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Biomedical subjects

S L Jacques

Publications and source records attributed to S L Jacques.

At least 37 records · Page 2Linked to original sources
PubMed1996

Melanin granule model for laser-induced thermal damage in the retina.

An analytical model for thermal damage of retinal tissue due to absorption of laser energy by finite-sized melanin granules is developed. Since melanin is the primary absorber of visible and near-IR light in the skin and in the retina, bulk heating of tissue can be determined by superposition of individual melanin granule effects. Granules are modeled as absorbing spheres surrounded by an infinite medium of water. Analytical solutions to the heat equation result in computations that are quick and accurate. Moreover, the model does not rely on symmetric beam profiles, and so arbitrary images can be studied. The important contribution of this model is to provide a more accurate biological description of sub-millisecond pulse exposures than previous retinal models, while achieving agreement for longer pulses. This model can also be naturally extended into the sub-microsecond domain by including vaporization as a damage mechanism. It therefore represents the beginning of a model which can be applied across the entire pulse duration domain.

Animals↗
PubMed1996

Finite element analysis of temperature controlled coagulation in laser irradiated tissue.

The Theoretical study of thermal damage processes in laser irradiated tissue provides further insight into the design of optimal coagulation procedures. Controlled laser coagulation of tissue was studied theoretically using a finite element method with a modulating laser heat source to simulate feedback controlled laser delivery with a constant surface temperature. The effects of uncertainty in scattering and absorption properties of the tissue, thermal denaturation induced changes in optical properties, and surface convection were analyzed. Compared to a single pulse CW irradiation in which a doctor would presumably stop CW laser delivery after noticing some effect such as vaporization or carbonization, the constant surface temperature scenario provided a better overall control over the coagulation process. In particular, prediction of coagulative damage in a constant temperature scenario was less sensitive to uncertainties in optical properties and their dynamic changes during the course of coagulation. Also, subsurface overheating under surface convective conditions could be compensated for under constant temperature irradiation by lowering the surface temperature.

Animals↗
PubMed1995

MCML--Monte Carlo modeling of light transport in multi-layered tissues.

A Monte Carlo model of steady-state light transport in multi-layered tissues (MCML) has been coded in ANSI Standard C; therefore, the program can be used on various computers. Dynamic data allocation is used for MCML, hence the number of tissue layers and grid elements of the grid system can be varied by users at run time. The coordinates of the simulated data for each grid element in the radial and angular directions are optimized. Some of the MCML computational results have been verified with those of other theories or other investigators. The program, including the source code, has been in the public domain since 1992.

Absorption↗
PubMed1995

Infrared video imaging of subsurface vessels: a feasibility study for the endoscopic management of gastrointestinal bleeding.

The feasibility of infrared video imaging of subsurface vessels in the stomach was investigated both experimentally and in more detail using computer simulations of light propagation. Infrared video imaging was first attempted in several experimental situations. Images of a human arm illuminated with infrared light (wavelength > 700 nm) revealed subcutaneous venous structures not revealed by visible light (wavelength of 500 to 600 nm). An infrared-sensitive video endoscope was used to view both a human arm and normal stomach wall. Infrared illumination within the stomach enhanced only the larger subsurface vessels. Infrared transillumination of a rat skin flap window chamber allowed video recording of images during injection of an absorbing dye, indocyanine green, into the blood volume and showed that indocyanine green can enhance the contrast in infrared images of small vessels. Computer simulations of vessels of varying depths and sizes indicated successful detection was possible by infrared imaging. Computer simulations demonstrated that the shadow caused by an imaged subsurface vessel has two characteristics: (1) the central loss of reflectance, which indicates the size of the vessel, and (2) the full-width half-maximum of the reflectance loss, which indicates the depth of the vessel. The simulations further suggested that images of small vessels can be dramatically enhanced (68-fold) by indocyanine green, which attenuates the transmittance of scattered light from behind the vessels to the surface for observation. On the other hand, indocyanine green enhances the contrast of large vessels to a lesser degree (2.6-fold). The ultimate goal is to develop an endoscopic video imaging system capable of capturing reflected light from the stomach wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

The influence of boundary conditions on the accuracy of diffusion theory in time-resolved reflectance spectroscopy of biological tissues.

The applicability of diffusion theory for the determination of tissue optical properties from time-resolved reflectance spectroscopy is investigated. Analytical expressions from diffusion theory using the three most commonly assumed boundary conditions at the air-tissue interface are compared with time-resolved Monte Carlo simulations and measurements on tissue phantoms. The effects of the choice of the boundary conditions on the accuracy of the findings for the optical parameters are quantified, and criteria for accurate curve-fitting algorithms are developed.

Algorithms↗
PubMed1995

In vivo autofluorescence of an unpigmented melanoma in mice. Correlation of spectroscopic properties to microscopic structure.

Recently, fluorescence spectroscopy and imaging have been under investigation for in vivo diagnosis of several types of superficial cancer, including primary melanomas of the skin. Here we report on a detailed investigation of the autofluorescence properties of a K1735P melanoma implanted intradermally in the ears of syngeneic C3H/HeN mice. Although this tumour can produce melanin in some cases, it appeared as an unpigmented lesion in our experiments. Excitation-emission maps in the wavelength range of 360-700 nm were recorded from tumours and normal ears. The control ears and the tumour-bearing ears showed fluorescence in a broad range of excitation and emission wavelengths. Valleys of decreased fluorescence were observed in the 385-425 nm range and could be related to absorption of the excitation light by haemoglobin, oxyhaemoglobin and a third unknown absorber. The spectroscopic differences between the malignant melanoma and the control skin could be related to either differences in blood oxygenation or the tissue dimensions. However, no spectroscopic features were detected reflecting intrinsic differences between the melanoma and normal tissue.

Animals↗
PubMed1995

Influence of blood vessels on the measurement of hemoglobin oxygenation as determined by time-resolved reflectance spectroscopy.

We report the development of a heterogeneous resin-tube model to study the influence of blood vessels on the apparent absorption of the system, mu a(sys), using a time-resolved technique. The experimental results show that mu a(sys) depends on the absorption inside the tubes, mu a(tube), tube diameters, and tube-to-sample volume ratios. A mathematical expression relating mu a(sys) and mu a(tube) is derived based on the experimental results and is verified by time-resolved Monte Carlo simulations for heterogeneous models. This analytical formula predicts that the apparent absorption coefficient measured on a biological organ is a volume-weighted sum of the absorption coefficients of different absorbing components. We present some apparent absorption coefficients measured in vivo in animals and humans and discuss improved algorithms that calculate the hemoglobin saturation by including background-tissue absorption and blood vessel distribution.

Blood Vessels↗
PubMed1995

Dynamic epidermal cooling during pulsed laser treatment of port-wine stain. A new methodology with preliminary clinical evaluation.

BACKGROUND AND DESIGN: The clinical objective in the treatment of a patient with port-wine stain (PWS) undergoing laser therapy is to maximize thermal damage to the PWS, while at the same time minimizing nonspecific injury to the normal overlying epidermis. With dynamic cooling, the epidermis can be cooled selectively. When a cryogen spurt is applied to the skin surface for an appropriately short period of time (on the order of tens of milliseconds), the cooling remains localized in the epidermis, while leaving the temperature of the deeper PWS vessels unchanged. RESULTS: Comparative measurements obtained by a fast infrared imaging detector demonstrated that the surface temperature prior to laser exposure could be reduced by as much as 40 degrees C using the dynamic cooling technique. No skin surface textural changes were noted on PWS test sites cooled with a 20- to 80-millisecond cryogen spurt after flashlamp-pumped pulsed dye laser (FLPPDL) exposure (lambda = 585 nm; tau p = 450 microseconds) at the maximum light dosage possible (10 J/cm2). In contrast, epidermal necrosis occurred on the uncooled sites after such exposure. Six months after laser exposure, clinically significant blanching on the cooled sites indicates laser photothermolysis of PWS blood vessels did occur. CONCLUSIONS: Our preliminary experiments demonstrate the feasibility of selectively cooling the normal overlying epidermis without affecting the temperature of the deeper PWS vessels. Furthermore, protection of the epidermis from thermal injury, produced by melanin light absorption at clinically relevant wavelengths, can be achieved effectively. An additional advantage of dynamic epidermal cooling is reduction of patient discomfort associated with FLPPDL therapy. Further studies are under way to determine an optimum strategy for applying this dynamic cooling technique during pulsed laser treatment of patients with PWS and others with selected dermatoses (dermal melanocytic lesions and tattoos).

Absorption↗
PubMed1994

Error estimation of measuring total interaction coefficients of turbid media using collimated light transmission.

The error of measuring the total interaction coefficients of turbid media using collimated light transmission was estimated with an analytical expression, which was verified with accurate Monte Carlo simulations. The expression is based on the Henyey-Greenstein phase function of scattering and the probabilities of non-scattered and singly scattered photons transmitted through a tissue slab with a unit anisotropy factor.

Anisotropy↗
PubMed1994

Photodynamic therapy with photofrin II induces programmed cell death in carcinoma cell lines.

The mode of cell death following photodynamic therapy was investigated from the perspective of programmed cell death or apoptosis. Human prostate carcinoma cells (PC3), human non-small cell lung carcinoma (H322a) and rat mammary carcinoma (MTF7) were treated by photodynamic therapy. An examination of extracted cellular DNA by gel electrophoresis showed the characteristic DNA ladder indicative of internucleosomal cleavage of DNA during apoptosis. The magnitude of the response and the photodynamic therapy dosage required to induce DNA fragmentation were different in PC3 and MTF7. The MTF7 cells responded with rapid apoptosis at the dose of light and drug that yielded 50% cell death (LD50). In contrast, PC3 showed only marginal response at the LD50 but had a marked response at the LD85. Thus, apoptosis did not ensue as quickly in PC3 as in MTF7. The H322a cells were killed by photodynamic therapy but failed to exhibit any apoptotic response. The results also suggested that apoptosis in these cell lines has a minor requirement for de novo protein synthesis and no requirement for de novo RNA synthesis. This study indicates that although apoptosis can occur during photodynamic therapy-induced cell death, this response is not universal for all cancer cell lines.

Animals↗
PubMed1994

Optimized radial and angular positions in Monte Carlo modeling.

In Monte Carlo simulations of light transport in tissues, a grid system is set up to score physical quantities. This study of cylindrically symmetrical problems found that the optimized radial and angular positions for the averaged physical quantities in each grid element are off-center. The error of the extrapolated physical quantities at the light-incidence point using the centered radial positions is up to 14.3%.

Biophysical Phenomena↗
PubMed1993

XeCl laser ablation of atherosclerotic aorta: luminescence spectroscopy of ablation products.

XeCl laser ablation of atherosclerotic aorta tissue was investigated. Luminescence spectra of ablation products were measured for soft and hard arterial tissues. A pronounced difference observed between plume luminescence for various plaques and normal vessel wall correlates with the chemical composition of the tissue. The mechanism of plume luminescence appeared to be thermochemical excitation ablation products (particles, atoms, molecules, etc.) in the air. The process of soft tissue ablation was delayed with respect to the exciting laser pulse at relatively low laser fluences close to the ablation threshold. The kinetics of the ablation process as a function of laser-pulse energy fluence is reported. The data indicate that tissue ejection mechanism, which involves vapor bubbles formation, expansion and explosion, is suitable for the description of the XeCl excimer laser ablation of soft tissues.

Angioplasty, Laser↗
PubMed1993

Gestational age correlates with skin reflectance in newborn infants of 24-42 weeks gestation.

Accurate gestational age determination is limited in very low birthweight infants using neurological and physical assessments. As one of the markers of intrauterine development, skin maturation is assessed qualitatively by pediatricians. Based on this observation, we hypothesize that skin reflectance relates directly to gestational age. Light was delivered and collected from the skin through a topically placed optical patch. Reflected light was detected by the spectrophotometer and corrected by an adjacent laptop computer to yield the true total diffuse reflectance as a function of wavelength between 380-820 nm. The calculated reflectance at 837 nm (R837) where it is independent of melanin, was determined by extrapolation from the reflectance at 650 and 750 nm. Sixty-four neonates of different races with gestational ages of 24-42 weeks were studied at 2-151 h of age. R837 was related exponentially to gestational age (GA) by the equation R837 = Rmax(1-exp[-(GA-G0)/tau]), where Rmax is the maximal value of R837, G0 is an apparent delay time before dermal scattering increases rapidly, and tau is a time constant, r = 0.88, p < 0.001. In summary, the extrapolated skin reflectance offers a quantitative and objective assessment of gestational age which is independent of melanin and sex.

Black People↗
PubMed1993

XeCl laser-induced fluorescence of atherosclerotic arteries. Spectral similarities between lipid-rich lesions and peroxidized lipoproteins.

Autofluorescence spectroscopy of arterial surfaces provides information about the distribution and composition of atherosclerotic plaques. The aim of the study was to determine whether accumulation of peroxidized lipoproteins in arterial walls, a process postulated to play a role in initiating atherosclerotic changes, can be demonstrated by fluorescence spectroscopy. XeCl excimer laser (308 nm)-induced fluorescence of human aortas containing early lipid-rich noncollagenous lesions exhibited marked red shifts and broadening of the fluorescence spectra compared with spectra from nonatherosclerotic aortas. Similar profiles were observed in spectra obtained from oxidatively modified low density lipoprotein but not native low density lipoprotein. In hypercholesterolemic rabbits with early foam cell lesions, spectral shifts resembled those of oxidized beta-very low density lipoprotein, the major lipoprotein accumulating in arteries of rabbits fed cholesterol. XeCl laser-fluorescence spectroscopy of arterial surfaces may be useful for the identification of arteries accumulating modified lipoproteins (oxidized low density lipoprotein), a chemical change indicative of atherosclerosis in its early and probably reversible stages.

Angioscopes↗
PubMed1993

Hybrid model of Monte Carlo simulation and diffusion theory for light reflectance by turbid media.

Light reflectance by semi-infinite turbid media is modeled by a hybrid of Monte Carlo simulation and diffusion theory, which combines the accuracy of Monte Carlo simulation near the source and the speed of diffusion theory distant from the source. For example, when the turbid medium has the following optical properties--absorption coefficient 1 cm-1, scattering coefficient 100 cm-1, anisotropy 0.9, and refractive-index-matched boundary--the hybrid simulation is 7 times faster than the pure Monte Carlo simulation (100,000 photon packets were traced), and the difference between the two simulations is within 2 standard deviations of the Monte Carlo simulation.

Absorption↗
PubMed1992

Optical properties of Intralipid: a phantom medium for light propagation studies.

Intralipid is an intravenous nutrient consisting of an emulsion of phospholipid micelles and water. Because Intralipid is turbid and has no strong absorption bands in the visible region of the electromagnetic spectrum, and is readily available and relatively inexpensive, it is often used as a tissue simulating phantom medium in light dosimetry experiments. In order to assist investigators requiring a controllable medium that over a finite range of wavelengths is optically equivalent to tissue, we have compiled previously published values of the optical interaction coefficients of Intralipid, most of which were measured at a wavelength of 633 nm. We have extended the measurements of the absorption and reduced scattering coefficients from 460 to 690 nm and the total attenuation coefficient from 500 to 890 nm. These measurements show that, for stock 10% Intralipid, the absorption coefficient varies from 0.015 to 0.001 cm-1 between 460 and 690 nm, the reduced scattering coefficient varies from 92 to 50 cm-1 between 460 and 690 nm, the total attenuation coefficient varies from 575 to 150 cm-1 between 500 and 890 nm, and the average cosine of scatter varies from 0.87 to 0.82 between 460 and 690 nm. With these data, we discuss the design of an optically tissue-equivalent phantom consisting of Intralipid and black India ink.

Absorption↗
PubMed1992

XeCl laser ablation of atherosclerotic aorta: optical properties and energy pathways.

The energetics of 308-nm excimer laser irradiation of human aorta were studied. The heat generation that occurred during laser irradiation of atherosclerotic aorta equaled the absorbed laser energy minus the fraction of energy for escaping fluorescence (0.8-1.6%) and photochemical decomposition (2%). The absorbed laser energy is equal to the total delivered light energy minus the energy lost as specular reflectance (2.4%, air/tissue) and diffuse reflectance (11.5-15.5%). Overall, about 79-83.5% of the delivered light energy was converted to heat. We conclude that the mechanism of XeCl laser ablation of soft tissue involves thermal overheating of the irradiated volume with subsequent explosive vaporization. The optical properties of normal wall of human aorta and fibrous plaque, both native and denatured were determined. The light scattering was significant and sufficient to cause a subsurface fluence (J/cm2) in native aorta that equaled 1.8 times the broad-beam radiant exposure, phi o (2.7 phi o for denatured aorta). An optical fiber must have a diameter of at least 800 microns to achieve a maximum light penetration (approximately 200 microns for phi o/e) in the aorta along the central axis of the beam.

Aorta↗