Geometric & Radiometric Vignetting Associated with a 72-Facet, Off-Axis, Polygon Mirror for Swept Source Optical Coherence Tomography (SS-OCT)

Optical Coherence Tomography (OCT) has a broad range of applications in 2D and volumetric imaging of micron scale structures typically used on inaccessible objects such as the retina of the eye. This report focuses on Swept Source OCT (SS-OCT), favoured for its faster scanning speeds and therefore faster data acquisition (highly favourable when imaging live patients). SS-OCT relies on the scanning of a narrow laser line at speeds typically in excess of 100?kHz. We have employed ZemaxTM ray tracing software to simulate one method of splitting the spectrum of a broadband, near-infrared source, into its component wavelengths by reflecting the spectrum from an off-axis, 72-facet polygon mirror at a frequency of 48?kHz. We specifically addressed the geometric and radiometric vignetting associated with the reflected spectrum off an individual mirrored facet and how this may impose limitations to the incident beam size and hence lead to a loss in the power available from the source. It was found that for certain configurations up to 44% of the light was lost at the edges of the spectrum due to both radiometric and geometric vignetting, which may result in an effective swept range of <50?nm from an initial bandwidth of 100?nm. Our simulations account for real refractive errors and losses in the beam caused by lens aberrations, and produce a model of the sampling function of wavelength against time

Quantitative assessment of rat bone regeneration using complex master-slave optical coherence tomography

Background: The need for hard and soft tissues in oral implantology determined the development of methods and techniques to increase bone volume and their quality with different alternative materials used as substituents of patient’s natural bone. In addition, laser radiation can be used to accelerate the repair of fractures and to produce an increased volume of formed callus, as well as an increased bone mineral density. Methods: The aim of this work is to evaluate the capability of an in-house developed multimodal complex master slave (CMS) enhanced swept source (SS) optical coherence tomography (OCT) imaging instrument to analyze the increase in the quantity and the improvement of the quality of newly-formed bone using low level laser therapy (LLLT). Bone formation is quantitatively assessed in 5 mm cylindrical defects made in the calvaria part of the skull of living rats. Samples are divided in three study groups: A, a negative control group, for which the natural healing process of the defect is investigated; B, a positive control group, for which bovine graft is used to stimulate bone formation, and C, a study group, in which bovine graft is added to the created defects and LLLT is applied throughout the entire healing period. The animals are sacrificed after 14, 21, and 30 days, and the samples are imaged using the multimodal CMS/SS-OCT instrument. Results: The method allows for the simultaneous monitoring of the bone tissue via two perpendicular cross-sections and nine en-face images taken at adjustable depths into the sample. A global image with course axial resolution allows for the positioning of the field-of-view of the system on the area of interest on the tissue. The quantitative assessment of the process of bone formation is completed using the differences in brightness between the native bone, the artificial bone graft, and the newly-formed bone. Conclusions: Group C is demonstrated to have a higher volume of newly-formed bone than Group B, which is better from this point of view than Group A. By analyzing the evolution of this volume of new bone in time, the most significant difference was after 21 days, therefore approximately after two thirds of the total time interval analyzed. After 30 days, the volumes of bone tend to move closer, as they begin to fill the available gap. The study demonstrates that OCT can assess quantitatively the positive impact of LLLT on bone regeneration

Theoretical approach on a galvanometric scanner with an enhanced duty cycle

The paper explores the possibilities of achieving a galvanometric scanner with an enhanced, as close as possible to 100%, duty cycle (η) even for high scan, i.e. high oscillation, frequencies. Nowadays solutions provide high η, but up to certain frequencies. The study of this limit frequency, of its relationship with the duty cycle, and the ascertainment of the scanning and command functions that may produce better results, is the final scope of this work. The scanning device is considered in a setup characteristic to the dimensional, usually on-line, industrial measurements. A detailed theoretical study is performed, starting with the equation of the mobile element of the galvoscanner. The expressions of the active torque and of the necessary command function that has to be used are obtained, with regard to the desired scanning function. This is considered linear and symmetrical on its active portions and with non-linear returning portions that have to be performed as fast as possible. Two such functions for the returning portions are considered and studied: parabolic and sinusoidal. The best scanning function, with regard to achieving the objectives of the device (high duty cycle for high frequencies), is obtained and the way the necessary command function has to be deduced is discussed

Modeling a galvoscanner with an optimized scanning function

The paper presents the modeling of a galvanometer-based scanning device with an increased duty cycle, i.e. a high efficiency of using the available time for the scanning process. From the basic dynamic equations of the oscillating element, the active torque and the command function that have to be used are derived. An analytical study is performed on the possible profiles of the scanning function, and an optimum solution is demonstrated, in order to obtain an as small as possible inertia torque and an as high as possible duty cycle. The active torque and the command functions are deduced for this optimum scanning law. A MathCAD study of the command function with regard to the desired scanning (oscillating) frequency completes the modeling process. © Springer Science +Business Media, B.V. 2010

Progress in Biomedical Optics and Imaging - Proceedings of SPIE: Introduction

The front matter associated with SPIE Proceedings Volume 8925, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing

Optical imaging of oral squamous cell carcinoma using optical coherence tomography and micro CT

Oral squamous cell carcinoma (OSCC) constitutes 90% of oral cancer. Early detection is a cornerstone to improve survival and to reduce diagnostic delay. We propose optical coherence tomography (OCT), as a non-invasive diagnosis method. OCT represents a new high-resolution optical technique that permits 3D, real-time imaging of near surface abnormalities in complex tissues. In the present study half of the excisional biopsy was directed to the pathologist and the other half was assigned for OCT and Micro-CT investigation. For the OCT imaging it was used an OCT prototype (1300 nm), Synchrotron Radiation Micro-CT and histopathology validated the results. Areas of OSCC of the buccal mucosa were identified in the OCT images by the disruption of the basement membrane, an epithelial layer that was highly variable in thickness, with areas of erosion, extensive epithelial down-growth and invasion into the sub-epithelial layers. In this respect, OCT seems to be a highly promising imaging modality. © (2014) Trans Tech Publications, Switzerland

Evaluation of metal-polymeric fixed partial prosthesis using optical coherence tomography

Metal-Polymeric fixed partial prosthesis is the usual prosthetic treatment for many dental patients. However, during the mastication the polymeric component of the prosthesis is fractured and will be lost. This fracture is caused by the material defects or by the fracture lines trapped inside the esthetic components of the prosthesis. This will finally lead to the failure of the prosthetic treatment. Nowadays, there is no method of identification and forecast for the materials defects of the polymeric materials. The aim of this paper is to demonstrate the capability of Optical Coherence Tomography (OCT) as a non-invasive clinical method that can be used for the evaluation of metal-polymeric fixed partial prostheses. Twenty metal-polymeric fixed partial prostheses were used for this study. The esthetic component of the prostheses has been Adoro (Ivoclar). Optical investigations of the metal prostheses have revealed no material defects or fracture lines. All the prostheses were temporary cemented in the oral cavities of the patients for six month. The non-invasive method used for the investigations was OCT working in Time Domain mode at 1300 nm. The evaluations of the prostheses were performed before and after their cementation in the patient mouths. All the imagistic results were performed in 2D and than in 3D, after the reconstruction. The results obtained after the OCT evaluation allowed for the identification of 4 metal-polymeric fixed partial prostheses with material defects immediately after finishing the technological procedures. After 6 month in the oral environment other 3 fixed partial prostheses revealed fracture lines. In conclusion, OCT proved to be a valuable tool for the noninvasive evaluation of the metal-polymeric fixed partial prostheses. © 2013 SPIE

Design and testing of prototype handheld scanning probes for optical coherence tomography

Three simple and low-cost configurations of handheld scanning probes for optical coherence tomography have been developed. Their design and testing for dentistry applications are presented. The first two configurations were built exclusively from available off-the-shelf optomechanical components, which, to the best of our knowledge, are the first designs of this type. The third configuration includes these components in an optimized and ergonomic probe. All the designs are presented in detail to allow for their duplication in any laboratory with a minimum effort, for applications that range from educational to high-end clinical investigations. Requirements that have to be fulfilled to achieve configurations which are reliable, ergonomic - for clinical environments, and easy to build are presented. While a range of applications is possible for the prototypes developed, in this study the handheld probes are tested ex vivo with a spectral domain optical coherence tomography system built in-house, for dental constructs. A previous testing with a swept source optical coherence tomography system has also been performed both in vivo and ex vivo for ear, nose, and throat - in a medical environment. The applications use the capability of optical coherence tomography to achieve real-time, high-resolution, non-contact, and non-destructive interferometric investigations with micrometer resolutions and millimeter penetration depth inside the sample. In this study, testing the quality of the material of one of the most used types of dental prosthesis, metalo-ceramic is thus demonstrated. © IMechE 2014

Handheld scanning probes for Optical Coherence Tomography: Developments, applications and perspectives

We present the handheld scanning probes that we have recently developed in our current project for biomedical imaging in general and for Optical Coherence Tomography (OCT) in particular. OCT is an established, but dynamic imagistic technique based on laser interferometry, which offers micrometer resolutions and millimeters penetration depths. With regard to existing devices, the newly developed handheld probes are simple, light and relatively low cost. Their design is described in detail to allow for the reproduction in any lab, including for educational purposes. Two probes are constructed almost entirely from off-the-shelf components, while a third, final variant is constructed with dedicated components, in an ergonomic design. The handheld probes have uni-dimensional (1D) galvanometer scanners therefore they achieve transversal sections through the biological sample investigated - in contrast to handheld probes equipped with bi-dimensional (2D) scanners that can also achieve volumetric (3D) reconstructions of the samples. These latter handheld probes are therefore also discussed, as well as the possibility to equip them with galvanometer 2D scanners or with Risley prisms. For galvanometer scanners the optimal scanning functions studied in a series of previous works are pointed out; these functions offer a higher temporal efficiency/duty cycle of the scanning process, as well as artifact-free OCT images. The testing of the handheld scanning probes in dental applications is presented, for metal ceramic prosthesis and for teeth. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Research lead student projects on multi-disciplinary optomechatronics with applications in biomedical imaging

The education side of an optomechatronics consortium of academic and industrial partners is presented. The consortium covers a variety of disciplines including mechanical design, theory of mechanisms, mechatronics, as well as optical engineering with applications in specific biomedical fields, such as dentistry and gastroenterology. The five teams involved in the project compound senior and young researchers, including graduate and undergraduate students). The contribution of each partner is presented, with examples of specific methodology in conducting student projects on subjects inspired by research. © Springer International Publishing Switzerland 2014