Ultrasound-mediation of self-illuminating reporters improves imaging resolution in optically scattering media

Recent advances in ultrasound-controlled fluorescence technology for deep tissue optical imaging

Fluorescence imaging is a noninvasive and dynamic real-time imaging technique; however, it exhibits poor spatial resolution in centimeter-deep tissues because biological tissues are highly scattering media for optical radiation. The recently developed ultrasound-controlled fluorescence (UCF) imaging is a novel imaging technique that can overcome this bottleneck. Previous studies suggest that the effective contrast agent and sensitive imaging system are the two pivotal factors for generating high-resolution UCF images ex vivo and/or in vivo. Here, this review highlights the recent advances (2015–2020) in the design and synthesis of contrast agents and the improvement of imaging systems to realize high-resolution UCF imaging of deep tissues. The imaging performances of various UCF systems, including the signal-to-noise ratio, imaging resolution, and imaging depth, are specifically discussed. In addition, the challenges and prospects are highlighted. With continuously increasing research interest in this field and emerging multidisciplinary applications, UCF imaging with higher spatial resolution and larger imaging depth may be developed shortly, which is expected to have a far-reaching impact on disease surveillance and/or therapy.

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The unique UCF technique in high resolution imaging was described.

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The contrast agents and imaging systems of UCF imaging were discussed.

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Recent advances and prospects of NIR-UCF technique were summarized.

In vivo ultrasound-switchable fluorescence imaging

The conventional fluorescence imaging has limited spatial resolution in centimeter-deep tissue because of the tissue's high scattering property. Ultrasound-switchable fluorescence (USF) imaging, a new imaging technique, was recently proposed to realize high-resolution fluorescence imaging in centimeter-deep tissue. However, in vivo USF imaging has not been achieved so far because of the lack of stable near-infrared contrast agents in a biological environment and the lack of data about their biodistributions. In this study, for the first time, we achieved in vivo USF imaging successfully in mice with high resolution. USF imaging in porcine heart tissue and mouse breast tumor via local injections were studied and demonstrated. In vivo and ex vivo USF imaging of the mouse spleen via intravenous injections was also successfully achieved. The results showed that the USF contrast agent adopted in this study was very stable in a biological environment, and it was mainly accumulated into the spleen of the mice. By comparing the results of CT imaging and the results of USF imaging, the accuracy of USF imaging was proved.