Abstract
Fluorescence imaging in centimeter-deep tissues with high resolution is highly desirable for many biomedical applications. Recently, we have developed a new imaging modality, ultrasound-switchable fluorescence (USF) imaging, for achieving this goal. In our previous work, we successfully achieved USF imaging with several types of USF contrast agents and imaging systems. In this study, we introduced a new USF imaging system: an intensified charge-coupled device (ICCD) camera-based, time-domain USF imaging system. We demonstrated the principle of time-domain USF imaging by using two USF contrast agents. With a series of USF imaging experiments, we demonstrated the tradeoffs among different experimental parameters (i.e., data acquisition time, including CCD camera recording time and intensifier gate delay; focused ultrasound (FU) power; and imaging depth) and the image qualities (i.e., signal-to-noise ratio, spatial resolution, and temporal resolution). In this study, we also discussed several imaging strategies for achieving a high-quality USF image via this time-domain system.
Highlights
Fluorescence imaging in deep biological tissue is extremely desirable because it reveals the tissue’s structural, functional, and molecular information with high-sensitivity, non-ionizing radiation and good penetration[1,2,3,4,5]
We have recently developed a technique that belongs to the latter category: ultrasound switchable fluorescence (USF) imaging[17,18,23,24,25,26,27,28,29,42]
As our previous work has described[23], we used the following parameters to quantify the performance of a USF contrast: an on-to-off ratio of fluorescence strength (Ion/Ioff), an on-to-off ratio of fluorescence lifetime, an adjustable temperature threshold to switch on fluorophores (Tth), a narrow temperature transition bandwidth (TBW), and the fluorophore’s peak excitation and peak emission wavelength, which determines the light penetration depth in a biological tissue
Summary
Fluorescence imaging in deep biological tissue is extremely desirable because it reveals the tissue’s structural, functional, and molecular information with high-sensitivity, non-ionizing radiation and good penetration[1,2,3,4,5]. USF has a similar spatial resolution to other deep-tissue optical imaging technologies developed in the recent years, such as photoacoustic tomography[43,44], time-reversed ultrasonically encoded optical focusing[11,12,13,14,15,16], and ultrasound-modulated fluorescence[21,32,33]. As our previous work has described[23], we used the following parameters to quantify the performance of a USF contrast: an on-to-off ratio of fluorescence strength (Ion/Ioff), an on-to-off ratio of fluorescence lifetime (τon/τoff), an adjustable temperature threshold to switch on fluorophores (Tth), a narrow temperature transition bandwidth (TBW), and the fluorophore’s peak excitation (λex) and peak emission (λem) wavelength, which determines the light penetration depth in a biological tissue. Several experimental parameters (i.e., data acquisition time including CCD camera recording time and intensifier gate delay, FU power, and imaging depth) need to be optimized in the time-domain USF imaging and they can affect image qualities (i.e., SNR, spatial resolution, and temporal resolution)
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