Numerical jitter estimation for swept source optical coherence tomography

The study presents a noninvasive, real-time monitoring technique for the cross-sectional imaging of the laser-tissue soldering process with a swept-source optical coherence tomography (SSOCT) system. The study also aims at performing a comparative study of the laser-tissue soldering (LTS) process using optimized compositions of albumin as solder biomaterials. The experimental study was conducted both ex vivo and in vivo to assess the superiority of the LTS process over conventional methods using a noninvasive imaging tool. In our attempt to combine the two techniques into one diagnostic tool, we have used the SSOCT system for a thoroughgoing investigation of the process in real-time. Laser-assisted tissue soldering was performed using a pulsed near-infrared (NIR) laser with a central wavelength of 980 nm, an output power of 5 W, and beam diameter (1/e 2 ) of 6 mm. Here, the SSOCT system has been utilized to observe and analyze the transitions taking place in real-time without disrupting the process. For the comparative study, we have used serum albumin in a 70% w/v concentration and albumin-PEG conjugate in a 6:1 ratio as soldering materials. Different stages of the laser interaction process were monitored with OCT B-scans of the incision area. Also, the basis of biomaterial-tissue interaction was studied with the help of Fourier-transform infrared spectroscopy (FTIR) analysis of the soldering materials. FTIR spectrum alludes to the fact that the intertwining of the soldering biomaterial with tissue collagen creates adhesion. Biomaterial serum albumin with 70% w/v concentration as soldering material demonstrates complete sealing of tissue at the incision with 3 minutes of laser irradiation. SSOCT B-scans have been useful in imaging the incision noninvasively at different stages. Both ex vivo and in vivo demonstration of the LTS process were presented with a clinical resemblance. OCT can be of great value to determine the wound contraction in case of incisional wounds or sealed wounds produced by the LTS procedure. Also, volumetric measurements of percentage reduction in wound area can be done with OCT. SSOCT system can be a potential imaging modality for real-time noninvasive imaging of surgical procedures like LTS. Lasers Surg. Med. © 2021 Wiley Periodicals LLC.

Optical coherence tomography (OCT) has become a useful and common diagnostic tool within the field of ophthalmology. Although presently a commercial technology, research continues in improving image quality and applying the imaging method to other tissue types. Swept-wavelength lasers based upon fiber ring cavities containing fiber Fabry-P´erot tunable filters (FFP-TF), as an intracavity element, provide swept-source optical coherence tomography (SS-OCT) systems with a robust and scalable platform. The FFP-TF can be fabricated within a large range of operating wavelengths, free spectral ranges (FSR), and finesses. To date, FFP-TFs have been fabricated at operating wavelengths from 400 nm to 2.2 µm, FSRs as large as 45 THz, and finesses as high as 30 000. The results in this paper focus on presenting the capability of the FFP-TF as an intracavity element in producing swept-wavelength lasers sources and quantifying the trade off between coherence length and sweep range. We present results within a range of feasible operating conditions. Particular focus is given to the discovery of laser configurations that result in maximization of sweep range and/or power. A novel approach to the electronic drive of the PZT-based FFP-TF is also presented, which eliminates the need for the existence of a mechanical resonance of the optical device. This approach substantially increases the range of drive frequencies with which the filter can be driven and has a positive impact for both the short all-fiber laser cavity (presented in this paper) and long cavity FDML designs as well.

A swept-source optical coherence tomography (OCT) system using mid-infrared light is demonstrated using commercially available light source and photodetectors. The light source is a tunable external cavity quantum cascade laser (QCL) with four laser modules and a wavelength range of 5.4μm – 12.8μm. The laser output is pulsed and has a maximum allowable duty cycle of 8%. A thermoelectrically cooled photovoltaic detector with a peak sensitivity at 8μm is configured in a Michelson interferometer setup. Noise from three sources are characterized: the analogue-to-digital converter (ADC), the detectors and the relative intensity noise (RIN). The ADC and the detector have a noise spectral density of 2.8 pW/√Hz and 21.4 pW/√Hz over a bandwidth of 100 MHz respectively; the value of RIN is -102 dB/Hz. The OCT system is used to collect the reflectivity profile of a mirror, which is measured with a signal to noise ratio (SNR) of 17.5 dB. Decreasing the time of sweep from 1s to 200ms has the effect of reducing the SNR by 4 dB.

To reassess the anatomical basis of optic disc pit maculopathy using swept source optical coherence tomography and to characterize the broader structural abnormalities comprising the optic pit complex. Sixteen patients with optic disc pit maculopathy were imaged using a high-resolution swept source optical coherence tomography system (DREAM optical coherence tomography). Cross-sectional and volume-rendered scans were analyzed for lamina cribrosa defects, intraneural cavitations, and pathways for fluid entry into or beneath the retina. All eyes demonstrated lamina cribrosa defects with associated cavitations extending a mean of 1855 ± 492 µ m posterior to a modified Bruch membrane opening. Four distinct patterns by which fluid entered the retina were observed: (1) direct channels from cavitations into the retina, (2) perivascular hyporeflective spaces, (3) intraneural channels extending toward cystoid spaces, and (4) isolated retinal cysts without a visible interconnection. Vitreous remnants, trabecular structures, or disorganized connective tissue were found within the optic nerve pit in several eyes. In 13% of cases, the pit was not visible by ophthalmoscopy due to overlying tissue. These structural variations frequently coexisted, and associated abnormalities extended beyond the optic disc margins. Optic disc pit maculopathy is associated with a spectrum of deep optic nerve abnormalities, collectively termed the optic pit complex. The combination of laminar disruption, cavitations, and multiple anatomical conduits for fluid ingress broadens the morphologic understanding of this condition. Swept source optical coherence tomography enables visualization of structures not accessible by ophthalmoscopy and may improve diagnostic precision, guide treatment decisions, and clarify the diverse mechanisms contributing to fluid accumulation in optic disc pit maculopathy.

<i>In vivo</i> three dimensional endoscopic imaging of rabbit and human gastrointestinal tracts was demonstrated based on an endoscopic swept source optical coherence tomography (SSOCT) system. The endoscopic SSOCT system is composed of a high speed SSOCT, a fast scanning rotational microelectromechanical system (MEMS) probe and real time data acquisition and imaging processing. The 2.2 mm rotational MEMS probe was miniature enough to be able to fit into the 2.8 mm biopsy channel of a standard endoscope. The gastrointestinal tracts of patients were imaged together with normal endoscopic examination. The epithelial, mucosal, lamina propria, and submucosal layers can be clearly seen on the OCT images.

We present a swept source optical coherence tomography (OCT) system at 1060 nm equipped with a wavefront sensor at 830 nm and a deformable mirror in a closed-loop adaptive optics (AO) system. Due to the AO correction, the confocal profile of the interface optics becomes narrower than the OCT axial range, restricting the part of the B-scan (cross section) with good contrast. By actuating on the deformable mirror, the depth of the focus is changed and the system is used to demonstrate Gabor filtering in order to produce B-scan OCT images with enhanced sensitivity throughout the axial range from a Drosophila larvae. The focus adjustment is achieved by manipulating the curvature of the deformable mirror between two user-defined limits. Particularities of controlling the focus for Gabor filtering using the deformable mirror are presented.

In this paper, we consider possibilities to compensate the chromatic aberration effects in the swept source optical coherence tomography system with line-field illumination (LF SSOCT) in spectral range 1260-1360 nm and reflected light acquisition by linear array InGaAs photo detector. Compensation of chromatic aberrations is provided by combined use of optimized optical system design with sharp focusing independent on light wavelength and fringe processing algorithm which allows accurate spectral fringe frequency evaluation even in the case of nonlinearity of the wavenumber tuning. Experimental results confirmed significant enhancement of imaging quality including LF SSOCT mode.

We describe a novel buffering technique for increasing the A-scan rate of swept source optical coherence tomography (SSOCT) systems employing low duty cycle swept source lasers. This technique differs from previously reported buffering techniques in that it employs a fast optical switch, capable of switching in 60 ns, instead of a fused fiber coupler at the end of the buffering stage, and is therefore appreciably more power efficient. The use of the switch also eliminates patient exposure to light that is not used for imaging that occurs at the end of the laser sweep, thereby increasing the system sensitivity. We also describe how careful management of polarization can remove undesirable artifacts due to polarization mode dispersion. In addition, we demonstrate how numerical compensation techniques can be used to modify the signal from a Mach-Zehnder interferometer (MZI) clock obtained from the original sweep to recalibrate the buffered sweep, thereby reducing the complexity of systems employing lasers with integrated MZI clocks. Combining these methods, we constructed an SSOCT system employing an Axsun technologies laser with a sweep rate of 100kHz and 6dB imaging range of 5.5mm. The sweep rate was doubled with sweep buffering to 200 kHz, and the imaging depth was extended to 9 mm using coherence revival. We demonstrated the feasibility of this system by acquiring images of the anterior segments and retinas of healthy human volunteers.

Choroidal Neovascularization Analyzed on Ultrahigh-Speed Swept-Source Optical Coherence Tomography Angiography Compared to Spectral-Domain Optical Coherence Tomography Angiography

&lt;p&gt;In this work, we explored the potential of measuring shear wave propagation using optical coherence elastography (OCE) in an inhomogeneous phantom and carotid artery samples based on a sweptsource optical coherence tomography (OCT) system. Shear waves were generated using a piezoelectric transducer transmitting sine-wave bursts of 400 μs duration, applying acoustic radiation force (ARF) to inhomogeneous phantoms and carotid artery samples, synchronized with a swept-source OCT (SS-OCT) imaging system. The phantoms were composed of gelatin and titanium dioxide whereas the carotid artery samples were embedded in gel. Differential OCT phase maps, measured with and without the ARF, detected the microscopic displacement generated by shear wave propagation in these phantoms and samples of different stiffness. We present the technique for calculating tissue mechanical properties by propagating shear waves in inhomogeneous tissue equivalent phantoms and carotid artery samples using the ARF of an ultrasound transducer, and measuring the shear wave speed and its associated properties in the different layers with OCT phase maps. This method lays the foundation for future in-vitro and in-vivo studies of mechanical property measurements of biological tissues such as vascular tissues, where normal and pathological structures may exhibit significant contrast in the shear modulus. &lt;/p&gt;

Development of high resolution functional retinal imaging tools is of great interest to clinical and experimental ophthalmology because the alterations in retinal function, at cellular resolution, hold the promise of being more sensitive for disease diagnostic then the purely retinal morphology-based assays. In this work we present our initial design and implementation of mouse retinal imaging system that incorporates full-field (FF) swept- source (SS) optical coherence tomography (OCT) with dedicated light stimulation channel for high-speed measurements of light evoked responses in photoreceptors of mice. The Optoretinograpahy (ORG) results acquired with our FF-SS-OCT system are compared with those acquired with our standard raster scanning mouse ORG-OCT system.

A swept-source optical coherence tomography (SS-OCT) system is used to clinically scan oral lesions in different oral carcinogenesis stages, including normal oral mucosa control, mild dysplasia (MiD), moderate dysplasia (MoD), early-stage squamous cell carcinoma (ES-SCC), and well-developed SCC (WD-SCC), for diagnosis purpose. On the basis of the analyses of the SS-OCT images, the stages of dysplasia (MiD and MoD), and SCC (ES-SCC and WD-SCC) can be differentiated from normal control by evaluating the depth-dependent standard deviation (SD) values of lateral variations. In the dysplasia stage, the boundary between the epithelium (EP) and lamina propria (LP) layers can still be identified and the EP layer becomes significantly thicker than that of normal control. Also, in a certain range of the EP layer above the EP/LP boundary, the SD value becomes larger than a certain percentage of the maximum level, which is observed around the EP/LP boundary. On the other hand, in the ES-SCC and WD-SCC stages, the EP/LP boundary disappears. Because of the higher density of connective tissue papillae in the ES-SCC stage, the SD values of the slowly varying lateral scan profiles in the ES-SCC samples are significantly larger than those in the WD-SCC sample. Also, ES-SCC can be differentiated from WD-SCC by comparing the exponential decay constants of averaged A-mode scan profiles. Because of the higher tissue absorption in the WD-SCC lesion, the decay constants in the WD-SCC samples are significantly higher than those in the ES-SCC samples.

Background: Parkinson’s Disease (PD) is the second-most common neurodegenerative disease affecting the elderly population. The eye has been referred to as a window to the brain due to its inseparable relationship with the central nervous system. The development of Swept-Source Optical Coherence Tomography (SS-OCT) and Optical Coherence Tomography Angiography (OCTA) technologies has offered us a better imaging modality to study the impact of PD on the retina. Method: Seventy-five eyes of 42 early-stage PD patients and 150 eyes of 75 matched healthy controls were enrolled in the current study. We performed SS-OCT and SS-OCTA to assess retinal nerve fiber layer (RNFL), ganglion cell layer (GCL) + inner plexiform layer (IPL), internal nuclear layer (INL) thickness, and retinal flow density and flow ratio. Results: Our study indicates decreasing superficial and deep flow density in most regions of the retina. Superficial and deep flow parameters were also associated with RNFL, GCL+IPL, and INL thickness. ROC analysis reveals superficial flow density demonstrated an Area Under Curve (AUC) of 0.688, which is greater than deep flow density and retinal thickness measurements. Conclusion: To the best of our knowledge, we are the first study using SS-OCT and SS-OCTA to study superficial and deep retinal flow changes in early-stage PD patients. Our study suggests decreasing retinal flow density provides greater diagnostic power than retinal thickness measurements in the early stage of PD. SS-OCTA parameters could potentially serve as imaging biomarkers in PD diagnosis and staging.

Abstract1— Optical coherence tomography (OCT) is a non-invasive biomedical imaging technique that provides high speed and high resolution three dimensional and cross sectional images of biological samples, in vivo and in situ. OCT applications targeting small animals is believed to bring developments in medical techniques, instruments, diagnosis and therapies for a number of human diseases as always have been the case of animal experimentation. With the swept source OCT (SS-OCT) system presented in this work, we were able to achieve performance parameters that meet the requirements to image the retina of small animals. Performance characteristics include 105 dB for system sensitivity, a roll-off below 1 dB/mm over 3 mm depth and an axial resolution of 8 μm. We describe the layout and acquisition/processing solutions towards fast imaging of in vivo samples.

Oral examination requires comprehensive visual assessment of microcirculatory tissue bed as guidance for acquiring biopsy samples. Due to limited visual resolution and subjective evaluation criteria, physicians usually have limited access to the detailed state of diseases, consequently have difficulty in managing oral treatment at early stage. An endoscopic microscopy may help improve the detectable resolution on regional mucosa surface, but hardly reach deeper structures/vasculatures that reveals pathological origination and development. We propose a novel use of long ranging swept source optical coherence tomography (SS-OCT) system with unprecedented imaging field of view of 1600 mm2 for anatomic and microvascular imaging of human oral mucosa tissue in vivo. This system is further applied to identify and analyze oral mucosa lesions in situ without a need for invasive biopsy. Qualitative assessment of the structure characteristics (i.e. collagen fibrosis, volume of salivary glands, and tissue scattering) during wound healing delineates the anatomical lesion development accompanied with tissue inflammation. Quantitative assessment of the vasculature network (i.e. capillary loop density and vessel morphological orientations) reveals pathological and nutritional underpinnings of microcirculation for oral lesion recovery. Specifically, the progression of oral capillary angiogenesis, indicated by elevations in capillary loop density, occurs within 12 hours of disease onset and peaks at day 7 thereafter, which provide invaluable information for the time course of therapeutic treatment. Our demonstration shows potential movement of oral cavity OCT microangiography toward clinical translations.