Myocardium optics literature

Beek JF, Blokland P, Posthumus P, Aalders M, Pickering JW, Sterenborg HJ, van Gemert MJ. In vitro double-integrating-sphere optical properties of tissues between 630 and 1064 nm. Phys Med Biol 1997 Nov;42(11):2255-2261

The optical properties (absorption and scattering coefficients and the scattering anisotropy factor) were measured in vitro for cartilage, liver, lung, muscle, myocardium, skin, and tumour (colon adenocarcinoma CC 531) at 630, 632.8, 790, 850 and 1064 nm. Rabbits, rats, piglets, goats, and dogs were used to obtain the tissues. A double-integrating-sphere setup with an intervening sample was used to determine the reflectance, and the diffuse and collimated transmittances of the sample. The inverse adding-doubling algorithm was used to determine the optical properties from the measurements. The overall results were comparable to those available in the literature, although only limited data are available at 790-850 nm. The results were reproducible for a specific sample at a specific wavelength. However, when comparing the results of different samples of the same tissue or different lasers with approximately the same wavelength (e.g. argon dye laser at 630 nm and HeNe laser at 632.8 nm) variations are large. We believe these variations in optical properties should be explained by biological variations of the tissues. In conclusion, we report on an extensive set of in vitro absorption and scattering properties of tissues measured with the same equipment and software, and by the same group. Although the accuracy of the method requires further improvement, it is highly likely that the other existing data in the literature have a similar level of accuracy.

Agah R, Gandjbakhche AH, Motamedi M, Nossal R, Bonner RF. Dynamics of temperature dependent optical properties of tissue: dependence on thermally induced alteration. IEEE Trans Biomed Eng 1996 Aug;43(8):839-846

Thermal damage in heated bovine myocardial tissue is assessed from measured changes in total reflection and transmission of light. Mathematical expressions, based on random walk analysis of light propagation within tissue slabs, are used to relate the diffuse reflection and transmittance to the absorption coefficient, mua, and effective scattering coefficient, mu's, for samples of myocardial tissue which were subjected to rapid step changes in temperature. Time-dependent changes in mu's, indicate two processes, one with a fast and temperature-dependent rate the other with a slow and apparently temperature-independent rate. For final temperatures above 56.8 degrees C and for the first 500 s after the temperature change, the optical parameters are well fit by exponential forms that exhibit temperature-dependent time constants as predicted by Arrhenius reaction rate theory of thermal damage. The scattering changes are associated with an apparent activation energy, delta E, of 162 kJ/mole and a frequency constant, A, of 3 x 10(23) s-1. This method provides a means for estimating optical coefficients which are needed to assess laser tissue dosimetry.

Splinter R, Svenson RH, Littmann L, Tuntelder JR, Chuang CH, Tatsis GP, Thompson M. Optical properties of normal, diseased, and laser photocoagulated myocardium at the Nd:YAG wavelength. Lasers Surg Med 1991;11(2):117-124. Laser and Applied Technologies Laboratory, Carolinas Heart Institute and Heineman Medical Research Center, Charlotte, North Carolina 28232.

Laser photocoagulation of the myocardium effectively destroys arrhythmogenic foci. The purpose of this study was 1) to compare the optical properties of canine myocardium before and after photocoagulation, 2) to compare the canine model with clinical cases by measuring the optical properties of human myocardium, and 3) to assess the optical properties of human myocardial scar and epicardial fat tissue. Measured optical properties were the absorption coefficient, mu a; scattering coefficient, mu s; and scattering anisotropy factor, g. Optical measurements were performed at 1064 nm wavelength on thin plane parallel tissue slices using the integrating sphere method with glass hemispheres on either side of the sample. The study showed 1) an increase of the scattering coefficient by 40% and a two- to threefold increase in reduced scattering coefficient as a result of photocoagulation; 2) that the mu a (0.035 +/- 0.024 mm-1) and mu s (17.9 +/- 3.8 mm-1) of human myocardium were not significantly different from mu a (0.043 +/- 0.021 mm-1) and mu s (17.3 +/- 2.2 mm-1) of canine myocardium, whereas the human g (0.964 +/- 0.005) was slightly different from the canine g (0.974 +/- 0.008); and 3) that the mu a (0.021 +/- 0.016 mm-1) of epicardial fat and mu s (13.8 +/- 1.1 mm-1) of myocardial scar were significantly lower than those of normal myocardium. A dynamic model of laser-tissue interaction incorporating these changes and inhomogeneities is necessary to better describe light distribution during laser photocoagulation.

Derbyshire GJ, Bogen DK, Unger M. Thermally induced optical property changes in myocardium at 1.06 microns. Lasers Surg Med 1990;10(1):28-34

Light in the visible and near-infrared region is diffusely scattered in tissues by macromolecules. It was therefore hypothesized that tissue coagulation caused by high-power continuous wave laser irradiation might significantly alter tissue optical properties, resulting in a redistribution of laser energy during the laser ablation process. Infrared transmittance studies confirmed the hypothesis by demonstrating an irreversible decrease in light transmittance (45%) during heating of a 0.75 mm thick slice of tissue. Absorption and scattering coefficients were then determined from transmittance and reflectance measurements on thin slices of raw and coagulated myocardium irradiated with a Nd:YAG laser (1.06 microns). The scattering coefficient was found to increase fourfold (0.427 mm-1 --- 1.74 mm-1) during tissue coagulation, while the absorption coefficient remained relatively unchanged (0.044 mm-1 --- 0.051 mm-1). Calculations indicate that the coagulation-induced changes in tissue optical properties substantially increase surface back-scattering and reduce tissue penetration.

Phys Med Biol 1997 Jan;42(1):177-198 Characterization of post mortem arterial tissue using time-resolved photoacoustic spectroscopy at 436, 461 and 532 nm. Beard PC, Mills TN Department of Medical Physics and Bioengineering, University College London, UK.

Time-resolved photoacoustic spectroscopy has been used to characterize post mortem arterial tissue for the purpose of discriminating between normal and atheromatous areas of tissue. Ultrasonic thermoelastic waves were generated in post mortem human aorta by the absorption of nanosecond laser pulses at 436, 461 and 532 nm produced by a frequency doubled Q-switched Nd:YAG laser in conjunction with a gas filled Raman cell. A PVDF membrane hydrophone was used to detect the thermoelastic waves. At 436 nm, differences in the photoacoustic signatures of normal tissue and atherorma were found to be highly variable. At 461 nm, there was a clear and reproducible difference between the photacoustic response of atheroma and normal tissue as a result of increased optical attenuation in atheroma. At 532 nm, the generation of subsurface thermoelastic waves provided a means of determining the structure and thickness of the tissue sample. It is suggested that pulsed photoacoustic spectroscopy at 461 and 532 nm may find application in characterizing arterial tissue in situ by providing information about both the composition and thickness of the vessel wall.

Lasers Surg Med 1985;5(3):235-237 Optical properties of human blood vessel wall and plaque. van Gemert MJ, Verdaasdonk R, Stassen EG, Schets GA, Gijsbers GH, Bonnier JJ

Optical properties of blood vessel wall and plaque from human cadaver material are presented for the argon laser (514.5 nm), He-Ne laser (633 nm), and the Nd-YAG laser (1,060 nm) wavelengths. Measurements were performed with an integrating sphere arrangement and analyzed in terms of Kubelka-Munk absorption and scattering coefficients.

Aorta optics literature

Welch AJ, Gardner C, Richards-Kortum R, Chan E, Criswell G, Pfefer J, Warren S. Propagation of fluorescent light. Lasers Surg Med 21(2):166-178, 1997.

BACKGROUND AND OBJECTIVE: In general, the remitted fluorescence spectrum is affected by the scattering and absorption properties of tissue. Other important factors are boundary conditions, geometry of the tissue sample, and the quantum yield of tissue fluorophores. Each of these factors is examined through a series of Monte Carlo simulations. STUDY DESIGN/MATERIALS AND METHODS: Monte Carlo modeling is used to simulate the propagation of excitation light and the resulting fluorescence. Remitted fluorescence is determined for semi-infinite single and multiple layer geometries and for cubic geometries representing small tissue samples. Monte Carlo results are compared to approximations obtained with a heuristic model. RESULTS: Remitted fluorescence as a function of (1) the depth of fluorescence generation and (2) radial escape position is presented for semi-infinite single and multiple layer geometries. Fluorescence from a small tissue sample is simulated in terms of a cubic geometry, and losses from the sides and bottom are presented as a function of cube dimensions in terms of optical depth of the excitation wavelength. Monte Carlo results for a homogeneous semi-infinite layer are compared to a simple, fast heuristic model. CONCLUSION: Both Monte Carlo simulations and the heuristic model clearly detail the volume of tissue interrogated by fluorescence. Since approximately 35-40% of the remitted fluorescence is due to photons originally directed away from the surface, distal layers affect the remitted fluorescence. Fluorescence spectra from small biopsy samples may not produce the correct line shape owing to wavelength dependent losses.

Cilesiz IF, Welch AJ. Optical properties of human aorta: are they affected by cryopreservation? Lasers Surg Med 4(4):396-402, 1994.

This study was undertaken to investigate the effects of freezing upon the in vitro optical properties of human aorta from 300 nm to 800 nm. Freezing significantly decreased absorption coefficient over most of the spectrum from 300 nm to 800 nm. The only significant changes in the reduced scattering coefficient were from 300 nm to 335 nm.

Oraevsky AA, Jacques SL, Pettit GH, Saidi IS, Tittel FK, Henry PD. XeCl laser ablation of atherosclerotic aorta: optical properties and energy pathways. Lasers Surg Med 12(6):585-597, 1992.

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, H (2.7H 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 H/e) in the aorta along the central axis of the beam.

Bowker TJ, Edwards P, Hall TA, Regel M, Bown SG, Fox KM, Poole-Wilson PA, Rickards AF. Optical transmission of normal and atheromatous arterial wall: a spectral analysis. Cardiovasc Res 20(6):393-397, 1986.

In laser angioplasty one of the factors influencing the immediate damage (and therefore the risk of acute arterial perforation) is the optical absorption characteristics of the target tissue. In an attempt to evaluate the differences in optical absorptive properties, the transmission spectrograms of samples of normal and atheromatous human postmortem aortic wall were measured over the visible spectrum. Optical transmission varied inversely with sample thickness and directly with wavelength through both normal and atheromatous samples. Over the whole visible spectrum atheromatous tissue transmitted less per unit thickness than normal tissue. This differential effect was, however, most pronounced at 500 nm, where atheromatous tissue transmitted light 5-10 times less strongly than normal aortic wall. Such wavelength dependent differential optical absorption could provide a means for the selective photovaporisation of atheroma in laser angioplasty.

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