. The spectra acquired with the spectrometer of an SDOCT are usually linear in wavelength, which should be linearly resampled in wavenumber before Fourier transform. Then the depth axis along each A-scan can be marked based on the wavenumber resolution of the spectrometer. In our project, we propose a novel method to calibrate the spectrometer. An easy and cost-effective way to generate Doppler frequency shift is introduced. Compared with previous methods, our method does not need additional hardware, such as a piezo shifter or a calibration light source. We prove that this Doppler frequency shift can be used to linearize the spectra from the wavelength domain to wavenumber domain. In addition, experiments prove that tissue images can be directly used for calibration without requiring mirror images. In other words, the calibration can be accomplished in situ, which is very useful for some clinical applications as the images can be calibrated by itself during or after imaging without relying on accurate manual calibration before imaging. For retinal imaging, this method may avoid spectrometer calibration using a model eyeball in the sample arm. In the further step, to mark depth axis, an interference signal is generated by coverslip which can provide maximum probing depth.
Q-switched (QS) Tm:YAG laser ablation mechanisms on urinary calculi are still unclear to researchers. Here, dependence of water content in calculus phantom on calculus ablation performance was investigated. White gypsum cement was used as a calculus phantom model. The calculus phantoms were ablated by a total 3-J laser pulse exposure (20 mJ, 100 Hz, 1.5 s) and contact mode with N=15 sample size. Ablation volume was obtained on average 0.079, 0.122, and 0.391 mm3 in dry calculus in air, wet calculus in air, and wet calculus in-water groups, respectively. There were three proposed ablation mechanisms that could explain the effect of water content in calculus phantom on calculus ablation performance, including shock wave due to laser pulse injection and bubble collapse, spallation, and microexplosion. Increased absorption coefficient of wet calculus can cause stronger spallation process compared with that caused by dry calculus; as a result, higher calculus ablation was observed in both wet calculus in air and wet calculus in water. The test result also indicates that the shock waves generated by short laser pulse under the in-water condition have great impact on the ablation volume by Tm:YAG QS laser.
Vaporization and coagulation are two fundamental processes that can be performed during laser-tissue ablation. We demonstrated a method allowing quasi-dynamically observing of the cross-sectional images of tissue response during ablation. The results showed that coagulation depth is relatively constant during vaporization, which supports the excellent hemostasis of green laser benign prostate hyperplasia (BPH) treatment. We also verified a new technology for real-time, in situ tissue temperature monitoring, which may be promising for in vivo tissue vaporization degree feedback during laser ablation to improve the vaporization efficiency and avoid complications.
Q-switched Tm:YAG laser ablation mechanisms on urinary calculi are still unclear to researchers. In this study, dependence of water content in calculus phantom on calculus ablation performance was investigated. White gypsum cement was used as a calculus phantom model. The calculus phantoms were ablated at single pulse and contact mode in three different conditions: dry calculus in air, wet calculus in air, and wet calculus in water. Ablation volume was obtained on average 0.006, 0.008, and 0.008 mm3 in dry calculus in air, wet calculus in air, and wet calculus in water groups, respectively. There were three proposed ablation mechanisms that could explain the effect of water content in calculus phantom on calculus ablation performance, including shock wave due to bubble collapse, spallation, and microexplosion. Shock wave generation due to bubble collapse in wet calculus in water condition had negligible effect on calculus ablation as captured by a needle hydrophone and cannot be a primary mechanism for calculus ablation in this study. Increased absorption coefficient of wet calculus can cause stronger spallation process compared with that caused by dry calculus; and as a result, higher calculus ablation was observed in both wet calculus in air and wet calculus in water. Vaporization of interstitial water in porous calculus phantom can also help enhance calculus ablation efficiency. There were some limitations in this study including use of small sample size and lack of employing real urinary calculus, which should be addressed in future experiment.
BACKGROUND Complete catheter-tissue contact and permanent tissue destruction are
essential for efficient radio-frequency ablation (RFA) during cardiac arrhythmia treatment.
Current methods of monitoring lesion formation are indirect and unreliable. We aim to develop
optical coherence tomography (OCT) as an imaging guidance for RFA.
OBJECTIVES The purpose of this study is to evaluate the feasibility of using OCT catheter to
image endocardia wall in active beating hearts through percutaneous access. This is a critical
step toward image guided RFA in a clinic setting.
METHODS A cone-scanning forward-viewing OCT catheter was advanced into active beating
hearts through percutaneous access in four swine. The OCT catheter was steered by an
introducer to touch the endocardia wall. The images were then acquired at 10 frames per
second at an axial resolution and lateral resolution of 15 μm.
RESULTS We report the first in vivo intracardiac OCT imaging through percutaneous access
with a thin and flexible OCT catheter. We are able to acquire high quality OCT images in active
beating hearts, observe the polarization-related artifacts induced by the birefringence of
myocardium and readily evaluate catheter-tissue contact.
CONCLUSIONS It is feasible to acquire OCT images in beating hearts through percutaneous
access. The observations indicate that OCT could be a promising technique for in vivo guidance
of RFA.
Complete catheter-tissue contact and permanent tissue destruction are essential for efficient radio-frequency ablation (RFA) during cardiac arrhythmia treatment. Current methods of monitoring lesion formation are indirect and unreliable. The purpose of this study is to evaluate the feasibility of using optical coherence tomography (OCT) catheter to image endocardial wall in actively beating hearts through percutaneous access. We reported the first in vivo intracardiac OCT imaging through percutaneous access with a thin and flexible OCT catheter. This is a critical step toward image-guided RFA in a clinical setting. A cone-scanning forward-viewing OCT catheter was advanced into beating hearts through percutaneous access in four swine. The OCT catheter was steered by an introducer to touch the endocardial wall. We are able to acquire high quality OCT images in beating hearts, observe the polarization-related artifacts induced by the birefringence of myocardium, and readily evaluate catheter-tissue contact. The observations indicate that OCT could be a promising technique for in vivo guidance of RFA.
Coronary calcified plaque (CP) is both an important marker of atherosclerosis and major determinant of the success of coronary stenting. Intracoronary optical coherence tomography (OCT) with high spatial resolution can provide detailed volumetric characterization of CP. We present a semiautomatic method for segmentation and quantification of CP in OCT images. Following segmentation of the lumen, guide wire, and arterial wall, the CP was localized by edge detection and traced using a combined intensity and gradient-based level-set model. From the segmentation regions, quantification of the depth, area, angle fill fraction, and thickness of the CP was demonstrated. Validation by comparing the automatic results to expert manual segmentation of 106 in vivo images from eight patients showed an accuracy of 78±9%. For a variety of CP measurements, the bias was insignificant (except for depth measurement) and the agreement was adequate when the CP has a clear outer border and no guide-wire overlap. These results suggest that the proposed method can be used for automated CP analysis in OCT, thereby facilitating our understanding of coronary artery calcification in the process of atherosclerosis and helping guide complex interventional strategies in coronary arteries with superficial calcification.
Radio-frequency ablation (rfa) is the standard of care for the treatment of cardiac arrhythmias; however, there are no direct measures of the successful delivery of ablation lesions. Optical coherence tomography (OCT) imaging has the potential to provide real-time monitoring of cardiac rfa therapy, visualizing lesion formation and assessing tissue contact in the presence of blood. A rfa-compatible forward-imaging conical scanning probe is prototyped to meet this need. The forward-imaging probe provides circular scanning, with a 2-mm scan diameter and 30-µm spot size. During the application of rf energy, dynamics are recorded at 20 frames per second with a 40-kHz A-line rate. Real-time monitoring of cardiac rfa lesion formation and imaging in the presence of blood is demonstrated ex vivo in a swine left ventricle with a forward, flexible, circular scanning OCT catheter.
We propose a novel method for speckle reduction for optical coherence tomography based on angular compounding by B-scan Doppler-shift encoding (AngularCBD). By decentering the probe beam from the pivot of a scanning mirror, the illumination angle represented by different components of the beam can be encoded in Doppler shift. Compounding multiple images reconstructed from different Doppler-shift bands, we can suppress speckle without sacrificing image acquisition speed. Speckle reduction with AngularCBD is demonstrated by imaging a phantom and tissue sample in vitro and in vivo.
We propose a novel method for speckle reduction based on angular compounding by B-scan Doppler shift encoding (ACBD). By de-centering the beam from the pivot of a scanning mirror, the illumination angle can be encoded by Doppler shift detected by B-scan analysis. Compounding multiple images reconstructed from different Doppler-shift bands, we can suppress speckle without sacrificing image acquisition speed. Speckle reduction with ACBD is demonstrated by imaging a phantom and a living avian embryo
We report a broad-band continuum light source with high power, low noise and a smooth
spectrum centered at 1.15 &mgr;m for ultrahigh-resolution optical coherence tomography (OCT). The
continuum is generated by self-phase modulation using a compact 1.059 &mgr;m femtosecond laser
pumping a novel photonic crystal fiber, which has a convex dispersion profile with no zero
dispersion wavelengths. The emission spectrum ranges from 800 to 1300 nm and results in a
measured axial resolution of ~2.8 &mgr;m in air. We demonstrate ultrahigh-resolution OCT imaging
of biological tissue using this light source.
In conventional single mode fiber, Self Phase Modulation (SPM) and Degenerate Cross Phase Modulation (DXPM) are the main non linear effects contributing to continuum generation. By controlling the polarization state of the light pumping the fiber and by selecting the polarization state out of the fiber, the spectrum of continuum generation can be optimized for optical coherence tomography (OCT). We investigate the effects of polarization control and selection on continuum light source consisting of a femotosecond Nd:glass laser and ultra high numerical aperture (UHNA) single mode fiber. The point Spread Function (PSF) can be improved by controlling linear input polarization or by selecting one of two orthogonal polarization modes at the output.
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