Modulation of ultrasound-switchable fluorescence for improving signal-to-noise ratio.

Simultaneously achieving high signal-to-noise ratio (SNR) (or sensitivity) and high resolution is desired in biomedical imaging. However, conventional imaging modality has a tradeoff between SNR (or sensitivity) and resolution. We developed a method to simultaneously achieve high SNR (or sensitivity) and high resolution for fluorescence imaging in deep tissue. We first introduce a recently developed deep-tissue high-resolution imaging technique termed as ultrasound-switchable fluorescence (USF). An approach of modulating ultrasound exposure time is adopted to increase the detectability of the USF signal. The control parameters of modulation of ultrasound—such as (1) frequency, (2) duty cycle, and (3) exposure duration—are varied to study their influence on the USF signal and SNR. We conclude that high SNR can be achieved by modulating ultrasound exposure without sacrificing the spatial resolution. This is important for future fluorescence molecular imaging of cancer in deep tissue.