[MARMAM] Shining light on dolphin physiology

Andreas Fahlman afahlman at whoi.edu
Thu Jul 13 23:16:39 PDT 2023

Dear MarMamers
We would like to share our new open-access publication that investigated the use of Near Infrared Spectroscopy as a non-invasive tool to study physiology in the bottlenose dolphin. We report preliminary data which indicate that this technology allows us to measure blood flow and tissue and blood oxygenation in this dolphins. The details about the paper can be found below, and please send me or Alex Ruesch (aruesch at andrew.cmu.edu) an email if you have any questions.

Title: Evaluating feasibility of functional near-infrared spectroscopy in dolphins
Authors: Ruesch, A., Acharya, D., Bulger, E., Cao, J., McKnight, J. C., Manley, M., Fahlman, A., Shinn-Cunningham, B. G. and Kainerstorfer, J. M.
Journal: Journal of Biomedical Optics
doi: 10.1117/1.JBO.28.7.075001
Abstract: Significance: Using functional near-infrared spectroscopy (fNIRS) in bottlenose dolphins (Tursiops truncatus) could help to understand how echolocating animals perceive their environment and how they focus on specific auditory objects, such as fish, in noisy marine settings.
Aim: To test the feasibility of near-infrared spectroscopy (NIRS) in medium-sized marine mammals, such as dolphins, we modeled the light propagation with computational tools to determine the wavelengths, optode locations, and separation distances that maximize sensitivity to brain tissue.
Approach: Using frequency-domain NIRS, we measured the absorption and reduced scattering coefficient of dolphin sculp. We assigned muscle, bone, and brain optical properties from the literature and modeled light propagation in a spatially accurate and biologically relevant model of a dolphin head, using finite-element modeling. We assessed tissue sensitivities for a range of wavelengths (600 to 1700 nm), source-detector distances (50 to 120 mm), and animal sizes (juvenile model 25% smaller than adult).
Results: We found that the wavelengths most suitable for imaging the brain fell into two ranges: 700 to 900 nm and 1100 to 1150 nm. The optimal location for brain sensing positioned the center point between source and detector 30 to 50 mm caudal of the blowhole and at an angle 45 deg to 90 deg lateral off the midsagittal plane. Brain tissue sensitivity comparable to human measurements appears achievable only for smaller animals, such as juvenile bottlenose dolphins or smaller species of cetaceans, such as porpoises, or with source-detector separations ≫100 mm in adult dolphins.
Conclusions: Brain measurements in juvenile or subadult dolphins, or smaller dolphin species, may be possible using specialized fNIRS devices that support optode separations of >100 mm. We speculate that many measurement repetitions will be required to overcome hemodynamic signals originating predominantly from the muscle layer above the skull. NIRS measurements of muscle tissue are feasible today with source-detector separations of 50 mm, or even less..

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