Dr. Dilip Paithankar Profile

Dr. Dilip Paithankar

Director, Technical Project Management at IPG Medical Corp

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Publications (6)

Proceedings Article | 23 March 2007 Paper

Variable depth skin heating with lasers

Dilip Paithankar, E. Victor Ross

Proceedings Volume 6424, 64240P (2007) https://doi.org/10.1117/12.701307

KEYWORDS: Skin, Laser irradiation, Absorption, Injuries, Monte Carlo methods, Pulsed laser operation, Laser applications, Thermal modeling, Tissues, Laser induced damage

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SPIE Journal Paper | 1 July 2003 Open Access

Subsurface skin renewal by treatment with a 1450-nm laser in combination with dynamic cooling

Dilip Paithankar, Joan Clifford, Bilal Saleh, E. Victor Ross, Christina Hardaway, David Barnette

JBO, Vol. 8, Issue 03, (July 2003) https://doi.org/10.1117/12.10.1117/1.1586703

KEYWORDS: Skin, Cryogenics, Injuries, Absorption, Biopsy, Collagen, Tissues, Monte Carlo methods, Thermal modeling, Laser scattering

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Proceedings Article | 17 May 2000 Paper

Subsurface wrinkle removal by laser treatment in combination with dynamic cooling

Dilip Paithankar, James Hsia, E. Ross

Proceedings Volume 3907, (2000) https://doi.org/10.1117/12.386229

KEYWORDS: Skin, Collagen, Tissue optics, Injuries, Cryogenics, Absorption, Light scattering, Monte Carlo methods, Scattering, Tissues

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Proceedings Article | 7 May 1997 Paper

Imaging of fluorescence yield and lifetime from multiply scattered light re-emitted from random media

Eva Sevick-Muraca, Dilip Paithankar

Proceedings Volume 2980, (1997) https://doi.org/10.1117/12.273516

KEYWORDS: Luminescence, Tissues, Absorption, Image restoration, Light scattering, Computer simulations, Reconstruction algorithms, Chromophores, Sensors, Geometrical optics

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Proceedings Article | 5 April 1996 Paper

Fluorescent yield and lifetime imaging in tissues and other scattering media

Dilip Paithankar, Alvin Chen, Eva Sevick-Muraca

Proceedings Volume 2679, (1996) https://doi.org/10.1117/12.237585

KEYWORDS: Tissues, Sensors, Absorption, Modulation, Phase shift keying, Luminescence, Magnetic resonance imaging, Scattering media, Scattering, Tissue optics

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The progression of disease is certainly accompanied by biochemical changes. Since early detection promises a greater efficacy for therapeutic intervention, non-invasive biomedical optics may offer the opportunity for detecting biochemical changes thereby improving prognosis by providing early diagnosis. Magnetic resonance imaging (MRI) is an example of a modality that has successfully monitored the relaxation of spin states of paramagnetic nuclei in order to provide biomedical imaging and biochemical spectroscopy of tissues. In this paper, we discuss an optical analog of MRI, called fluorescence lifetime imaging. instead of monitoring the relaxation of a spin state, lifetime imaging depends upon monitoring the relaxation of an electronically activated state which is brought about by the absorption of a photon. Figure 1 is the Jablonski diagram outlining the electronic transitions which occur following the absorption of light. Relaxation from the activated state to the ground state can occur via either non-radiative or fluorescent decay, depending upon the local environment. The mean time between the events of the absorption of an excitation photon and the radiative relaxation process which produces a fluorescent photon is known as the lifetime, (tau) , of the activated state. Typically, endogenous fluorophores have lifetimes on the order of nanoseconds while exogenous compounds have lifetimes ranging from sub nanosecond to tens of nanoseconds. If the spin state of the electron in the activated state is 'flipped' (referred to as a 'intersystem crossing') then radiative relaxation requires extra time since paired electrons of the same spin are forbidden. Consequently, the resulting phosphorescence lifetime is on the order of milliseconds. The lifetime of the activated probe is dependent on its environment much the same as the time for relaxation of the spin states of paramagnetic nuclei in MRI and NMR depends upon local environment. There are two mechanisms responsible for reducing the lifetime of an activated probe: (1) energy transfer from the activated state to a donor molecule(s), and (2) collisional quenching of the activated state. For an activated probe experiencing collisional quenching, the measured lifetime, (tau) , can be used to determine metabolite or quencher concentration [Q], from the empirical Stern-Volmer relationship. Consequently, a map of lifetime provides a map of metabolite or quencher concentration. In this paper, we report computational experiments which point to the feasibility of the optical analog to MRI: fluorescence lifetime imaging in tissues and other scattering media.

Proceedings Article | 1 April 1996 Paper

Analysis of photon migration for optical diagnosis

Eva Sevick-Muraca, Dilip Paithankar, Christina Hutchinson, Tamara Troy

Proceedings Volume 2680, (1996) https://doi.org/10.1117/12.237599

KEYWORDS: Luminescence, Tissues, Spectroscopy, Scattering, Demodulation, Fluorescence spectroscopy, Absorption, Light scattering, Tissue optics, Modulation

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The opportunity to monitor the onset and progression of disease may be enabled by the smart implementation of biomedical optical engineering approaches to monitor tissue biochemistry. Uncorrected, these biochemical disturbances manifest themselves in microscopic structural changes which lead to gross pathophysiology and symptoms by which the disease is outwardly identified. Biomedical optical engineering techniques offer the opportunity to detect these biochemical changes and provide diagnostic information at earlier stages in the disease process, enabling greater efficacy of therapeutic intervention. In this paper, we concentrate on the fluorescence and phosphorescence lifetime spectroscopy due to advantages these techniques have to offer in tissues. The development of fluorescent and phosphorescent dyes which excite and re-emit in the near-infrared wavelength region promises the capacity for non- invasive biochemical sensing in tissues. Fluorescence intensity and fluorescence lifetime spectroscopies are established methods by which a fluorophore can provide sensing in dilute, non-scattering samples. However, fluorescence intensity or fluorescence lifetime spectroscopy in tissues or other scattering media is a complex problem. In order to extract the intrinsic fluorescence intensity for identification of the fluorophore concentration and yield, a priori information about tissue absorption and scattering must be obtained or assumed. Yet in tissues, the optical properties of absorption and scattering are highly variable. Nonetheless when successful, fluorescence intensity spectroscopy enables determination of the product of fluorescent yield and fluorophore concentration. In contrast to fluorescence intensity spectroscopy, fluorescence-lifetime tissue spectroscopy offers the ability to directly determine metabolite concentration independently of the concentration of fluorophore, whether it is endogenous or exogenous. Instead of monitoring the fluorescent intensity due to the re- emission process, the 'lifetime' or stability of the photon-activated fluorophore is measured. The lifetime of the activated state is defined as the mean time between absorption of the excitation photon and re-emission of a fluorescent photon. Typically, endogenous fluorophores have lifetimes on the order of nanoseconds while exogenous compounds have lifetimes ranging from sub nanosecond to milliseconds.

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