A surface topology and motion compensation system for microsurgery guidance and intervention based on common-path optical coherence tomography

Oblique injection depth correction by a two parallel OCT sensor guided handheld SMART injector

We present a SMART injector with two parallel common-path optical coherence tomography fibers to enable angle measurements and injection depth corrections for oblique subretinal injection. The two optical fibers are attached to opposite sides of a 33 G needle with known offsets and designed to pass through a 23 G trocar that has an inner diameter of 0.65 mm. By attaching a SMART system to a rotational stage, the measured angles are calibrated for minimal error from reference angles. A commercial eye model was used to evaluate the control performance, and injection experiments were performed on a phantom made of agarose gel and a porcine eye.

Spectral 3D reconstruction of impressionist oil paintings based on macroscopic OCT imaging

Art conservators have adopted optical technologies to improve conservation efforts; laser triangulation, stereophotogrammetry, structured light, laser scanners, and time of flight sensors have been deployed to capture the 3D information of sculptures and architectures. Optical coherence tomography (OCT) has introduced new imaging methods to study the surface features and subsurface structures of delicate cultural heritage objects. However, the field of view of OCT severely limits the scanning area. We present a hybrid scanning platform combined with an effective algorithm for real-time sampling and artifact removal to achieve macroscopic OCT (macro-OCT) imaging and spectral 3D reconstruction of impressionist style oil paintings.

Optical coherence tomography using physical domain data compression to achieve MHz A-scan rates

The three-dimensional volumetric imaging capability of optical coherence tomography (OCT) leads to the generation of large amounts of data, which necessitates high speed acquisition followed by high dimensional image processing and visualization. This signal acquisition and processing pipeline demands high A-scan rates on the front end, which has driven researchers to push A-scan acquisition rates into the MHz regime. To this end, the optical time-stretch approach uses a mode locked laser (MLL) source, dispersion in optical fiber, and a single analog-to-digital converter (ADC) to achieve multi-MHz A-scan rates. While enabling impressive performance this Nyquist sampling approach is ultimately constrained by the sampling rate and bandwidth of the ADC. Additionally such an approach generates massive amounts of data. Here we present a compressed sensing (CS) OCT system that uses a MLL, electro-optic modulation, and optical dispersion to implement data compression in the physical domain and rapidly acquire real-time compressed measurements of the OCT signals. Compression in the analog domain prior to digitization allows for the use of lower bandwidth ADCs, which reduces cost and decreases the required data capacity of the sampling interface. By leveraging a compressive A-scan optical sampling approach and the joint sparsity of C-scan data we demonstrate 14.4-MHz to 144-MHz A-scan acquisition speeds using a sub-Nyquist 1.44 Gsample/sec ADC sampling rate. Furthermore we evaluate the impact of data compression and resulting imaging speed on image quality.

Improving visible light OCT of the human retina with rapid spectral shaping and axial tracking

Visible light optical coherence tomography (OCT) theoretically provides finer axial resolution than near-infrared OCT for a given wavelength bandwidth. To realize this potential in the human retina in vivo, the unique technical challenges of visible light OCT must be addressed. We introduce three advances to further the performance of visible light OCT in the human retina. First, we incorporate a grating light valve spatial light modulator (GLV-SLM) spectral shaping stage to modify the source spectrum. This enables comfortable subject alignment with a red light spectrum, and image acquisition with a broad "white light" spectrum, shaped to minimize sidelobes. Second, we develop a novel, Fourier transform-free, software axial motion tracking algorithm with fast, magnetically actuated stage to maintain near-optimal axial resolution and sensitivity in the presence of eye motion. Third, we implement spatially dependent numerical dispersion compensation for the first time in the human eye in vivo. In vivo human retinal OCT images clearly show that the inner plexiform layer consists of 3 hyper-reflective bands and 2 hypo-reflective bands, corresponding with the standard anatomical division of the IPL. Wavelength-dependent images of the outer retina suggest that, beyond merely improving the axial resolution, shorter wavelength visible light may also provide unique advantages for visualizing Bruch's membrane.

Robot-assisted tremor control for performance enhancement of retinal microsurgeons

Pars plana vitrectomy is a challenging, minimally invasive microsurgical procedure due to its intrinsic manoeuvres and physiological limits that constrain human capability. An important human limitation is physiological hand tremor, which can significantly increase the risk of iatrogenic retinal damage resulting from unintentional manoeuvres that affect anatomical and functional surgical outcomes. The limitations imposed by normal physiological tremor are more evident and challenging during ‘micron-scale’ manoeuvres such as epiretinal membrane and internal limiting membrane peeling, and delicate procedures requiring coordinated bimanual surgery such as tractional retinal detachment repair. Therefore, over the previous three decades, attention has turned to robot-assisted surgical devices to overcome these challenges. Several systems have been developed to improve microsurgical accuracy by cancelling hand tremor and facilitating faster, safer and more effective microsurgeries. By markedly reducing tremor, microsurgical precision is improved to a level beyond present human capabilities. In conclusion, robotics offers potential advantages over free-hand microsurgery as it is currently performed during ophthalmic surgery and opens the door to a new class of revolutionary microsurgical modalities. The skills transfer that is beyond human capabilities to robotic technology is a logical next step in microsurgical evolution.

70 μm diameter optical probe for common-path optical coherence tomography in air and liquids

We investigate and validate a novel method to fabricate ultrathin optical probes for common-path optical coherence tomography (CP-OCT). The probes are obtained using a 65 μm barium titanate microsphere inserted into an inward concave cone chemically etched at the end of a single-mode fiber. We demonstrate that the high refractive index (n=1.95) of the barium titanate microspheres allows one to maintain high sensitivity even while imaging in liquids, reaching a sensitivity of 83 dB. Due to its low cost, flexibility, and ease of use, the probe holds promise for the development of a new generation of ultrathin needle-based OCT systems.

Demonstration of Subretinal Injection Using Common-Path Swept Source OCT Guided Microinjector

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.

Motorized Micro-Forceps with Active Motion Guidance based on Common-Path SSOCT for Epiretinal Membranectomy

In this study, we built and tested a handheld motion-guided micro-forceps system using common-path swept source optical coherence tomography (CP-SSOCT) for highly accurate depth controlled epiretinal membranectomy. A touch sensor and two motors were used in the forceps design to minimize the inherent motion artifact while squeezing the tool handle to actuate the tool and grasp, and to independently control the depth of the tool-tip. A smart motion monitoring and a guiding algorithm were devised to provide precise and intuitive freehand control. We compared the involuntary tool-tip motion occurring while grasping with a standard manual micro-forceps and our touch sensor activated micro-forceps. The results showed that our touch-sensor-based and motor-actuated tool can significantly attenuate the motion artifact during grasping (119.81 μm with our device versus 330.73 μm with the standard micro-forceps). By activating the CP-SSOCT based depth locking feature, the erroneous tool-tip motion can be further reduced down to 5.11μm. We evaluated the performance of our device in comparison to the standard instrument in terms of the elapsed time, the number of grasping attempts, and the maximum depth of damage created on the substrate surface while trying to pick up small pieces of fibers (Ø 125 μm) from a soft polymer surface. The results indicate that all metrics were significantly improved when using our device; of note, the average elapsed time, the number of grasping attempts, and the maximum depth of damage were reduced by 25%, 31%, and 75%, respectively.

Common-path phase-sensitive optical coherence tomography provides enhanced phase stability and detection sensitivity for dynamic elastography

Phase-sensitive optical coherence elastography (PhS-OCE) is an emerging optical technique to quantify soft-tissue biomechanical properties. We implemented a common-path OCT design to enhance displacement sensitivity and optical phase stability for dynamic elastography imaging. The background phase stability was greater in common-path PhS-OCE (0.24 ± 0.07nm) than conventional PhS-OCE (1.60 ± 0.11μm). The coefficient of variation for surface displacement measurements using conventional PhS-OCE averaged 11% versus 2% for common-path PhS-OCE. Young's modulus estimates showed good precision (95% CIs) for tissue phantoms: 24.96 ± 2.18kPa (1% agar), 49.69 ± 4.87kPa (1.5% agar), and 116.08 ± 12.14kPa (2% agar), respectively. Common-path PhS-OCE effectively reduced the amplitude of background dynamic optical phase instability to a sub-nanometer level, which provided a larger dynamic detection range and higher detection sensitivity for surface displacement measurements than conventional PhS-OCE.

Development and preliminary results of bimanual smart micro-surgical system using a ball-lens coupled OCT distance sensor

Bimanual surgery enhances surgical effectiveness and is required to successfully accomplish complex microsurgical tasks. The essential advantage is the ability to simultaneously grasp tissue with one hand to provide counter traction or exposure, while dissecting with the other. Towards enhancing the precision and safety of bimanual microsurgery we present a bimanual SMART micro-surgical system for a preliminary ex-vivo study. To the best of our knowledge, this is the first demonstration of a handheld bimanual microsurgical system. The essential components include a ball-lens coupled common-path swept source optical coherence tomography sensor. This system effectively suppresses asynchronous hand tremor using two PZT motors in feedback control loop and efficiently assists ambidextrous tasks. It allows precise bimanual dissection of biological tissues with a reduction in operating time as compared to the same tasks performed with conventional one-handed approaches.

Automated working distance adjustment enables optical coherence tomography of the human larynx in awake patients

Optical coherence tomography (OCT) provides structural information of laryngeal tissue which is comparable to histopathological analysis of biopsies taken under general anesthesia. In awake patients, movements impede clinically useful OCT acquisition. Therefore, an automatic compensation of movements was implemented into a swept source OCT-laryngoscope. Video and OCT beam path were combined in one tube of 10-mm diameter. Segmented OCT images served as distance sensor and a feedback control adjusted the working distance between 33 and 70 mm by synchronously translating the reference mirror and focusing lens. With this motion compensation, the tissue was properly visible in up to 88% of the acquisition time. During quiet respiration, OCT contrasted epithelium and lamina propria. Mean epithelial thickness was measured to be 109 and [Formula: see text] in female and male, respectively. Furthermore, OCT of mucosal wave movements during phonation enabled estimation of the oscillation frequency and amplitude. Regarding clinical issues, the OCT-laryngoscope with automated working distance adjustment may support the estimation of the depth extent of epithelial lesions and contribute to establish an indication for a biopsy. Moreover, OCT of the vibrating vocal folds provides functional information, possibly giving further insight into mucosal behavior during the vibratory cycle.

Accurate real-time depth control for CP-SSOCT distal sensor based handheld microsurgery tools

This paper presents a novel intuitive targeting and tracking scheme that utilizes a common-path swept source optical coherence tomography (CP-SSOCT) distal sensor integrated handheld microsurgical tool. To achieve micron-order precision control, a reliable and accurate OCT distal sensing method is required; simultaneously, a prediction algorithm is necessary to compensate for the system delay associated with the computational, mechanical and electronic latencies. Due to the multi-layered structure of retina, it is necessary to develop effective surface detection methods rather than simple peak detection. To achieve this, a shifted cross-correlation method is applied for surface detection in order to increase robustness and accuracy in distal sensing. A predictor based on Kalman filter was implemented for more precise motion compensation. The performance was first evaluated using an established dry phantom consisting of stacked cellophane tape. This was followed by evaluation in an ex-vivo bovine retina model to assess system accuracy and precision. The results demonstrate highly accurate depth targeting with less than 5 μm RMSE depth locking.

Injection-depth-locking axial motion guided handheld micro-injector using CP-SSOCT

This paper presents a handheld micro-injector system using common-path swept source optical coherence tomography (CP-SSOCT) as a distal sensor with highly accurate injection-depth-locking. To achieve real-time, highly precise, and intuitive freehand control, the system used graphics processing unit (GPU) to process the oversampled OCT signal with high throughput and a smart customized motion monitoring control algorithm. A performance evaluation was conducted with 60-insertions and fluorescein dye injection tests to show how accurately the system can guide the needle and lock to the target depth. The evaluation tests show our system can guide the injection needle into the desired depth with 4.12 um average deviation error while injecting 50 nl of fluorescein dye.

Hand scanning optical coherence tomography imaging using encoder feedback

We present a new method for generating micron-scale OCT images of interstitial tissue with a hand scanning probe and a linear optical encoder that senses probe movement relative to a fixed reference point, i.e., tissue surface. Based on this approach, we demonstrate high resolution optical imaging of biological tissues through a very long biopsy needle. Minor artifacts caused by tissue noncompliance are corrected using a software algorithm which detects the simple repetition of the adjacent A-scans. This hand-scanning OCT imaging approach offers the physician the freedom to access imaging sites of interest repeatedly.

Optical coherence tomography scanning with a handheld vitreoretinal micromanipulator

An active handheld micromanipulator has been developed that is capable of automated intraocular acquisition of B-mode and C-mode optical coherence tomography scans that are up to 4 mm wide. The manipulator is a handheld Gough-Stewart platform actuated by ultrasonic linear motors. The manipulator has been equipped with a Fourier-domain common-path intraocular OCT probe that fits within a 25-gauge needle. The paper describes the systems and techniques involved, and presents preliminary results of B-mode and C-mode scans.

Fiber-optic OCT sensor guided "SMART" micro-forceps for microsurgery

A handheld Smart Micromanipulation Aided Robotic-surgery Tool (SMART) micro-forceps guided by a fiber-optic common-path optical coherence tomography (CP-OCT) sensor is presented. A fiber-optic CP-OCT distance and motion sensor is integrated into the shaft of a micro-forceps. The tool tip position is manipulated longitudinally through a closed loop control using a piezoelectric motor. This novel forceps design could significantly enhance safety, efficiency and surgical outcomes. The basic grasping and peeling functions of the micro-forceps are evaluated in dry phantoms and in a biological tissue model. As compared to freehand use, targeted grasping and peeling performance assisted by active tremor compensation, significantly improves micro-forceps user performance.

Fiber-optic OCT sensor guided "SMART" micro-forceps for microsurgery

A handheld Smart Micromanipulation Aided Robotic-surgery Tool (SMART) micro-forceps guided by a fiber-optic common-path optical coherence tomography (CP-OCT) sensor is presented. A fiber-optic CP-OCT distance and motion sensor is integrated into the shaft of a micro-forceps. The tool tip position is manipulated longitudinally through a closed loop control using a piezoelectric motor. This novel forceps design could significantly enhance safety, efficiency and surgical outcomes. The basic grasping and peeling functions of the micro-forceps are evaluated in dry phantoms and in a biological tissue model. As compared to freehand use, targeted grasping and peeling performance assisted by active tremor compensation, significantly improves micro-forceps user performance.

Motion-compensated hand-held common-path Fourier-domain optical coherence tomography probe for image-guided intervention

A motion-compensated, hand-held, common-path, Fourier-domain optical coherence tomography imaging probe has been developed for image-guided intervention during microsurgery. A hand-held prototype instrument was achieved by integrating an imaging fiber probe inside a stainless steel needle and attached to the ceramic shaft of a piezoelectric motor housed in an aluminum handle. The fiber probe obtains A-scan images. The distance information was extracted from the A-scans to track the sample surface distance and a fixed distance was maintained by a feedback motor control which effectively compensated hand tremor and target movements in the axial direction. Real-time data acquisition, processing, motion compensation, and image visualization and saving were implemented on a custom CPU-GPU hybrid architecture. We performed 10× zero padding to the raw spectrum to obtain 0.16 µm position accuracy with a compensation rate of 460 Hz. The root-mean-square error of hand-held distance variation from target position was measured to be 2.93 µm. We used a cross-correlation maximization-based shift correction algorithm for topology correction. To validate the system, we performed free-hand OCT M-scan imaging using various samples.

Active tremor cancellation by a "smart" handheld vitreoretinal microsurgical tool using swept source optical coherence tomography

Microsurgeons require dexterity to make precise and stable maneuvers to achieve surgical objectives and to minimize surgical risks during freehand procedures. This work presents a novel, common path, swept source optical coherence tomography-based "smart" micromanipulation aided robotic-surgical tool (SMART) that actively suppresses surgeon hand tremor. The tool allows enhanced tool tip stabilization, more accurate targeting and the potential to lower surgical risk. Freehand performance is compared to smart tool-assisted performance and includes assessment of the one-dimensional motion tremor in an active microsurgeon's hand. Surgeon hand tremor-the ability to accurately locate a surgical target and maintain tool tip offset distances-were all improved by smart tool assistance.

Optical imaging modalities for biomedical applications

Optical photographic imaging is a well known imaging method that has been successfully translated into biomedical applications such as microscopy and endoscopy. Although several advanced medical imaging modalities are used today to acquire anatomical, physiological, metabolic, and functional information from the human body, optical imaging modalities including optical coherence tomography, confocal microscopy, multiphoton microscopy, multispectral endoscopy, and diffuse reflectance imaging have recently emerged with significant potential for non-invasive, portable, and cost-effective imaging for biomedical applications spanning tissue, cellular, and molecular levels. This paper reviews methods for modeling the propagation of light photons in a biological medium, as well as optical imaging from organ to cellular levels using visible and near-infrared wavelengths for biomedical and clinical applications.

Real-time three-dimensional Fourier-domain optical coherence tomography video image guided microsurgeries

The authors describe the development of an ultrafast three-dimensional (3D) optical coherence tomography (OCT) imaging system that provides real-time intraoperative video images of the surgical site to assist surgeons during microsurgical procedures. This system is based on a full-range complex conjugate free Fourier-domain OCT (FD-OCT). The system was built in a CPU-GPU heterogeneous computing architecture capable of video OCT image processing. The system displays at a maximum speed of 10 volume/s for an image volume size of 160 × 80 × 1024(X × Y × Z) pixels. We have used this system to visualize and guide two prototypical microsurgical maneuvers: microvascular anastomosis of the rat femoral artery and ultramicrovascular isolation of the retinal arterioles of the bovine retina. Our preliminary experiments using 3D-OCT-guided microvascular anastomosis showed optimal visualization of the rat femoral artery (diameter<0.8 mm), instruments, and suture material. Real-time intraoperative guidance helped facilitate precise suture placement due to optimized views of the vessel wall during anastomosis. Using the bovine retina as a model system, we have performed "ultra microvascular" feasibility studies by guiding handheld surgical micro-instruments to isolate retinal arterioles (diameter ~0.1 mm). Isolation of the microvessels was confirmed by successfully passing a suture beneath the vessel in the 3D imaging environment.

Distortion-free freehand-scanning OCT implemented with real-time scanning speed variance correction

Hand-held OCT systems that offer physicians greater freedom to access imaging sites of interest could be useful for many clinical applications. In this study, by incorporating the theoretical speckle model into the decorrelation function, we have explicitly correlated the cross-correlation coefficient to the lateral displacement between adjacent A-scans. We used this model to develop and study a freehand-scanning OCT system capable of real-time scanning speed correction and distortion-free imaging—for the first time to the best our knowledge. To validate our model and the system, we performed a series of calibration experiments. Experimental results show that our method can extract lateral scanning distance. In addition, using the manually scanned hand-held OCT system, we obtained OCT images from various samples by freehand manual scanning, including images obtained from human in vivo.

Tissue surface as the reference arm in Fourier domain optical coherence tomography

We present a simple method applicable to common-path Fourier domain optical coherence tomography (OCT) in which the tissue surface is used as the reference arm. We propose using aluminium hydroxide powder as a potential tissue surface diffuser to allow wider application of this method. This technique allows one to avoid placing a reference arm reflective element, such as glass plate, on tissue, and intrinsically avoids both coherent and complex conjugate mirror artifacts associated with glass plates. Aluminium hydroxide can be sprayed onto tissue using spray nozzles commonly found in endoscopes. The sensitivity of the tissue reference arm common-path OCT image is 94 dB for a 50-[micro sign]s charge-coupled device integration time, and 97.5 dB for a 200-[micro sign]s CCD integration time.

Common-path low-coherence interferometry fiber-optic sensor guided microincision

We propose and demonstrate a common-path low-coherence interferometry (CP-LCI) fiber-optic sensor guided precise microincision. The method tracks the target surface and compensates the tool-to-surface relative motion with better than ± 5 μm resolution using a precision micromotor connected to the tool tip. A single-fiber distance probe integrated microdissector was used to perform an accurate 100 μm incision into the surface of an Intralipid phantom. The CP-LCI guided incision quality in terms of depth was evaluated afterwards using three-dimensional Fourier-domain optical coherence tomography imaging, which showed significant improvement of incision accuracy compared to free-hand-only operations.

Real-time intraoperative 4D full-range FD-OCT based on the dual graphics processing units architecture for microsurgery guidance

Real-time 4D full-range complex-conjugate-free Fourier-domain optical coherence tomography (FD-OCT) is implemented using a dual graphics processing units (dual-GPUs) architecture. One GPU is dedicated to the FD-OCT data processing while the second one is used for the volume rendering and display. GPU accelerated non-uniform fast Fourier transform (NUFFT) is also implemented to suppress the side lobes of the point spread function to improve the image quality. Using a 128,000 A-scan/second OCT spectrometer, we obtained 5 volumes/second real-time full-range 3D OCT imaging. A complete micro-manipulation of a phantom using a microsurgical tool is monitored by multiple volume renderings of the same 3D date set with different view angles. Compared to the conventional surgical microscope, this technology would provide the surgeons a more comprehensive spatial view of the microsurgical site and could serve as an effective intraoperative guidance tool.

Towards automatic calibration of Fourier-Domain OCT for robot-assisted vitreoretinal surgery

We present a new real-time automatic spectral calibration (ASC) method for Fourier domain optical coherence tomography (FD OCT) that can be automatically performed by the system. The ASC method proposed can be performed during OCT scanning operation and does not require an external calibrating light source or a commercial optical spectrum analyzer. Spectral data used for calibration can be interferograms obtained from an arbitrary sample which may have complicated internal structures, such as ones found in biological tissue. Moreover, our ASC method incorporates known robot motion to calibrate physical pixel spacing of the A-scan in static or dynamic environments. Experimental results show that our ASC method can provide high-performance calibration for FD OCT in terms of axial resolution and ranging accuracy without increasing hardware complexity.

Graphics processing unit accelerated non-uniform fast Fourier transform for ultrahigh-speed, real-time Fourier-domain OCT

We implemented fast Gaussian gridding (FGG)-based non-uniform fast Fourier transform (NUFFT) on the graphics processing unit (GPU) architecture for ultrahigh-speed, real-time Fourier-domain optical coherence tomography (FD-OCT). The Vandermonde matrix-based non-uniform discrete Fourier transform (NUDFT) as well as the linear/cubic interpolation with fast Fourier transform (InFFT) methods are also implemented on GPU to compare their performance in terms of image quality and processing speed. The GPU accelerated InFFT/NUDFT/NUFFT methods are applied to process both the standard half-range FD-OCT and complex full-range FD-OCT (C-FD-OCT). GPU-NUFFT provides an accurate approximation to GPU-NUDFT in terms of image quality, but offers >10 times higher processing speed. Compared with the GPU-InFFT methods, GPU-NUFFT has improved sensitivity roll-off, higher local signal-to-noise ratio and immunity to side-lobe artifacts caused by the interpolation error. Using a high speed CMOS line-scan camera, we demonstrated the real-time processing and display of GPU-NUFFT-based C-FD-OCT at a camera-limited rate of 122 k line/s (1024 pixel/A-scan).

Compressive SD-OCT: the application of compressed sensing in spectral domain optical coherence tomography

We applied compressed sensing (CS) to spectral domain optical coherence tomography (SD OCT) and studied its effectiveness. We tested the CS reconstruction by randomly undersampling the k-space SD OCT signal. We achieved this by applying pseudo-random masks to sample 62.5%, 50%, and 37.5% of the CCD camera pixels. OCT images are reconstructed by solving an optimization problem that minimizes the l(1) norm of a transformed image to enforce sparsity, subject to data consistency constraints. CS could allow an array detector with fewer pixels to reconstruct high resolution OCT images while reducing the total amount of data required to process the images.

Endoscopic Functional Fourier Domain Common Path Optical Coherence Tomography for Microsurgery

A single-arm interferometer based optical coherence tomography (OCT) system known as common-path OCT (CPOCT) is rapidly progressing towards practical application. Due in part to the simplicity and robustness of its design, Fourier Domain CPOCT (FD-CP-OCT) offers advantages in many endoscopic sensing and imaging applications. FD-CP-OCT uses simple, interchangeable fiber optic probes that are easily integrated into small and delicate surgical tools. The system is capable of providing not only high resolution imaging but also optical sensing. Here, we report progress towards practical application of FD-CP-OCT in the setting of delicate microsurgical procedures such as intraocular retinal surgery. To meet the challenges presented by the microsurgical requirements of these procedures, we have developed and initiated the validation of applicable fiber optic probes. By integrating these probes into our developing imaging system, we have obtained high resolution OCT images and have also completed a demonstration of their potential sensing capabilities. Specifically, we utilize multiple SLEDs to demonstrate sub 3-micron axial resolution in water; we propose a technique to quantitatively evaluate the spatial distribution of oxygen saturation levels in tissue; and we present evidence supportive of the technology's surface sensing and tool guidance potential by demonstrating topological and motion compensation capabilities.

Real-time 4D signal processing and visualization using graphics processing unit on a regular nonlinear-k Fourier-domain OCT system

We realized graphics processing unit (GPU) based real-time 4D (3D+time) signal processing and visualization on a regular Fourier-domain optical coherence tomography (FD-OCT) system with a nonlinear k-space spectrometer. An ultra-high speed linear spline interpolation (LSI) method for lambda-to-k spectral re-sampling is implemented in the GPU architecture, which gives average interpolation speeds of >3,000,000 line/s for 1024-pixel OCT (1024-OCT) and >1,400,000 line/s for 2048-pixel OCT (2048-OCT). The complete FD-OCT signal processing including lambda-to-k spectral re-sampling, fast Fourier transform (FFT) and post-FFT processing have all been implemented on a GPU. The maximum complete A-scan processing speeds are investigated to be 680,000 line/s for 1024-OCT and 320,000 line/s for 2048-OCT, which correspond to 1GByte processing bandwidth. In our experiment, a 2048-pixel CMOS camera running up to 70 kHz is used as an acquisition device. Therefore the actual imaging speed is camera- limited to 128,000 line/s for 1024-OCT or 70,000 line/s for 2048-OCT. 3D Data sets are continuously acquired in real time at 1024-OCT mode, immediately processed and visualized as high as 10 volumes/second (12,500 A-scans/volume) by either en face slice extraction or ray-casting based volume rendering from 3D texture mapped in graphics memory. For standard FD-OCT systems, a GPU is the only additional hardware needed to realize this improvement and no optical modification is needed. This technique is highly cost-effective and can be easily integrated into most ultrahigh speed FD-OCT systems to overcome the 3D data processing and visualization bottlenecks.

Common-Path Optical Coherence Tomography for Biomedical Imaging and Sensing

This paper describes a development of a fiber optic common-path optical coherence tomography (OCT) based imaging and guided system that possess ability to reliably identify optically transparent targets that are on the micron scale; ability to maintain a precise and safe position from the target; ability to provide spectroscopic imaging; ability to imaging biological target in 3-D. The system is based on a high resolution fiber optic Common-Path OCT (CP-OCT) that can be integrated into various mini-probes and tools. The system is capable of obtaining >70K A-scan per second with a resolution better than 3 μm. We have demonstrated that the system is capable of one-dimensional real-time depth tracking, tool motion limiting and motion compensation, oxygen-saturation level imaging, and high resolution 3-D images for various biomedical applications.