The relationship between laser pulse duration (τ p) and stress confinement time (τ sr) was studied using acoustic-based measurements of material absorption coefficient (μ a). A numerical model was developed to simulate stress signals. Experimental photoacoustic measurements at several values of τ were performed to estimate μ a of water. A numerical deconvolution technique was implemented to overcome the limitation of conventional photoacoustics, resulting in up to a 30% improvement in photoacoustic-based estimates of the sample μ a.

Infrared laser ablation of urinary calculi was investigated as a function of wavelength to determine the relation of ablation threshold fluences, ablation depths, and optical absorption. A simple photothermal ablation model was employed to examine this relationship. Human urinary calculi composed of > 95% uric acid, > 95% cystine, > 95% calcium oxalate monohydrate (COM), and > 90% magnesium ammonium phosphate hexahydrate (MAPH) were used. Various wavelengths between 2.1 and 6.5 μm were selected to perform threshold fluence and ablation depth measurements. The laser source for this study was the tunable pulsed infrared free electron laser (FEL) at Vanderbilt University. Experimental results indicated a correlation of threshold fluence and ablation depth to the optical absorption properties of the calculi. When calculus optical absorption increased, the threshold fluences decreased. Although the ablation depths increased with calculus optical absorption, results indicated that in certain calculi the ablation depth was affected by optical attenuation through the ablation plume. These observations were in agreement with the photothermal ablation model, but fractures in striated calculi at higher optical absorptions, indicated the contribution of a photomechanical mechanism. Threshold fluences and ablation depths are a function of the wavelength dependent absorption properties of the calculi. These observations suggest that the 3-μm and 6-μm absorption bands are optimal for ablation or fragmentation of urinary calculus.

Cryopreservation of cartilage has been investigated for decades and is currently an established protocol. However, the reliability and applicability of cartilage cryopreservation for the use in electromechanical reshaping (EMR) has not been studied exclusively. A system to cryopreserve large numbers of tissue specimens provides a steady source of cartilage of similar quality for experimentation at later dates. This will reduce error that may arise from different cartilage stock, and has the potential to maximize efficiency under time constraints. Our study utilizes a unique methodology to cryopreserve septal cartilage for use in EMR studies. Rabbit septal cartilage specimens were harvested and standardized to 20 x 8 x 1 mm, and placed in one of three solutions (normal saline, PBS, 10% DMSO in PBS) for four hours in a cold storage room at 4 degrees Celsius. Then, each cartilage specimen was vacuumed and sealed in an anti-frost plastic bag and stored in a freezer at -80 degrees Celsius for 1 to 3 weeks duration. EMR was performed using 2 and 6 volts for 2 minutes application time. Bend angle measurements of the cryopreserved cartilage specimens were compared to bend angles of fresh cartilage which underwent EMR using the same parameters. Results demonstrate that normal saline, phosphate buffered saline (PBS), and PBS with DMSO were effective in cryopreservation, and indicated no significant differences in bend angle measurements when compared to no cryopreservation. Our methodology to cryopreserve cartilage specimens provides a successful approach for use in conducting large-scale EMR studies. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Grafts obtained from peripheral regions of costal cartilage have an inherent tendency to warp over time. Laser irradiation provides a potential method to control the warping process, thus yielding stable grafts for facial reconstructive surgery. In our current study, we propose a simple and well-fitting model that numerically describes the degree of warping of laser irradiated costal cartilage grafts. Using a Nd:YAG laser (λ=1.32μm) at various exposure settings, grafts harvested from the peripheral regions of porcine costal cartilage were irradiated. The resulting graft geometry was objectively fitted to a curve using a quadratic regression model. The coefficient of determination (R2) demonstrated a very strong fit for all grafts modeled. A quadratic regression is simple to perform and results in a single numerical value that appropriately describes the degree of cartilage warping. Our proposed model is valuable in assessing the effect of laser irradiation on the warping process of costal cartilage. © 2010 Copyright SPIE - The International Society for Optical Engineering.

One common component of otolaryngological surgeries is the reshaping of cartilage. Previous studies have demonstrated the efficient achievement of this procedure through electromechanical reshaping (EMR), a technique that involves the direct application of voltage to cartilage that is mechanically deformed in a jig. Two main parameters, voltage and application time, may be regulated to achieve varying degrees of shape change. Although prior research has correlated these EMR parameters with degree of shape change, it remains necessary to correlate the same parameters with the degree of change in the mechanical properties of tissue. Once this is accomplished, an ideal balance may be determined, in which shape change is maximized while intrinsic tissue damage is minimized This study satisfies this need by providing comprehensive data on the pre- and post-EMR stiffness of both septal and auricular cartilage over a range of voltages (2-8V) with constant application time (2 min for septal, 3 min for auricular). EMR was applied using flat platinum electrodes to one of two 15 mm X 5 mm samples obtained from the same cartilage specimen, while the second sample was maintained as a control. Following a 15 min re-hydration period, the Young's modulus of the tissue was calculated for both the control and experimental sample from data obtained through a uniaxial tension test. A general reduction in stiffness was observed beginning at 3V, with the magnitude of reduction increasing at 6V. © 2010 Copyright SPIE - The International Society for Optical Engineering.

We developed a multiphoton microscope which integrates an all normal dispersion fiber laser, a double cladding photonic crystal fiber and a MEMS mirror scanner based hand-held probe. The fiber laser has a central wavelength of 1.06μm,a repetition rate of 76MHz and maximum average output power of more than 1W. The MEMS mirror based probe is compact and Second harmonic generation and two photon excited fluorescence images of biological sample were demonstrated. © 2010 Copyright SPIE - The International Society for Optical Engineering.

An emerging clinical treatment option for articular cartilage injury includes bone marrow stimulation techniques, such as microfracture, which has grown increasingly popular among athletes. During the microfracture procedure, the surgeon penetrates the subchondral bone with an awl and creates "microholes" deep enough to ensure bleeding from the bone marrow. This procedure triggers a spontaneous repair response that results in the formation of fibrocartilaginous repair tissue. This preliminary study aimed to evaluate the potential use of femtosecond lasers and Erbium:YAG lasers as alternatives to microfracture surgery of the knee by assessing the effects of ablation on bovine femoral condyles. Bovine femoral condyles were obtained and 8mm cube blocks were extracted. The specimen were ablated with various laser dosimetry parameters and observed using a high power dissecting microscope to examine the effects of the lasers. Further imaging with conventional histology (hematoxylin and eosin staining) was done to provide more accurate information. Preliminary results show some carbonization but demonstrate little thermal damage to surrounding tissues. The femtosecond laser offers a more precise and efficient ablation than the Erbium:YAG laser, but both are demonstrated to be possible alternatives to the surgical-skill dependent microfracture procedure. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Objectives: To describe the current and promising new applications of Optical Coherence Tomography (OCT) as a helpful tool when imaging the different sites in the head and neck. We used the OCT Niris system, which is the first commercially available OCT device for applications outside the field of ophthalmology. Methods: OCT images were obtained of normal, benign, premalignant and malignant lesions in different areas of the head and neck. The OCT imaging system has a tissue penetration depth of approximately 1-2mm, a scanning range of 2mm and a spatial depth resolution of approximately 10-20μm. Imaging was performed using a flexible probe in two different settings, the outpatient clinic and the operating room. Results: High-resolution cross-sectional images from the larynx were obtained with the patient awake, without the need for general anesthesia, under direct visualization with a flexible fiberoptic endoscope. The OCT probe was inserted through the nasal cavity and placed in slight contact with the laryngeal tissue. In the ears, cholesteatoma was differentiated from inflamed middle ear mucosa by the different hyperintensity. In the neck, normal as well as different pathologies of the thyroid were identified. Conclusions: This system is non invasive and easy to incorporate into the operating room setting as well as the outpatient clinic. It requires minimal set-up and only one person is required to operate the system. OCT has the distinctive capability to obtain highresolution images, and the microanatomy of different sites can be observed. OCT technology has the potential to offer a quick, efficient and reliable imaging method to help the surgeon not only in the operating room but also in the clinical setting to guide surgical biopsies and aid in clinical decision making of different head and neck pathologies, especially those arising form the larynx. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Acquired subglottic stenosis is a narrowing of the airway caused by prolonged endotracheal intubation. Currently, there are no non-invasive means to diagnose the disease. A previous study by this same group introduced optical coherence tomography (OCT) as a means of monitoring the progression of stenosis. The aim of the current study was to qualitatively and quantitatively analyze OCT images obtained from a subglottic stenosis model of the rabbit airway. 15 rabbits were used throughout the study, and a MEMs based OCT probe was utilized. The OCT images obtained were analyzed using a free software program, 3D Slicer. The region of scarred tissue was grown out and measured quantitatively. This study demonstrated the feasibility of using a program to quantify the progression of scarring in OCT images, in addition to qualitatively correlating between histology, endoscopic, and OCT images. Future works may include utilization of a long-range probe and use of a pressure necrosis model to better emulate the actual onset of neonatal subglottic stenosis. © 2013 SPIE.

Electromechanical reshaping (EMR) of cartilage is a promising noninvasive technique with potential for broad application in reconstructive surgery. EMR involves applying direct current electrical fields to localized stress regions and initiating a series of oxidation-reduction reactions, thus effecting a shape change. Previous EMR studies have focused on macroscopic structural measurements of the shape change effect or monitoring of electrical current flow. Only limited investigation of structural changes in the tissue at the histologic level have been performed, and not in real time. This study is the first to use optical coherence tomography (OCT) to examine structural changes in cartilage during EMR. Two platinum needle electrodes were inserted into fixed rectangular rabbit nasal septal cartilage specimens. The spectral domain OCT probe was then positioned above the section of cartilage in which the anode needle was inserted. A constant voltage of 6V was applied for 3 minutes, and images were obtained (8 frames/second). OCT was also performed in specimens undergoing dehydration under ambient conditions and during pH changes produced by the addition of HCl, as both processes accompany EMR. The OCT data identified distinct findings among the three conditions, suggesting that EMR causes a much greater degree of reshaping on a molecular level than dehydration or a change in pH alone. OCT provides a means to gauge structural changes in the tissue matrix during EMR. The application of OCT to image the EMR process will add to our understanding of the mechanisms of action involved and potentially facilitate optimization of this process. © 2010 Copyright SPIE - The International Society for Optical Engineering.