A Monte Carlo model for the absorption and flux distributions of light in tissue

Wilson, Brian C.; Adam, Gh.

doi:10.1118/1.595361

Cited by 625 publications

(310 citation statements)

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“…Furthermore, by fitting the individual data from each mouse, absorption (μ a ) and effective (μ eff ) coefficients were determined with SE (least-squares curve fit, R 2 > 0.95): 635 nm: μ a = 2.14 ± 0.15 cm −1 , μ eff = 6.61 ± 0.53 cm −1 ; 532 nm: μ a = 13.7 ± 1.33 cm −1 , μ eff = 41.1 ± 4.04 cm −1 ; and 473 nm: μ a = 10.6 ± 0.486 cm −1 , μ eff = 31.8 ± 1.46 cm −1 . These coefficients can be used for Monte Carlo modeling to predict light propagation in vivo for a variety of illuminators and light source geometries (39)(40)(41)(42). Based on the superior light transmission of red light in vivo, we elected to use the red light-sensitive halorhodopsin Jaws (43).…”

Section: Significancementioning

confidence: 99%

FEF inactivation with improved optogenetic methods

Acker

Pino

Boyden

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

102

114

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Optogenetic methods have been highly effective for suppressing neural activity and modulating behavior in rodents, but effects have been much smaller in primates, which have much larger brains. Here, we present a suite of technologies to use optogenetics effectively in primates and apply these tools to a classic question in oculomotor control. First, we measured light absorption and heat propagation in vivo, optimized the conditions for using the red-light-shifted halorhodopsin Jaws in primates, and developed a large-volume illuminator to maximize light delivery with minimal heating and tissue displacement. Together, these advances allowed for nearly universal neuronal inactivation across more than 10 mm 3 of the cortex. Using these tools, we demonstrated large behavioral changes (i.e., up to several fold increases in error rate) with relatively low light power densities (≤100 mW/mm 2 ) in the frontal eye field (FEF). Pharmacological inactivation studies have shown that the FEF is critical for executing saccades to remembered locations. FEF neurons increase their firing rate during the three epochs of the memory-guided saccade task: visual stimulus presentation, the delay interval, and motor preparation. It is unclear from earlier work, however, whether FEF activity during each epoch is necessary for memory-guided saccade execution. By harnessing the temporal specificity of optogenetics, we found that FEF contributes to memory-guided eye movements during every epoch of the memory-guided saccade task (the visual, delay, and motor periods).primate | optogenetics | FEF | Jaws | memory-guided saccade T he frontal eye field (FEF) is an important brain area for making saccades to remembered locations. FEF neurons increase their firing rate during three epochs of memory-guided saccades: (i) target presentation, (ii) delay period, and (iii) motor preparation. Pharmacological inactivation of the FEF impairs memory-guided saccades (1-7), but because pharmacological inactivation inhibits all FEF neuronal activity, it is unclear if the FEF's role is specific to one or more task epochs (8,9). By selectively inactivating the FEF during each task epoch, we can determine whether visual-, delay-, or motor-related firing (or some combination of the three types of firing) contributes to memory-guided saccades.The ideal tool for this study is optogenetics, which allows for millisecond-precise, light-driven neuronal control. Unfortunately, although optogenetics is widely used to study functional physiology and disease models in rodents and invertebrates, technical challenges have limited the use of optogenetics in the nonhuman primate brain, which has a volume ∼100-fold larger than the rodent brain (10). Pioneering studies in monkeys reported small behavioral effects with excitatory (11-14) and inhibitory opsins (15-17). These studies used large light power densities (several hundreds of milliwatts per square meter to 20 W/mm 2 ) but illuminated only small volumes, at most 1 mm 3 , due to both the chosen wavelength and light-deliver...

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Section: Significancementioning

confidence: 99%

FEF inactivation with improved optogenetic methods

Acker

Pino

Boyden

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

102

114

View full text Add to dashboard Cite

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“…The scattering coefficient (cm ‐1 ) is measured from experimental techniques originating from Mie scattering due to collagen fibres and from Rayleigh scattering due to small tissue structures, respectively (25) . Scattering in tissue by photons is characterized by the Henyey‐Greenstein scattering phase function, 26 , 27 , 28 , 29 which is mathematically expressed in the form

P (θ) = \frac{1 ‐ {normalg}^{2}}{{(1 + {normalg}^{2} ‐ 2 g Cos (θ))}^{3 / 2}}

…”

Section: Methodsmentioning

confidence: 99%

Mathematical modeling of the optimum pulse structure for safe and effective photo epilation using broadband pulsed light

Ash

Donne

Daniel

et al. 2012

J Applied Clin Med Phys

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The objective of this work is the investigation of intense pulsed light (IPL) photoepilation using Monte Carlo simulation to model the effect of the output dosimetry with millisecond exposure used by typical commercial IPL systems. The temporal pulse shape is an important parameter, which may affect the biological tissue response in terms of efficacy and adverse reactions. This study investigates the effect that IPL pulse structures, namely free discharge, square pulse, close, and spaced pulse stacking, has on hair removal. The relationship between radiant exposure distribution during the IPL pulse and chromophore heating is explored and modeled for hair follicles and the epidermis using a custom Monte Carlo computer simulation. Consistent square pulse and close pulse stacking delivery of radiant exposure across the IPL pulse is shown to generate the most efficient specific heating of the target chromophore, whilst sparing the epidermis, compared to free discharge and pulse stacking pulse delivery. Free discharge systems produced the highest epidermal temperature in the model. This study presents modeled thermal data of a hair follicle in situ, indicating that square pulse IPL technology may be the most efficient and the safest method for photoepilation. The investigation also suggests that the square pulse system design is the most efficient, as energy is not wasted during pulse exposure or lost through interpulse delay times of stacked pulses.PACS number: 87.10.Rt

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“…[3][4][5][6][7][8] To compute light distributions according to tissue geometry and optical properties, including refractive index n, absorption coefficient a , scattering coefficient s , and anisotropy factor g, we have written a Monte Carlo program in C for tissues with buried objects. We used the delta-scattering technique 9 for photon tracing to greatly simplify the algorithm because this technique allows a photon packet to be traced without directly dealing with photon crossings of interfaces between different types of tissues.…”

Section: Methodsmentioning

confidence: 99%

Optimal beam size for light delivery to absorption-enhanced tumors buried in biological tissues and effect of multiple-beam delivery: a Monte Carlo study

Wang¹,

Nordquist²,

Chen³

1997

Appl. Opt.

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Optimal laser light delivery into turbid biological tissues was studied by using Monte Carlo simulations based on the delta-scattering technique. The goal was to deliver efficiently the maximum amount of optical power into buried tumors being treated while avoiding potential damage to normal tissue caused by strong optical power deposition underneath the tissue surface illuminated by the laser beam. The buried tumors were considered to have much higher absorption than the surrounding normal tissue because of selective uptake of the absorption-enhancement dye. The power delivering efficiency to buried tumors was investigated for various diameters of the laser beam. An optimal beam diameter was estimated to achieve the maximum product of the power coupling efficiency and the power delivered to the buried tumor. The distribution of power deposition was simulated for single-beam delivery and multiple-beam delivery as well. The simulated results showed that with an appropriate dye enhancement and an optimal laser delivery configuration, a high selectivity for laser treatment of tumor could be achieved.

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A Monte Carlo model for the absorption and flux distributions of light in tissue

Cited by 625 publications

References 0 publications

FEF inactivation with improved optogenetic methods

FEF inactivation with improved optogenetic methods

Mathematical modeling of the optimum pulse structure for safe and effective photo epilation using broadband pulsed light

Optimal beam size for light delivery to absorption-enhanced tumors buried in biological tissues and effect of multiple-beam delivery: a Monte Carlo study

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