Yuan Baohong
Catholic University of America, Department of Biomedical Engineering, Pangborn Hall, 620 Michigan Avenue, NE, Washington, DC 20064, USA.
J Biomed Opt. 2009 Mar-Apr;14(2):024043. doi: 10.1117/1.3120493.
Ultrasound-modulated fluorescence from a fluorophore-quencher-labeled microbubble system driven by a single ultrasound pulse was theoretically quantified by solving a modified Herring equation (for bubble oscillation), a two-energy-level rate equation (for fluorophore excitation), and a diffusion equation (for light propagation in tissue). The efficiency of quenching caused by fluorescence resonance energy transfer (FRET) between the fluorophore and the quencher was modulated when the microbubble oscillates in size driven by the ultrasound pulse. Both intensity- and lifetime-based imaging methods are discussed in three different illumination modes of the excitation light: continuous wave (DC), frequency domain (FD), and time domain (TD). Results show that microbubble expansion opens a time period during which the quenching efficiency is dramatically reduced so that the emitted fluorescence strength and fluorophore lifetime are significantly increased. The modulation efficiency may even reach 100%. In addition, an important finding in this study is that in TD illumination mode, the modulated fluorescence photons may be temporally separated from the unmodulated photons, which makes the modulation efficiency limited only by thermal noise of the measurement system.
通过求解修正的赫林方程（用于气泡振荡）、双能级速率方程（用于荧光团激发）和扩散方程（用于光在组织中的传播），从理论上对由单个超声脉冲驱动的荧光团 - 猝灭剂标记微泡系统的超声调制荧光进行了量化。当微泡在超声脉冲驱动下尺寸发生振荡时，荧光团与猝灭剂之间荧光共振能量转移（FRET）引起的猝灭效率会受到调制。在激发光的三种不同照明模式下讨论了基于强度和寿命的成像方法：连续波（DC）、频域（FD）和时域（TD）。结果表明，微泡膨胀会开启一个时间段，在此期间猝灭效率会显著降低，从而使发射的荧光强度和荧光团寿命显著增加。调制效率甚至可能达到100%。此外，本研究中的一个重要发现是，在时域照明模式下，调制荧光光子可能会在时间上与未调制光子分离，这使得调制效率仅受测量系统热噪声的限制。
