Optics InfoBase is the Optical Society's online library for flagship journals, partn... more Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.
Bleeding is common after liver resection and establishing hemostasis with sutures or argon beam c... more Bleeding is common after liver resection and establishing hemostasis with sutures or argon beam coagulation can be difficult. In our laboratory, concentrated albumin applied to the liver surface before argon beam coagulation improves sealing of the resected surface of the liver, including closure of blood vessels and ducts not generally seen with standard argon beam coagulation. Domestic swine underwent heparinization, then laparotomy and wedge resection of the left medial segment of the liver, using finger fracture technique. Blood vessels and ducts 5 mm or greater were ligated. For achieving hemostasis, the animals were randomized to either a control group using argon beam coagulation alone (n = 15) or an albumin group using argon beam coagulation with concentrated 38% albumin (n = 13). After initial hemostasis, the resected liver surfaces were packed for 3 minutes. Repeated applications of argon beam coagulation with or without albumin were performed as needed, followed by 3 minu...
Abstract An optical fiber probe was developed for endoscopic determination of tissue optical prop... more Abstract An optical fiber probe was developed for endoscopic determination of tissue optical properties. Reduced scattering and absorption coefficients were determined using an empirical/spectral light transport model. The method was validated against diffusion and adding-doubling models.
BW4B.3.pdf Biomedical Optics and 3D Imaging OSA 2012 BW4B.3.pdf Biomedical Optics and 3D Imaging ... more BW4B.3.pdf Biomedical Optics and 3D Imaging OSA 2012 BW4B.3.pdf Biomedical Optics and 3D Imaging OSA 2012 ... Validation of a Monte Carlo Model for Determination of ... Paulo R. Bargo1, Steven L. Jacques2 and Scott A. Prahl3 1 - Johnson & Johnson Consumer Company, Inc., 199 Grandview Rd., Skillman NJ, 08558, 2 - Oregon Health and Science University, 3303 SW Bond Ave CH13B, Portland, OR 97239, 3 - Oregon Medical Laser Center, 9205 SW Barnes Rd, Portland, OR 97225 pbargo@its.jnj.com, ...
Frontiers in Optics 2011/Laser Science XXVII, 2011
Abstract: We discuss the use of an un-modified differential interference contrast microscope for ... more Abstract: We discuss the use of an un-modified differential interference contrast microscope for characterization of the scatter and absorption properties of thin tissue samples. A simple calibration process is discussed and a phase-stepping procedure it demonstrated for acquiring phase information exclusive of absorption effects. The procedure results in two-dimensional displays of the local polar and azimuthal ray deviation. Alternatively, we show that these angular deviation maps can be integrated to provide estimates of the phase. We demonstrate the calibration ...
Page 1. Influence of anisotropy in the depolarization ability of microspheres solutions Jessica C... more Page 1. Influence of anisotropy in the depolarization ability of microspheres solutions Jessica C. Ramella-Roman Johns Hopkins University, APL, 11100 Johns Hopkins Road, Laurel MD, 20723-6099 jramella@bme.ogi.edu Scott A. Prahl Oregon Medical Laser Center, 9555 SW Barnes Rd, Portland OR, 97255 prahl@bme.ogi.edu Steve L. Jacques Oregon Health and Science University, 3181 SW Sam Jackson Park, Portland OR, 97239 sjacques@bme.ogi.edu, ...
Photodynamic therapy (PDT) is a minimally invasive therapeutic modality used for the management o... more Photodynamic therapy (PDT) is a minimally invasive therapeutic modality used for the management of a variety of cancers and benign diseases. The destruction of unwanted cells and tissues in PDT is achieved by the use of visible or near-infrared radiation to activate a light-absorbing compound (a photosensitizer, PS), which, in the presence of molecular oxygen, leads to the production of singlet oxygen and other reactive oxygen species. These cytotoxic species damage and kill target cells. The development of new PSs with properties optimized for PDT applications is crucial for the improvement of the therapeutic outcome. This review outlines the principles of PDT and discusses the relationship between the structure and physicochemical properties of a PS, its cellular uptake and subcellular localization, and its effect on PDT outcome and efficacy.
We present a novel, noncontact method for the determination of quantitative optical properties of... more We present a novel, noncontact method for the determination of quantitative optical properties of turbid media from 430 to 1050 nm. Through measuring the broadband reflectance from an unknown sample as a function of the spatial frequency of the projected illumination patterns, the absolute absorption and reduced scattering coefficients can be calculated without a priori assumptions of the chromophores present. This technique, which is called spatially modulated quantitative spectroscopy (SMoQS), was validated through the quantification of optical properties of homogenous liquid phantoms with known concentrations of absorbers and scatterers. The properties of the phantoms were recovered across the range of values prepared with R(2) values of 0.985 and 0.996 for absorption and reduced scattering, respectively. A measurement was also performed on skin tissue as a demonstration of the method's performance in vivo. The resultant absorption spectrum was well described by a multichromophore fit, and the quantitative values for oxy- and deoxyhemoglobin, water, and melanin were within published ranges for skin.
Page 1. Oxygen saturation and blood-volume derivation from multi-wavelength time-resolved optical... more Page 1. Oxygen saturation and blood-volume derivation from multi-wavelength time-resolved optical tomography data. Elizabeth MC Hillman, Simon. R. Arridge† , Jeremy C. Hebden, David T. Delpy. University College London ...
Page 1. 9:30am - 10:OOam (Invited) ML7.3 Mechanisms of Laser Thrombolysis S. Prahl, St. Vincent H... more Page 1. 9:30am - 10:OOam (Invited) ML7.3 Mechanisms of Laser Thrombolysis S. Prahl, St. Vincent Hospital and Medical Center, Portland, OR Summary not available. 299
Optics InfoBase is the Optical Society's online library for flagship journals, partn... more Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.
Bleeding is common after liver resection and establishing hemostasis with sutures or argon beam c... more Bleeding is common after liver resection and establishing hemostasis with sutures or argon beam coagulation can be difficult. In our laboratory, concentrated albumin applied to the liver surface before argon beam coagulation improves sealing of the resected surface of the liver, including closure of blood vessels and ducts not generally seen with standard argon beam coagulation. Domestic swine underwent heparinization, then laparotomy and wedge resection of the left medial segment of the liver, using finger fracture technique. Blood vessels and ducts 5 mm or greater were ligated. For achieving hemostasis, the animals were randomized to either a control group using argon beam coagulation alone (n = 15) or an albumin group using argon beam coagulation with concentrated 38% albumin (n = 13). After initial hemostasis, the resected liver surfaces were packed for 3 minutes. Repeated applications of argon beam coagulation with or without albumin were performed as needed, followed by 3 minu...
Abstract An optical fiber probe was developed for endoscopic determination of tissue optical prop... more Abstract An optical fiber probe was developed for endoscopic determination of tissue optical properties. Reduced scattering and absorption coefficients were determined using an empirical/spectral light transport model. The method was validated against diffusion and adding-doubling models.
BW4B.3.pdf Biomedical Optics and 3D Imaging OSA 2012 BW4B.3.pdf Biomedical Optics and 3D Imaging ... more BW4B.3.pdf Biomedical Optics and 3D Imaging OSA 2012 BW4B.3.pdf Biomedical Optics and 3D Imaging OSA 2012 ... Validation of a Monte Carlo Model for Determination of ... Paulo R. Bargo1, Steven L. Jacques2 and Scott A. Prahl3 1 - Johnson & Johnson Consumer Company, Inc., 199 Grandview Rd., Skillman NJ, 08558, 2 - Oregon Health and Science University, 3303 SW Bond Ave CH13B, Portland, OR 97239, 3 - Oregon Medical Laser Center, 9205 SW Barnes Rd, Portland, OR 97225 pbargo@its.jnj.com, ...
Frontiers in Optics 2011/Laser Science XXVII, 2011
Abstract: We discuss the use of an un-modified differential interference contrast microscope for ... more Abstract: We discuss the use of an un-modified differential interference contrast microscope for characterization of the scatter and absorption properties of thin tissue samples. A simple calibration process is discussed and a phase-stepping procedure it demonstrated for acquiring phase information exclusive of absorption effects. The procedure results in two-dimensional displays of the local polar and azimuthal ray deviation. Alternatively, we show that these angular deviation maps can be integrated to provide estimates of the phase. We demonstrate the calibration ...
Page 1. Influence of anisotropy in the depolarization ability of microspheres solutions Jessica C... more Page 1. Influence of anisotropy in the depolarization ability of microspheres solutions Jessica C. Ramella-Roman Johns Hopkins University, APL, 11100 Johns Hopkins Road, Laurel MD, 20723-6099 jramella@bme.ogi.edu Scott A. Prahl Oregon Medical Laser Center, 9555 SW Barnes Rd, Portland OR, 97255 prahl@bme.ogi.edu Steve L. Jacques Oregon Health and Science University, 3181 SW Sam Jackson Park, Portland OR, 97239 sjacques@bme.ogi.edu, ...
Photodynamic therapy (PDT) is a minimally invasive therapeutic modality used for the management o... more Photodynamic therapy (PDT) is a minimally invasive therapeutic modality used for the management of a variety of cancers and benign diseases. The destruction of unwanted cells and tissues in PDT is achieved by the use of visible or near-infrared radiation to activate a light-absorbing compound (a photosensitizer, PS), which, in the presence of molecular oxygen, leads to the production of singlet oxygen and other reactive oxygen species. These cytotoxic species damage and kill target cells. The development of new PSs with properties optimized for PDT applications is crucial for the improvement of the therapeutic outcome. This review outlines the principles of PDT and discusses the relationship between the structure and physicochemical properties of a PS, its cellular uptake and subcellular localization, and its effect on PDT outcome and efficacy.
We present a novel, noncontact method for the determination of quantitative optical properties of... more We present a novel, noncontact method for the determination of quantitative optical properties of turbid media from 430 to 1050 nm. Through measuring the broadband reflectance from an unknown sample as a function of the spatial frequency of the projected illumination patterns, the absolute absorption and reduced scattering coefficients can be calculated without a priori assumptions of the chromophores present. This technique, which is called spatially modulated quantitative spectroscopy (SMoQS), was validated through the quantification of optical properties of homogenous liquid phantoms with known concentrations of absorbers and scatterers. The properties of the phantoms were recovered across the range of values prepared with R(2) values of 0.985 and 0.996 for absorption and reduced scattering, respectively. A measurement was also performed on skin tissue as a demonstration of the method's performance in vivo. The resultant absorption spectrum was well described by a multichromophore fit, and the quantitative values for oxy- and deoxyhemoglobin, water, and melanin were within published ranges for skin.
Page 1. Oxygen saturation and blood-volume derivation from multi-wavelength time-resolved optical... more Page 1. Oxygen saturation and blood-volume derivation from multi-wavelength time-resolved optical tomography data. Elizabeth MC Hillman, Simon. R. Arridge† , Jeremy C. Hebden, David T. Delpy. University College London ...
Page 1. 9:30am - 10:OOam (Invited) ML7.3 Mechanisms of Laser Thrombolysis S. Prahl, St. Vincent H... more Page 1. 9:30am - 10:OOam (Invited) ML7.3 Mechanisms of Laser Thrombolysis S. Prahl, St. Vincent Hospital and Medical Center, Portland, OR Summary not available. 299
Photo-cured dental composites are widely used in dental practices to restore teeth due to the est... more Photo-cured dental composites are widely used in dental practices to restore teeth due to the esthetic appearance of the composites and the ability to cure in situ. However, their complex optical characteristics make it difficult to understand the light transport within the composites and to predict the depth of cure. Our previous work showed that the absorption and scattering coefficients of the composite changed after the composite was cured. The static Monte Carlo simulation showed that the penetration of radiant exposures differed significantly for cured and uncured optical properties. This means that a dynamic model is required for accurate prediction of radiant exposure in the composites. The purpose of this study was to develop and verify a dynamic Monte Carlo (DMC) model simulating light propagation in dental composites that have dynamic optical properties while photons are absorbed. The composite was divided into many small cubes, each of which had its own scattering and absorption coefficients. As light passed through the composite, the light was scattered and absorbed. The amount of light absorbed in each cube was calculated using BeerÕs Law and was used to determine the next optical properties in that cube. Finally, the predicted total reflectance and transmittance as well as the optical property during curing were verified numerically and experimentally. Our results showed that the model predicted values agreed with the theoretical values within 1\% difference. The DMC model results are comparable with experimental results within 5\% differences.
Photo-cured dental composites are widely used in dental practices to restore teeth due to the es... more Photo-cured dental composites are widely used in dental practices to restore teeth due to the esthetic appearance of the composites and the ability to cure in situ. However, their complex optical characteristics make it difficult to understand the light transport within the composites and to predict the depth of cure. Our previous work showed that the absorption and scattering coefficients of the composite changed after the composite was cured. The static Monte Carlo simulation showed that the penetration of radiant exposures differed significantly for cured and uncured optical properties. This means that a dynamic model is required for accurate prediction of radiant exposure in the composites. The purpose of this study was to develop and verify a dynamic Monte Carlo (DMC) model simulating light propagation in dental composites that have dynamic optical properties while photons are absorbed. The composite was divided into many small cubes, each of which had its own scattering and absorption coefficients. As light passed through the composite, the light was scattered and absorbed. The amount of light absorbed in each cube was calculated using BeerÕs Law and was used to determine the next optical properties in that cube. Finally, the predicted total reflectance and transmittance as well as the optical property during curing were verified numerically and experimentally. Our results showed that the model predicted values agreed with the theoretical values within 1\% difference. The DMC model results are comparable with experimental results within 5\% differences.
In this study an optical fiber fluorescence Monte Carlo model was developed to determine a light ... more In this study an optical fiber fluorescence Monte Carlo model was developed to determine a light transport correction factor that can be used in conjunction with optical fiber fluorescence measurements to find fluorophore concentrations in turbid media. This model was validated against theoretical and experimental tests for the absorbing-only and turbid cases. The model assumes that the fluorophore is uniformly distributed over the sample volume and that the tissue is homogenous.
Reconstruction of an image (or shape or wavefront) from measurements of the derivatives of the im... more Reconstruction of an image (or shape or wavefront) from measurements of the derivatives of the image in two orthogonal directions is a common problem. We demonstrate how a particular reconstructor, commonly referred to as the Fried algorithm, can be used with megapixel derivative images to recover the original image. Large datasets are handled by breaking the derivative images into smaller tiles, applying the Fried algorithm and stitching the tiles back together. The performance of the algorithm is demonstrated using differential interference contrast microscopy on a known test object.
Differential interference contrast (DIC) microscopy uses a Nomarski prism to split the illuminati... more Differential interference contrast (DIC) microscopy uses a Nomarski prism to split the illumination light into two orthogonally polarized beams that are displaced (sheared) relative to one other. A second Nomarski prism recombines the two beams after the light passes through the objective. The DIC image is directly related to the spatial derivative of the phase of light passing through image. The derivative of the phase can be quantitatively recovered from a series of phase-stepped DIC images [1]. In this talk, we extend the process to recover the original phase of the object. By using derivative images in two orthogonal shear directions, the Fried technique enables reconstruction of the phase over a small 32x32 pixel tile. Stitching together multiple tiles allows the phase to be recovered over the entire image. We demonstrate the method by processing DIC images of a sample with known phase properties. [1] Duncan et al., JOSA:A, 28, 1297-1306 (2011).
We present a clinically-relevant method for producing and sterilizing dissolvable albumin stents... more We present a clinically-relevant method for producing and sterilizing dissolvable albumin stents to provide intralumenal support in vascular anastomosis, and a method for photothermally welding vessels using a 1.9$\,\mu$m diode laser with albumin solder and water as the chromophore. The axial tensile strength and burst pressure of welded vessels were tested in-vitro. Optimized weld parameters yielded tensile strengths of 4.4$\pm$1.2\,N and burst pressures of 400$\pm$180\,mmHg with stay sutures (95\%CL). It was concluded that stay sutures would be necessary in vivo due to degradation of the tensile strength with exposure to moisture. Stent dissolution was monitored with UV absorbance measurements in PBS, which produced similar results when compared to measurements by weight in blood ($P = 0.99$). Sterilization by 25 kGy $\gamma$-irradiation did not cause significant changes ($P > 0.6$) in stent solubility, which was primarily volume and geometry-dependent. Under simulated intravascular flow conditions, 3\,mm stents dissolved completely with 2.7$\pm$1.3\,mL/mg (95\%CL).
The present invention provides a denatured albumin lamina, useful for repairing lesions on solid ... more The present invention provides a denatured albumin lamina, useful for repairing lesions on solid visceral organs. The lamina comprises human serum albumin, formed into a thin, pliant sheet and denatured. The denatured lamina can be sterilized and stored until used. As well, it can be impregnated with a variety of bioagents. A method for repairing a lesion on a solid visceral organ includes applying an energy-absorbing proteinaceous material to a lesion site on the solid visceral organ lesion; irradiating the proteinaceous material with energy sufficient to fuse the energy-absorbing material at least partially to the lesion site; applying a biocompatible denatured albumin lamina onto the proteinaceous material on the lesion site; and irradiating the biocompatible albumin lamina and the proteinaceous material with energy sufficient to fuse the biocompatible albumin lamina to the proteinaceous material and/or the lesion site. A laser solder can be deployed beneath the lamina to aid in welding it to the organ surface using laser light energy.
\textbf{Background and Objectives:} Despite numerous advances, lumpectomies remain a technically ... more \textbf{Background and Objectives:} Despite numerous advances, lumpectomies remain a technically challenging procedure and margin status is critical its success. Positive margins following lumpectomy usually lead to a second surgery to clear the margins. This not only increases morbidity but also prolongs the course of treatment and creates additional cost. A visible, spherical glowball of light centered on the lesion may not only be able to assist in locating the lesion but also in resecting it with uniform margins. \\[3mm] \textbf{Methods:} Eight patients underwent a light guided lumpectomy. Subjects with non-palpable breast lesions undergoing lumpectomy for breast malignancy with radiographic measurable disease were included in the study. Instead of a bare Kopans wire, an optical wire was designed that incorporated a Kopans wire with an optical fiber. \\[3mm] \textbf{Results:} The optical wires were placed in the same manner as a Kopans wire. During the light-guided lumpectomies, the optical fiber was illuminated and emitted a sphere of light surrounding the lesion. This light was used to localize and resect the lesion. Seven of eight light guided lumpectomies resulted in negative margins. \\[3mm] \textbf{Conclusions:} This procedure may result in a decrease in positive margins and in more uniformly spherical specimens. This could result in fewer procedures, reduced cost, and better cosmesis.
Systems and methods of utilizing a frequency modulation technique to determine an unknown distanc... more Systems and methods of utilizing a frequency modulation technique to determine an unknown distance between at least one source and at least one detector in an light scattering medium without knowing the optical properties of the medium are described. Modulated light is emitted from a light source to an optical scattering and absorbing medium and at least a portion of the modulated light is detected with a detector. A calibration factor is determined and then an unknown distance between at least one source and at least one detector can be determined, thereby providing a distance measurement.
The invention is for an optical wire lumpectomy (OWL) system. This system has three components: a... more The invention is for an optical wire lumpectomy (OWL) system. This system has three components: an optical wire, an optical fiber, and a light source. The optical wire is a replacement for the Kopans wire commonly used for wire-localized breast lumpectomies. The optical wire consists of a metallic hook, a translucent plastic tube, a crimping ring to retain the hook in the tube. A metallic wire is inserted into the tube to provide rigidity. Before surgery, the optical wire is placed by a radiologist with x-ray or ultrasonic guidance in exactly the same manner as a traditional Kopans wire. At surgery, the metallic wire is removed and an optical fiber is inserted into the optical wire. The optical fiber is coupled to a light source to create a glowball of light around a breast lesion. The glowball helps the surgeon find and remove the lesion.
We present a Monte Carlo method for propagating partially coherent fields through complex systems... more We present a Monte Carlo method for propagating partially coherent fields through complex systems using Monte Carlo sampling of Huygens-Fresnel fields. Using this method to generate an intemediate GreenÕs function allows significant improvement in performance. A Gaussian copula is used to synthesize a random source with an arbitrary spatial coherence function. Physical optics and Monte Carlo predictions of the first- and second-order statistics of the field are shown for the propogation of coherent and partially coherent sources through a limiting aperture and an f/1 imaging system. Convergence criteria are presented for judging the quality of the Monte Carlo predictions.
The primary absorber in dental resins is the photoinitiator, which starts the photo polymerizatio... more The primary absorber in dental resins is the photoinitiator, which starts the photo polymerization process. We studied the quantum yield of conversion of camphorquinone (CQ), a blue light photoinitiator, using 3M FreeLight LED and VIP lamps as the light curing units at 5 different irradiances. The molar extinction coefficient, $\varepsilon_{469}$, of CQ was measured to be 46$\pm$2\,cm$^{-1}$/(mol/L) at 469\,nm. We found that the reciprocity of irradiance and exposure time holds for the conversion of the photoinitiator CQ. That is, irradiance $\times$ the exposure time = radiant exposure is a constant. The relationship between the CQ absorption coefficient and the radiant exposure was the same for the 5 irradiances and fit an exponential function: $\mu_{a469}(H) = \mu_{ao} \exp(-H/H_{\mathrm{threshold}})$, where $\mu_{ao}$ is 4.46$\pm$0.05\,cm$^{-1}$, and $H_{\mathrm{threshold}}$=43$\pm$4\,J/cm$^2$. Combining this exponential relationship with CQ molar extinction coefficient and the absorbed photon energy (i.e., the product of the radiant exposure with the absorption coefficient), we plotted CQ concentration [number of molecules/cm$^3$] as a function of the accumulated absorbed photons per volume. The slope of the relationship is the quantum yield of the CQ conversion. Therefore, in our formulation (0.7 w\% CQ with reducing agents 0.35 w\% DMAEMA and 0.05 w\% BHT) the quantum yield was solved to be 0.07$\pm$0.01\, CQ conversion per absorbed photon.
Differential reflection measurements with side-by-side multimode optical fibers provides a method... more Differential reflection measurements with side-by-side multimode optical fibers provides a method to determine the relative absorption properties of optically turbid media such as skin that can be related by Beer's law. However, absolute values of absorption cannot be obtained without a better understanding of the effects of the optical scattering by the medium being measured. Using two 400\,micron diameter fibers, where one fiber emits light and both fibers collect light, we present results of measurements on varying concentrations of lipid emulsion, allowing us to change the scattering properties while keeping the absorption small, relative to scattering and constant. We use a Monte Carlo model (validated by the experimental results) to elucidate the average weighted path-length that collected photons travel for each fiber. We find that the difference between the two fibers in the average distance that collected light travels is constant for reduced scattering coefficients in the range of 10--100\,cm$^{-1}$. The differential reflectance has a non-linear relationship to the reduced scattering coefficient of the sample. We found that for tissues the scattering coefficient may be established using a linear fit of the differential reflectance in the spectral range of 675--800\,nm where the absorption coefficient is much smaller than the reduced scattering coefficient.
The present invention provides a denatured albumin lamina, useful for repairing lesions on solid... more The present invention provides a denatured albumin lamina, useful for repairing lesions on solid visceral organs. The lamina comprises human serum albumin, formed into a thin, pliant sheet and denatured. The denatured lamina can be sterilized and stored until used. As well, it can be impregnated with a variety of bioagents. A method for repairing a lesion on a solid visceral organ includes applying an energy-absorbing proteinaceous material to a lesion site on the solid visceral organ lesion; irradiating the proteinaceous material with energy sufficient to fuse the energy-absorbing material at least partially to the lesion site; applying a biocompatible denatured albumin lamina onto the proteinaceous material on the lesion site; and irradiating the biocompatible albumin lamina and the proteinaceous material with energy sufficient to fuse the biocompatible albumin lamina to the proteinaceous material and/or the lesion site. A laser solder can be deployed beneath the lamina to aid in welding it to the organ surface using laser light energy.
\textit{Objective:} This investigation was done in order to find optimal indocyanine green (ICG) ... more \textit{Objective:} This investigation was done in order to find optimal indocyanine green (ICG) concentration and energy irradiance in laser vascular welding. \textit{Background Data:} Many studies have shown that laser tissue welding with albumin solder/ICG may be an effective technique in surgical reconstruction. However, there are few report regarding optimal laser settings and concentrations of ICG within the albumin solder in laser-assisted vascular anastomosis. \textit{Methods:} Porcine carotid artery strips ($N=120$) were welded end-to-end by diode laser with 50\% albumin solder with 0.01, 0.1, and 1.0\,mM ICG and at irradiances of 27.7, 56.7, and 76.9\,W/cm$^2$, respectively. Temperature was measured by inserting thermocouples outside and inside the vessel. Tensile strength and histology were studied. \textit{Results:} Temperature and strength of the anastomosis significantly decreased (all $p<0.05$) with increasing ICG concentration at 56.7\,W/cm$^2$. Histological study showed minimal thermal injury limited to adventitia and no appreciable difference between all groups. \textit{Conclusions:} ICG concentration within solder is the most important factor affecting both vascular temperature and tensile strength. The optimal balance between strength and minimal thermal injury may be achieve primarily at 56.7\,W/cm$^2$ and 0.01\,mM ICG.
Evaluation of tissue fiber architecture is important for optimally engineering tissues. We prese... more Evaluation of tissue fiber architecture is important for optimally engineering tissues. We present a non-destructive reflection mode optical fiber system that is sensitive to the orientation of tissue fibers within the same plane as the surface of the tissue. Our system uses a single 1000 micron diameter optical fiber that is bifurcated to separate emitted from collected light. The face of the 1000 micron fiber is polished at a 65 degree angle to the central axis of the optical fiber for two reasons: to eliminate effects of specular reflections from the tissue/fiber-face interface and to give directionality to the light emitted into the tissue. We present results using this fiber system to measure 15 micron thick cross-sections of in vitro porcine heart muscle and full thickness ($\sim$2\,mm) digested aortic elastin rotated 360 degrees in 15 degree increments. These results are correlated to concurrent transmission measurements of small angle light scattering (SALS) recorded using a CCD camera to conclusively determine the orientation of the fibrous architecture of each tissue type. We show a 14\% peak-to-peak change in reflection signal on the heart muscle tissue and a 6\% peak-to-peak change on the digested elastin.
We present a new probe design that utilizes two different size diameter fibers with the face poli... more We present a new probe design that utilizes two different size diameter fibers with the face polished at a 65~degree angle to make independent diffuse light reflection measurements. The device consists of 200 and 1000~microns diameter fibers that measure the amount of diffuse light scattered back into the emitting fiber. Only one fiber emits and collects light at a time using a 632\,nm He-Ne laser source. Repeated measurements are presented of an epoxy block tissue phantom ($N=12$) and from in vivo skin ($N=13$) on the ventral side of the forearm. The new probe design is demonstrated to reduce measurement variability in the 1000~micron diameter fiber from a standard deviation of 1.5 percent down to 0.6 percent and for the 200 ~micron diameter fiber from a standard deviation of 7.3 percent, down to 1.2 percent, as compared to a prior probe design with fibers polished at 90~degrees. We also present measurements of a first surface mirror, which demonstrate a reduction in specular reflection noise collected by the 65~degree polished fibers. Finally, measurements are presented for an array of Intralipid and India ink tissue phantoms with optical properties in the range of tissues, where scattering ranges $13-28$\,cm$^{-1}$ and absorption ranges $0.1-1.6$\,cm$^{-1}$ at 632\,nm to show the ability to resolve changes in optical properties.
A theoretical model is presented for the sensitivity of a fluorescence-based molecularly imprinte... more A theoretical model is presented for the sensitivity of a fluorescence-based molecularly imprinted polymer (MIP) sensor. This sensor consists of a layer of MIP on a transparent substrate; the analyte binds in the MIP layer and is detected by fluorescence emission perpendicular to the layer surface. The MIP thickness, analyte concentration, and the optical absorption characteristics of the MIP are included in the model. To test the model, we fabricated urethane-based MIP sensors imprinted with anthracene. These sensors ranged in thickness from 100-2000~microns and had anthracene concentrations of 0-600~ppm. The theoretical prediction for fluorescence emission from these sensors showed excellent agreement and suggests that the theoretical model may be used to facilitate optical MIP sensor design. Finally, the rebinding rate for the MIP sensors was measured to be about 4\% of the theoretical number of imprinted sites or roughly six times the background binding rate of anthracene to non-imprinted polymers.
The purpose is to determine the absorption and reduced scattering coefficients of human skin in v... more The purpose is to determine the absorption and reduced scattering coefficients of human skin in vivo for wavelengths 250--400\,nm using a sized-fiber device. The method involves sized-fiber reflectance measurements that use two different diameter fibers at 200 and 600 microns, which independently emit and collect light. Reflectances for each fiber are converted to the absorption and reduced scattering coefficient based on Monte Carlo simulations. The device is validated using phantoms with known optical properties. Because the source fiber is also used to collect its emitted light, highly localized measurements of tissue are possible. Larger diameter fibers collect more light from deeper in the tissue. A device with 200 and 600 micron fibers collects light that travel less than 5 reduced mean free paths into the tissue. However for a 600 micron fiber, half of the returning photons travel less than 1.9 reduced mean free paths. For the 200 micron, this depth drops to 1.3 mean free paths. Due to the small sampling depth of this sized-fiber device, in vivo optical property measurements of the epidermis are possible with minimal interference from the dermis. We measured the optical properties of the epidermis of 10 individuals in vivo from 250--400\,nm from the ventral side of the forearm. At 400\,nm in wavelength, a typical reduced mean free path is 50 microns for human skin. Mineral oil is applied to the skin to fill voids in the stratum corneum. Results are presented as the wavelength dependent absorption and reduced scattering coefficients for the individuals where skin tones range from very fair to very dark skin. A comparison of our results and published ex vivo measurements is presented. We conclude with the advantages and disadvantages of localized fiber measurements and demonstrate the capability of this technique to determine optical properties at short wavelengths.
Sized-fiber reflectometry describes a device and method for determining the absorption and reduce... more Sized-fiber reflectometry describes a device and method for determining the absorption and reduced scattering properties of tissue. The device consists of two fibers with different diameters, 200 and 600 microns, that measure the amount of diffuse light scattered back into the emitting fiber. Only one fiber emits and collects light at a time. The diffuse light collected by a 200 micron fiber travels to a mean depth of 1.2 mean free paths while light travels to a mean depth of 1.9 mean free paths for a 600 micron fiber, where a mean free path is the mean distance of travel for a photon between scattering or absorption events. Localized in vivo reflectance for a spectrum of 380--800\,nm are presented for skin on the dorsal-side of the forearm with mild pressure induced erythema for six individuals. The skin tones vary from very fair to very dark skin. Absorption and reduced scattering coefficients are determined using a reflectance mapping for 200 and 600 micron fibers based on Monte Carlo simulations. The optical properties of the skin for each individual are presented for 5 wavelengths at 422, 514, 633, 650 and 797\,nm.
Video Reflectometry is a relatively simple technique to determine of the optical properties of b... more Video Reflectometry is a relatively simple technique to determine of the optical properties of biological tissues. The video image captures the spatially resolved diffuse reflectance, $R_d(r)$, generated by a narrow light beam normally incident on the surface of the tissue. The video system uses a CCD camera in combination with optical density filters that allows recording of the reflectance signal over a large dynamic range. In this paper, we describe the theoretical framework for evaluating experimental measurements using Monte Carlo simulations. The influence of various factors on the derived optical properties is presented. The specific factors explored are (1) mis-focusing of the camera on the surface, (2) tilting of incident beam, (3) finite beam diameter. We present experimental results of the performance of the system on using Teflon disks as optical standards. Finally, we report on the effect of the reading direction of CCD pixels on the profile of diffuse reflection curves.
\textbf{Introduction}: Photocured polymers are widely used in dental applications and as tissue... more \textbf{Introduction}: Photocured polymers are widely used in dental applications and as tissue engineering constructs. The physical and mechanical properties of the composite change during curing; the appearance of the composite also changes. This talk summarizes insights gained into the photopolymerization process by quantitatively monitoring appearance.\\[3mm] \textbf{Methods}: The composite were 50:50 weight ratio of BIS-GMA:TEGDMA mixed with various sizes of strontium glass as filler and different concentrations (0--0.175 wt\%) of camphorquinone (CQ). The curing irradiance was 100--400\,mW/cm2. Total reflection and total transmission spectra of filled and unfilled 1\,mm thick composite samples were measured before and after curing. Total transmittance was measured every 50\,ms from 400--900\,nm during curing. The refractive index of the unfilled resins was also measured during curing using an Abb{\'e} refractometer. Before and after reflectance and transmittance values were converted to scattering and absorption properties using the inverse adding-doubling technique. Transmission data during curing was analyzed by using red light to monitor changes in scattering and blue light to assess changes in absorption.\\[3mm] \textbf{Results}: The absorption spectrum of uncured composite measured matched the absorption spectrum of CQ in unfilled resin. Uncured composite with and without CQ had the same scattering coefficient spectrum. The absorption and scattering coefficient at 469\,nm of composites with five different CQ concentrations decayed exponentially as a function of radiant exposure. The refractive index increased with radiant exposure.\\[3mm] \textbf{Conclusion}: The optical properties of a composite affect the light distribution within the composite during curing. Changes is absorption are caused by changes in CQ absorption. Mie scattering calculation indicate that scattering changes are directly attributable to index of refraction changes of the resin during curing.
Depth of cure of composites is a function of light transport through the material as it polymeriz... more Depth of cure of composites is a function of light transport through the material as it polymerizes. Objectives: To measure the scattering and absorption properties of unfilled resins and composites during photo-activated curing. Methods: The composite was 50:50 weight ratio of BIS-GMA:TEGDMA mixed with 25 wt\% strontium glass (avg.\ 2 micron). The total reflection and total transmission spectra of unfilled resin and composite samples (1\,mm thick $\times$ 25\,mm diameter) were measured during light curing (150mW/cm$^2$ for varied times). The composites were prepared with six different concentrations (0, 0.044, 0.058, 0.088, 0.116, and 0.175 wt\%) of camphorquinone (CQ). The refractive index of the unfilled resins with four equivalent CQ concentrations was measured during curing with an Abbe refractometer. Results: The absorption spectrum of uncured composite matched the absorption spectrum of CQ in unfilled resin. Uncured composite with and without CQ had the same scattering coefficient spectrum. The extinction coefficient of CQ in composite was 4:5$\pm$0.1mm$^{-1}$/(mol/L), equal to that of CQ in unfilled resin. The absorption and scattering coefficients at 469\,nm of composites with five different CQ concentrations decayed exponentially as a function of radiant exposure (figure). The refractive index increased with radiant exposure; Mie scattering calculations suggest that the index of refraction changes are responsible for scattering changes in the composite. Conclusion: The optical properties of a composite affect the light distribution within the composite during curing. Changes in absorption are caused by changes in CQ absorption. Changes in scattering are directly attributable to index of refraction changes of the resin during curing. Supported by NIH/NIDCR Grant 1R21-DE016758.
Reciprosity, i.e. equal cure based on equal radiant exposure (mJ/cm$^2$) independent of exposur... more Reciprosity, i.e. equal cure based on equal radiant exposure (mJ/cm$^2$) independent of exposure time/irradiance, has in general been shown to hold for dental composites, but with limitations. Objective: To develop depth of cure profiles to determine the limits of reciprosity for experimental dental composites having varied monomer content, photoinitiator type, and filler shape. Methods: Composites were produced with Bis-GMA:TEGDMA of 50:50, 70:30, and 90:10 with camphoroquinone (CQ)/EDMAB (1:2) or PPD (1:2; 50:50 mixture); and 62 wt\% spherical or irregular 0.4\,$\mu$m silanated glass. The same radiant exposure (5730 mJ/cm$^2$) was used to cure composites (15 mm diameter x 10 mm deep) using a Demi light (10 mm tip; Kerr) at (573 mW/cm$^2$) for 10 seconds and comparing with the same light transmitting through neutral density filters (72 mW/cm$^2$) for 80 seconds. The relatively low radiant exposure was chosen to accentuate the differences between the composites. After 24 hours, the specimens were bisected with a diamond saw and polished. Knoop Hardness (KHN) measurements were made (100 g; 15 seconds) in equidistant 1 mm squares across the width and depth (n=3/group). Regression was used to determine reciprosity (slope near 1.0 for plot of KHN 10s vs 80s). Results: Reciprosity was evident for the 70:30 and 90:10 resins (see figure-left) at nearly all measurable depths. Reciprosity only held for the 50:50 resin with CQ at 4 mm, but up to 3 mm with PPD (see figure-right). When reciprosity did not hold, longer exposure time tended to produce increased hardness at greater depths. Overall, reciprocity was less evident for composites with irregular compared to spherical fillers. Conclusions: Reciprosity was a function of monomer composition, being most evident for composites of higher viscosity (i.e. more bis-GMA), especially with spherical fillers. Longer exposure with lower irradiance was more effective for achieving depth of cure. Supported by NIH/NIDCR 1R21DE016758
The goal of the present work is to characterize theoretically and experimentally a simple two-fib... more The goal of the present work is to characterize theoretically and experimentally a simple two-fiber optic probe for spectroscopy applications in turbid biological media such as human skin. First, we perform a review of the wavelength dependence of optical parameters of this tissue. The validity of the diffusion approximation is evaluated for a simple model of skin in term of the restriction that scattering should dominate over absorption. The spectral bands where the diffusion theory fails are found for this model. Second, radially-resolved diffuse reflectance is compared using both Monte Carlo and the diffusion techniques. The optimal source-detector distance that minimizes errors is identified. In addition, a two-fiber optic probe was built and characterized to record spectra from in-vivo skin and phantoms mimicking some interesting real situation and in-vivo spectra from volunteers are used to evaluate an algorithm to extract intrinsic tissue optical properties. The derived optical properties are presented.
\textit{Objectives}: Since photoinitiator systems for dental resins based on camphorquinone (CQ)... more \textit{Objectives}: Since photoinitiator systems for dental resins based on camphorquinone (CQ) present color disadvantages, trimethylbenzoyl-diphenyl-phosphine oxide (TPO) could be a substitute. However, there are remaining considerations about its curing efficiency. The aims of the present investigation were: to characterize the relationship between the photoinitiator absorption spectra and the light spectrum emitted from a QTH light (Absorbed power density, PD$_{\mathit{abs}}$); and to evaluate the kinetics of polymerization and the degree of conversion (DC) at different depths for unfilled and filled dimethacrylate resins.\\[3mm] \textit{Methods}: CQ+EDMAB (control); TPO and TPO+EDMAB were used in 50:50 Bis-GMA/TEGDMA resins. Photoinitiator absorption and QTH-light emission were evaluated using a spectrophotometer, kinetics of polymerization with differential scanning calorimetry (DSC), and DC at top and bottom surfaces of 2\,mm thick discs via FTIR ($n=3$). One way ANOVA/Tukey's ($p<0.05$) was used to analyze the results from DSC and two-way ANOVA/Tukey's ($p<0.05$) for those from FTIR.\\[3mm] \textit{Results}: CQ presented higher PD$_{\mathit{abs}}$ than TPO (364 and 223\,mW/cm$^3$, respectively). The DSC revealed that TPO and TPO+EDMAB produced a faster reaction than CQ+EDMAB. There were no differences for DC among the photoinitiators for unfilled materials, whereas only the combination TPO+EBMAB was able to produce similar DC as CQ+EDMAB for filled materials.\\[3mm] \begin{tabular}{l|cccccc} Group tested & \multicolumn{2}{c}{DC(\%) and $R_P^{\mathit{max}}$ (\%/s) by DSC} & \multicolumn{2}{c}{DC(\%) by FTIR in unfilled resins} & \multicolumn{2}{c}{DC(\%) by FTIR in composites}\\ \hline & DC & $R_P^{\mathit{max}}$& Surface & 2\,mm depth & Surface & 2\,mm depth\\ CQ+EDMAB & $59\pm1^b$ & $3.8\pm0.0^b$ & $70\pm2$ & $73\pm4$ & $54\pm1^a$ & $52\pm3^a$\\ TPO & $62\pm1^a$ & $6.0\pm0.2^a$ & $70\pm3$ & $69\pm1$ & $48\pm2^b$ & $46\pm1^b$\\ TPO+EDMAB & $64\pm2^a$ & $6.6\pm0.4^a$ & $72\pm2$ & $70\pm3$ & $56\pm2^a$ & $51\pm4^a$\\ \hline \multicolumn{7}{l}{\it Different lower case letters in each column means statistically significant differences.} \end{tabular} \vskip2mm \textit{Conclusions}: CQ presented higher PD$_{\mathit{abs}}$ than TPO, but TPO exhibited higher reactivity. DC was similar for unfilled resins. For composites, TPO alone produced lower DC, but the combination TPO+EDBMA produced similar DC as CQ+EDMAB at the surface and 2\,mm deep.
We compare the anisotropy factor of mixed scatterers using simple theoretical model with direct e... more We compare the anisotropy factor of mixed scatterers using simple theoretical model with direct experimental validation. Two different mixtures of microspheres were used. The scattering anisotropy, absorption and scattering coefficients for monodisperse samples were derived from unscattered light transmission, and total transmission and total diffuse reflection using the Inverse Adding-Doubling method. The monodisperse samples were mixed in different ratios and the optical properties of the mixtures were found. By comparing the analytical Mie theory values for the optical properties with the experimental results, we can estimate the limits of applicability of the proposed model for the scattering anisotropy.
Characterization of the multiscale scatter properties is essential for an understanding of the un... more Characterization of the multiscale scatter properties is essential for an understanding of the underlying structural organization of biological tissues. Such characterizations will lead to improved diagnoses and new imaging concepts. We present a particularly simple means of performing the requisite scatter measurements with a differential interference contrast microscope. The resulting characterization is in terms of spatially resolved maps of the (polar and azimuthal) angular ray deviations of the scattered light. With such data, tissues can be characterized in terms of their first and second order scatter properties. We discuss a simple means of calibrating a DIC microscope, the measurement procedure and quantitative interpretation of the ensuing data. First and second order statistics are presented for a variety of tissue types.
Hemorrhage from injuries of solid organs, such as liver, spleen and kidney is commonly difficult ... more Hemorrhage from injuries of solid organs, such as liver, spleen and kidney is commonly difficult to control using conventional suture or electrocautery. In our laboratory, a 38% albumin associated with argon ion beam coagulation applied to liver resection to seal the active bleeding surface of the liver. This study investigated the long-term host response to the concentrated albumin used in the liver repairs.
Successful laser-assisted tissue welding was implemented to provide proper weld strength with min... more Successful laser-assisted tissue welding was implemented to provide proper weld strength with minimized tissue thermal injury. We investigated and compared the weld strengths and morphologic changes in porcine small intestinal submucose (SIS) and porcine ureteral tissues with various concentration of indocyanine green (ICG) and with a solid albumin sheet. The study showed that the tissues were welded at lower ICG concentration (0.05\,mM) with minimized tissue thermal damage using an 800\,nm wavelength diode laser.
Mass removal experiments have been performed at the Oregon Medical Laser Center with 10 to 100\,m... more Mass removal experiments have been performed at the Oregon Medical Laser Center with 10 to 100\,mJ one microsecond laser pulses at optical wavelengths. Above the energy threshold for bubble formation, the laser mass ablation efficiency ($\mu$g/mJ) for removal of gel surrogate thrombus is nearly constant for a given experimental geometry and gel absorption coefficient. The efficiency in 'contact' experiments, in which the optical fiber delivering the energy is in close proximity to the absorbing gel, is approximately three times that of 'non-contact' experiments, in which the optical fiber is approximately 1\,mm from the gel. Mass removal occurs hundreds of microseconds after the laser deposition. Experimental data and numerical simulations are consistent with the hypothesis that jet formation during bubble collapse plays a dominant role in mass removal. This hypothesis suggests a model in which the mass removed scales linearly with the maximum bubble volume and explains the distinctive features, including the magnitude, of the mass removal.
We compare Los Alamos numerical simulations with Oregon Medical Laser Center laser deposition exp... more We compare Los Alamos numerical simulations with Oregon Medical Laser Center laser deposition experiments conducted with gelatin thrombus surrogates specifically chosen for relevance to clinical laser thrombolysis. Initial idealized calculations suggest that a surprisingly large fraction of the absorbed laser energy appears as acoustic radiation. We build on these results here by investigating geometrical affects, material property variations, and sources of dissipation including viscosity and plastic flow, as well as acoustic radiation, in an effort to explain flow effects observed in the experiments. In particular, strong jetting is observed in the simulations when the gelatin is given a kinematic viscosity in excess of approximately 1.0\,cm$^2$/s. Jetting is clearly evident in the experiments.
A recurring problem in laser applications is estimating the thermal response of target tissues to... more A recurring problem in laser applications is estimating the thermal response of target tissues to laser irradiation. This typically involves using an optical model to determine the distribution of absorbed laser energy and then using a thermal model to establish the temperature during and after laser irradiation. To avoid such modelling and yet allow one to obtain fast, accurate estimates of temperature, a series of charts for laser irradiation of semi-infinite homogeneous media with adiabatic boundaries is presented. These charts were created using analytic solutions of the temperature for absorbing-only media with simple pulsed source geometries. Through the use of non-dimensional parameters, these charts allow one to make rapid estimates of the spatial and temporal thermal distributions following laser irradiation for arbitrary pulse durations and absorption coefficients.
PUVA therapy may prove effective in preventing restenosis of vessels following balloon angioplast... more PUVA therapy may prove effective in preventing restenosis of vessels following balloon angioplasty to open vessels narrowed by atherosclerosis. The technique relies on the ability of PUVA (psoralen administration followed by ultraviolet A irradiation) to cause crosslinks and monoadducts that prevent cellular proliferation without causing cell death. Such PUVA treatment has been successful in controlling cutaneous cell proliferation of psoriasis. The efficacy of PUVA treatment depends on the drug concentration and the light dose. The amount of light delivered is easily modified to adapt to variations in the drug concentration if the drug levels in the vessel wall are known. This paper demonstrates the feasibility of assaying psoralen levels in tissues and in serum samples using psoralen fluorescence as an indictor.
Pulsed Photothermal Radiometry (PPTR) measures blackbody radiation emitted by a sample after abso... more Pulsed Photothermal Radiometry (PPTR) measures blackbody radiation emitted by a sample after absorption of an optical pulse. A method for analyzing PPTR signals has been developed which extracts the internal heat source distribution from measurements of the surface temperature. This method is applicable to materials with uniform thermal properties, but having optical properties which vary as a function of depth. A robust algorithm has been obtained using singular value decomposition. This algorithm has been validated using agar-gelled phantoms containing various mixtures of dye and scatterers. PPTR measurements using 630\,nm light were made on ten subjects whose skin was exposed to twice their minimum erythma dose of mid-ultraviolet light. Measurements were made on both exposed and unexposed skin sites on days 2, 5, 10, 15 and 20 following exposure. Since the dominant absorber in skin at 630\,nm is melanin, the internal heat source distribution should be directly related to the melanin profile. These profiles are compared with diffuse reflection measurements and with each subject's minimal erythema dose.
A method is described for finding the optical properties (scattering, absorption, and scattering ... more A method is described for finding the optical properties (scattering, absorption, and scattering anisotropy) of a slab of turbid material using reflection and transmission measurements. Previously, it has been difficult or impossible to quantify a method's intrinsic error due to restrictions on the boundary conditions, the scattering anisotropy, the ratio of scattering to absorption, or the thickness of the slab. By eliminating these constraints, the inverse adding-doubling method is applicable to turbid media with any optical thickness, albedo, or phase function and its intrinsic error may be quantified. \vskip2mm The method assumes normal irradiance of a homogeneous turbid slab. The slab may have anisotropic scattering and a different index of refraction from its surroundings. The slab may or may not be bounded by glass. The optical properties are obtained by iterating an adding-doubling solution of the radiative transport equation until the calculated values of the reflection and transmission match the measured ones. Exhaustive numerical tests show that the intrinsic error of the derived optical properties is less than 1\% when the reflection and transmission values are greater than 5\%. Experimental work with Intralipid-10\% phantoms supports these bounds.
The optical properties of human aorta were measured during low power argon laser irradiation ($\s... more The optical properties of human aorta were measured during low power argon laser irradiation ($\sim$100\,mW/mm$^2$). The delta-Eddington optical model was iterated to determine the optical properties. The results indicated that the transport albedo was nearly constant (~0.96) until the onset of tissue charring, after which it decreased quickly. The optical depth gradually declined (after an abrupt initial increase) until tissue charring when it dropped sharply. The anisotropy dropped initially and increased linearly with time of exposure.
The purpose of this research was to establish the theoretical temperature distribution and ablati... more The purpose of this research was to establish the theoretical temperature distribution and ablation characteristics in atherosclerotic plaque resulting from both direct argon laser irradiation and the application of a metal contact probe. The plaque was assumed to be a single-layered homogeneous medium, and the laser light distribution within the tissue was calculated using a delta-Eddington approximation. One dimensional temperature distributions and ablation depths were calculated using an immobolized finite element method. Thermal and optical properties of the tissue were assumed to remain constant. Ablation front positions and temperature profiles at times prior to ablation, at the onset of ablation, and during the ablation process were calculated for both modalities. Additionally, ablation velocities were calculated as a function of both tissue water content and heat flux transmitted through the metal probe tip. For the typical operating conditions used, calculated values agreed qualitatively with experimental results. Temperature calculations after the onset of ablation indicated high sub-surface temperature rises beyond the surface threshold temperature for the direct irradiation case but monotonically decreasing profiles for the metal probe. However, deeper within the tissue, calculated temperatures appeared to be higher for the probe than for direct irradiation.
A thermal washout technique is being developed which measures perfusion form the tissue surface. ... more A thermal washout technique is being developed which measures perfusion form the tissue surface. This perfusion measurement is similar to other indicator washout techniques. The basic approach is to apply a heat source to the surface of a tissue for exactly 60 seconds. The heat source is then removed and the temperature recovery is monitored with a calibrated thermal camera. Blood flow significantly affects local heat transfer making this technique quite sensitive. Highly perfused tissue will absorb more heat and, hence will have a smaller temperature increase and a faster recovery back to baseline. \vskip2mm The finite element numerical method is used to model the heat transfer problem with realistic geometries and boundary conditions. The relationship between the actual perfusion and the measured temperature response is determined using both analytical and numerical techniques. It is important that the boundary and initial conditions be carefully controlled and monitored during both the warming and cooling phases. \textit{In vivo} experiments with alcohol fixed canine kidneys demonstrate the feasibility of the technique. The disturbing factors include: uncertainty of the temperature measurement, uncertainty of the time measurement, baseline temperature gradients, and perfusion gradients.
A thermal washout technique is capable of measuring perfusion from the tissue surface. A cold app... more A thermal washout technique is capable of measuring perfusion from the tissue surface. A cold applicator is held on the tissue for 60 seconds. During this time the tissue surface is cooled. The applicator is removed, and a thermal camera is used to monitor the rewarming of the tissue surface. Since blood flow significantly affects local heat transfer, this technique is quite senstive. Tissue with a high perfusion can sink more heat, hence will have a smaller initial temperature change and a faster recovery back to baseline.
Two numerical solutions for radiative transport in tissue are presented: the Monte Carlo and the ... more Two numerical solutions for radiative transport in tissue are presented: the Monte Carlo and the adding-doubling methods. Both methods are appropriate for tissues with internal reflection at boundaries and anisotropic scattering patterns. The adding-doubling method yields accurate solutions in one-dimension. The slower Monte Carlo method is the only exact solution available for finite beam irradiance of tissue. Convolution formulas for calculation of fluence rates for circularly symmetric flat and Gaussian irradiances using the Monte Carlo impulse response are presented.
This chapter describes a technique for extracting an internal thermal profile using measurements ... more This chapter describes a technique for extracting an internal thermal profile using measurements of the surface temperature. The method is applicable to materials and tissues with uniform thermal properties and non-uniform optical properties. The technique is based on singular value decomposition and works reasonably well down to depths of about 500\,$\mu$m. The uncertainty in the location of the internal temperature layers grows linearly with the depth of the layer. The inversion algorithm is tested using computer simulations and experiments on colored glass. Analysis of \textit{in vivo} data from a tanning experiment on human skin is presented to show the potential of the technique.
The diffusion approximation of the radiative transport equation is used extensively because close... more The diffusion approximation of the radiative transport equation is used extensively because closed-form analytical solutions can be obtained. The previous chapter gave closed-form solutions to the one-dimensional diffusion equation. In this chapter, the classic searchlight problem of a finite beam of light normally incident on a slab or semi-infinite medium will be solved in the time-independent diffusion approximation. The solution follows naturally once the Green's function for the problem is known, and so the Green's function subject to homogeneous Robin boundary conditions will be given for semi-infinite and slab geometries. The diffuse radiant fluence rates are then found for impulse, flat (constant), and Gaussian shaped finite beam irradiances. \vskip2mm How do Green's functions help solve the problem of a finite beam incident on a turbid medium? As unscattered light propagates through the medium, it is scattered and becomes diffuse. This initial scattering event acts as a source of diffuse light. The Green's function describes the distribution resulting from a point source of diffuse light. Since the unscattered light decays exponentially with increasing depth in the slab, the Green's function for an irradiation point on the surface may be obtained by convolving the Green's function with the proper exponential function. Again using superposition, the response for an arbitrary source distribution is obtained by adding the contributions of all point irradiances. This description is not quite complete because it neglects the contribution from boundary conditions, however the analytic derivation in this chapter is complete. \vskip2mm The solutions for the searchlight problem are expressed as definite integrals or infinite series. There are a number of possible ways of obtaining solutions to the diffusion equation. Green's functions for a slab geometry [Reynolds 1976] have been known for some time. Somewhat surprisingly, the Green's function for a semi-infinite medium is not readily available in the literature and is included for completeness. The solutions for the semi-infinite and slab geometries are extended to include exponentially attenuating line sources. Finally, we present equations for calculating the internal fluence rates for finite beam irradiances (flat top and Gaussian) on slab and semi-infinite media with inhomogeneous Robin boundary conditions. \vskip2mm To avoid the usually complicated expressions that arise in solutions for a semi-infinite geometry, some authors use monopole and dipole methods. Both techniques generate solutions that satisfy the diffusion equation at the expense of satisfying the boundary conditions. The solutions and compromises inherent in using the dipole and monopole techniques are briefly discussed.
This chapter describes the adding-doubling method for solving the radiative transport equation. T... more This chapter describes the adding-doubling method for solving the radiative transport equation. The advantages and disadvantages of the method are presented, followed by sections describing its theory and computer implementation. A detailed example is given with intermediate numerical results. Accurate tables with values of reflection and transmission for slabs of varying thicknesses with mismatched boundaries are given.
W{\"a}re Gewebe ein ausschlie\ss lich lichtabsorbierendes und nicht lichtstreuendes Medium, so k{... more W{\"a}re Gewebe ein ausschlie\ss lich lichtabsorbierendes und nicht lichtstreuendes Medium, so k{\"o}nnte die r{\"a}umliche Lichtverteilung bei einer Laserbestrahlung mit Hilfe einer einfachen exponentiellen D{\"a}mpfung beschrieben werden. In diesem Fall w{\"a}re Dosimetrie einfach. Wir wissen jedoch, da{\ss}Gewebe ein tr{\"u}bes Medium ist und Licht streut. Vernachl{\"a}ssigt man die Streuung des Lichtes, so weicht die angenommene Lichtverteilung im Gewebe wesentlich von der wirklichen Lichtverteilung ab.\ Direkt unter der Oberfl{\"a}che kann die auf das Gewebe fallende Lichtintensit{\"a}t infolge von Streuprozessen im Inneren erh{\"o}ht werden, so da{\ss}mehr Licht f{\"u}r Absorption verf{\"u}gbar ist. Besonders in einem Wellenl{\"a}ngenbereich, in dem das Material wenig absorbiert (bei vielen Geweben zwischen 600\,nm und 1500\,nm), kann infolge von Streuprozessen die auftreffende Lichtintensit{\"a}t um einen Faktor 2 bis 3 zunehmen. In Hohlraumorganen, wie z.B. der Harnblase, kann die auf das Gewebe fallende Lichtintensit{\"a}t noch weiter ansteigen (Faktor 4 bis 7). Streuung erh{\"o}ht auch seitlich des einfallenden Lichtstrahls die verf{\"u}gbare Lichtintensit{\"a}t. Wie wesentlich Streuprozesse bei der Lichtausbreitung (im Gewebe) sind, h{\"a}ngt ab von Streu- sowie Absorptionseigenschaften, dem Brechungsindex des Gewebes und dem Durchmesser des Laserstrahls. Der Sinn de Kapitels ist es, den Einflu{\ss}der Streuung auf die Lichtverteilung im Gewebe zu demonstrieren. Die Diskussion soll sich im wesentlichen auf Abbildungen konzentrieren und weniger eine mathematische Beschreibung der Probleme darstellen; dennoch werden einige mathematische Definitionen angegeben. \vskip2mm Innerhalb des Wellenl{\"a}ngenbereichs der klinischen Lasermedizin (etwa 193\,nm bis 10600\,nm) kann der Absorptionskoeffizient des Gewebes stark variieren, wobei der Streukoeffizient monoton mit steigender Wellenl{\"a}nge abnimmt. Das Verh{\"a}ltnis der Koeffizienten {\"a}ndert sich ebenfalls wesentlich mit der Wellenl{\"a}nge des Laserlichts. Abb.\ 1 zeigt ein Beispiel der Abh{\"a}ngigkeit der Absorption und Streuung von der Wellenl{\"a}nge in vaskul{\"a}rem Gewebe. Abb.\ 1c stellt die Albedo (das Verh{\"a}ltnis aus Streukoeffizienten zur Summe von Streu- und Absorptionskoffizient) von vaskul{\"a}rem Gewebe {\"u}ber der Wellenl{\"a}nge dar.
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Papers by Scott Prahl