Measurement of light transmission and fluence rate in mouse brain in vivo (Conference Presentation)

John J. Macklin; Austin R. Graves; Joseph M. Stujenske; Adam W. Hantman; Katie C. Bittner

doi:10.1117/12.2253041

19 April 2017 Measurement of light transmission and fluence rate in mouse brain in vivo(Conference Presentation)

John J. Macklin, Austin R. Graves, Joseph M. Stujenske, Adam W. Hantman, Katie C. Bittner

Proceedings Volume 10052, Optogenetics and Optical Manipulation; 100520F (2017) https://doi.org/10.1117/12.2253041
Event: SPIE BiOS, 2017, San Francisco, California, United States

Abstract

Optogenetic experiments require light delivery, typically using fiber optics, to light-gated ion channels genetically targeted to specific brain regions. Understanding where light is—and isn’t—in an illuminated brain can be a confounding factor in designing experiments and interpreting results. While the transmission of light, i.e. survival of forward-directed and forward–scattered light, has been extensively measured in vitro, light scattering can be significantly different in vivo due to blood flow and other factors. To measure irradiance in vivo, we constructed a pipette photodetector tipped with fluorescent quantum dots that function as a light transducer. The quantum dot fluorescence is collected by a waveguide and sent to a fiber-coupled spectrometer. The device has a small photo-responsive area (~ 10 um x 15 um), enabling collection of micron-resolution irradiance profiles, and can be calibrated to determine irradiance with detection limits of 0.001 mW/mm2. The photodetector has the footprint of a micro-injection pipette, so can be inserted into almost any brain region with minimal invasiveness. With this detector, we determined transverse and axial irradiance profiles in mice across multiple brain regions at 5 source wavelengths spanning the visible spectrum. This profile data is compared to in vitro measurements obtained on tissue slices, and provides a means to derive scattering coefficients for specific brain regions in vivo. The detector is straightforward to fabricate and calibrate, is stable in air storage > 9 months, and can be easily installed in an electrophysiology setup, thereby enabling direct measurement of light spread under conditions used in optogenetics experiments.

Conference Presentation

Citation Download Citation

John J. Macklin, Austin R. Graves, Joseph M. Stujenske, Adam W. Hantman, and Katie C. Bittner "Measurement of light transmission and fluence rate in mouse brain in vivo(Conference Presentation)", Proc. SPIE 10052, Optogenetics and Optical Manipulation, 100520F (19 April 2017); https://doi.org/10.1117/12.2253041

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KEYWORDS

Brain

In vivo imaging

Optical testing

Light scattering

Optogenetics

Calibration

In vitro testing

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