Long-range optical coherence tomography has been developed to image the upper airway, obtaining high resolution, cross-sectional images of the hollow structure. The information obtained from the anatomical structure of the airway is important to objectively identify regions of airway obstruction. This paper describes a technique to create 3D reconstructions of the upper airway from LR-OCT images. Herein we outline the necessary steps to generate these 3D models, including image processing techniques, manual tissue segmentation in Mimics, anatomical curvature bending, and the final STL model rendition. These 3D models were used to qualitatively analyze structural changes before and after surgical interventions. The reconstructions could also be used for further computational fluid dynamics analysis.
Electromechanical reshaping (EMR) of cartilage has been suggested as an alternative to the classical surgical techniques
of modifying the shape of facial cartilages. The method is based on exposure of mechanically deformed cartilaginous
tissue to a low level electric field. Electro-chemical reactions within the tissue lead to reduction of internal stress, and
establishment of a new equilibrium shape. The same reactions offset the electric charge balance between collagen and
proteoglycan matrix and interstitial fluid responsible for maintenance of cartilage mechanical properties. The objective
of this study was to investigate correlation between the electric charge transferred during EMR and equilibrium elastic
modulus.
We used a finite element model based on the triphasic theory of cartilage mechanical properties to study how electric
charges transferred in the electro-chemical reactions in cartilage can change its mechanical responses to step
displacements in unconfined compression. The concentrations of the ions, the strain field and the fluid and ion velocities
within the specimen subject to an applied mechanical deformation were estimated and apparent elastic modulus (the ratio
of the equilibrium axial stress to the axial strain) was calculated as a function of transferred charge. The results from
numerical calculations showed that the apparent elastic modulus decreases with increase in electric charge transfer. To
compare numerical model with experimental observation we measured elastic modulus of cartilage as a function of
electric charge transferred in electric circuit during EMR. Good correlation between experimental and theoretical data
suggests that electric charge disbalance is responsible for alteration of cartilage mechanical properties.
Electromechanical reshaping of cartilage is a novel modality that has significant clinical applications in otolaryngology
and plastic surgery. Although EMR dosimetry has been extensively studied, little is known about the mechanisms of
EMR, of which local tissue pH changes is believed to play a role. In this study, rabbit nasal septal cartilage is subject to a
number of experiments aimed at elucidating pH-related changes using phenol red. The lateral extent and magnitude of
pH change as well as factors that impact pH change are studied. Increasing voltage and application appear to increase the
area and intensity of color change. With parameters known to produce thermal tissue injury, a transitional zone likely
representing a confluence of acid-base products is noted in the region around the bend axis. Furthermore, rehydration
and pH indicator application time do not appear to play a role in the quality of pH change. These simple experiments
may provide insight into the role of pH changes in EMR that may allow correlation of dosimetry to tissue damage,
further optimizing the clinical potential of EMR.
Electro Mechanical Reshaping (EMR) with platinum needle electrodes has been recently developed to shape cartilage
without conventional cut and suture surgery. This study investigates the relationship between the voltage applied, the
electrical current measured during EMR, and the resulting shape. Monitoring the electrical current provides information
to model the electro-chemistry, which will aid in determining the onset of shape stabilization. Porcine costal grafts,
rabbit auricular, and porcine auricular tissue were bent into a 90° angle using a moulage. Platinum needle electrodes
were then placed in contact with the cartilage and a constant voltage was applied for a set time. The electrical current
was measured during the process and total charge transferred was calculated. The cartilage specimen was then removed
from the jig and photographed after one minute in order to determine the resulting bend angle. Results show that a higher
current in tissue is produced with increasing applied voltage. Each current trace is unique and is dependent on tissue
thickness and inter-electrode distances. Understanding the electrical current process ultimately leads to optimizing EMR
and feedback control. Voltage, for example, could be varied in real-time during EMR to produce a constant chemical
reaction rate and potentially reduce total tissue dehydration in contact with electrodes. In conclusion, electric current
traces provide information about chemical kinetics during EMR that depend on exposure settings, and monitoring these
traces is an important step in optimizing the reshaping process.
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.
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.
Electromechanical reshaping (EMR) of cartilage is a novel technique that has significant potential for use in facial reconstructive surgery. EMR achieves permanent shape change by initiating electrochemical redox reactions in the vicinity of stress concentrations, thereby altering mechanical properties of tissue matrix. This study reports the use of a six electrode needle-based geometric configuration to reshape cartilage. Rectangular samples (24 x 12 x 1 mm) of rabbit nasal septal cartilages were bent at a right angle in a precision-machined reshaping jig. Two parallel arrays of three platinum needle electrodes were each inserted into cartilage along the bend at 3 mm from the bend line. One array served as an anode and the other as cathode. Constant voltage at 1, 2, 4, 6, and 8 volts was applied to the arrays for 2 minutes. The specimens were then removed from the jig and rehydrated for 15 minutes in phosphate buffered saline. Following rehydration, bend angles and thicknesses were measured. Bend angle increased with increasing voltage and application time. No statistically significant bending was observed below 6 volts for 2 minutes application time. Maximum bend angle of 33 ± 8 degrees or reshaping degree of 33% was observed at 8 volts applied for 2 minutes. Current flow was small (< 0.1 A) for each case. Sample thickness was 0.9 ± 0.2 mm. ANOVA analysis showed that cartilage thickness had no significant impact on the extent of reshaping at given voltage and application time. The six needle electrode geometric configuration conforms to the voltage- and time-dependent trends predicted by previous EMR studies. In the future, the reshaping properties of other geometric configurations will be explored.
Successful application of laser cartilage reshaping (LCR) for the in-situ treatment of structural deformities in the nasal septum, external ear and trachea requires a better understanding of the evolution of cartilage mechanical properties with temperature. We develop a method of Radio Frequency (RF) heating for reliable evaluation of mechanical changes in septal cartilage undergoing heating and used obtained data to model the mechanical changes in cartilage at steady state following laser heating. Cartilage specimens harvested from porcine septum were secured between two flat parallel copper platens connected to a surgical radiofrequency source. The current was user-selectable and controlled to achieve any desired heating rate mimicking heating rate obtained during laser irradiation. Surface and internal temperatures were monitored by an IR camera and embedding a small electrically insulated thermocouple inside the specimen. Cylindrical and rectangular samples were fashioned from the heated specimens and their equilibrium elastic modulus was measured in a step unconfined compression and tension experiments, respectively. Functional dependencies of the elastic modulus and maximum temperature were interpolated from the measurements. The calculated elastic modulus profiles were incorporated into a numerical model of uniaxial unconfined compression and tension of laser irradiated samples. The reaction force to a 0.1 strain was calculated and compared with the reaction force obtained in analogous mechanical measurements experiment. The results of the numerical simulation of uniaxial compression of laser heated samples demonstrate good correlation with experimentally obtained reaction force. Generalization of this methodology to incorporate orthogonal mechanical properties may aid in optimizing clinical LCR procedures.
We used 5.0 MHz ultrasonic pulses to monitor stress relaxation in Nd:YAG (λ = 1.32 μm) laser irradiated porcine nasal septal cartilage. Cartilage is irradiated in both uniaxial compression and curved deformation. A thin beam load cell and IR thermocouple measure strain (Vpp) and temperature (°C), respectively. We show that the propagation speed of the ultrasonic pulse is indicative of permanent stress relaxation in porcine nasal septal cartilage.
Background: Tracheal cartilage deformities due to trauma, prolonged endotracheal intubation or infection are difficult to correct. Current treatment options such as dilation, laser ablation, stent placement, and segmental resection are only temporary or carry significant risks. The objectives of this project were to design and test a laser activated endotracheal stent system that can actively modify the geometry of tracheal cartilage, leading to permanent retention of a new and desirable tracheal geometry.
Methods: Ex vivo rabbit tracheal cartilage (simulating human neonate trachea) were irradiated with an Er: Glass laser, (λ= 1.54um, 0.5W-2.5W, 1 sec to 5 sec). Shape change and gross thermal injury were assessed visually to determine the best laser power parameters for reshaping. A rigid endoscopic telescope and hollow bronchoscope were used to record endoscopic images. The stent was constructed from nitinol wire, shaped into a zigzag configuration. An ex vivo testing apparatus was also constructed.
Results: The best laser power parameter to produce shape change was 1 W for 6-7 seconds. At this setting, there was significant shape change with only minimal thermal injury to the tracheal mucosa, as assessed by visual inspection. The bronchoscopy system functioned adequately during testing in the ex vivo testing apparatus.
Conclusion: We have successfully designed instrumentation and created the capability to endoscopically reshape tracheal cartilage in an ex vivo rabbit model. The results obtained in ex vivo tracheal cartilage indicated that reshaping using Er: Glass laser can be accomplished.
Stenotic, collapsed, and flow-restricted tracheal airways may result from blunt trauma, chronic infection, and the prolonged endotracheal intubation. This pilot investigation characterizes the degree of shape change produced by Ho:YAG laser (λ=2.12 μm) irradiation of rabbit and pig trachea tissue as a function of laser dosimetry and application protocol. Force displacement curves were generated using fresh lagomorph and porcine tracheal cartilage rings secured in a modified single beam cantilever geometry. These specimens were then irradiated for varying amounts of time and power with the objective of straightening these curved specimens. The degree of shape change was documented photographically. Force and surface temperature were monitored. Confocal microscopy was then used in combination a vital staine (“live-dead assay”) to determine the level of viability of straightened cartilage for selected exposure time-power pairs. Laser Cartilage Reshaping of the trachea may provide a new method to treat severe tracheal injuries without the need for classic open surgical techniques. This pilot investigation is the first step toward demonstrating the feasibility of this technique. Long-term, the design of stents combined with laser irradiation may provide a means to alter tracheal shape.
A new non-thermal method of altering the shape of cartilage to create mechanically stable new morphologies was developed using low DC voltage electric fields (electroforming). In cartilage electroforming, voltage is applied to the surfaces of cartilage specimens held in mechanical deformation by a jig made of two large surface area electrodes for 2-5 minutes. Following removal of the specimen from the jig, permanent shape change is observed. Electric resistance and mechanical stress were monitoring during electroforming. Strong correlation between resistance and stress was observed suggesting that the mechanism of stress relaxation is electrically mediated and may provide a mean to monitor electroforming.
Dielectric properties of cartilage have received comparatively little interest and few studies have examined the effect of the applying electric currents to mechanically deformed cartilages. The objective of this study was to determine the dependence of shape change on electrode composition during a process we have described as “electroforming.” Porcine nasal septal cartilage specimens (16 x 5 x 2 mm) were mechanically deformed between two semicircular electrodes. Direct current (DC) current was applied to establish charge separation and electrical streaming potential. Voltage (<10 V) and application time (0-6 minutes) were varied, and shape change was measured using analytic representation. Surface features were evaluated using light microscopy. While shape change strongly correlated with voltage and time for all electrode materials, the voltage and application time that produced maximum shape change (curvature of the jig, ~ 160°) varied for each material. Aluminum is more effective for electroforming than gold as it yields the lowest set of plateau values. Surface features indicated that electrodeposition occurs depending upon the voltage and the standard reduction potential of electrodes. The results from this study provide insight into the dependence of shape change on the external electrical environment of cartilage and how optimal shape change can be produced with nominal electrodeposition.
Much interest has been placed on the permanent reshaping of cartilage for facial reconstructive surgery using lasers. An alternate way to reshape cartilage is to heat the tissue in a water bath while maintaining the specimen in mechanical deformation. The objective of this study was to measure the circular bend angle of a cartilage specimen produced by varying the temperature and immersion time in a water bath. Rectangular cartilage specimens (18 x 4 x 1.5 mm) were bent in a semicircular jig (diameter 11 mm) and then immersed in a saline bath at temperatures between 50 - 80°C. The immersion times were 5, 20, 80, 160 and 320 seconds at each temperature. The distance between the ends of each specimen was measured before reshaping and at 15 minutes and 24 hours after immersion in order to calculate the resulting bend angle. The largest bend angle occurred in the specimen immersed in saline at 74°C for 320 seconds, illustrating a definite thermal influence on the physical shape of the cartilage sample. The critical immersion times and bath temperatures where definite shape change occurred were determined.
The optimization of electrosurgical procedures requires a rigorous understanding of the electrical, thermal, mechanical and chemical events accompanying the ablation process. Modeling is indispensable and is needed to further advance this technology. This study introduces a novel tissue electrosurgical ablation model based on interstitial vapor nucleation and expansion. The model describes interstitial vapor nucleation and bubble growth using a homogeneous nulceation theory and Rayleigh equation. Electrosurgical incisions were made on beef muscle while equivalent electrical circuit patameters were monitored as a function of power settings and scalpel geometries. Thermal damage was measured using light and polarization microscopy. Results were compared with predictions produced by a numerical simulation, which modeled the tissue and electrosurgical scalpel interaction as a function of power settings and scalpel geometry.
We developed a 3D thermo-electrical model of RF tissue cutting that takes into account variations in electrical and thermal properties with temperature and water content, dynamics of water evaporation and thermal and electrical processes at the tissue-scalpel interface. The model predicts measurable parameters of the electric circuit (tissue impedance, ESU output RMS voltage and current) and tissue cutting rate. Results of numerical simulations suggest that high circuit impedance during electrosurgical cutting can result not only from tissue dehydration but from the configuration of the electric field as well. It appears that the area of tissue-scalpel electric contact is significantly smaller than the area of the scalpel itself but is large enough to rule out electric sparks as a major mechanism of electrosurgical cutting.
Tissue optical properties are necessary parameters for prescribing light dosimetry in photomedicine. In many diagnostic or therapeutic applications where optical fiber probes are used, pressure is often applied to the tissue to reduce index mismatch and increase light transmittance. In this study, we have measured in vitro optical properties as a function of pressure with a visible-IR spectrophotometer. A spectral range of 400 - 1800 nm with a spectral resolution of 5 nm was used for all measurements. Skin specimens of two Hispanic donors and three caucasian donors were obtained from the tissue bank. Each specimen, sandwiched between microscope slides, was compressed by a spring-loaded apparatus. Then diffuse reflectance and transmittance of each sample were measured at no load and at approximately 0.1 and 1 kgf/cm2. Under compression, tissue thicknesses were reduced up to 78%. Generally, reflectance decreased while the overall transmittance increased under compression. The absorption and reduced scattering coefficients were calculated using the inverse adding doubling method. Compared with the no-load controls, there was an increase in the absorption and scattering coefficients among most of the compressed specimens.
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