Roy Aditya, Ben-Yakar Adela
The University of Texas at Austin, Department of Mechanical Engineering, 204 East Dean Keeton Street, Stop C2200, Austin, Texas 78712, USA.
The University of Texas at Austin, Department of Biomedical Engineering, 107 West Dean Keeton Street, Stop C0800, Austin, Texas 78712, USA.
Biomed Opt Express. 2024 Jan 3;15(2):540-557. doi: 10.1364/BOE.507517. eCollection 2024 Feb 1.
Two-photon excitation fluorescence microscopy has become an effective tool for tracking neural activity in the brain at high resolutions thanks to its intrinsic optical sectioning and deep penetration capabilities. However, advanced two-photon microscopy modalities enabling high-speed and/or deep-tissue imaging necessitate high average laser powers, thus increasing the susceptibility of tissue heating due to out-of-focus absorption. Despite cooling the cranial window by maintaining the objective at a fixed temperature, average laser powers exceeding 100-200 mW have been shown to exhibit the potential for altering physiological responses of the brain. This paper proposes an enhanced cooling technique for inducing a laminar flow to the objective immersion layer while implementing duty cycles. Through a numerical study, we analyze the efficacy of heat dissipation of the proposed method and compare it with that of the conventional, fixed-temperature objective cooling technique. The results show that improved cooling could be achieved by choosing appropriate flow rates and physiologically relevant immersion cooling temperatures, potentially increasing safe laser power levels by up to three times (3×). The proposed active cooling method can provide an opportunity for faster scan speeds and enhanced signals in nonlinear deep brain imaging.
双光子激发荧光显微镜凭借其固有的光学切片和深层穿透能力，已成为在高分辨率下追踪大脑神经活动的有效工具。然而，能够实现高速和/或深层组织成像的先进双光子显微镜模式需要高平均激光功率，因此由于离焦吸收而增加了组织发热的易感性。尽管通过将物镜保持在固定温度来冷却颅窗，但已表明平均激光功率超过100 - 200毫瓦时具有改变大脑生理反应的可能性。本文提出了一种增强冷却技术，在实施占空比的同时，使层流流向物镜浸没层。通过数值研究，我们分析了所提出方法的散热效果，并将其与传统的固定温度物镜冷却技术进行比较。结果表明，通过选择合适的流速和生理相关的浸没冷却温度，可以实现更好的冷却效果，潜在地将安全激光功率水平提高多达三倍（3倍）。所提出的主动冷却方法可为非线性深部脑成像中更快的扫描速度和增强信号提供机会。
